• Type: 1st generation cephalosporin
  • Dosage forms
    • Tabs: 250mg, 500mg, 750mg
    • Liquid: 125mg/5mL; 250mg/5mL
  • Common Trade Names: Keflex, Keftab, Biocef

Adult Dosing


  • 250-500mg PO q6h
  • Max: 4g/day

Strep Pharyngitis

  • 500mg PO q12h x 10 days

Uncomplicated UTI

  • 500mg PO q12h x 7-14 days

Cellulitis and Other Skin Infections

  • 60-120 kg: 500 mg Q6H 1 gram Q8H.
  • >120 kg: 1 g Q6H. [1]

Pediatric Dosing


  • 25-50mg/kg/day PO divided q6-12h
  • Max: 500mg/dose

Otitis Media

  • 75-100mg/kg/day PO divided q12h x 10 days
  • Max: 4,000mg/24h

Community Acquired Pneumonia (>3 Months)

  • 75-100mg/kg/day PO divided q12h x 10 days

Streptococcal Pharyngitis (>1 Year)

  • 40mg/kg/day PO divided q12h x 10 days
  • Max: 500mg/dose

Skin Infections

  • 25-50mg/kg/day PO divided q12h
  • Max: 500mg/dose

Special Populations

  • Pregnancy Rating: B
  • Lactation risk categories: Enters breast milk/L3
  • Renal
    • Adult
      • CrCl 50-90: give q6-8h
      • CrCl 10-50: give q8-12h
      • CrCl <10: give q12-24h
      • Hemodialysis: give dose after dialysis, no supplement
      • Peritoneal dialysis: no supplement
    • Pediatric
      • CrCl 30-50: give q8h
      • CrCl 10-29: give q12h
      • CrCl <10: give q24h
      • Hemodialysis: give dose after dialysis, no supplement
      • Peritoneal dialysis: no supplement
  • Hepatic (Adult & Pediatric)
    • Not defined


Adverse Drug Reactions




  • Half-life: 1h (~20hr ESRD)
  • Metabolism: Minimal
  • Excretion: Primarily urine (>90% unchanged)
  • Mechanism of Action:
    • Bactericidal, inhibits cell wall

Antibiotic Sensitivities[2]

Group Organism Sensitivity
Gram Positive Strep. Group A, B, C, G S
Strep. Pneumoniae S
Viridans strep S
Strep. anginosus gp X1
Enterococcus faecalis R
Enterococcus faecium X1
Staph. Epidermidis I
C. jeikeium R
L. monocytogenes R
Gram Negatives N. gonorrhoeae R
N. meningitidis R
Moraxella catarrhalis R
H. influenzae R
E. coli S
Klebsiella sp S
E. coli/Klebsiella ESBL+ R
E coli/Klebsiella KPC+ R
Enterobacter sp, AmpC neg R
Enterobacter sp, AmpC pos R
Serratia sp R
Serratia marcescens X1
Salmonella sp R
Shigella sp R
Proteus mirabilis S
Proteus vulgaris R
Providencia sp. R
Morganella sp. R
Citrobacter freundii R
Citrobacter diversus R
Citrobacter sp. R
Aeromonas sp X1
Acinetobacter sp. R
Pseudomonas aeruginosa R
Burkholderia cepacia R
Stenotrophomonas maltophilia R
Yersinia enterocolitica X1
Francisella tularensis X1
Brucella sp. X1
Legionella sp. R
Pasteurella multocida R
Haemophilus ducreyi X1
Vibrio vulnificus X1
Misc Chlamydophila sp X1
Mycoplasm pneumoniae X1
Rickettsia sp X1
Mycobacterium avium X1
Anaerobes Actinomyces X1
Bacteroides fragilis R
Prevotella melaninogenica X1
Clostridium difficile X1
Clostridium (not difficile) X1
Fusobacterium necrophorum X1
Peptostreptococcus sp. S


  • S susceptible/sensitive (usually)
  • I intermediate (variably susceptible/resistant)
  • R resistant (or not effective clinically)
  • S+ synergistic with cell wall antibiotics
  • U sensitive for UTI only (non systemic infection)
  • X1 no data
  • X2 active in vitro, but not used clinically
  • X3 active in vitro, but not clinically effective for Group A strep pharyngitis or infections due to E. faecalis
  • X4 active in vitro, but not clinically effective for strep pneumonia

See Also


  1. Reduction of Inappropriate Antibiotic Use and Improved Outcomes by Implementation of an Algorithm-Based Clinical Guideline for Nonpurulent Skin and Soft Tissue Infections. Ann Emerg Med. 2020 Feb 13. pii: S0196-0644(19)31453-2. doi: 10.1016/j.annemergmed.2019.12.012. [Epub ahead of print]
  2. Sanford Guide to Antimicrobial Therapy 2014
  • Sanford 2010
  • Epocrates
  • Lexicomp