Keflex Dosing for Uncomplicated UTI
For uncomplicated cystitis in adults, the recommended dose is cephalexin 500 mg every 12 hours (twice daily) for 7 to 14 days. 1
FDA-Approved Dosing
The FDA label specifically states that for uncomplicated cystitis in patients over 15 years of age, 500 mg may be administered every 12 hours, with treatment continued for 7 to 14 days. 1
- The standard adult dosage range is 1 to 4 grams daily in divided doses. 1
- For uncomplicated UTI specifically, the twice-daily 500 mg regimen is explicitly approved. 1
Important Context: Not a First-Line Agent
Cephalexin should be considered an alternative rather than first-line therapy for uncomplicated UTI. 2
- The Infectious Diseases Society of America considers β-lactams like cephalexin as alternative agents, noting inferior efficacy and more adverse effects compared to other UTI antimicrobials. 2
- Cephalexin remains appropriate when first-line agents (such as nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin) cannot be used. 2
Twice Daily vs Four Times Daily Dosing
Recent evidence strongly supports twice-daily dosing as equally effective to four-times-daily dosing, with the advantage of improved adherence. 3, 4
- A 2023 multicenter study found no difference in treatment failure between 500 mg twice daily (12.7% failure) versus 500 mg four times daily (17% failure, P = 0.343). 3
- Another 2025 study confirmed no statistically significant difference in treatment failure rates (18.7% vs 15.0%, P = 0.465) between twice-daily and four-times-daily dosing. 4
- Twice-daily dosing may improve patient adherence without compromising effectiveness. 3, 4
Treatment Duration
- The FDA-approved duration is 7 to 14 days for uncomplicated cystitis. 1
- A 2023 study demonstrated that short courses (5-7 days) of twice-daily cephalexin achieved 81.1% clinical success rates. 5
Pharmacologic Rationale
- Cephalexin achieves urinary concentrations of 500-1000 micrograms/mL following 250-500 mg oral doses, which is many times greater than the minimum inhibitory concentration for usual urinary pathogens. 6
- 70-100% of the dose is excreted unchanged in urine within 6-8 hours. 6
Common Pitfalls to Avoid
- Do not use cephalexin as first-line empiric therapy when other recommended agents are available and appropriate. 2
- Dose adjustment required in patients with creatinine clearance <30 mL/min, proportional to reduced renal function. 6
- Avoid prescribing four-times-daily dosing when twice-daily dosing is equally effective and improves adherence. 3, 4