What is the recommended dose of cephalexin (a cephalosporin antibiotic) for an uncomplicated urinary tract infection (UTI)?

Cephalexin Dosing for Urinary Tract Infections

For uncomplicated UTIs in adults, cephalexin should be dosed at 500 mg orally every 12 hours for 7-14 days. 1

Adult Dosing Recommendations

The FDA-approved dosing for cephalexin in uncomplicated cystitis is:

• 500 mg orally every 12 hours for 7-14 days 1
• Total daily dose should be within 1-4 grams per day 1

This twice-daily dosing regimen is supported by recent research showing that 500 mg twice daily is as effective as 500 mg four times daily for uncomplicated UTIs, with similar treatment failure rates (12.7% vs 17%, p=0.343) 2. The twice-daily regimen may improve patient adherence while maintaining efficacy.

Pharmacokinetic Considerations

Cephalexin is:

• Rapidly absorbed in the upper intestine
• Achieves high urinary concentrations (500-1000 μg/mL following 250-500 mg doses)
• Primarily excreted unchanged in the urine (70-100% within 6-8 hours) 3
• These concentrations far exceed the minimum inhibitory concentrations for common UTI pathogens

Special Populations

Pediatric Patients

• Recommended dosage: 25-50 mg/kg/day in divided doses 1
• For severe infections, dosage may be doubled 1

Renal Impairment

• Dose adjustment required for patients with creatinine clearance <30 mL/min 3
• Reduction should be proportional to the decreased renal function

Alternative Antibiotic Options

While cephalexin is effective for UTIs, other first-line options include:

• Nitrofurantoin 100 mg twice daily for 5 days
• Fosfomycin 3g single dose
• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days 4

Clinical Considerations

Advantages of Cephalexin

• Excellent urinary penetration 3
• Good activity against most common UTI pathogens
• Can be administered in relatively high oral doses without gastrointestinal irritation 3
• Low incidence of allergic reactions compared to other beta-lactams 3

Potential Pitfalls

1. Resistance concerns: Local antibiogram data should guide therapy when available
2. Duration of therapy: Complete the full 7-14 day course even if symptoms resolve earlier
3. Renal function: Adjust dosing in patients with significant renal impairment
4. Complicated UTIs: May require longer treatment duration or alternative agents

Monitoring and Follow-up

• Clinical improvement should be expected within 48-72 hours
• If symptoms persist, consider:
  • Repeat urine culture
  • Alternative antibiotic therapy
  • Evaluation for urological abnormalities

Conclusion

Cephalexin remains an effective option for uncomplicated UTIs with a simplified twice-daily dosing regimen of 500 mg every 12 hours for 7-14 days. This regimen balances efficacy with improved adherence compared to more frequent dosing schedules.