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 (Bradley 2021; Red Book [AAP 2021]; manufacturer's labeling). Note: At these daily doses, dosing less frequently than every 6 hours may be inadequate for many Staphylococcus aureus isolates (Gwee 2020).
Severe infection: Oral: 75 to 100 mg/kg/day divided every 6 to 8 hours; maximum daily dose: 4,000 mg/day (Bradley 2021; Red Book [AAP 2021]).
Catheter (peritoneal dialysis), exit-site or tunnel infection: 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 (ISPD [Warady 2012]).
Duration of therapy (ISPD [Warady 2012]):
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.
Endocarditis, prophylaxis before invasive dental or respiratory tract procedures (alternative agent for nonanaphylactic penicillin allergy): Limited data available:
Note: Recommended only in patients who are at highest risk for infective endocarditis (IE) or adverse outcomes (eg, history of IE, prosthetic heart valves or prosthetic material used to repair valves, unrepaired cyanotic congenital heart disease, repaired congenital heart disease with prosthetic material or device during first 6 months after procedure, repaired congenital heart disease with residual defects at the site or adjacent to site of prosthetic patch or device, heart transplant recipients with cardiac valvulopathy) (AHA [Baltimore 2015]; AHA [Wilson 2021]; AHA/ACC [Nishimura 2017]).
Infants, Children, and Adolescents: Oral: 50 mg/kg administered 30 to 60 minutes prior to procedure; maximum dose: 2,000 mg/dose (AHA [Wilson 2021]).
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; maximum dose: 1,000 mg/dose (DeRonde 2018; Ramchandar 2020). 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 (Ramchandar 2020; Saavedra-Lozano 2017).
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 (Autmizguine 2013; DeRonde 2018; Gwee 2020).
Otitis media, acute (AOM): Pathogen-directed therapy: Note: Not recommended for empiric therapy; patient should be under the care of an experienced clinician (AAP [Lieberthal 2013]).
Children >1 year and Adolescents <15 years: Oral: 75 to 100 mg/kg/day divided every 6 hours; 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 (manufacturer's labeling). For patients with severe disease or who are <2 years of age, treat for 10 days; for patients ≥2 years of age with mild to moderate disease, treatment for 5 to 7 days is likely adequate (AAP [Lieberthal 2013]; Kozyrskyj 2010).
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 (Bradley 2021; IDSA/PIDS [Bradley 2011]). The usual total duration of therapy for uncomplicated pneumonia is 5 to 10 days (Pernica 2021; Same 2021).
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 (Chen 2011; IDSA [Stevens 2014]; Ondusko 2018; Pallin 2013; Tack 1997; manufacturer's labeling). Typical duration is 5 days for uncomplicated infection but may be extended if clinical response is inadequate (Galli 2019; IDSA [Stevens 2014]).
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 (Bass 1997; IDSA [Stevens 2014]; Tack 1997).
Streptococcal pharyngitis/tonsillitis, group A (alternative agent for nonanaphylactic penicillin allergy): Infants, Children, and Adolescents: Oral: 40 mg/kg/day divided every 12 hours for 10 days; maximum dose: 500 mg/dose (IDSA [Shulman 2012]).
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 (Elo 1975; Fennell 1975; Helin 1984; Lashkar 2018; Red Book [AAP 2021]; Stein 2015; manufacturer's labeling).
Severe (eg, pyelonephritis): Oral: 50 to 100 mg/kg/day divided every 6 to 8 hours; maximum dose: 1,000 mg/dose (AAP 2011; Balighian 2018; Bradley 2021; Fennell 1975; Stein 2015; manufacturer's labeling).
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) (Afolabi 2020; Balighian 2018; Fox 2020; Lashkar 2018; Stein 2015).
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.
(For additional information see "Cephalexin: Drug information")
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) (AHA [Wilson 2007]; AHA [Wilson 2021]).
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 (Berbari 2019):
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 (Berbari 2019; IDSA [Osmon 2013]).
Streptococci, beta-hemolytic (alternative agent): 500 mg every 6 to 8 hours (Berbari 2019; IDSA [Osmon 2013]).
Cutibacterium spp (alternative agent): 500 mg every 6 to 8 hours (IDSA [Osmon 2013]; Kanafani 2020).
Skin and soft tissue infection:
Note: Not an appropriate agent if methicillin-resistant S. aureus is suspected or confirmed (Baddour 2021; IDSA [Stevens 2014]; Spelman 2021).
Cellulitis (nonpurulent)/erysipelas, mild: Oral: 500 mg 4 times daily for at least 5 days (duration should be extended up to 14 days if not resolved/slow response) (IDSA [Stevens 2014]; Spelman 2021).
Impetigo or ecthyma: Note: For impetigo, reserve systemic therapy for patients with numerous lesions or in outbreak settings to decrease transmission (IDSA [Stevens 2014]).
Oral: 250 to 500 mg 4 times daily for 7 days (Baddour 2021; IDSA [Stevens 2014]).
Streptococcal pharyngitis, group A (alternative agent for mild, nonanaphylactic penicillin allergy):
Note: Cephalosporin selection depends on the type of hypersensitivity reaction to penicillin (Pichichero 2021).
Oral: 500 mg twice daily for 10 days (IDSA [Shulman 2012]; Pichichero 2021; manufacturer's labeling).
Urinary tract infection:
Asymptomatic bacteriuria (≥105 CFU per mL) in pregnancy: Oral: 250 to 500 mg every 6 hours for 4 to 7 days (ACOG 2020; Hooton 2021a; IDSA [Nicolle 2019]; Pedler 1985).
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 (Hooton 2021b; IDSA/ESCMID [Gupta 2011]).
Oral: 250 to 500 mg every 6 hours for 5 to 7 days (Bolding 1978; Elhanan 1994; Hooton 2021b; Johnson 1972; Menday 2000).
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 (AUA/CUA/SUFU [Anger 2019]; Hooton 2021c).
Continuous prophylaxis: Oral: 125 to 250 mg once daily (AUA/CUA/SUFU [Anger 2019]; Gower 1975).
Postcoital prophylaxis (females with cystitis temporally related to sexual intercourse): Oral: 250 mg as a single dose immediately before or after sexual intercourse (AUA/CUA/SUFU [Anger 2019]; Pfau 1992).
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 Bathini 2019; Golightly 2013; Linquist 1970; manufacturer's labeling):
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%) (Kabins 1970):
250 to 500 mg every 12 to 24 hours (Golightly 2013; expert opinion). Administer after hemodialysis on dialysis days.
Peritoneal dialysis: Limited clearance by peritoneal dialysis (Bunke 1983).
250 to 500 mg every 12 to 24 hours (Golightly 2013; expert opinion).
There are no dosage adjustments provided in the manufacturer's labeling.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product
Capsule, Oral:
Daxbia: 333 mg [DSC] [contains brilliant blue fcf (fd&c blue #1), fd&c yellow #10 (quinoline yellow), fd&c yellow #6 (sunset yellow)]
Keflex: 250 mg [DSC], 500 mg [DSC], 750 mg [DSC] [contains brilliant blue fcf (fd&c blue #1), fd&c yellow #10 (quinoline yellow), fd&c yellow #6 (sunset yellow)]
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
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, Oral:
Generic: 250 mg, 500 mg
Suspension Reconstituted, Oral:
Keflex: 125 mg/5 mL (100 mL, 200 mL); 250 mg/5 mL (200 mL)
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:
Keflex: 250 mg, 500 mg
Generic: 250 mg, 500 mg
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).
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.
Capsule: Store at 25°C (77°F); excursions permitted to 15ºC to 30ºC (59ºF to 86ºF).
Powder for oral suspension: Store at 20°C to 25°C (68°F to 77°F). Refrigerate after reconstitution; discard after 14 days.
Tablet: Store at 20°C to 25°C (68°F to 77°F).
Treatment of the following susceptible bacterial infections: Acute otitis media caused by Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Streptococcus pyogenes, or Moraxella catarrhalis; respiratory tract infections (including pharyngitis) caused by S. pneumoniae or S. pyogenes; skin and skin structure infections caused by S. aureus or S. pyogenes; bone infections caused by S. aureus or Proteus mirabilis; and genitourinary tract infections (including acute prostatitis) caused by Escherichia coli, P. mirabilis, or Klebsiella pneumoniae (All indications: FDA approved in ages >1 year and adults); has also been used for prophylaxis of endocarditis before invasive dental or respiratory tract procedures and treatment of exit-site or tunnel infections in patients with peritoneal dialysis catheters.
Cephalexin may be confused with cefaclor, ceFAZolin, ciprofloxacin
Keflex may be confused with Keppra, Valtrex
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.
None known.
Aminoglycosides: Cephalosporins may enhance the nephrotoxic effect of Aminoglycosides. Cephalosporins may decrease the serum concentration of Aminoglycosides. Risk C: Monitor therapy
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
Immune Checkpoint Inhibitors: Antibiotics may diminish the therapeutic effect of Immune Checkpoint Inhibitors. 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
Multivitamins/Minerals (with ADEK, Folate, Iron): May decrease the serum concentration of Cephalexin. Specifically, the zinc contained in many multivitamins may decrease cephalexin absorption. Management: Consider administering multivitamins at least 3 hours after cephalexin. Risk D: Consider therapy modification
Multivitamins/Minerals (with AE, No Iron): May decrease the serum concentration of Cephalexin. Specifically, the zinc contained in many multivitamins may decrease cephalexin absorption. Management: Consider administering multivitamins at least 3 hours after cephalexin. Risk D: Consider therapy modification
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
Zinc Salts: May decrease the absorption of Cephalexin. Management: Consider administering oral zinc salts at least 3 hours after cephalexin. Risk D: Consider therapy modification
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 obese females 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]).
With prolonged therapy, monitor renal, hepatic, and hematologic function periodically; monitor for signs of anaphylaxis with first dose; number and type of stools/day for diarrhea.
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).
Capsules (Cephalexin Oral)
250 mg (per each): $0.19 - $0.87
500 mg (per each): $0.34 - $1.97
750 mg (per each): $7.69
Suspension (reconstituted) (Cephalexin Oral)
125 mg/5 mL (per mL): $0.23 - $0.24
250 mg/5 mL (per mL): $0.23 - $0.29
Tablets (Cephalexin Oral)
250 mg (per each): $4.18
500 mg (per each): $8.22
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