• 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 PositiveStrep. Group A, B, C, GS
Strep. PneumoniaeS
Viridans strepS
Strep. anginosus gpX1
Enterococcus faecalisR
Enterococcus faeciumX1
Staph. EpidermidisI
C. jeikeiumR
L. monocytogenesR
Gram NegativesN. gonorrhoeaeR
N. meningitidisR
Moraxella catarrhalisR
H. influenzaeR
E. coliS
Klebsiella spS
E. coli/Klebsiella ESBL+R
E coli/Klebsiella KPC+R
Enterobacter sp, AmpC negR
Enterobacter sp, AmpC posR
Serratia spR
Serratia marcescensX1
Salmonella spR
Shigella spR
Proteus mirabilisS
Proteus vulgarisR
Providencia sp.R
Morganella sp.R
Citrobacter freundiiR
Citrobacter diversusR
Citrobacter sp.R
Aeromonas spX1
Acinetobacter sp.R
Pseudomonas aeruginosaR
Burkholderia cepaciaR
Stenotrophomonas maltophiliaR
Yersinia enterocoliticaX1
Francisella tularensisX1
Brucella sp.X1
Legionella sp.R
Pasteurella multocidaR
Haemophilus ducreyiX1
Vibrio vulnificusX1
MiscChlamydophila spX1
Mycoplasm pneumoniaeX1
Rickettsia spX1
Mycobacterium aviumX1
Bacteroides fragilisR
Prevotella melaninogenicaX1
Clostridium difficileX1
Clostridium (not difficile)X1
Fusobacterium necrophorumX1
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
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