Recommended Duration of Keflex (Cephalexin) for Uncomplicated UTIs
For uncomplicated urinary tract infections (UTIs), Keflex (cephalexin) should be administered for 7 days at a dose of 500 mg every 12 hours. 1, 2
Evidence-Based Recommendation
The FDA-approved labeling for cephalexin specifically states that for uncomplicated cystitis in patients over 15 years of age, a dosage of 500 mg may be administered every 12 hours, and that cystitis therapy should be continued for 7 to 14 days 2. Current clinical practice guidelines from European Urology, as summarized in Praxis Medical Insights, indicate that shorter courses are preferable to minimize resistance while maintaining efficacy 1.
Dosing Options
- Standard regimen: 500 mg every 12 hours for 7 days 2
- Alternative dosing: Recent evidence suggests that twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing (500 mg QID) for uncomplicated UTIs 3, 4
Supporting Evidence
Recent research strongly supports the efficacy of twice-daily cephalexin dosing for UTIs:
- A 2023 retrospective multicenter cohort study found no significant difference in treatment failure between patients treated with cephalexin 500 mg twice daily versus 500 mg four times daily (12.7% vs 17%, p=0.343) 3
- A 2025 study comparing twice-daily versus four-times-daily dosing for UTIs diagnosed in the emergency department showed no statistically significant difference in treatment failure rates (18.7% vs 15.0%, p=0.465) 4
Clinical Considerations
Patient Adherence
Twice-daily dosing may improve patient adherence compared to more frequent dosing schedules 3. This is particularly important for ensuring complete treatment of the infection.
Antimicrobial Stewardship
While cephalexin is not considered a first-line agent for uncomplicated UTIs according to IDSA guidelines, it remains an effective option with excellent urinary penetration 3. First-line options typically include:
- Nitrofurantoin 100 mg twice daily for 5 days
- Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days
- Fosfomycin 3 g single dose 1
Special Populations
- Renal impairment: Dosage adjustment is required for patients with creatinine clearance <30 mL/min 5
- Pregnant women: Cephalexin is generally considered safe in pregnancy, but treatment decisions should prioritize agents with established safety profiles 1
- Pediatric patients: For children, the recommended daily dosage is 25 to 50 mg/kg in divided doses 2
Monitoring and Follow-up
- Routine post-treatment urinalysis or urine cultures are not indicated if symptoms resolve 1
- If symptoms do not resolve by the end of treatment or recur within 2 weeks, obtain urine culture and antimicrobial susceptibility testing, and retreat with a 7-day regimen using another agent 1
Conclusion
The 7-day duration for cephalexin represents an optimal balance between ensuring complete eradication of the infection while minimizing the risk of adverse effects and antimicrobial resistance. Twice-daily dosing (500 mg BID) is supported by recent evidence as being equally effective as more frequent dosing regimens, which may improve patient adherence.