Usual dosage range: Oral: 250 mg to 1 g every 6 hours or 500 mg every 12 hours (maximum: 4 g/day).
Endocarditis, prophylaxis (dental or invasive respiratory tract procedures) (alternative agent for patients with nonsevere, non-IgE-mediated penicillin allergy) (off-label use): Oral: 2 g 30 to 60 minutes prior to procedure; if inadvertently not given prior to the procedure, may be administered up to 2 hours after the procedure. Note: Reserve for select situations (cardiac condition with the highest risk of adverse endocarditis outcomes and procedure likely to result in bacteremia with an organism that can cause endocarditis) (Ref).
Mastitis, lactational:
Note: Reserve for nonsevere infection in the absence of risk for resistant pathogens (eg, methicillin-resistant S. aureus) (Ref).
Oral: 500 mg 4 times daily for 10 to 14 days; shorter courses (eg, 5 to 7 days) may be considered for patients with rapid clinical resolution (Ref).
Prosthetic joint infection (off-label use): Oral: Treatment (following pathogen-specific IV therapy in patients undergoing 1-stage exchange or debridement with retention of prosthesis). Note: Duration ranges from a minimum of 3 months to indefinitely, depending on patient-specific factors (Ref):
Staphylococci (methicillin-susceptible): 500 mg every 6 to 8 hours or 1 g every 8 to 12 hours. For the first 3 to 6 months of therapy, combine with rifampin (Ref).
Streptococci, beta-hemolytic (alternative agent): 500 mg every 6 to 8 hours (Ref).
Cutibacterium spp (alternative agent): 500 mg every 6 to 8 hours (Ref).
Skin and soft tissue infection:
Note: Not an appropriate agent if methicillin-resistant S. aureus is suspected or confirmed (Ref).
Cellulitis (nonpurulent)/erysipelas, mild: Oral: 500 mg 4 times daily for ≥5 days but may extend up to 14 days depending on severity and clinical response (Ref).
Impetigo or ecthyma: Note: For impetigo, reserve systemic therapy for patients with numerous lesions or in outbreak settings to decrease transmission (Ref).
Oral: 250 to 500 mg 4 times daily for 7 days (Ref).
Urinary tract infection:
Asymptomatic bacteriuria (≥105 CFU per mL) in pregnancy: Oral: 250 to 500 mg every 6 hours for 4 to 7 days (Ref).
Cystitis, acute uncomplicated or acute simple cystitis (infection limited to the bladder without signs/symptoms of upper tract, prostate, or systemic infection), treatment (alternative agent): Note: Use only when first-line agents cannot be used; limited evidence suggests inferior efficacy of oral beta-lactams (Ref).
Oral: 250 to 500 mg every 6 hours for 5 to 7 days (Ref).
Cystitis, prophylaxis for recurrent infection:
Note: May be considered in nonpregnant women with bothersome, frequently recurrent cystitis despite nonantimicrobial preventive measures. The optimal duration has not been established; duration ranges from 3 to 12 months, with periodic reassessment (Ref).
Continuous prophylaxis: Oral: 125 to 250 mg once daily (Ref).
Postcoital prophylaxis (females with cystitis temporally related to sexual intercourse): Oral: 250 mg as a single dose immediately before or after sexual intercourse (Ref).
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 A. Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Note: Renally adjusted dose recommendations are based on doses of 250 to 500 mg every 6 to 8 hours or 500 mg to 1 g every 12 hours.
Altered kidney function (expert opinion derived from (Ref)):
CrCl ≥30 mL/minute: No dosage adjustment necessary.
CrCl 15 to <30 mL/minute: 250 to 500 mg every 8 to 12 hours.
CrCl <15 mL/minute: 250 to 500 mg every 12 to 24 hours.
Hemodialysis, intermittent (thrice weekly): Dialyzable (50%) (Ref):
250 to 500 mg every 12 to 24 hours (Ref). Administer after hemodialysis on dialysis days.
Peritoneal dialysis: Limited clearance by peritoneal dialysis (Ref).
250 to 500 mg every 12 to 24 hours (Ref).
There are no dosage adjustments provided in the manufacturer's labeling.
Refer to adult dosing.
(For additional information see "Cephalexin: Pediatric drug information")
General dosing, susceptible infection:
Infants, Children, and Adolescents:
Mild to moderate infection: Oral: 25 to 50 mg/kg/day divided every 6 to 12 hours; maximum daily dose: 2,000 mg/day (Ref). Note: At these daily doses, dosing less frequently than every 6 hours may be inadequate for many Staphylococcus aureus isolates (Ref).
Severe infection: Oral: 75 to 100 mg/kg/day divided every 6 to 8 hours; maximum daily dose: 4,000 mg/day (Ref).
Endocarditis, prophylaxis before invasive dental procedures (alternate agent): Limited data available:
Note: Alternative agent for use in patients with penicillin or ampicillin allergy, excluding those with a history of anaphylaxis, angioedema, or urticaria (Ref). Recommended only in patients who are at highest risk for infective endocarditis (IE) or adverse outcomes (eg, history of IE, cardiac valve repair using prosthetic valves or material, unrepaired cyanotic congenital heart disease [CHD], left ventricular assist device or implantable heart, repaired CHD with prosthetic material or device during first 6 months after procedure, pulmonary artery valve or conduit placement [eg, Melody valve, Contegra conduit], repaired CHD with residual defects at the site or adjacent to site of prosthetic patch or device, heart transplant recipients with cardiac valvulopathy) (Ref).
Infants, Children, and Adolescents: Oral: 50 mg/kg as a single dose administered 30 to 60 minutes prior to dental procedure; maximum dose: 2,000 mg/dose (Ref).
Exit-site or tunnel infection, peritoneal dialysis catheter: Limited data available:
Infants, Children, and Adolescents: Oral: 10 to 20 mg/kg/day once daily or divided every 12 hours; maximum dose: 1,000 mg/dose (Ref).
Duration of therapy (Ref):
Exit-site infection: ≥2 weeks and for at least 7 days after complete resolution; ≥3 weeks for S. aureus.
Tunnel infection: 2 to 4 weeks.
Osteoarticular infection, acute (eg, septic [bacterial] arthritis, osteomyelitis): Step-down therapy following parenteral treatment:
Infants, Children, and Adolescents: Oral: 100 to 150 mg/kg/day divided every 6 to 8 hours; usual maximum dose: 1,000 mg/dose (Ref); some experts recommend a higher maximum dose of 1,500 mg/dose (Ref). Minimum total duration is 2 to 3 weeks for septic arthritis and 3 to 4 weeks for osteomyelitis; however, duration is often longer and individualized based on several factors, including causative pathogen, response to therapy, and normalization of inflammatory markers (Ref).
Note: In some cases (eg, S. aureus infection), an every-6-hour frequency may be preferred to optimize dosing; if using every-8-hour frequency, use doses on the higher end of the range (Ref).
Otitis media, acute (AOM) (alternative agent): Note: Not recommended for empiric therapy; may be considered when a susceptible pathogen has been isolated (Ref).
Children and Adolescents <15 years: Oral: 75 to 100 mg/kg/day divided every 6 hours for 10 days; maximum dose not established for AOM. Usual maximum adult dose for other indications: Mild to moderate infections: 500 mg/dose; severe infections: 1,000 mg/dose (Ref).
Pneumonia, community-acquired: Pathogen-directed therapy for mild infection or step-down therapy following parenteral treatment:
Infants >3 months, Children, and Adolescents: Oral: 75 to 100 mg/kg/day divided every 6 to 8 hours; maximum daily dose: 4,000 mg/day (Ref). The usual total duration of therapy for uncomplicated pneumonia is 5 to 10 days (Ref).
Skin and soft tissue infection (SSTI): Note: Not appropriate as monotherapy if methicillin-resistant S. aureus is suspected or confirmed.
Cellulitis, erysipelas, purulent/fluctuant SSTI: Infants, Children, and Adolescents: Oral: 25 to 100 mg/kg/day divided every 6 to 8 hours; maximum dose: 500 mg/dose (Ref). Doses on the higher end of the range are preferred for more severe infection or when methicillin-susceptible Staphylococcus aureus is suspected (Ref). Typical duration is 5 days for uncomplicated infection but may be extended if clinical response is inadequate (Ref).
Impetigo, ecthyma: Infants, Children, and Adolescents: Oral: 25 to 50 mg/kg/day divided every 6 to 8 hours; usual adult dose: 250 to 500 mg every 6 hours; maximum daily dose: 2,000 mg/day. Duration of treatment is 7 days (Ref).
Streptococcus, group A; pharyngitis/tonsillitis (alternative agent for nonanaphylactic penicillin allergy): Children and Adolescents: Oral: 40 mg/kg/day divided every 12 hours for 10 days; maximum dose: 500 mg/dose (Ref).
Urinary tract infection:
Infants, Children, and Adolescents:
Mild to moderate (eg, cystitis): Oral: 25 to 50 mg/kg/day divided every 6 to 12 hours; maximum dose: 500 mg/dose (Ref).
Severe (eg, pyelonephritis): Oral: 50 to 100 mg/kg/day divided every 6 to 8 hours; maximum dose: 1,000 mg/dose (Ref).
Duration of therapy: Should be individualized based on patient age, severity/extent of infection, and clinical response; typical duration is 7 to 14 days, though it may be as short as 3 to 5 days (eg, for uncomplicated cystitis in patients ≥2 years of age) (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Weight-based dosing: Infants, Children, and Adolescents: There are no recommendations in the manufacturer's labeling; the following adjustments have been recommended (Aronoff 2007). Note: Renally-adjusted dose recommendations are based on doses of 25 to 50 mg/kg/day divided every 6 hours: Oral:
CrCl >50 mL/minute/1.73 m2: No adjustment necessary.
CrCl 30 to 50 mL/minute/1.73 m2: 5 to 10 mg/kg/dose every 8 hours (maximum dose: 500 mg/dose).
CrCl 10 to 29 mL/minute/1.73 m2: 5 to 10 mg/kg/dose every 12 hours (maximum dose: 500 mg/dose).
CrCl <10 mL/minute/1.73 m2: 5 to 10 mg/kg/dose every 24 hours (maximum dose: 500 mg/dose).
Intermittent hemodialysis: 5 to 10 mg/kg/dose every 24 hours after dialysis (maximum dose: 500 mg/dose).
Peritoneal dialysis: 5 to 10 mg/kg/dose every 24 hours (maximum dose: 500 mg/dose).
Fixed dosing: Adolescents ≥15 years: Oral:
CrCl ≥60 mL/minute: No dosage adjustment necessary.
CrCl 30 to 59 mL/minute: No adjustment necessary; maximum recommended daily dose: 1,000 mg/day.
CrCl 15 to 29 mL/minute: 250 mg every 8 to 12 hours.
CrCl 5 to 14 mL/minute (not yet on dialysis): 250 mg every 24 hours.
CrCl 1 to 4 mL/minute (not yet on dialysis): 250 mg every 48 to 60 hours.
There are no dosing adjustments provided in the manufacturer's labeling.
Clostridioides difficile infection has occurred with cephalexin, including Clostridioides difficile associated diarrhea and Clostridioides difficile colitis (Ref).
Mechanism: Dose- and time-related; related to cumulative antibiotic exposure. Cephalexin may cause disruption of the intestinal microbiota resulting in the overgrowth of pathogens, such as C. difficile (Ref).
Onset: Varied; may start on the first day of antibiotic therapy or up to 3 months postantibiotic (Ref).
Risk factors:
• Antibiotic exposure (highest risk factor) (Ref)
• Type of antibiotic (Ref)
• Long durations in a hospitalization or other healthcare setting (recent or current) (Ref)
• Older adults (Ref)
• Immunocompromised conditions (Ref)
• A serious underlying condition (Ref)
• GI surgery/manipulation (Ref)
• Antiulcer medications (eg, proton pump inhibitors, H2 blockers) (Ref)
• Chemotherapy (Ref)
Immune hemolytic anemia has occurred in patients receiving cephalosporins, including very rarely cephalexin (Ref). Positive direct Coombs test, acute intravascular hemolysis, and pigment nephropathy have been reported (Ref).
Mechanism: Non–dose-related; immunologic (ie, induces complement activating drug-dependent antibodies [mainly IgM-type] resulting in immune-complexes) (Ref); however, nonimmune cases have also been reported (Ref).
Onset: Varied; occurs several minutes to 9 days after the first dose (Ref).
Risk factors:
• Cross-reactivity with other cephalosporins (Ref)
Hypersensitivity reactions (immediate and delayed) range from skin rash to rare cases of anaphylaxis (Ref). Severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome and toxic epidermal necrolysis (Ref), drug rash with eosinophilia and systemic symptoms (Ref), and acute generalized exanthematous pustulosis (Ref) have been reported.
Mechanism: Non–dose-related; immunologic. Immediate hypersensitivity reactions (eg, anaphylaxis, urticaria) are IgE-mediated. Delayed hypersensitivity reactions, including maculopapular rash and SCARs, are T-cell-mediated (Ref).
Onset: Immediate hypersensitivity reactions: Rapid; occurs within 1 hour of administration but may occur up to 6 hours after exposure (Ref). Delayed hypersensitivity reactions: Maculopapular reactions: Intermediate; occurs 7 to 10 days after initiation. Other reactions (including SCARs): Varied; occurs 1 to 8 weeks after initiation (Ref).
Risk factors:
• Cross-reactivity between penicillins and cephalosporins and among cephalosporins is mostly related to side chain similarity (Ref). For cephalexin, ampicillin, and amoxicillin share identical or similar side chains, respectively, and cross-reactions with these specifically have been reported (Ref).
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
Frequency not defined:
Dermatologic: Erythema multiforme, genital pruritus
Gastrointestinal: Abdominal pain, diarrhea, dyspepsia, gastritis, nausea, pruritus ani, vomiting
Genitourinary: Genital candidiasis, vaginal discharge, vaginitis
Hematologic & oncologic: Eosinophilia, neutropenia, thrombocytopenia
Hepatic: Cholestatic jaundice, increased serum alanine aminotransferase, increased serum aspartate aminotransferase
Hypersensitivity: Anaphylaxis
Nervous system: Agitation, confusion, dizziness, fatigue, hallucination, headache
Neuromuscular & skeletal: Arthralgia, arthritis, arthropathy
Renal: Interstitial nephritis
Postmarketing:
Dermatologic: Acute generalized exanthematous pustulosis (Da Cunha 2018), skin rash (Goh 2021), Stevens-Johnson syndrome (Murray 1992), toxic epidermal necrolysis (Haferman 2014), urticaria (Goh 2021)
Gastrointestinal: Clostridioides difficile associated diarrhea (Wilcox 2017), Clostridioides difficile colitis (Wilcox 2017)
Hematologic & oncologic: Acute intravascular hemolysis (Forbes 1972), hemolytic anemia (Thiessen 2017), positive direct Coombs test (Baradhi 2015)
Hepatic: Hepatitis (Skoog 2004)
Hypersensitivity: Angioedema (Goh 2021)
Immunologic: Drug reaction with eosinophilia and systemic symptoms (Machnikowski 2021)
Renal: Renal disease (pigment nephropathy from immune hemolytic anemia) (Baradhi 2015)
Hypersensitivity to cephalexin, other cephalosporins, or any component of the formulation
Concerns related to adverse effects:
• Elevated INR: May be associated with increased INR, especially in nutritionally-deficient patients, prolonged treatment, hepatic or renal disease.
• Penicillin allergy: Use with caution in patients with a history of penicillin allergy, especially IgE-mediated reactions (eg, anaphylaxis, angioedema, urticaria).
• Seizure disorder: Use with caution in patients with a history of seizure disorder; high levels, particularly in the presence of renal impairment, may increase risk of seizures.
• Superinfection: Prolonged use may result in fungal or bacterial superinfection.
Disease-related concerns:
• Renal impairment: Use with caution in patients with renal impairment; modify dosage in severe impairment.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Capsule, Oral:
Keflex: 250 mg [DSC], 500 mg [DSC], 750 mg [DSC] [contains fd&c blue #1 (brilliant blue), fd&c yellow #6 (sunset yellow), quinoline yellow (d&c yellow #10)]
Generic: 250 mg, 500 mg, 750 mg
Suspension Reconstituted, Oral:
Generic: 125 mg/5 mL (100 mL, 200 mL); 250 mg/5 mL (100 mL, 200 mL)
Tablet, Oral:
Generic: 250 mg, 500 mg
Yes
Capsules (Cephalexin Oral)
250 mg (per each): $0.19 - $0.87
500 mg (per each): $0.34 - $1.97
750 mg (per each): $9.38
Suspension (reconstituted) (Cephalexin Oral)
125 mg/5 mL (per mL): $0.23 - $2.40
250 mg/5 mL (per mL): $0.23 - $3.60
Tablets (Cephalexin Oral)
250 mg (per each): $4.56
500 mg (per each): $8.96
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.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, Oral:
Generic: 250 mg, 500 mg
Suspension Reconstituted, Oral:
Generic: 125 mg/5 mL (100 mL, 150 mL, 200 mL); 250 mg/5 mL (100 mL, 120 mL, 150 mL, 200 mL)
Tablet, Oral:
Generic: 250 mg, 500 mg
Oral: Administer without regard to food. If GI distress, take with food. Give around-the-clock to promote less variation in peak and trough serum levels.
Oral: Administer without regard to food.
Oral suspension: Shake suspension well before use. Administer with an accurate measuring device; do not use a household teaspoon (overdosage may occur).
Bone infections: Treatment of bone infections caused by Staphylococcus aureus and/or Proteus mirabilis.
Otitis media: Treatment of otitis media caused by Streptococcus pneumoniae, Haemophilus influenzae, S. aureus, Streptococcus pyogenes, and Moraxella catarrhalis.
Respiratory tract infections: Treatment of respiratory tract infections (including pharyngitis) caused by S. pneumoniae and S. pyogenes.
Skin and soft tissue infections: Treatment of skin and soft tissue infections caused by S. aureus and/or S. pyogenes.
Urinary tract infections: Treatment of genitourinary tract infections, including acute prostatitis, caused by Escherichia coli, P. mirabilis, and Klebsiella pneumoniae.
Endocarditis, prophylaxis; Prosthetic joint infection
Cephalexin may be confused with cefaclor, ceFAZolin, ciprofloxacin
Keflex may be confused with Keppra, Valtrex
Substrate of OAT1/3
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.
Aminoglycosides: Cephalosporins may enhance the nephrotoxic effect of Aminoglycosides. Cephalosporins may decrease the serum concentration of Aminoglycosides. Risk C: Monitor therapy
Bacillus clausii: Antibiotics may diminish the therapeutic effect of Bacillus clausii. Management: Bacillus clausii should be taken in between antibiotic doses during concomitant therapy. Risk D: Consider therapy modification
BCG (Intravesical): Antibiotics may diminish the therapeutic effect of BCG (Intravesical). Risk X: Avoid combination
BCG Vaccine (Immunization): Antibiotics may diminish the therapeutic effect of BCG Vaccine (Immunization). Risk C: Monitor therapy
Cholera Vaccine: Antibiotics may diminish the therapeutic effect of Cholera Vaccine. Management: Avoid cholera vaccine in patients receiving systemic antibiotics, and within 14 days following the use of oral or parenteral antibiotics. Risk X: Avoid combination
Fecal Microbiota (Live) (Oral): May diminish the therapeutic effect of Antibiotics. Risk X: Avoid combination
Fecal Microbiota (Live) (Rectal): Antibiotics may diminish the therapeutic effect of Fecal Microbiota (Live) (Rectal). Risk X: Avoid combination
Furosemide: May enhance the nephrotoxic effect of Cephalosporins. Risk C: Monitor therapy
Immune Checkpoint Inhibitors (Anti-PD-1, -PD-L1, and -CTLA4 Therapies): Antibiotics may diminish the therapeutic effect of Immune Checkpoint Inhibitors (Anti-PD-1, -PD-L1, and -CTLA4 Therapies). Risk C: Monitor therapy
Lactobacillus and Estriol: Antibiotics may diminish the therapeutic effect of Lactobacillus and Estriol. Risk C: Monitor therapy
MetFORMIN: Cephalexin may increase the serum concentration of MetFORMIN. Risk C: Monitor therapy
Probenecid: May increase the serum concentration of Cephalosporins. Risk C: Monitor therapy
Sodium Picosulfate: Antibiotics may diminish the therapeutic effect of Sodium Picosulfate. Management: Consider using an alternative product for bowel cleansing prior to a colonoscopy in patients who have recently used or are concurrently using an antibiotic. Risk D: Consider therapy modification
Sucroferric Oxyhydroxide: May decrease the serum concentration of Cephalexin. Management: Administer cephalexin at least 1 hour before administration of sucroferric oxyhydroxide. Risk D: Consider therapy modification
Typhoid Vaccine: Antibiotics may diminish the therapeutic effect of Typhoid Vaccine. Only the live attenuated Ty21a strain is affected. Management: Avoid use of live attenuated typhoid vaccine (Ty21a) in patients being treated with systemic antibacterial agents. Postpone vaccination until 3 days after cessation of antibiotics and avoid starting antibiotics within 3 days of last vaccine dose. Risk D: Consider therapy modification
Vitamin K Antagonists (eg, warfarin): Cephalosporins may enhance the anticoagulant effect of Vitamin K Antagonists. Risk C: Monitor therapy
Peak antibiotic serum concentration is lowered and delayed, but total drug absorbed is not affected. Cephalexin serum levels may be decreased if taken with food. Management: Administer without regard to food.
Cephalexin crosses the placenta and produces therapeutic concentrations in the fetal circulation and amniotic fluid (Creatsas 1980).
Based on available data, cephalosporin antibiotics, including cephalexin, are generally considered compatible for use during pregnancy (Ailes 2016; Bookstaver 2015; Crider 2009; Czeizel 2001; Lamont 2014; Muanda 2017a; Muanda 2017b). An increased risk of major birth defects or other adverse fetal or maternal outcomes has generally not been observed following use of cephalexin during pregnancy.
Peak concentrations in pregnant patients are similar to those in nonpregnant patients. Prolonged labor may decrease oral absorption (Griffith 1983; Paterson 1972).
Cephalexin is one of the recommended antibiotics for use prior to vaginal delivery in patients at high risk for endocarditis. This includes patients with congenital heart disease, prosthetic valves, previous infective endocarditis, or cardiac transplant. Cephalexin is given 30 to 60 minutes prior to a vaginal delivery; the dose for endocarditis prophylactic is the same as nonpregnant patients (ACOG 2018).
Cephalosporins are an alternative for group B streptococcus prophylaxis in pregnant patients who are penicillin allergic and at low risk for anaphylaxis; cephalexin may be used if an oral agent is appropriate (ACOG 2020).
Cephalexin may be considered for post–cesarean delivery prophylaxis in patients with obesity as part of a combination therapy in patients who may not have received recommended antibiotic prophylaxis (ACOG 2018; Valent 2017).
Untreated urinary tract infections during pregnancy are associated with an increased risk of developing pyelonephritis, low birth weight, and preterm labor. Use of cephalexin may also be considered for the treatment of asymptomatic bacteriuria during pregnancy (de Rossi 2020; IDSA [Nicolle 2019]).
Cephalexin is present in breast milk.
Data related to the presence of cephalexin in breast milk are available from multiple studies:
• The transfer of cephalexin into human milk was studied in 2 to 3 women who were 5 to 7 days postpartum. After an oral dose of cephalexin 500 mg, milk concentrations were 0.2 to 0.4 mcg/mL at 2 hours, 0.6 to 0.8 mcg/mL at 4 hours, and trace to 0.2 mcg/mL at 6 hours. Only trace amounts of cephalexin were reported in the maternal milk at 1 hour after the dose (Matsuda 1984).
• Information is available from 6 mothers given a single dose of cephalexin 1 g orally on the third postpartum day. The average peak maternal serum concentration was 22.9 mcg/mL 1 hour after the dose. The mean peak milk concentration was 0.51 mcg/mL (range: 0.24 to 0.85 mcg/mL) 4 to 5 hours after the dose (Kafetzis 1981).
• Slightly higher concentrations of cephalexin were detected in the breast milk of a woman treated for erysipelas/cellulitis in her right breast 9 days after cesarean delivery. Treatment was with cephalexin 500 mg in combination with probenecid given orally 4 times a day and continued for ~3 weeks. On day 16 of cephalexin/probenecid therapy, 12 milk samples were obtained over a period of ~16 hours. The average concentration of cephalexin in breast milk was 0.745 mcg/mL (range: ~0.4 to 1 mcg/mL). Using the average milk concentration of 0.745 mcg/mL, the authors estimated the exposure to the breastfeeding infant to be 0.112 mg/kg/day (relative infant dose: 0.5% based on the weight-adjusted maternal dose) (Ilett 2006).
• According to the manufacturer, the relative infant dose (RID) of cephalexin is <1% of the weight adjusted maternal dose. In general, breastfeeding is considered acceptable when the RID is <10% (Anderson 2016; Ito 2000).
Diarrhea has been reported in breastfeeding infants (Ilett 2006; Ito 1993). A severe allergic reaction was reported in a 4-month-old infant exposed to cephalexin via breast milk; the infant was previously treated for a urinary tract infection with a different cephalosporin 9 days prior to the reaction that likely caused an initial sensitization (Chu 2019). In general, antibiotics that are present in breast milk may cause non–dose-related modification of bowel flora. Monitor infants for GI disturbances, such as thrush or diarrhea (WHO 2002).
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.
Cephalexin is a recommended antibiotic for the empiric treatment of bacterial mastitis in patients who are breastfeeding. Antibiotic use may be considered when symptoms are present for >24 hours and have not responded to conservative measures, or the patient has symptoms such as fever or tachycardia. Consider a milk culture if symptoms do not improve after 48 hours of antibiotic therapy. The diagnosis of mastitis does not require interruption of breastfeeding (ABM [Mitchell 2022]; WHO 2000).
With prolonged therapy monitor renal, hepatic, and hematologic function periodically; monitor for signs of anaphylaxis during first dose
Inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins (PBPs) which in turn inhibits the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls, thus inhibiting cell wall biosynthesis. Bacteria eventually lyse due to ongoing activity of cell wall autolytic enzymes (autolysins and murein hydrolases) while cell wall assembly is arrested.
Absorption: Rapid (90%); delayed in young children and may be decreased up to 50% in neonates
Distribution: Widely into most body tissues and fluids, including gallbladder, liver, kidneys, bone, sputum, bile, and pleural and synovial fluids; CSF penetration is poor
Protein binding: 10% to 15%
Half-life elimination: Neonates: 5 hours; Children 3 to 12 months: 2.5 hours; Adults: 0.5 to 1.2 hours (prolonged with renal impairment)
Time to peak, serum: ~1 hour
Excretion: Urine (>90% as unchanged drug) within 8 hours
Anti-infective considerations:
Parameters associated with efficacy:
Time dependent; associated with time free drug concentration (fT) > minimum inhibitory concentration (MIC):
Enterobacterales: Goal: 30% to 40% fT > MIC (bacteriostatic), 60% to 70% fT > MIC (bactericidal) (Craig 1998; Turnidge 1998).
Staphylococcus spp.: Goal: 24% fT > MIC (in vitro) (Turnidge 1998).
Streptococcus spp. and H. influenzae: Goal: >40% fT > MIC (Craig 1998; Turnidge 1998).
Expected drug concentration in normal renal function:
Children 1 to 16 years of age, Cmax (peak):
50 mg/kg every 8 hours, steady state: 59 mg/L (range: 22 to 155 mg/L) (Autmizguine 2013).
Adults, Cmax (peak):
250 mg, single dose: 7 to 9 mg/L (Griffith 1983).
500 mg, single dose: 14 to 18 mg/L (Griffith 1983).
1 g, single dose: 28 to 32 mg/L (Griffith 1983).
Postantibiotic effect: Generally <1 hour; varies based on organism (Craig 1991; Craig 1998).
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