What is the treatment dose and duration of Keflex (cephalexin) for urinary tract infections (UTIs)?

Keflex (Cephalexin) Treatment Dosage and Duration for UTI

For urinary tract infections (UTIs), cephalexin should be dosed at 500 mg orally four times daily for 7-14 days in adults, with twice daily dosing being an acceptable alternative for uncomplicated UTIs to improve adherence. 1, 2

Adult Dosing Recommendations

Uncomplicated UTIs

• Dosage: 500 mg orally
• Frequency: Four times daily (traditional) or twice daily (alternative)
• Duration: 7-14 days 2, 1
  • 7 days is generally sufficient for uncomplicated cases
  • 14 days may be needed for more complex cases

Complicated UTIs

• Dosage: 500 mg orally
• Frequency: Four times daily
• Duration: 7-14 days (14 days for men when prostatitis cannot be excluded) 2

Pediatric Dosing Recommendations

• Dosage: 50-100 mg/kg/day divided into four doses 2, 1
• Duration: 7-14 days 2

Factors Affecting Treatment Decisions

Dosing Frequency Considerations

• Recent evidence suggests twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated UTIs 3, 4
• Treatment failure rates were not significantly different between twice daily and four times daily regimens (18.7% vs 15.0%, p=0.465) 4
• Twice-daily dosing may improve patient adherence while maintaining efficacy 3

Duration Considerations

• The European Association of Urology and American Academy of Pediatrics both recommend 7-14 days of treatment 2
• Shorter durations (7 days) may be considered when:
  • The patient is hemodynamically stable
  • The patient has been afebrile for at least 48 hours
  • There are relative contraindications to longer antibiotic courses 2
• Longer durations (14 days) are recommended for:
  • Males when prostatitis cannot be excluded
  • Complicated UTIs with systemic symptoms
  • Patients with underlying urological abnormalities 2

Special Populations

Renal Impairment

• Dosage adjustment required for patients with creatinine clearance <30 ml/min 5
• The reduction should be proportional to the reduced renal function

Elderly Patients

• Standard adult dosing can be used unless renal function is impaired
• Twice-daily dosing may improve adherence in elderly patients 6

Clinical Pearls and Pitfalls

• Local resistance patterns: Always consider local susceptibility patterns when selecting cephalexin for UTI treatment 2
• Urine concentrations: Cephalexin achieves high urinary concentrations (500-1000 μg/ml) following standard oral doses, which exceeds the MIC for most urinary pathogens 5
• Avoid for febrile infants: For febrile infants with UTIs, parenteral therapy is often preferred initially 2
• Catheter-associated UTIs: Screening for and treatment of catheter-associated asymptomatic bacteriuria is not recommended 2
• Timing of administration: Cephalexin is absorbed in the upper intestine (not stomach) and achieves rapid distribution to tissues 5

By following these evidence-based recommendations for cephalexin dosing in UTIs, clinicians can optimize treatment outcomes while minimizing adverse effects and promoting antimicrobial stewardship.