Version July 2025
Bowel preparation before colonoscopy (off-label use): Note: This preparation should be avoided in patients with renal impairment, heart failure, decompensated cirrhosis, or baseline electrolyte abnormalities (Ref). There is no standard dosing for administration; the following recommendations are suggested by some experts.
Single agent:
Single-dose, same-day (for afternoon procedures): Oral: 1.5 bottles (450 mL or 15 oz) taken 8 hours prior to procedure, followed by clear liquids (at least three 240 mL glasses) over 2 hours. Four hours prior to the procedure, administer a second 1.5 bottle dose followed by clear liquids (three 240 mL glasses) over 1 hour (Ref).
Split-dose (evening before procedure): Oral: 1 to 1.5 bottles (300 to 450 mL or 10 to 15 oz) in the early evening (ie, between 6 and 8 PM) followed by clear liquids (at least three 240 mL glasses) over 2 hours. Patient should also be given a clear liquid diet the day prior to the procedure. Six hours prior to the colonoscopy, administer a second 1 to 1.5 bottle dose followed by clear liquids (three 240 mL glasses) over 1 hour(Ref).
Adjunctive therapy: Oral: 1 bottle (300 mL or 10 oz) in the afternoon (4 PM) the day before the procedure, followed 1 hour later by low-volume polyethylene glycol electrolyte lavage solution (Ref).
Constipation, occasional: Oral: Solution: 195 to 300 mL as a single dose or in divided doses per 24 hours.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason A. Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Altered kidney function:
eGFR ≥60 mL/minute/1.73 m2: Oral: No dosage adjustment necessary (Ref).
eGFR 30 to <60 mL/minute/1.73 m2:
Bowel preparation before colonoscopy: Oral: Avoid use (Ref).
Constipation, occasional: Oral: Consider alternative agents. If alternatives are not available, no dosage adjustment necessary, but use with caution and at the lowest effective dose (Ref).
eGFR <30 mL/minute/1.73 m2: Oral: Avoid use (Ref).
Augmented renal clearance (measured urinary CrCl ≥130 mL/minute/1.73 m2): Note: Augmented renal clearance (ARC) is a condition that occurs in certain critically ill patients without organ dysfunction and with normal serum creatinine concentrations. Younger patients (<55 years of age) admitted post trauma or major surgery are at highest risk for ARC, as well as those with sepsis, burns, or hematologic malignancies. An 8- to 24-hour measured urinary CrCl is necessary to identify these patients (Ref).
Oral: No dosage adjustment necessary (Ref).
Hemodialysis, intermittent (thrice weekly): Oral: Avoid use (Ref).
Peritoneal dialysis: Oral: Avoid use (Ref).
CRRT: Oral: Avoid use (Ref).
PIRRT (eg, sustained, low-efficiency diafiltration): Oral: Avoid use (Ref).
There are no dosage adjustments provided in the manufacturer’s labeling; however, magnesium is renally excreted.
Bowel preparation before colonoscopy (off-label use): The American Society for Gastrointestinal Endoscopy does not recommend use in the elderly (Ref). Of note, case reports of hypermagnesemia resulting in adverse outcomes in older adults with normal renal function have been reported following therapeutic and supratherapeutic doses (Ref).
Constipation, occasional: 150 to 300 mL as a single dose or daily for short-term use only. Use with caution due to risk for hypermagnesemia and magnesium toxicity (Ref).
(For additional information see "Magnesium citrate: Pediatric drug information")
Bowel preparation: Limited data available: Oral: Oral Solution: Children >6 years and Adolescents: 4 to 6 mL/kg/day; may administer as a single dose or in divided doses the day before the procedure; maximum daily dose: 300 mL/day (Ref).
Constipation:
Note: Use of magnesium citrate has generally been replaced with other laxatives (eg, PEG solutions, lactulose) less likely to cause adverse effects (eg, electrolyte disturbances); it is no longer included in the NASPHGAN guidelines (Ref):
Oral solution:
Children 2 to <6 years: Oral: 60 to 90 mL as a single dose or in divided doses.
Children 6 to <12 years: Oral: 90 to 210 mL as a single dose or in divided doses.
Children ≥12 years and Adolescents: Oral: 150 to 300 mL as a single dose or in divided doses.
There are no dosage adjustments provided in the manufacturer's labeling; however, magnesium is renally excreted. Patients in severe renal failure should not receive magnesium due to toxicity from accumulation. Patients with a CrCl <25 mL/minute receiving magnesium should have serum magnesium levels monitored.
There are no dosage adjustments provided in the manufacturer's labeling.
There are no adverse reactions listed in the manufacturer's labeling.
OTC labeling: When used for self-medication, do not use if on low salt diet
Disease-related concerns:
• Constipation (self-medication, OTC use): Appropriate use: For occasional use only; serious side effects may occur with prolonged use. For use only under the supervision of a physician in patients with kidney dysfunction, sodium- or magnesium-restricted diets, abdominal pain/nausea/vomiting, with a sudden change in bowel habits which has persisted for >2 weeks, or use of a laxative for >1 week. If rectal bleeding develops or a bowel movement does not occur after use, discontinue use and consult a health care provider.
• Neuromuscular disease: Use with extreme caution in patients with myasthenia gravis or other neuromuscular disease.
• Renal impairment: Use with caution in patients with renal impairment; accumulation of magnesium may lead to magnesium intoxication.
1 g magnesium citrate ≈ elemental magnesium 160 mg = magnesium 13.17 mEq = magnesium 6.59 mmol
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Solution, Oral:
Citroma: 1.745 g/30 mL (296 mL) [low sodium; contains alcohol, usp, benzoic acid, disodium edta]
Freskaro Magnesium Citrate: 1.745 g/30 mL (296 mL) [sugar free; contains benzoic acid, edetate (edta) disodium; lemon flavor]
FT Magnesium Citrate: 1.745 g/30 mL (296 mL) [contains alcohol, usp, benzoic acid, edetate (edta) disodium]
GoodSense Magnesium Citrate: 1.745 g/30 mL (296 mL) [saccharin free; contains benzoic acid, disodium edta]
OneLax Magnesium Citrate: 1.745 g/30 mL (296 mL) [dye free, sugar free; contains disodium edta, saccharin sodium, sodium benzoate]
OneLax Magnesium Citrate: 1.745 g/30 mL (296 mL) [dye free, sugar free; contains disodium edta, saccharin sodium, sodium benzoate; cherry flavor]
OneLax Magnesium Citrate: 1.745 g/30 mL (296 mL) [dye free, sugar free; contains disodium edta, saccharin sodium, sodium benzoate; lemon flavor]
Generic: 1.745 g/30 mL (296 mL)
Tablet, Oral:
Generic: 100 mg
Tablet Chewable, Oral:
SlowMag MG Muscle Hlth/Recover: 85 mg [berry flavor]
May be product dependent
Chewable (SlowMag MG Muscle Hlth/Recover Oral)
85 mg (per each): $0.17
Solution (Citroma Oral)
1.745 g/30 mL (per mL): $0.00
Solution (Freskaro Magnesium Citrate Oral)
1.745 g/30 mL (per mL): $0.00
Solution (OneLax Magnesium Citrate Oral)
1.745 g/30 mL (per mL): $0.01
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.
Oral: To increase palatability, chill the solution prior to administration. When used for occasional constipation, administer each dose with 8 oz (240 mL) of liquid.
Oral: Administer with full glass (240 mL [8 oz]) of liquid; to increase palatability of the oral solution, chill the solution prior to administration.
Constipation, occasional: Treatment of occasional constipation.
Bowel preparation before colonoscopy
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 drug interactions program by clicking on the “Launch drug interactions program” link above.
Alfacalcidol: May increase serum concentration of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving alfacalcidol. If magnesium-containing products must be used with alfacalcidol, serum magnesium concentrations should be monitored closely. Risk D: Consider Therapy Modification
Alpha-Lipoic Acid: Magnesium Salts may decrease absorption of Alpha-Lipoic Acid. Alpha-Lipoic Acid may decrease absorption of Magnesium Salts. Management: Separate administration of alpha-lipoic acid from that of any magnesium-containing compounds by several hours. If alpha-lipoic acid is given 30 minutes before breakfast, then administer oral magnesium-containing products at lunch or dinner. Risk D: Consider Therapy Modification
Aluminum Hydroxide: Citric Acid Derivatives may increase absorption of Aluminum Hydroxide. Risk C: Monitor
Baloxavir Marboxil: Polyvalent Cation Containing Products may decrease serum concentration of Baloxavir Marboxil. Risk X: Avoid
Bictegravir: Polyvalent Cation Containing Products may decrease serum concentration of Bictegravir. Management: Administer bictegravir at least 2 hours before or 6 hours after polyvalent cation containing products. Coadministration of bictegravir with or 2 hours after most polyvalent cation products is not recommended. Risk D: Consider Therapy Modification
Bisphosphonate Derivatives: Polyvalent Cation Containing Products may decrease serum concentration of Bisphosphonate Derivatives. Management: Avoid administration of oral medications containing polyvalent cations within: 2 hours before or after tiludronate/clodronate/etidronate; 60 minutes after oral ibandronate; or 30 minutes after alendronate/risedronate. Risk D: Consider Therapy Modification
Cabotegravir: Polyvalent Cation Containing Products may decrease serum concentration of Cabotegravir. Management: Administer polyvalent cation containing products at least 2 hours before or 4 hours after oral cabotegravir. Risk D: Consider Therapy Modification
Calcitriol (Systemic): May increase serum concentration of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving calcitriol. If magnesium-containing products must be used with calcitriol, serum magnesium concentrations should be monitored closely. Risk D: Consider Therapy Modification
Calcium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may increase adverse/toxic effects of Calcium Polystyrene Sulfonate. More specifically, concomitant use of calcium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Risk X: Avoid
Deferiprone: Polyvalent Cation Containing Products may decrease serum concentration of Deferiprone. Management: Separate administration of deferiprone and oral medications or supplements that contain polyvalent cations by at least 4 hours. Risk D: Consider Therapy Modification
Dolutegravir: Magnesium Salts may decrease serum concentration of Dolutegravir. Management: Administer dolutegravir at least 2 hours before or 6 hours after oral magnesium salts. Administer the dolutegravir/rilpivirine combination product at least 4 hours before or 6 hours after oral magnesium salts. Risk D: Consider Therapy Modification
Doxercalciferol: May increase hypermagnesemic effects of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving doxercalciferol. If magnesium-containing products must be used with doxercalciferol, serum magnesium concentrations should be monitored closely. Risk D: Consider Therapy Modification
Eltrombopag: Polyvalent Cation Containing Products may decrease serum concentration of Eltrombopag. Management: Administer eltrombopag at least 2 hours before or 4 hours after oral administration of any polyvalent cation containing product. Risk D: Consider Therapy Modification
Elvitegravir: Polyvalent Cation Containing Products may decrease serum concentration of Elvitegravir. Management: Administer elvitegravir-containing products 2 hours before, or 2 to 6 hours after, the administration of polyvalent cation containing products. Risk D: Consider Therapy Modification
Gabapentin: Magnesium Salts may increase CNS depressant effects of Gabapentin. Specifically, high dose intravenous/epidural magnesium sulfate may enhance the CNS depressant effects of gabapentin. Magnesium Salts may decrease serum concentration of Gabapentin. Management: Administer gabapentin at least 2 hours after use of a magnesium-containing antacid. Monitor patients closely for evidence of reduced response to gabapentin therapy. Monitor for CNS depression if high dose IV/epidural magnesium sulfate is used. Risk D: Consider Therapy Modification
Levonadifloxacin: Magnesium Salts may decrease serum concentration of Levonadifloxacin. Risk X: Avoid
Levothyroxine: Magnesium Salts may decrease serum concentration of Levothyroxine. Management: Separate administration of oral levothyroxine and oral magnesium salts by at least 4 hours. Risk D: Consider Therapy Modification
Multivitamins/Fluoride (with ADE): Magnesium Salts may decrease serum concentration of Multivitamins/Fluoride (with ADE). Specifically, magnesium salts may decrease fluoride absorption. Management: To avoid this potential interaction separate the administration of magnesium salts from administration of a fluoride-containing product by at least 1 hour. Risk D: Consider Therapy Modification
Neuromuscular-Blocking Agents: Magnesium Salts may increase neuromuscular-blocking effects of Neuromuscular-Blocking Agents. Risk C: Monitor
PenicillAMINE: Polyvalent Cation Containing Products may decrease serum concentration of PenicillAMINE. Management: Separate the administration of penicillamine and oral polyvalent cation containing products by at least 1 hour. Risk D: Consider Therapy Modification
Phosphate Supplements: Magnesium Salts may decrease serum concentration of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an oral magnesium salt as possible to minimize the significance of this interaction. Risk D: Consider Therapy Modification
Quinolones: Magnesium Salts may decrease serum concentration of Quinolones. Management: Administer oral quinolones several hours before (4 h for moxi/pe/spar/enox-, 2 h for others) or after (8 h for moxi-, 6 h for cipro/dela-, 4 h for lome/pe/enox-, 3 h for gemi-, and 2 h for levo-, nor-, or ofloxacin or nalidixic acid) oral magnesium salts. Risk D: Consider Therapy Modification
Raltegravir: Magnesium Salts may decrease serum concentration of Raltegravir. Management: Avoid the use of oral / enteral magnesium salts with raltegravir. No dose separation schedule has been established that adequately reduces the magnitude of interaction. Risk X: Avoid
Roxadustat: Polyvalent Cation Containing Products may decrease serum concentration of Roxadustat. Management: Administer roxadustat at least 1 hour after the administration of oral polyvalent cation containing products. Risk D: Consider Therapy Modification
Sodium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may increase adverse/toxic effects of Sodium Polystyrene Sulfonate. More specifically, concomitant use of sodium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Risk X: Avoid
Tetracyclines: Magnesium Salts may decrease absorption of Tetracyclines. Only applicable to oral preparations of each agent. Management: Avoid coadministration of oral magnesium salts and oral tetracyclines. If coadministration cannot be avoided, administer oral magnesium at least 2 hours before, or 4 hours after, oral tetracyclines. Monitor for decreased tetracycline therapeutic effects. Risk D: Consider Therapy Modification
Trientine: Polyvalent Cation Containing Products may decrease serum concentration of Trientine. Management: Avoid concomitant use of trientine and polyvalent cations. If oral iron supplements are required, separate the administration by 2 hours. For other oral polyvalent cations, give trientine 1 hour before, or 1 to 2 hours after the polyvalent cation. Risk D: Consider Therapy Modification
Unithiol: May decrease therapeutic effects of Polyvalent Cation Containing Products. Risk X: Avoid
Magnesium crosses the placenta; serum concentrations in the fetus are similar to those in the mother (Idama 1998; Osada 2002).
When dietary changes and lifestyle modifications are insufficient, agents other than magnesium citrate are recommended for the treatment of constipation in pregnant women (Gomes 2018; Shin 2015).
Magnesium is present in breast milk; concentrations remain constant during the first year of lactation and are not influenced by dietary intake under normal conditions (IOM 1997).
Some products may contain potassium and/or sodium.
Serum magnesium: 1.6 to 2.6 mg/dL (SI: 0.7 to 1.1 mmol/L or 1.3 to 2.1 mEq/L); slightly different ranges are reported by different laboratories
Promotes bowel evacuation by causing osmotic retention of fluid which distends the colon with increased peristaltic activity
Onset of laxative effect: Oral solution: 0.5 to 6 hours
Absorption: Oral: Up to 30%
Excretion: Urine (IOM 1997); feces (as unabsorbed drug)
