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Cephalexin

Pronunciation

Pronunciation

(sef a LEKS in)

Index Terms

  • Cephalexin Monohydrate

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Slideshow: When Harmless Bacteria Turn Bad: Group B Strep

Capsule, Oral:

Keflex: 250 mg, 500 mg, 750 mg [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

Brand Names: U.S.

  • Keflex

Pharmacologic Category

  • Antibiotic, Cephalosporin (First Generation)

Pharmacology

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

Excretion

Urine (80% to 100% as unchanged drug) within 8 hours

Time to Peak

Serum: ~1 hour

Half-Life Elimination

Neonates: 5 hours; Children 3-12 months: 2.5 hours; Adults: 0.5 to 1.2 hours (prolonged with renal impairment)

Protein Binding

6% to 15%

Use: Labeled Indications

Bone infections: Treatment of bone infections caused by Staphylococcus aureus and/or Proteus mirabilis.

Genitourinary tract infections: Treatment of genitourinary tract infections, including acute prostatitis, caused by Escherichia coli, P. mirabilis, and Klebsiella pneumoniae.

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 caused by S. pneumoniae and S. pyogenes.

Skin and skin structure infections: Treatment of skin and skin structure infections caused by S. aureus and/or S. pyogenes.

Use: Unlabeled

Chronic antimicrobial suppression of prosthetic joint infection

Contraindications

Hypersensitivity to cephalexin, any component of the formulation, or other cephalosporins

Dosage

Usual dosage range:

Children >1 year and Adolescents <15 years: Oral: 25 to 100 mg/kg/day divided every 6 to 8 hours (maximum daily dose: 4 g/day)

Adolescents ≥15 years and Adults: Oral: 250 to 1,000 mg every 6 hours or 500 mg every 12 hours; maximum daily dose: 4 g/day

Indication-specific dosing:

Infants >3 months and Children: Oral:

Community-acquired pneumonia (CAP) (IDSA/PIDS 2011), S. aureus (methicillin-susceptible), mild infection or step-down therapy (preferred): 75 to 100 mg/kg/day in 3 to 4 divided doses

Children: Oral:

Furunculosis: 25 to 50 mg/kg/day in 4 divided doses

Impetigo: 25 to 50 mg/kg/day in 3 to 4 divided doses; continue for 7 days, depending upon clinical response (IDSA [Stevens 2014])

Otitis media: 75 to 100 mg/kg/day in 4 divided doses

Prophylaxis against infective endocarditis (dental, oral, or respiratory tract procedures): 50 mg/kg 30 to 60 minutes prior to procedure (maximum: 2 g). Note: American Heart Association (AHA) guidelines now recommend prophylaxis only in patients undergoing invasive procedures and in whom underlying cardiac conditions may predispose to a higher risk of adverse outcomes should infection occur.

Severe infections: 50 to 100 mg/kg/day in divided doses every 6 to 8 hours

Skin abscess: 50 mg/kg/day in 4 divided doses (maximum: 4 g)

Skin and skin structure infections:

Manufacturer’s labeling: Children >1 year: 25 to 50 mg/kg/day in divided doses every 6 to 12 hours

Alternate recommendations: Children: 25 to 50 mg/kg/day divided every 6 hours (IDSA [Stevens 2014])

Streptococcal pharyngitis: Children >1 year: 25 to 50 mg/kg/day divided every 12 hours. Note: Recommended by the Infectious Disease Society of America (IDSA) as an alternative agent for group A streptococcal pharyngitis in penicillin-allergic patients (avoid in patients with immediate-type hypersensitivity to penicillin) at a dose of 40 mg/kg/day divided twice daily (maximum: 1,000 mg daily) for 10 days (Shulman 2012).

Adolescents ≥15 years and Adults: Oral:

Cellulitis and mastitis: 500 mg every 6 hours

Furunculosis/skin abscess: 250 mg 4 times/day

Prophylaxis against infective endocarditis (dental, oral, or respiratory tract procedures): 2 g 30 to 60 minutes prior to procedure. Note: American Heart Association (AHA) guidelines now recommend prophylaxis only in patients undergoing invasive procedures and in whom underlying cardiac conditions may predispose to a higher risk of adverse outcomes should infection occur.

Prophylaxis in patients with prosthetic joint implants undergoing dental procedures which produce bacteremia (off-label use): 2 g 1 hour prior to procedure (ADA/AAOS 2003). Note: In general, patients with prosthetic joint implants do not require prophylactic antibiotics prior to dental procedures. In planning an invasive oral procedure, dental consultation with the patient's orthopedic surgeon may be advised to review the risks of infection (Sollecito 2015).

Prosthetic joint infection, chronic oral antimicrobial suppression (off-label use): Oral:

Propionibacterium spp (alternative to penicillin or amoxicillin): 500 mg every 6 to 8 hours (Osmon 2013)

Staphylococci, oxacillin-susceptible (preferred): 500 mg every 6 to 8 hours (Osmon 2013)

Streptococci, beta-hemolytic (alternative to penicillin or amoxicillin): 500 mg every 6 to 8 hours (Osmon 2013)

Skin and skin structure infections:

Manufacturer’s labeling: 250 mg every 6 hours or 500 mg every 12 hours

Alternate recommendations: 500 mg every 6 hours (IDSA [Stevens 2014])

Streptococcal pharyngitis: 500 mg every 12 hours. Note: Recommended by the Infectious Disease Society of America (IDSA) as an alternative agent for group A streptococcal pharyngitis in penicillin-allergic patients (avoid in patients with immediate-type hypersensitivity to penicillin) with a duration of 10 days (Shulman 2012).

Uncomplicated cystitis: 250 mg every 6 hours or 500 mg every 12 hours for 7 to 14 days

Adults: Oral:

Impetigo: 250 mg every 6 hours; continue for 7 days, depending upon clinical response (IDSA [Stevens 2014])

Streptococcal skin infections: 500 mg every 6 hours (IDSA [Stevens 2014])

Surgical site infection (trunk or extremity [away from axilla or perineum]) (off-label use): Oral: 500 mg every 6 hours (IDSA [Stevens 2014])

Dosage adjustment in renal impairment: Adolescents ≥15 years and Adults:

CrCl ≥ 60 mL/minute: No dosage adjustment necessary.

CrCl 30 to 59 mL/minute: No dosage adjustment necessary; do not exceed 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 every 24 hours.

CrCl 1 to 4 mL/minute (not yet on dialysis): 250 mg every 48 to 60 hours.

End-stage renal disease (ESRD) on intermittent hemodialysis: There are no dosage adjustments provided in the manufacturer’s labeling; however, the following guidelines have been used by some clinicians (Aronoff, 2007): Oral: 250 to 500 mg every 12 to 24 hours; moderately dialyzable (20% to 50%); give dose after dialysis session

Peritoneal dialysis: There are no dosage adjustments provided in the manufacturer’s labeling; however, the following guidelines have been used by some clinicians (Aronoff, 2007): Oral: 250 to 500 mg every 12 to 24 hours

Dosage adjustment in hepatic impairment: There are no dosage adjustments provided in the manufacturer’s labeling.

Administration

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.

Dietary Considerations

Take without regard to food. If GI distress, take with food.

Storage

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).

Drug Interactions

BCG (Intravesical): Antibiotics may diminish the therapeutic effect of BCG (Intravesical). Avoid combination

BCG Vaccine (Immunization): Antibiotics may diminish the therapeutic effect of BCG Vaccine (Immunization). Monitor therapy

MetFORMIN: Cephalexin may increase the serum concentration of MetFORMIN. 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. 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. Consider therapy modification

Probenecid: May increase the serum concentration of Cephalosporins. 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. Consider therapy modification

Typhoid Vaccine: Antibiotics may diminish the therapeutic effect of Typhoid Vaccine. Only the live attenuated Ty21a strain is affected. Management: Vaccination with live attenuated typhoid vaccine (Ty21a) should be avoided in patients being treated with systemic antibacterial agents. Use of this vaccine should be postponed until at least 3 days after cessation of antibacterial agents. Consider therapy modification

Vitamin K Antagonists (eg, warfarin): Cephalosporins may enhance the anticoagulant effect of Vitamin K Antagonists. Monitor therapy

Zinc Salts: May decrease the absorption of Cephalexin. Management: Consider administering oral zinc salts at least 3 hours after cephalexin. Exceptions: Zinc Chloride. Consider therapy modification

Test Interactions

Positive direct Coombs', false-positive urinary glucose test using cupric sulfate (Benedict's solution, Clinitest®, Fehling's solution), false-positive serum or urine creatinine with Jaffé reaction, false-positive urinary proteins and steroids

Adverse Reactions

Frequency not defined.

Central nervous system: Agitation, confusion, dizziness, fatigue, hallucination, headache

Dermatologic: Erythema multiforme (rare), genital pruritus, skin rash, Stevens-Johnson syndrome (rare), toxic epidermal necrolysis (rare), urticaria

Gastrointestinal: Abdominal pain, diarrhea, dyspepsia, gastritis, nausea (rare), pseudomembranous colitis, vomiting (rare)

Genitourinary: Genital candidiasis, vaginal discharge, vaginitis

Hematologic & oncologic: Eosinophilia, hemolytic anemia, neutropenia, thrombocytopenia

Hepatic: Cholestatic jaundice (rare), hepatitis (transient, rare), increased serum ALT, increased serum AST

Hypersensitivity: Anaphylaxis, angioedema, hypersensitivity reaction

Neuromuscular & skeletal: Arthralgia, arthritis, arthropathy

Renal: Interstitial nephritis (rare)

Warnings/Precautions

Concerns related to adverse effects:

• Hypersensitivity: Allergic reactions (eg, rash, urticaria, angioedema, anaphylaxis, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis [TEN]) have been reported. If an allergic reaction occurs, discontinue immediately and institute appropriate treatment.

• 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, including C. difficile-associated diarrhea (CDAD) and pseudomembranous colitis; CDAD has been observed >2 months postantibiotic treatment.

Disease-related concerns:

• Renal impairment: Use with caution in patients with renal impairment; modify dosage in severe impairment.

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Other warnings/precautions:

• Direct Coombs tests: Positive direct Coombs tests and acute intravascular hemolysis has been reported. If anemia develops during or after therapy, discontinue use and work up for drug-induced hemolytic anemia.

Monitoring Parameters

With prolonged therapy monitor renal, hepatic, and hematologic function periodically; monitor for signs of anaphylaxis during first dose

Pregnancy Risk Factor

B

Pregnancy Considerations

Adverse events were not observed in animal reproduction studies. Cephalexin crosses the placenta and produces therapeutic concentrations in the fetal circulation and amniotic fluid. An increased risk of teratogenic effects has not been observed following maternal use of cephalexin. Peak concentrations in pregnant patients are similar to those in nonpregnant patients. Prolonged labor may decrease oral absorption.

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience dyspepsia or diarrhea. Have patient report immediately to prescriber ecchymosis, hemorrhaging, chills, pharyngitis, significant asthenia, illogical thinking, hallucinations, urinary retention, oliguria, vaginitis, or signs of pseudomembranous colitis (rare) (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.

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