Keflex (Cephalexin) Dosage for Uncomplicated UTI
For uncomplicated cystitis in adults, the recommended dose of cephalexin is 500 mg every 12 hours for 7 to 14 days, though cephalexin should be considered an alternative rather than first-line agent. 1, 2
Standard Dosing Regimen
The FDA-approved dosing for uncomplicated cystitis is 500 mg every 12 hours (twice daily) for 7-14 days in patients over 15 years of age. 1 This twice-daily regimen has been validated in recent clinical studies showing equivalent efficacy to the traditional four-times-daily dosing, with the advantage of improved adherence. 3
Alternative Dosing Options
- The traditional regimen of 250 mg every 6 hours (four times daily) remains an option, though the twice-daily 500 mg dosing is preferred for convenience and compliance. 1
- A 2023 multicenter study demonstrated no difference in treatment failure between 500 mg twice daily versus 500 mg four times daily (12.7% vs 17%, P=0.343), supporting the simpler twice-daily approach. 3
Treatment Duration
Continue therapy for 7-14 days for uncomplicated cystitis. 1 The FDA label specifies this range, with 7 days being appropriate for straightforward cases and 14 days for more persistent symptoms. 1
Important Clinical Considerations
Position as Alternative Therapy
Cephalexin is classified as an alternative rather than first-line agent for uncomplicated UTI by the Infectious Diseases Society of America, noting inferior efficacy and more adverse effects compared to other UTI antimicrobials. 2 First-line agents according to current European guidelines include fosfomycin, nitrofurantoin, and pivmecillinam. 4
- Use cephalexin when first-line agents cannot be used due to allergy, resistance patterns, or availability issues. 2
- Consider local resistance patterns when selecting empiric therapy, as β-lactams are only recommended when E. coli resistance is <20%. 4
Renal Dosing Adjustments
Patients with creatinine clearance less than 30 mL/min require dose reduction proportional to their reduced renal function. 5 Cephalexin is 70-100% renally excreted and achieves urinary concentrations of 500-1000 mcg/mL, far exceeding minimum inhibitory concentrations for typical uropathogens. 5
Common Pitfalls to Avoid
- Do not use cephalexin for catheter-associated UTI without extending duration to 7-14 days, as this represents a complicated rather than uncomplicated infection. 4
- Avoid confusing uncomplicated cystitis with pyelonephritis, which requires different treatment approaches and durations. 4
- Do not routinely perform post-treatment cultures in asymptomatic patients, but do obtain cultures if symptoms persist or recur within 2-4 weeks. 4
When to Consider Alternative Agents
If symptoms do not resolve by the end of treatment or recur within 2 weeks, obtain urine culture and susceptibility testing and assume the organism is not susceptible to cephalexin. 4 Retreatment should use a different antimicrobial class for 7 days. 4