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Drug Name: Cefazolin/Cephalexin

Click on the titles below for drug details

  • 1st generation cephalosporin
  • Bactericidal
  • Inhibit cell wall synthesis by binding to PBPs, which inhibits the final transpeptidation step for cell wall synthesis. Causes bacteria to ultimately lyse as the bacteria's autolytic enzymes break down the cell wall during active assembly
  • PO (cephalexin): with or without food
    • 25 mg/kg/dose BID or TID for mild-moderate infection
    • 100 mg/kg/day for more severe impetigo/erysipelas/SSTI
      • QID dosing (25 mg/kg/dose) may be difficult to ensure adherence
      • Consider splitting the same dose TID (e.g., 33 mg/kg/dose)
    • 50 mg/kg/dose q8hr for osteomyelitis (max 1500 mg/dose)
    • 20 mg/kg q12hr for non-anaphylactic PCN allergy for GAS pharyngitis
  • IV/IM (cefazolin)
    • 25-50 mg/kg/dose q8hr for MSSA/non-purulent SSTI/erysipelas/lymphadenitis (Do NOT use lower dosing for osteomyelitis)
    • 50 mg/kg/dose q8hr for osteomyelitis/septic arthritis without MRSA risk factors
    • Usual single dose maximum 2g
  • Cephalexin Dosage Forms:
    • 250mg and 500mg capsules; 750mg capsule uncommon
    • 250mg and 500mg tablet
    • 125mg/5mL and 250mg/5mL suspension
  • Patients with abnormal renal function (<50 mL/minute/1.73 m2) require renal dosing adjustment, generally extending the dosing interval. Talk to your friendly pharmacist.
  • Note: all indications are for suspected MSSA infections. If concern for MRSA risk factors, need to chose an alternate therapy with appropriate MRSA coverage
  • Cephalexin:
    • non-purulent cellulitis, paronychia, cystitis, impetigo, osteomyelitis, GAS pharyngitis
  • Cefazolin
    • Non-purulent cellulitis, erysipelas, lymphadenitis
    • Type I and II open fractures
    • Osteomyelitis or septic arthritis
    • Surgical prophylaxis
  • There are data that support that cefazolin CAN be used even with history of hypersensitivity to other cephalosporins given its molecular structure differing from other penicillin and cephalosporins.
  • C. diff infection: Dose and time related to recent or cumulative antibiotic exposure - at time of onset or up to 3 months post-therapy
  • Hemolytic anemia: occurs in first few hours to 7 days after 1st dose. Unknown mechanism. Extremely rare but can be fatal
  • Hypersensitivity: skin rash to anaphylaxis, anaphylactic shock. Also known to cause urticaria and angioedema
  • Some delayed hypersensitivity reactions such as SJS, TEN, serum sickness-like reaction
  • Does cross the placenta
  • Widely penetrates most areas of the body (e.g., excellent bone penetration). Cefazolin was previously thought to have poor CSF penetration, but more recent data suggests cefazolin is an option for CNS infections with susceptible pathogens though higher-than-normal dosing may be required.
  • Cephalexin has poor CNS penetration
  • Can cause rash and pruritis that are not serious but always monitor for more signs of serious allergic reactions like difficulty breathing, vomiting, swelling of the lips or tongue, worsening/spreading rash
  • Can cause some GI upset like diarrhea
  • Cephalexin: Administer with or without food - food may reduce GI upset