Version June 2023
Thyroid hormones, including levothyroxine, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines, such as those used for their anorectic effects.
Note: Levothyroxine is synthetic thyroxine (T4). Due to its prolonged half-life, levothyroxine steady-state concentrations are not achieved until ~6 weeks after therapy is initiated or dosage adjustment; therefore, the full effect at a given dose may not be apparent until then. Initiating therapy: Individual T4 requirements correlate better with lean body mass than total body weight; in patients with a BMI ≥30 kg/m2, initial dosing based on lean body weight is preferred to avoid overreplacement (Ref). Initial doses >200 mcg/day are rarely used, regardless of patient weight (Ref).
Deceased organ donor management (hormonal resuscitation for the deceased organ donor) (off-label use):
Note: Data supporting benefit are conflicting; if given, guidelines suggest use in hemodynamically unstable donors and/or potential cardiac donors with decreased left ejection fraction (<45%) (Ref).
IV: Initial: 20 mcg bolus, followed by a continuous infusion of 10 mcg/hour; levothyroxine is usually given as part of combination hormone therapy with vasopressin, methylprednisolone, and insulin (Ref).
Hypothyroidism:
Note: Dose is individualized according to clinical response and serum thyroid stimulating hormone (TSH) and/or free T4 concentrations (Ref). Average maintenance dose is ~1.6 mcg/kg/day; range of required doses is wide and varies from 50 to ≥200 mcg/day (Ref). Maintenance doses >300 mcg/day are rarely required; in patients who require high doses (eg, >2 mcg/kg/day), consider missed doses, malabsorption, and/or drug interactions (Ref).
Primary hypothyroidism: Note: Adjust initial dose by 12 to 25 mcg/day every 3 to 6 weeks based on clinical response and serum TSH and/or free T4 concentrations until TSH is normalized at a stable dose for ≥6 weeks (Ref).
Patients ≤60 years of age without evidence of coronary heart disease: Oral: Initial: 1.6 mcg/kg/day (Ref).
Patients >60 years of age without evidence of coronary heart disease: Oral: Initial: 25 to 50 mcg once daily (Ref).
Patients with coronary heart disease: Oral: Initial: 12.5 to 50 mcg once daily (Ref); monitor for the onset of cardiac symptoms (eg, angina) and decrease the dose if needed (Ref). Note: Patients without other significant comorbidities who have had recent successful interventions to treat ischemia (eg, coronary artery bypass grafting or coronary artery stenting) can initially receive up to 80% of the weight-based dose (1.6 mcg/kg/day) (Ref). See also the “Initiating therapy” note at the top of “Dosing: Adult” section.
Pregnant patients: Note: Thyroid function tests should be interpreted using population-based, trimester-specific reference ranges for TSH and assay method- and trimester-specific reference ranges for serum free T4 (Ref).
Preexisting hypothyroidism in patients receiving levothyroxine prenatally: Patients with suspected or confirmed pregnancy:
Oral: Immediately increase the current dose by ~20% to 30% (eg, administer 2 additional tablets weekly) and adjust dose as needed every 4 weeks (Ref).
Newly diagnosed overt hypothyroidism:
Oral: Initial: 1.6 mcg/kg/day; a lower dose of 1 mcg/kg/day may be used in some patients. Adjust dose by 12.5 to 25 mcg/day every 4 to 6 weeks if needed based on TSH levels to restore euthyroidism as soon as possible (Ref).
Newly diagnosed subclinical hypothyroidism (off-label use):
Note: The decision to treat is based on the degree of TSH elevation and the presence or absence of thyroid peroxidase antibodies. If treated, goal is to restore euthyroidism (Ref). Some experts treat pregnant patients with subclinical hypothyroidism (defined as TSH above trimester-specific normal reference range [or >4 milliunits/L if trimester-specific range unavailable] with normal free T4), regardless of thyroid peroxidase antibody status, and would consider treatment in select pregnant patients with TSH levels between 2.6 and 4 milliunits/L based on the presence or absence of thyroid peroxidase antibodies, clinical factors, and patient preferences (Ref).
Oral: Initial: 1 mcg/kg/day or 25 to 50 mcg daily; adjust dose by ~12.5 to 25 mcg/day as needed every 4 weeks (Ref). Therapy should be closely monitored and adjusted to avoid overtreatment, which may result in adverse maternal and fetal outcomes (Ref).
Postpartum dosage adjustment: In patients treated prenatally for hypothyroidism, decrease the dose to preconception levels following delivery. In patients who were initiated on levothyroxine during pregnancy, evaluate the need for continued treatment (Ref).
Subclinical hypothyroidism (off-label use):
Note: Treatment may be considered in select patients with TSH levels above normal reference range depending on degree of TSH abnormality, age, and symptoms (Ref). In patients with TSH >10 milliunits/L, treatment is generally warranted, whereas benefit of treatment in asymptomatic patients with TSH levels between 4.5 and 10 milliunits/L is not well established (Ref).
Adults <50 years of age without coronary heart disease: Oral: Initial: 1.5 mcg/kg/day (Ref).
Patients with coronary heart disease or ≥50 years of age: Oral: Initial: 25 to 50 mcg once daily (Ref).
Dosage adjustment: Initial dose is adjusted by 12 to 25 mcg/day once every 6 weeks until targeted TSH is achieved with a stable dose for ≥6 weeks; thereafter assess TSH level annually (Ref).
Postpartum thyroiditis (hypothyroid phase):
Note: For use in patients who are symptomatic, breastfeeding, or planning another pregnancy (Ref); some experts will treat asymptomatic patients who have a TSH ≥10 milliunits/L (Ref). Dosing recommendations and duration of treatment are not standardized; treatment is individualized according to clinical assessment:
Oral: An initial dose of 50 to 100 mcg once daily or 1.6 mcg/kg/day has been suggested (Ref). Adjust dose every 6 weeks if needed based on TSH levels (Ref).
Duration of therapy: After 6 to 12 months, may consider gradual tapering of the dose (eg, every 6 to 8 weeks) with a goal of discontinuation; levothyroxine should not be tapered in patients who are pregnant or attempting to conceive (Ref).
Secondary or tertiary (central) hypothyroidism:
Note: Patients with secondary or tertiary (central) hypothyroidism should undergo assessment of their pituitary-adrenal function prior to initiation of therapy. If shown to have adrenal insufficiency, concomitant administration of a glucocorticoid is recommended to prevent an adrenal crisis (Ref).
Oral: Initial: 1.6 mcg/kg/day; initiate treatment at a lower dose in older patients or patients with underlying coronary heart disease (Ref). Adjust dose based on clinical response and serum free T4 concentrations. TSH cannot be used to monitor therapy (Ref).
Myxedema coma:
IV: Initial loading dose of 200 to 400 mcg as a slow bolus; followed by a daily replacement dose of 50 to 100 mcg until the patient improves clinically and can transition to oral therapy; consider doses on the lower end of the dosing range for smaller or older patients and those with a history of or at risk for coronary disease or arrhythmia; concomitant glucocorticoid therapy (eg, stress doses of hydrocortisone) is required until the possibility of coexisting adrenal insufficiency is excluded (Ref); some experts administer liothyronine (T3) concomitantly with levothyroxine (T4) (Ref).
TSH suppression:
Well-differentiated thyroid cancer (papillary and follicular): Dosage is highly individualized as the degree of TSH suppression is initially based on the risk of disease recurrence using a staging system such as the American Thyroid Association (ATA) risk-of-recurrence stratification system (Ref). Long-term TSH suppression goals should account for response to therapy, risk of recurrent disease, age, and comorbid conditions (Ref).
Oral: Initial: 1.6 to 2 mcg/kg/day immediately postsurgery (Ref); adjust dose as needed in 6 weeks based on TSH suppression goals (Ref):
Note: For patients with ATA low- and intermediate-risk disease whose initial surgery was a lobectomy, some experts initiate therapy at a later time when TSH concentrations or disease status dictate a need (Ref).
Benign solitary nodules and nontoxic multinodular goiter: Routine use of levothyroxine for TSH suppression is not recommended in euthyroid patients with benign thyroid nodules in iodine-sufficient geographic areas. In patients deemed appropriate candidates, treatment should never be fully suppressive (ie, do not target TSH <0.1 milliunits/L) (Ref).
IV/IM replacement in patients who are temporarily unable to receive oral therapy:
IM (off-label route), IV (off-label use): Administer ~70% to 80% of the established oral dose once daily (Ref).
Dose conversion from other thyroid hormone products to levothyroxine:
Note: When switching from other thyroid hormone products to levothyroxine, monitor TSH levels 6 weeks after levothyroxine is initiated and adjust accordingly to maintain TSH levels in the target range (Ref).
Conversion from desiccated thyroid to levothyroxine: Oral: 60 or 65 mg/day of desiccated thyroid is equivalent to ~88 to 100 mcg/day of levothyroxine (Ref).
Conversion from levothyroxine/liothyronine combinations to levothyroxine: Oral: Liothyronine is ~4 times as potent as levothyroxine. Therefore, one approach is to multiply the liothyronine component by 4 and add this to the current levothyroxine component to get the new daily levothyroxine dose (Ref). For example, if the current dose is liothyronine 12.5 mcg/levothyroxine 50 mcg per day, the new levothyroxine dose would be calculated as follows:
New levothyroxine dose (mcg/day) = (4 × 12.5 mcg/day [current liothyronine dose]) + 50 mcg/day [current levothyroxine dose] = 100 mcg/day
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Mild to severe impairment: Initial: No dosage adjustment necessary (Ref).
Hemodialysis, intermittent (thrice weekly): Unlikely to be significantly dialyzed (Ref): No supplemental dose or dosage adjustment necessary (Ref).
Peritoneal dialysis: Unlikely to be significantly dialyzed (Ref): No dosage adjustment necessary (Ref).
CRRT: No dosage adjustment necessary (Ref).
PIRRT (eg, sustained, low-efficiency diafiltration): No dosage adjustment necessary (Ref).
There are no dosage adjustments provided in the manufacturer's labeling.
(For additional information see "Levothyroxine: Pediatric drug information")
Note: Oral solution is available in multiple concentrations; dosing should be presented in mcg of levothyroxine; use extra precaution when verifying product formulation and calculation of dose volumes.
Hypothyroidism, acquired or congenital: Note: Hyperactivity in older children may be minimized by starting at one-quarter (25%) of the recommended dose and increasing each week by that amount until the full dose is achieved (4 weeks).
Oral: Note: Doses should be adjusted based on clinical response and laboratory parameters. Brand name tablets are preferred over generic tablets for treating congenital hypothyroidism. Switching between different levothyroxine products and/or formulations may result in variations in the administered dose, alter thyroid-stimulating hormone (TSH) values, and is generally not recommended; if products or formulations are changed, close monitoring of TSH is recommended; patients with congenital hypothyroidism may be more sensitive to changes in formulations. Commercially available oral liquids may have a higher bioavailability than tablets; neonates and infants receiving commercially available oral liquids may need more frequent monitoring. Experts recommend against the use of extemporaneously prepared solutions/suspensions (Ref).
1 to 3 months: Oral: 10 to 15 mcg/kg/dose once daily; in severe cases of congenital hypothyroidism (serum T4 <5 mcg/dL), initiating at higher doses (12 to 17 mcg/kg/dose) may be necessary (Ref).
>3 to 6 months: Oral: 8 to 10 mcg/kg/dose once daily.
>6 to 12 months: Oral: 6 to 8 mcg/kg/dose once daily.
1 to 5 years: Oral: 5 to 6 mcg/kg/dose once daily.
6 to 12 years: Oral: 4 to 5 mcg/kg/dose once daily.
>12 years with incomplete growth and puberty: Oral: 2 to 3 mcg/kg/dose once daily.
Adolescents with growth and puberty complete: Oral: 1.6 mcg/kg/dose once daily; adjust dose by 12.5 to 25 mcg/day every 4 to 6 weeks as needed. Usual doses are ≤200 mcg/day (range: 100 to 125 mcg/day [70 kg adult]); doses ≥300 mcg/day are rare (consider poor compliance, malabsorption, and/or drug interactions).
Cardiac disease: Note: Lower initial doses are recommended.
Infants and Children: Oral: Initial: ~50% of target replacement dose; increase after 2 weeks based on free thyroxine levels (Ref).
Adolescents with growth and puberty complete: Oral: Initial: 12.5 to 25 mcg/day; adjust dose by 12.5 to 25 mcg increments at 6- to 8-week intervals as needed.
IV: Note: The relative bioavailability of injectable and oral levothyroxine has not been established; use caution when switching patients from oral to IV as accurate dosing conversions have not been established.
Infants, Children, and Adolescents: IV: Initial: ~75% to 80% of the oral dose (Ref).
Thyroid-stimulating hormone suppression in well differentiated thyroid cancer (papillary):
Infants, Children, and Adolescents: Oral: Highly individualized; doses >2 mcg/kg/day may be needed to suppress TSH to <0.1 milliunits/L in high-risk tumors; for intermediate-risk tumors, initial TSH suppression to 0.1 to 0.5 milliunits/L is recommended; for low-risk tumors, TSH may be maintained at 0.5 to 1 milliunits/L (Ref).
Deceased organ donor management (hormonal resuscitation for the deceased organ donor) (Ref):
Infants <6 months: IV: Initial: 5 mcg/kg bolus dose, followed by 1.4 mcg/kg/hour infusion.
Infants 6 to 12 months: IV: Initial: 4 mcg/kg bolus dose, followed by 1.3 mcg/kg/hour infusion.
Children 1 to 5 years: IV: Initial: 3 mcg/kg bolus dose, followed by 1.2 mcg/kg/hour infusion.
Children 6 to 12 years: IV: Initial: 2.5 mcg/kg bolus dose, followed by 1 mcg/kg/hour infusion.
Children ≥12 years and Adolescents ≤16 years: IV: Initial: 1.5 mcg/kg bolus dose, followed by 0.8 mcg/kg/hour infusion.
Adolescents >16 years: IV: Initial: 0.8 mcg/kg bolus dose, followed by 0.8 mcg/kg/hour infusion.
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
There are no dosage adjustments provided in the manufacturer's labeling.
There are no dosage adjustments provided in the manufacturer's labeling.
Refer to adult dosing.
Individual T4 requirements correlate better with lean body weight than total body weight (Ref); weight-based dosing may overestimate initial replacement doses in patients with obesity; as such, dosing in obesity must be individualized.
Cardiac symptoms (onset or worsening): Manufacturer labeling recommends reducing dosage or withholding therapy for 7 days and then resuming therapy at reduced dosage. Specific dosing recommendations are not provided.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, Oral:
Tirosint: 175 mcg, 200 mcg
Generic: 175 mcg, 200 mcg
Capsule, Oral, as sodium:
Tirosint: 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg
Generic: 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg
Solution, Intravenous:
Generic: 100 mcg/5 mL (5 mL)
Solution, Intravenous [preservative free]:
Generic: 100 mcg/5 mL (5 mL); 200 mcg/5 mL (5 mL); 500 mcg/5 mL (5 mL)
Solution, Oral:
Tirosint-SOL: 37.5 mcg/mL (1 mL); 44 mcg/mL (1 mL); 62.5 mcg/mL (1 mL)
Solution, Intravenous, as sodium [preservative free]:
Generic: 100 mcg/mL (1 mL)
Solution, Oral, as sodium:
Ermeza: 150 mcg/5 mL (75 mL, 150 mL) [contains edetate (edta) disodium]
Thyquidity: 100 mcg/5 mL (100 mL) [contains methylparaben sodium]
Tirosint-SOL: 13 mcg/mL (1 mL); 25 mcg/mL (1 mL); 50 mcg/mL (1 mL); 75 mcg/mL (1 mL); 88 mcg/mL (1 mL); 100 mcg/mL (1 mL); 112 mcg/mL (1 mL); 125 mcg/mL (1 mL); 137 mcg/mL (1 mL); 150 mcg/mL (1 mL); 175 mcg/mL (1 mL); 200 mcg/mL (1 mL)
Solution Reconstituted, Intravenous, as sodium [preservative free]:
Generic: 100 mcg (1 ea); 200 mcg (1 ea); 500 mcg (1 ea)
Tablet, Oral, as sodium:
Euthyrox: 25 mcg [contains corn starch]
Euthyrox: 25 mcg [scored; contains corn starch]
Euthyrox: 50 mcg [contains corn starch]
Euthyrox: 50 mcg [scored; contains corn starch]
Euthyrox: 75 mcg [contains corn starch]
Euthyrox: 75 mcg [scored; contains corn starch]
Euthyrox: 88 mcg [contains corn starch]
Euthyrox: 88 mcg [scored; contains corn starch]
Euthyrox: 100 mcg [contains corn starch]
Euthyrox: 100 mcg [scored; contains corn starch]
Euthyrox: 112 mcg [contains corn starch]
Euthyrox: 112 mcg [scored; contains corn starch]
Euthyrox: 125 mcg [contains corn starch]
Euthyrox: 125 mcg [scored; contains corn starch]
Euthyrox: 137 mcg [contains corn starch]
Euthyrox: 137 mcg [scored; contains corn starch]
Euthyrox: 150 mcg [contains corn starch]
Euthyrox: 150 mcg [scored; contains corn starch]
Euthyrox: 175 mcg [contains corn starch]
Euthyrox: 175 mcg [scored; contains corn starch]
Euthyrox: 200 mcg [contains corn starch]
Euthyrox: 200 mcg [scored; contains corn starch]
Levoxyl: 25 mcg [scored; contains fd&c yellow #6(sunset yellow)alumin lake]
Levoxyl: 50 mcg [scored]
Levoxyl: 75 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake]
Levoxyl: 88 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Levoxyl: 100 mcg [scored; contains fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Levoxyl: 112 mcg [scored; contains fd&c red #40(allura red ac)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake]
Levoxyl: 125 mcg [scored; contains fd&c red #40(allura red ac)aluminum lake, quinoline (d&c yellow #10) aluminum lake]
Levoxyl: 137 mcg, 150 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake]
Levoxyl: 175 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake, quinoline (d&c yellow #10) aluminum lake]
Levoxyl: 200 mcg [scored; contains quinoline (d&c yellow #10) aluminum lake]
Synthroid: 25 mcg [scored; contains fd&c yellow #6(sunset yellow)alumin lake]
Synthroid: 50 mcg [scored; contains corn starch]
Synthroid: 75 mcg [scored; contains corn starch, fd&c blue #2 (indigo carm) aluminum lake, fd&c red #40(allura red ac)aluminum lake]
Synthroid: 88 mcg [scored; contains corn starch, fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Synthroid: 100 mcg [scored; contains corn starch, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Synthroid: 112 mcg [scored; contains corn starch]
Synthroid: 125 mcg [scored; contains corn starch, fd&c blue #1 (brill blue) aluminum lake, fd&c red #40(allura red ac)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake]
Synthroid: 137 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake]
Synthroid: 150 mcg [scored; contains fd&c blue #2 (indigo carm) aluminum lake]
Synthroid: 175 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake]
Synthroid: 200 mcg [scored; contains fd&c red #40(allura red ac)aluminum lake]
Synthroid: 300 mcg [scored; contains fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Unithroid: 25 mcg [contains fd&c yellow #6(sunset yellow)alumin lake]
Unithroid: 50 mcg
Unithroid: 75 mcg [contains fd&c blue #2 (indigo carm) aluminum lake, fd&c red #40(allura red ac)aluminum lake]
Unithroid: 88 mcg [contains fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Unithroid: 100 mcg [contains fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Unithroid: 112 mcg
Unithroid: 125 mcg [contains fd&c blue #1 (brill blue) aluminum lake, fd&c red #40(allura red ac)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake]
Unithroid: 137 mcg [contains fd&c blue #1 (brill blue) aluminum lake]
Unithroid: 150 mcg [contains fd&c blue #2 (indigo carm) aluminum lake]
Unithroid: 175 mcg [contains fd&c blue #1 (brill blue) aluminum lake]
Unithroid: 200 mcg [contains fd&c red #40(allura red ac)aluminum lake]
Unithroid: 300 mcg [contains fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline yellow (d&c yellow #10)]
Generic: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Yes
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Solution, Injection:
Generic: 200 mcg/5 mL (5 mL); 500 mcg/5 mL (5 mL)
Solution Reconstituted, Injection, as sodium:
Synthroid: 500 mcg (1 ea, 10 ea)
Generic: 200 mcg (1 ea); 500 mcg (1 ea)
Tablet, Oral, as sodium:
Euthyrox: 25 mcg [DSC] [contains fd&c red #40(allura red ac)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Euthyrox: 50 mcg [DSC]
Euthyrox: 75 mcg [DSC] [contains fd&c blue #1 (brill blue) aluminum lake, fd&c blue #2 (indigo carm) aluminum lake, fd&c red #40(allura red ac)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake]
Euthyrox: 88 mcg [DSC] [contains fd&c blue #2 (indigo carm) aluminum lake, fd&c yellow #5 (tartrazine)aluminum lake]
Euthyrox: 100 mcg [DSC] [contains fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Euthyrox: 112 mcg [DSC]
Euthyrox: 125 mcg [DSC] [contains fd&c blue #1 (brill blue) aluminum lake, fd&c blue #2 (indigo carm) aluminum lake, fd&c red #40(allura red ac)aluminum lake, fd&c yellow #5 (tartrazine)aluminum lake, fd&c yellow #6(sunset yellow)alumin lake]
Euthyrox: 137 mcg [DSC] [contains fd&c blue #1 (brill blue) aluminum lake]
Euthyrox: 150 mcg [DSC], 175 mcg [DSC] [contains fd&c blue #2 (indigo carm) aluminum lake]
Euthyrox: 200 mcg [DSC]
Euthyrox: 300 mcg [DSC] [contains fd&c blue #1 (brill blue) aluminum lake, fd&c yellow #6(sunset yellow)alumin lake, quinoline (d&c yellow #10) aluminum lake]
Synthroid: 25 mcg [contains fd&c yellow #6 (sunset yellow)]
Synthroid: 50 mcg
Synthroid: 75 mcg [contains fd&c blue #2 (indigotine), fd&c red #40 (allura red ac dye)]
Synthroid: 88 mcg [contains fd&c blue #1 (brilliant blue), fd&c yellow #6 (sunset yellow), quinoline yellow (d&c yellow #10)]
Synthroid: 100 mcg [contains fd&c yellow #6 (sunset yellow), quinoline yellow (d&c yellow #10)]
Synthroid: 112 mcg
Synthroid: 125 mcg [contains fd&c blue #1 (brilliant blue), fd&c red #40 (allura red ac dye), fd&c yellow #6 (sunset yellow)]
Synthroid: 137 mcg [contains fd&c blue #1 (brilliant blue)]
Synthroid: 150 mcg [contains fd&c blue #2 (indigotine)]
Synthroid: 175 mcg [contains fd&c blue #1 (brilliant blue)]
Synthroid: 200 mcg [contains fd&c red #40 (allura red ac dye)]
Synthroid: 300 mcg [contains fd&c blue #1 (brilliant blue), fd&c yellow #6 (sunset yellow), quinoline yellow (d&c yellow #10)]
Generic: 50 mcg, 100 mcg, 150 mcg, 200 mcg
Oral: Administer consistently in the morning on an empty stomach, at least 30 to 60 minutes before food. Alternatively, may consistently administer at night 3 to 4 hours after the last meal (Ref). Do not administer within 4 hours of calcium- or iron-containing products or bile acid sequestrants.
Capsule: Must be swallowed whole; do not cut, crush, or chew.
Solution:
Ermeza: Administer directly into mouth using the 5 mL or 10 mL oral syringe (provided in carton); do not use a household teaspoon or tablespoon. For doses ≤5 mL, use the 5 mL syringe and round up or down to the nearest graduation mark (0.1 mL) and for doses >5 mL, use the 10 mL syringe and round up or down to the nearest graduation mark (0.2 mL).
Thyquidity: Administer directly into mouth using a calibrated oral syringe; do not use a household teaspoon or tablespoon.
Tirosint-SOL: May administer undiluted or diluted in water only (do not dilute with any other liquid); if administering undiluted, squeeze contents of single unit-dose ampule into mouth or onto a spoon and administer immediately. If diluting with water, squeeze contents of ampule into a glass or cup, stir, and then administer entire contents immediately. Rinse glass or cup with additional water and administer contents to ensure entire dose is consumed.
Tablet: Administer with a full glass of water (choking, gagging, and dysphagia have been reported with some formulations). May be crushed and suspended in 5 to 10 mL of water; suspension should be used immediately.
Nasogastric tube: Bioavailability of extemporaneously prepared levothyroxine (crushed tablets suspended in water) may be reduced if administered with enteral tube feeds; although data are limited, temporarily holding tube feeds before and after levothyroxine administration (eg, for 30 to 60 minutes) has been suggested (Ref). Alternatively, use of the oral solution (Tirosint-SOL) may not require interruption of tube feeds (Ref). Consider more frequent thyroid function test monitoring (eg, every 1 to 3 weeks) if prolonged administration of enteral tube feeds is required (Ref).
Parenteral: May be administered by IV injection at a maximum rate of 100 mcg/minute; may also be administered IM when oral administration is not feasible (off-label route).
Cadaveric organ recovery (hormonal resuscitation) (off-label use): After IV bolus administration, may administer as a continuous infusion (Ref).
Oral: Administer consistently on an empty stomach at the same time each day, either 30 to 60 minutes prior to breakfast or at night 3 to 4 hours after the last meal (Ref); allow families to choose morning or bedtime regimen based on convenience as efficacy is comparable between regimens (Ref). If administration on an empty stomach poses a challenge, particularly in neonates, infants, and small children, it may be administered with food (avoiding soy protein and vegetable fiber) to improve adherence and consistency of administration; consistent administration in relation to time of day and to food is most important (Ref). Do not administer within 4 hours of other medications known to interfere with levothyroxine absorption (eg, calcium- or iron-containing products or bile acid sequestrants).
Capsules: Children ≥6 years and Adolescents: Must be swallowed whole; do not cut, crush, chew, or attempt to dissolve capsules in water to prepare a suspension.
Solution:
Thyquidity: Administer directly into mouth using a calibrated oral syringe; do not use a household teaspoon or tablespoon.
Tirosint-SOL: May administer undiluted or diluted in water only (do not dilute with any other liquid).
Undiluted: Squeeze contents of single unit-dose ampule into mouth or onto a spoon and administer immediately.
Dilution with water: Squeeze contents of ampule into a glass or cup containing water, stir, and then administer entire contents immediately. Rinse glass or cup with additional water and administer contents to ensure entire dose is consumed.
Tablets: Administer with a full glass of water (choking, gagging, and dysphagia has been reported with some formulations). For infants and children who cannot swallow tablet whole, crush tablet and mix with small amount (5 to 10 mL) of water, breast milk, or non–soy-based formula and use immediately (Ref).
Nasogastric tube: Bioavailability of levothyroxine (crushed tablets suspended in water) is reduced if administered with enteral tube feeds. Since holding feedings may not be appropriate for some patients and holding feedings for at least 1 hour before and after levothyroxine administration may not completely resolve the interaction, an increase in dose (eg, additional 25 mcg in adults) may be necessary (Ref). Consider more frequent thyroid function test monitoring (eg, every 1 to 3 weeks) if prolonged administration of enteral tube feeds is required (Ref). Adult data suggest that use of the oral solution (Tirosint-SOL) may not require interruption of tube feeds (Ref).
Parenteral:
IV:
Hypothyroidism, acquired or congenital: Administer IV over 2 to 3 minutes.
Deceased organ donor management: IV bolus, followed by continuous IV infusion (Ref).
IM: May be administered intramuscularly when oral administration is not feasible (Ref).
Missed doses: Given the long half-life of levothyroxine, patients should be advised to take any missed doses (Ref).
Oral:
Hypothyroidism: Replacement or supplemental therapy in congenital or acquired hypothyroidism of any etiology. Specific indications include primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) hypothyroidism; secondary and tertiary hypothyroidism are also referred to as “central” hypothyroidism. Note: Levothyroxine monotherapy is recommended as the preferred thyroid preparation for the treatment of hypothyroidism (ATA [Jonklaas 2014]; ES [Fleseriu 2016]).
Pituitary thyrotropin-stimulating hormone suppression: An adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.
Injectable: Treatment of myxedema coma
Deceased organ donor management (hormonal resuscitation for the deceased organ donor); Subclinical hypothyroidism
Levothyroxine may be confused with lamoTRIgine, Lanoxin, levoFLOXacin, liothyronine
Levoxyl may be confused with Lanoxin, Levaquin, Luvox
Synthroid may be confused with Symmetrel
Oral solutions vary in concentration; consider total dosage in terms of mcg and not volume (mL) when converting between oral solution products.
Significant differences exist between oral and IV dosing. Use caution when converting from one route of administration to another.
To avoid errors due to misinterpretation of a decimal point, always express dosage in mcg (not mg).
Potentially life-threatening cardiovascular effects may occur with levothyroxine. The effects commonly result from overtreatment (Ref) but can also occur with initiation of levothyroxine, especially in patients with severe hypothyroidism or in patients with a history of cardiovascular disease or arrhythmias (Ref). Effects may include palpitations (Ref), tachycardia, exercise intolerance, dyspnea on exertion, widened pulse pressure, and atrial fibrillation (Ref); cardiac overload and arrhythmias have been described in infants.
Mechanism: Dose-related; several proposed mechanisms, including abnormal myocardial response to catecholamines (Ref) and increased number and sensitivity of adrenergic receptors in the cardiovascular system (Ref).
Risk factors:
• History of cardiovascular disease (Ref)
• Treatment initiation (Ref)
• Overtreatment (Ref)
• Older patients (conflicting data) (Ref)
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. Adverse reactions are primarily those of hyperthyroidism due to therapeutic overdosage.
Frequency not defined:
Cardiovascular: Angina pectoris, cardiac arrhythmia, cardiac failure, flushing, increased blood pressure, increased pulse, tachycardia
Dermatologic: Alopecia, diaphoresis, skin rash
Endocrine & metabolic: Goiter (exophthalmic; IV), menstrual disease, weight loss
Gastrointestinal: Abdominal cramps, diarrhea, increased appetite, vomiting
Genitourinary: Reduced fertility
Hepatic: Increased liver enzymes
Nervous system: Anxiety, emotional lability, fatigue, headache, heat intolerance, hyperactive behavior, idiopathic intracranial hypertension (children), insomnia, irritability, myasthenia, nervousness
Neuromuscular & skeletal: Craniosynostosis (infants; dose-related [ie, overtreatment]) (Penfold 1975), decreased bone mineral density (dose- and duration-related) (Coindre 1986; Schneider 1994), muscle spasm, slipped capital femoral epiphysis (children), tremor
Respiratory: Dyspnea
Miscellaneous: Fever
Postmarketing:
Cardiovascular: Acute myocardial infarction (Oe 2007), cardiomyopathy (takotsubo) (Balsa 2017), palpitations (Biondi 2000)
Dermatologic: Lichenoid eruption (Kaur 2003), urticaria (Sala 2008)
Gastrointestinal: Dysgeusia (Syed 2016)
Hepatic: Hepatitis (Hlaihel 2019)
Nervous system: Acute mania (Yu 2017), seizure
Injection: Uncorrected adrenal insufficiency; consider contraindications for oral therapy if using as a temporary substitute for oral treatment (off-label use) in patients with chronic hypothyroidism.
Oral: Uncorrected adrenal insufficiency; hypersensitivity to glycerol (Ermeza, Tirosint-SOL oral solution) and edetate disodium (Ermeza); Note: Consult individual product labeling as they may vary. Reported hypersensitivity to levothyroxine or any component of the formulation is not considered an absolute contraindication (ATA [Jonklaas 2014]); refer to "Warnings/Precautions."
Canadian labeling: Additional contraindications (not in US labeling): Hypersensitivity to levothyroxine or any component of the formulation; untreated pituitary insufficiency, subclinical thyrotoxicosis, overt thyrotoxicosis of any etiology, acute myocardial infarction, acute myocarditis, or acute pancarditis; pregnant women taking medications for hyperthyroidism (eg, methimazole, propylthiouracil). Note: Consult individual product labeling as they may vary.
Disease-related concerns:
• Adrenal insufficiency: Use with caution in patients with adrenal insufficiency; symptoms may be exaggerated or aggravated. Treatment with glucocorticoids should precede levothyroxine therapy in patients with adrenal insufficiency. Use is contraindicated in patients with uncorrected adrenal insufficiency.
• Benign thyroid nodules: Appropriate use: Routine use of T4 for thyroid stimulating hormone (TSH) suppression is not recommended in patients with benign thyroid nodules. Treatment should never be fully suppressive (TSH <0.1 milliunits/L) (AACE/ACE/AME [Gharib 2016]; ATA [Haugen 2016]).
- Use of T4 may be considered in association with iodine supplementation only in young patients residing in iodine-deficient areas with small thyroid nodules and no evidence of functional autonomy (AACE/ACE/AME [Gharib 2016]).
- Use should be avoided in postmenopausal patients, older adults, patients with cardiovascular disease, osteoporosis, large thyroid nodules or long-standing goiters, or low-normal TSH levels (AACE/ACE/AME [Gharib 2016]).
• Cardiovascular disease: May require lower initial dose and conservative dose titration. Refer to dosing.
• Diabetes: Use with caution in patients with diabetes mellitus (may worsen glycemic control) and diabetes insipidus (thyroid hormone increases glomerular filtration rate and downregulates aquaporin channels in the renal tubules, which could affect urinary output) (Mariani 2012).
• Osteoporosis: Thyroid hormone overreplacement may result in increased bone resorption and decreased bone mineral density, especially in postmenopausal patients; use the lowest effective dose to achieve therapy goals.
• Subacute thyroiditis: Transient and mild hypothyroidism during the recovery phase of subacute thyroiditis often can be managed without treatment; levothyroxine therapy may be required in patients with overt and clinical hypothyroidism (Farwell 2013).
Special populations:
• Older adults: Use with caution; May require lower initial dose and conservative dose titration. Refer to dosing.
Dosage form specific issues:
• Product interchangeability: Switching between different levothyroxine products may result in variations in the administered dose and altered TSH values and is not generally recommended; if formulations are changed, close monitoring of TSH is recommended (ATA [Jonklaas 2014]). Pediatric patients with congenital hypothyroidism may be more sensitive to changes in formulation (Carswell 2013).
Other warnings/precautions:
• Hypersensitivity: Patients with reported hypersensitivity to levothyroxine may be managed with dose reductions and slow titration, by switching formulations or products, or referral to an allergist (ATA [Jonklaas 2014]).
Overtreatment may result in craniosynostosis in infants and premature closure of epiphyses in children; monitor use closely. In neonates and infants, aspiration from avid suckling may occur during initiation of therapy (eg, first 2 weeks); monitor closely.
Some dosage forms may contain glycerol; glycerol may cause GI irritation and lead to vomiting and/or osmotic diarrhea. Pediatric patients ≤3 months of age are especially susceptible to fluid and electrolyte disturbances from glycerol-induced GI irritation; closely monitor these patients for signs and symptoms.
None known.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.
Amezinium: Thyroid Products may enhance the stimulatory effect of Amezinium. Risk C: Monitor therapy
Amiodarone: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Antacids: May increase the serum concentration of Thyroid Products. Risk C: Monitor therapy
Apalutamide: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Bile Acid Sequestrants: May decrease the serum concentration of Thyroid Products. Management: Administer oral thyroid products at least 4 hours prior to or one hour after bile acid sequestrants, or monitor for decreased serum concentrations and clinical effects of oral thyroid products during coadministration. Risk D: Consider therapy modification
Calcium Polystyrene Sulfonate: May decrease the serum concentration of Thyroid Products. Management: Consider administering thyroid products at least 4 hours prior to calcium polystyrene sulfonate. Monitor for signs and symptoms of hypothyroidism with concomitant use. Risk D: Consider therapy modification
Calcium Salts: May diminish the therapeutic effect of Thyroid Products. Management: Separate the doses of the thyroid product and the oral calcium supplement by at least 4 hours. Monitor for decreased therapeutic effects of thyroid products if an oral calcium supplement is initiated/dose increased. Risk D: Consider therapy modification
CarBAMazepine: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Cardiac Glycosides: Thyroid Products may decrease the serum concentration of Cardiac Glycosides. Specifically, returning to a euthyroid state from a hypothyroid state may decrease the serum concentration of cardiac glycosides. Risk C: Monitor therapy
Ciprofloxacin (Systemic): May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Estrogen Derivatives: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Etofenamate: May decrease the protein binding of Levothyroxine. Risk C: Monitor therapy
Fosphenytoin: May decrease the serum concentration of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Risk C: Monitor therapy
Furosemide: May decrease the protein binding of Thyroid Products. This may lead to a transient increase in free thyroid hormone concentrations and to a later decrease in total thyroid hormone concentrations. Risk C: Monitor therapy
Heparin: May decrease the serum concentration of Levothyroxine. Risk C: Monitor therapy
Imatinib: May decrease the serum concentration of Levothyroxine. Risk C: Monitor therapy
Iron Preparations: May decrease the serum concentration of Levothyroxine. Management: Separate oral administration of iron preparations and levothyroxine by at least 4 hours. Separation of doses is not required with parenterally administered iron preparations or levothyroxine. Risk D: Consider therapy modification
Isoproterenol: Levothyroxine may enhance the therapeutic effect of Isoproterenol. Risk C: Monitor therapy
Ketamine: Levothyroxine may enhance the hypertensive effect of Ketamine. Levothyroxine may enhance the tachycardic effect of Ketamine. Risk C: Monitor therapy
Lanthanum: May decrease the serum concentration of Thyroid Products. Management: Separate the administration of thyroid products and lanthanum by at least 4 hours. Risk D: Consider therapy modification
Magnesium Salts: May decrease the serum concentration of Levothyroxine. Management: Separate administration of oral levothyroxine and oral magnesium salts by at least 4 hours. Risk D: Consider therapy modification
Maprotiline: Levothyroxine may enhance the adverse/toxic effect of Maprotiline. Maprotiline may enhance the adverse/toxic effect of Levothyroxine. Risk C: Monitor therapy
Meclofenamate: May decrease the protein binding of Levothyroxine. Risk C: Monitor therapy
Mefenamic Acid: May decrease the protein binding of Levothyroxine. Risk C: Monitor therapy
Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Levothyroxine. Management: Separate oral administration of iron-containing multivitamins and levothyroxine by at least 4 hours. Monitor for decreased therapeutic effects of thyroid products if a multivitamin is initiated/dose increased. Risk D: Consider therapy modification
Nirmatrelvir and Ritonavir: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Orlistat: May decrease the serum concentration of Levothyroxine. Management: Separate administration of oral levothyroxine and orlistat by a least 4 hours. Monitor patients closely for signs and symptoms of hypothyroidism. Risk D: Consider therapy modification
Patiromer: May decrease the serum concentration of Levothyroxine. Management: Administer oral levothyroxine at least 3 hours before or 3 hours after patiromer. Risk D: Consider therapy modification
PHENobarbital: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Phenytoin: May decrease the serum concentration of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Risk C: Monitor therapy
Piracetam: May enhance the adverse/toxic effect of Thyroid Products. Specifically, symptoms including confusion, irritability, and sleep disorder have been described during concomitant use. Risk C: Monitor therapy
Polaprezinc: May decrease the serum concentration of Levothyroxine. Management: Separate administration of polaprezinc and levothyroxine by at least several hours, and monitor for reduced effects of levothyroxine during polaprezinc treatment. Risk D: Consider therapy modification
Primidone: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Raloxifene: May decrease the absorption of Levothyroxine. Management: Consider separating doses of raloxifene and levothyroxine by several hours. Monitor for reduced effects of levothyroxine and reduced serum concentrations of thyroxine if raloxifene and levothyroxine are used concomitantly. Risk D: Consider therapy modification
RifAMPin: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Ritonavir: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Selective Serotonin Reuptake Inhibitors: May diminish the therapeutic effect of Thyroid Products. Thyroid product dose requirements may be increased. Risk C: Monitor therapy
Semaglutide: May increase the serum concentration of Levothyroxine. Risk C: Monitor therapy
Sevelamer: May decrease the serum concentration of Levothyroxine. Management: Separate administration of sevelamer and levothyroxine by at least 4 hours to decrease the risk of a significant interaction. Monitor clinical and laboratory response to levothyroxine closely when used together with sevelamer. Risk D: Consider therapy modification
Sodium Iodide I131: Thyroid Products may diminish the therapeutic effect of Sodium Iodide I131. Management: Discontinue thyroid products before sodium iodide I-131 administration, and avoid concurrent use. Stop triiodothyronine (T3) 2 weeks before, and stop thyroxine (T4) 4 weeks before, sodium iodide I-131 administration. Risk X: Avoid combination
Sodium Polystyrene Sulfonate: May decrease the serum concentration of Thyroid Products. Management: Consider administering thyroid products at least 4 hours prior to sodium polystyrene sulfonate. Monitor for signs and symptoms of hypothyroidism with concomitant use. Risk D: Consider therapy modification
Somatropin: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Soybean: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Sucralfate: May decrease the serum concentration of Levothyroxine. Risk C: Monitor therapy
Sucroferric Oxyhydroxide: May decrease the serum concentration of Levothyroxine. Management: Administer oral/enteral levothyroxine at least 4 hours before administration of sucroferric oxyhydroxide. No interaction is anticipated with parenteral levothyroxine administration. Risk D: Consider therapy modification
Sympathomimetics: Levothyroxine may enhance the adverse/toxic effect of Sympathomimetics. Specifically, the risk of coronary insufficiency may be increased in patients with coronary artery disease. Levothyroxine may enhance the therapeutic effect of Sympathomimetics. Sympathomimetics may enhance the therapeutic effect of Levothyroxine. Risk C: Monitor therapy
Tolfenamic Acid: May decrease the protein binding of Levothyroxine. Risk C: Monitor therapy
Tricyclic Antidepressants: Thyroid Products may enhance the arrhythmogenic effect of Tricyclic Antidepressants. Thyroid Products may enhance the stimulatory effect of Tricyclic Antidepressants. Risk C: Monitor therapy
Vitamin K Antagonists (eg, warfarin): Thyroid Products may enhance the anticoagulant effect of Vitamin K Antagonists. Risk C: Monitor therapy
Taking levothyroxine with enteral nutrition may cause reduced bioavailability and may lower serum thyroxine levels leading to signs or symptoms of hypothyroidism. Soybean flour (infant formula), soy, grapefruit juice, espresso coffee, cottonseed meal, walnuts, calcium, iron, and dietary fiber may interfere with absorption of levothyroxine from the GI tract. Management: Take in the morning on an empty stomach at least 30 minutes before food. Alternatively, may consistently administer at night 3 to 4 hours after the last meal (AACE/ATA [Garber 2012]; ATA [Jonklaas 2014]). Consider an increase in dose if taken with enteral tube feed. Do not administer within 4 hours of calcium- or iron-containing products.
Overt hypothyroidism increases the risk of irregular menses and infertility; treatment with levothyroxine is recommended to normalize thyroid function in infertile patients with overt hypothyroidism who desire to become pregnant. Levothyroxine may also be used in infertile patients with subclinical hypothyroidism using assisted reproductive techniques to become pregnant (ATA [Alexander 2017]; ETA [Poppe 2021]).
Levothyroxine has not been shown to increase the risk of congenital abnormalities or miscarriage; however, normal levels of maternal thyroid hormones are required for fetal development. Untreated maternal hypothyroidism can be associated with adverse effects in both the mother and fetus, including spontaneous abortion, stillbirth, premature birth, low birth weight, impaired neurocognitive development in the offspring, abruptio placentae, gestational hypertension, and preeclampsia (ACOG 2020; ATA [Alexander 2017]).
Thyroid replacement therapy minimizes the risk of adverse pregnancy outcomes in patients with overt hypothyroidism and treatment is recommended for all patients with overt hypothyroidism during pregnancy (ACOG 2020; ATA [Alexander 2017]). Treatment may also improve some pregnancy outcomes in patients with subclinical hypothyroidism (ACOG 2020; Andersen 2020; Bein 2021). Treatment for subclinical hypothyroidism is not recommended for patients with negative thyroid peroxidase antibody status when thyroid-stimulating hormone (TSH) is in the normal pregnancy specific range (or <4 milliunits/L if trimester-specific range unavailable) (ATA [Alexander 2017]).
Levothyroxine is the preferred treatment of maternal hypothyroidism; other agents should not be used during pregnancy. Due to alterations of endogenous maternal thyroid hormones, hypothyroid patients treated with levothyroxine prior to pregnancy require a dose increase as soon as pregnancy is confirmed (ACOG 2020; ATA [Alexander 2017]). Close monitoring of pregnant patients is recommended (ATA [Alexander 2017]).
Patients in the hypothyroid phase of postpartum thyroiditis (who do not have Graves’) may also require levothyroxine treatment. This includes patients who are symptomatic, breastfeeding, planning another pregnancy, or have a TSH greater than the reference range. Dosing recommendations and duration of treatment are not standardized; treatment is individualized according to clinical assessment. Tapering of the dose with a goal of discontinuation, if possible, may begin after 6 to 12 months of treatment; the dose should be gradually decreased with TSH monitoring every 6 to 8 weeks (ATA [Alexander 2017]; Stagnaro-Green 2012).
Levothyroxine is present in breast milk.
As part of a prospective cohort study of breastfeeding mothers, 5 mother-infant pairs reported levothyroxine exposure (dose, duration, relationship to breastfeeding not provided). There were no reports of adverse reactions, including diarrhea, drowsiness, irritability, or poor feeding (Ito 1993).
Adequate thyroid hormone concentrations are required to maintain normal lactation. Patients with overt hypothyroidism or subclinical hypothyroidism experiencing poor lactation and who wish to breastfeed should be treated (ATA [Alexander 2017]).
According to the manufacturer, the decision to breastfeed during therapy should consider the risk of infant exposure, the benefits of breastfeeding to the infant, and the benefits of treatment to the mother. The World Health Organization considers levothyroxine to be compatible with breastfeeding (WHO 2002). When thyroid replacement therapy is needed in breastfeeding patients, use of levothyroxine is preferred (ATA [Alexander 2017]).
Pediatrics: Monitor closely for under/overtreatment. Undertreatment may decrease intellectual development and linear growth and lead to poor school performance due to impaired concentration and slowed mentation. Overtreatment may adversely affect brain maturation and accelerate bone age (leading to premature closure of the epiphyses and reduced adult height); craniosynostosis has been reported in infants. Perform routine clinical examinations at regular intervals (to assess mental and physical growth and development). Treated children may experience a period of catch-up growth. Monitor thyroid-stimulating hormone (TSH) and total or free T4 at 2 and 4 weeks after starting treatment, every 1 to 2 months during the first year of life, every 2 to 3 months between ages 1 to 3 years, and every 3 to 12 months thereafter until growth is completed (AAP 2006; ATA [Jonklaas 2014]); repeat tests 2 weeks after any change in dosage.
Adults: Heart rate, BP, new/worsened cardiac symptoms (eg, chest pain, palpitations, edema), clinical signs of hypo- and hyperthyroidism; bone mineral density (particularly with long-term use in postmenopausal patients).
Primary hypothyroidism:
Dosage adjustment phase: In patients who experience symptomatic improvement following initiation of therapy or dosage adjustment, measure TSH response at 6 weeks and adjust therapy as needed (ATA [Jonklaas 2014]). In those who continue to experience symptoms, consider measuring free T4 (FT4) and TSH at 3 weeks and increasing the dose if FT4 is below normal (Ross 2022a); the full effect of the dose may not be apparent at 3 weeks as levothyroxine does not achieve steady state until ~6 weeks post-initiation or dosage adjustment. Continue to measure serum TSH (and FT4 if levothyroxine steady state has not yet been achieved) every 3 to 6 weeks and adjust the dose until the TSH level is within the goal range (ATA [Jonklaas 2014]; Ross 2022e).
Maintenance phase: Once TSH levels are at goal, may recheck levels at 4 to 6 months and then annually if they remain within the goal range; if the levothyroxine dose is adjusted or if the formulation is changed, resume monitoring as instructed in the “Dosage adjustment phase” section above (ATA [Jonklaas 2014]; Ross 2022a).
Hypothyroidism in pregnant patients: Thyroid function tests should be interpreted using population-based, trimester-specific reference ranges for TSH and assay method- and trimester-specific reference ranges for serum free T4. TSH goals should target the lower half of the trimester-specific reference range (or <2.5 milliunits/L when trimester-specific targets are unavailable). Patients with or at risk for hypothyroidism should undergo TSH evaluation every 4 weeks until midgestation and at least once near 30 weeks' gestation; reassess TSH 2 to 4 weeks after initiation of therapy or dosage adjustment. In patients who were initiated on levothyroxine during pregnancy, the necessity of continuing treatment postpartum should be evaluated; some patients will not require continued therapy. TSH should be measured 6 weeks after dosage adjustment or discontinuation (ATA [Alexander 2017]).
Postpartum thyroiditis: Monitor TSH in ~4 to 8 weeks (or if new symptoms develop) following resolution of the thyrotoxic phase of PPT to screen for hypothyroid phase. In patients receiving treatment with levothyroxine during the hypothyroid phase, monitor TSH every 6 to 8 weeks and adjust the levothyroxine dose accordingly (ATA [Alexander 2017]).
Secondary or tertiary (central) hypothyroidism: Monitor response to treatment with measurement of FT4 concentrations; goal of treatment is to maintain FT4 concentrations in upper half of the reference range (or slightly higher than mid-normal) (ATA [Jonklaas 2014]; Ross 2022a). TSH levels should not be used to monitor response to therapy.
Subclinical hypothyroidism : Monitor TSH every 6 weeks and adjust the dose until the TSH level is within the goal range. Once TSH levels are at goal, may recheck levels annually if they remain within the goal range; if the levothyroxine dose is adjusted or if the formulation is changed, resume monitoring TSH every 6 weeks (ATA/AACE [Garber 2012]; ETA [Pearce 2013]; Ross 2022d).
Myxedema coma: Monitor thyroid function tests (FT4 or T4, T3) every 1 to 2 days; serial assessment of TSH trends may also be considered to determine trend towards improvement. Monitor clinical response (eg, mental status, temperature, respiratory function, cardiovascular status, electrolytes [eg, serum sodium]) to ensure adequate parenteral thyroid hormone replacement; monitor also for safety with parenteral therapy (eg, tachycardia, arrhythmia, myocardial infarction) (ATA [Jonklaas 2014]).
T4 (thyroxine) serum concentrations: Adults: ~4 to 12 mcg/dL (SI: 51 to 154 nmol/L). Note: Normal range in pregnancy: ~5.5 to 16 mcg/dL (SI: ~71 to 206 nmol/L)
T4 free (free thyroxine; free T4) serum concentrations: Adults: 0.7 to 1.8 ng/dL (SI: 9 to 23 pmol/L). A target range in the mid to upper half of the reference range has been suggested in patients with central hypothyroidism (ES [Fleseriu 2016]).
T3 total (triiodothyronine; total T3) serum concentrations: Adults: 80 to 230 ng/dL (SI: 1.2 to 3.5 nmol/L)
Thyroid-stimulating hormone (TSH) serum concentrations: Adults: Varies by laboratory and assay used; refer to laboratory provided reference range. If an upper and lower limit of normal for a third generation TSH assay is not available, a reference range of 0.45 to 4.12 milliunits/L should be considered (ATA/AACE [Garber 2012]). A higher target range of 4 to 6 milliunits/L has been suggested in patients >70 years of age (ATA [Jonklaas 2014]).
Subclinical hypothyroidism (elevated TSH; free T4 within normal range):
Severe (TSH ≥10 milliunits/L): These patients are at increased risk for heart failure and cardiovascular mortality and should be considered for treatment with L-thyroxine (ATA/AACE [Garber 2012]; ETA [Pearce 2013])
Mild to moderate (TSH 4 to 10 milliunits/L): Decision for when to treat should be tailored to individual patient based on age, symptoms, and cardiovascular risk (ATA/AACE [Garber 2012]; ETA [Pearce 2013])
Levothyroxine (T4) is a synthetic form of thyroxine, an endogenous hormone secreted by the thyroid gland. T4 is converted to its active metabolite, L-triiodothyronine (T3). Thyroid hormones (T4 and T3) then bind to thyroid receptor proteins in the cell nucleus and exert metabolic effects through control of DNA transcription and protein synthesis; involved in normal metabolism, growth, and development; promotes gluconeogenesis, increases utilization and mobilization of glycogen stores, and stimulates protein synthesis, increases basal metabolic rate
Onset of action: Oral: 3 to 5 days; peak therapeutic effect may require 4 to 6 weeks; IV: Within 6 to 8 hours
Absorption: Oral: Erratic (40% to 80% [per manufacturer]); reported bioavailability in fasting state is 79% to 81% (Dickerson 2010; Fish 1987). Absorption may be decreased by age and specific foods and drugs.
Protein binding: >99% bound to plasma proteins including thyroxine-binding globulin, thyroxine-binding prealbumin, and albumin
Metabolism: Hepatic to triiodothyronine (T3; active); ~80% thyroxine (T4) deiodinated in kidney and periphery; glucuronidation/conjugation also occurs; undergoes enterohepatic recirculation
Time to peak, serum: 2 to 4 hours
Half-life elimination: Euthyroid: 6 to 7 days; Hypothyroid: 9 to 10 days; Hyperthyroid: 3 to 4 days
Excretion: Urine (major route of elimination; decreases with age); feces (~20%)
Capsules (Levothyroxine Sodium Oral)
13 mcg (per each): $5.07
25 mcg (per each): $5.07
50 mcg (per each): $5.07
75 mcg (per each): $5.07
88 mcg (per each): $5.07
100 mcg (per each): $5.07
112 mcg (per each): $5.07
125 mcg (per each): $5.07
137 mcg (per each): $5.07
150 mcg (per each): $5.07
175 mcg (per each): $5.07
200 mcg (per each): $5.07
Capsules (Tirosint Oral)
13 mcg (per each): $5.33
25 mcg (per each): $5.33
50 mcg (per each): $5.33
75 mcg (per each): $5.33
88 mcg (per each): $5.33
100 mcg (per each): $5.33
112 mcg (per each): $5.33
125 mcg (per each): $5.33
137 mcg (per each): $5.33
150 mcg (per each): $5.33
175 mcg (per each): $5.33
200 mcg (per each): $5.33
Solution (Ermeza Oral)
150 mcg/5 mL (per mL): $2.07
Solution (Levothyroxine Sodium Intravenous)
100 mcg/5 mL (per mL): $17.98 - $26.61
100 mcg/mL (per mL): $89.92
200 mcg/5 mL (per mL): $53.21
500 mcg/5 mL (per mL): $133.03
Solution (Thyquidity Oral)
100 mcg/5 mL (per mL): $1.45
Solution (Tirosint-SOL Oral)
13 mcg/mL (per mL): $5.33
25 mcg/mL (per mL): $5.33
37.5 mcg/mL (per mL): $5.33
44 mcg/mL (per mL): $5.33
50 mcg/mL (per mL): $5.33
62.5 mcg/mL (per mL): $5.33
75 mcg/mL (per mL): $5.33
88 mcg/mL (per mL): $5.33
100 mcg/mL (per mL): $5.33
112 mcg/mL (per mL): $5.33
125 mcg/mL (per mL): $5.33
137 mcg/mL (per mL): $5.33
150 mcg/mL (per mL): $5.33
175 mcg/mL (per mL): $5.33
200 mcg/mL (per mL): $5.33
Solution (reconstituted) (Levothyroxine Sodium Intravenous)
100 mcg (per each): $110.17 - $126.70
200 mcg (per each): $228.42 - $264.00
500 mcg (per each): $570.78 - $633.49
Tablets (Euthyrox Oral)
25 mcg (per each): $0.55
50 mcg (per each): $0.62
75 mcg (per each): $0.68
88 mcg (per each): $0.70
100 mcg (per each): $0.70
112 mcg (per each): $0.81
125 mcg (per each): $0.82
137 mcg (per each): $0.83
150 mcg (per each): $0.85
175 mcg (per each): $1.01
200 mcg (per each): $1.01
Tablets (Levo-T Oral)
25 mcg (per each): $0.44
50 mcg (per each): $0.50
75 mcg (per each): $0.55
88 mcg (per each): $0.56
100 mcg (per each): $0.56
112 mcg (per each): $0.65
125 mcg (per each): $0.66
137 mcg (per each): $0.67
150 mcg (per each): $0.68
175 mcg (per each): $0.81
200 mcg (per each): $0.81
300 mcg (per each): $1.04
Tablets (Levothyroxine Sodium Oral)
25 mcg (per each): $0.09 - $1.63
50 mcg (per each): $0.09 - $1.63
75 mcg (per each): $0.09 - $1.63
88 mcg (per each): $0.13 - $1.63
100 mcg (per each): $0.09 - $1.63
112 mcg (per each): $0.09 - $1.63
125 mcg (per each): $0.09 - $1.63
137 mcg (per each): $0.19 - $1.63
150 mcg (per each): $0.09 - $1.63
175 mcg (per each): $0.10 - $1.63
200 mcg (per each): $0.13 - $1.63
300 mcg (per each): $0.13 - $1.63
Tablets (Levoxyl Oral)
25 mcg (per each): $0.88
50 mcg (per each): $1.00
75 mcg (per each): $1.11
88 mcg (per each): $1.13
100 mcg (per each): $1.13
112 mcg (per each): $1.31
125 mcg (per each): $1.33
137 mcg (per each): $1.35
150 mcg (per each): $1.37
175 mcg (per each): $1.63
200 mcg (per each): $1.58
Tablets (Synthroid Oral)
25 mcg (per each): $1.80
50 mcg (per each): $1.80
75 mcg (per each): $1.80
88 mcg (per each): $1.80
100 mcg (per each): $1.80
112 mcg (per each): $1.80
125 mcg (per each): $1.80
137 mcg (per each): $1.80
150 mcg (per each): $1.80
175 mcg (per each): $1.80
200 mcg (per each): $1.80
300 mcg (per each): $1.80
Tablets (Unithroid Oral)
25 mcg (per each): $4.78
50 mcg (per each): $4.78
75 mcg (per each): $4.79
88 mcg (per each): $4.80
100 mcg (per each): $4.81
112 mcg (per each): $4.82
125 mcg (per each): $4.82
137 mcg (per each): $4.83
150 mcg (per each): $4.83
175 mcg (per each): $4.84
200 mcg (per each): $4.84
300 mcg (per each): $4.85
Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.
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