What is the recommended dosing for cephalexin (Keflex)?

Cephalexin (Keflex) Dosing Guidelines

The recommended adult dosage for cephalexin (Keflex) is 250-500 mg orally every 6 hours or 500 mg every 12 hours, with a total daily dose ranging from 1-4 grams depending on infection severity and type. 1

Adult Dosing

Standard Adult Dosing:

• Usual adult dose: 250 mg every 6 hours 1
• Alternative dosing: 500 mg every 12 hours for:
  • Streptococcal pharyngitis
  • Skin and skin structure infections
  • Uncomplicated cystitis in patients over 15 years 1

Infection-Specific Dosing:

• Skin and soft tissue infections:

  • 500 mg orally 3-4 times daily 2
  • For MSSA infections: 75-100 mg/kg/day in 3-4 doses 2

• Urinary tract infections:

  • 500 mg every 12 hours for 7-14 days 1
  • Recent evidence suggests twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated UTIs 3

• Staphylococcal infections:

  • For methicillin-susceptible S. aureus: 75-100 mg/kg/day in 3-4 doses 2

Pediatric Dosing

• Standard pediatric dose: 25-50 mg/kg/day divided into 2-4 doses 1
• Streptococcal pharyngitis and skin infections: Total daily dose may be divided and administered every 12 hours 1
• Otitis media: 75-100 mg/kg/day in 4 divided doses 1
• Streptococcal infections: Treatment should continue for at least 10 days 1

Dosing in Special Populations

Renal Impairment:

• Patients with creatinine clearance <30 ml/min require dose reduction proportional to reduced renal function 4
• Can be determined by creatinine clearance or serum creatinine 4

Elderly Patients:

• Standard adult dosing is typically appropriate, but consider renal function 4
• Lower doses may be effective for long-term prophylaxis (125-250 mg daily) 5

Important Considerations

• Maximum daily dose: 4 grams; if higher doses are required, consider parenteral cephalosporins 1

• Duration of therapy:

  • Streptococcal infections: minimum 10 days 1
  • UTIs: 7-14 days 1
  • Skin infections: 7-10 days 2

• Administration: Can be taken with or without food; if GI upset occurs, take with food

• Suspension preparation:

  • Available in 125 mg/5 mL and 250 mg/5 mL concentrations
  • Must be reconstituted with specific water volumes as directed
  • After mixing, store in refrigerator; stable for 14 days 1

Clinical Pearls

• Cephalexin is rapidly absorbed from the upper intestine (not the stomach) and achieves high urinary concentrations 4
• For severe infections, dosage may be doubled 1
• Cephalexin does not penetrate host tissue cells, which may account for its low incidence of side effects 4
• Hemodialysis reduces serum concentration by approximately 58% 6
• Twice-daily dosing may improve patient adherence compared to four-times-daily dosing 3

Remember to adjust dosing based on infection severity, patient factors, and local resistance patterns.