What is the recommended dosing for Keflex (Cephalexin) in adults with bacterial infections?

Cephalexin (Keflex) Dosing for Adults with Bacterial Infections

For adults with bacterial infections, cephalexin (Keflex) is typically administered at a dosage of 250 mg every 6 hours or 500 mg every 12 hours, with a total daily dose ranging from 1 to 4 grams depending on infection severity. 1

Standard Dosing Regimens

Common Infections

• Standard adult dose: 250 mg every 6 hours (1 g daily) 1
• Alternative regimen: 500 mg every 12 hours for:
  • Streptococcal pharyngitis
  • Skin and skin structure infections
  • Uncomplicated cystitis in patients over 15 years 1

Infection-Specific Dosing

• Uncomplicated skin infections: 500 mg twice daily for 5-7 days 2
• Respiratory tract infections: 500 mg 3-4 times daily for 7-10 days 2
• Urinary tract infections:
  • 250-500 mg every 6-12 hours for 7-14 days 1
  • Recent evidence supports that 500 mg twice daily is as effective as 500 mg four times daily for uncomplicated UTIs 3

Dosing Considerations

Severe Infections

• For more severe infections or those caused by less susceptible organisms, larger doses may be needed 1
• If daily doses greater than 4 g are required, parenteral cephalosporins should be considered 1

Special Populations

• Renal impairment: Patients with creatinine clearances less than 30 ml/min require a reduction in dosage proportional to the reduced renal function 4
• Recent antibiotic use: Patients who have received antibiotics in the previous 4-6 weeks may require an alternative class or higher-dose regimen 2

Administration Guidelines

• Cephalexin is administered orally 1
• Can be taken with or without food, though absorption is high in the intestinal tract 4
• Available as capsules and oral suspension 1

Duration of Treatment

• Uncomplicated skin infections: 5-7 days 2
• Respiratory tract infections: 7-10 days 2
• Urinary tract infections: 7-14 days 1
• Streptococcal infections: Minimum 10 days to prevent rheumatic fever 1

Clinical Pearls

• Cephalexin has excellent bioavailability and urinary penetration, making it particularly effective for urinary tract infections 3
• The twice-daily dosing regimen (500 mg BID) has shown similar efficacy to four-times-daily dosing for uncomplicated UTIs, which may improve patient adherence 3
• Concentrations of 500-1000 μg/ml in urine follow 250-500 mg oral doses, which is many times greater than the minimum inhibitory concentration for common urinary tract pathogens 4

Common Pitfalls to Avoid

• Exceeding 4 g total daily dose without switching to parenteral therapy 1
• Inadequate duration of therapy, especially for streptococcal infections which require at least 10 days of treatment 1
• Failure to adjust dosing in patients with significant renal impairment 4
• Using cephalexin as monotherapy for infected bites, as it has poor activity against Pasteurella multocida 2