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

Recommended Dose of Cephalexin for Uncomplicated UTI

For uncomplicated urinary tract infections in adults, cephalexin should be dosed at 500 mg orally every 12 hours for 7 days. 1

Dosing Recommendations

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

• 500 mg every 12 hours for 7-14 days 1

This dosing regimen is supported by clinical evidence showing that twice-daily dosing is as effective as four-times-daily dosing for uncomplicated UTIs, with similar treatment failure rates and adverse events 2.

Treatment Duration

• For uncomplicated UTIs: 7 days of therapy is recommended 1
• This duration balances efficacy with minimizing antibiotic exposure
• Longer durations (up to 14 days) may be considered for more severe infections 1

Special Populations

Pediatric Patients

• For children: 25-50 mg/kg/day divided into 2-4 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 decreased renal function

Place in Therapy

It's important to note that cephalexin is considered a second-line agent for uncomplicated UTIs according to the Infectious Diseases Society of America (IDSA) guidelines 4. The guidelines state:

• β-Lactam agents, including cephalexin, are appropriate choices when first-line agents cannot be used 4
• β-Lactams generally have inferior efficacy and more adverse effects compared to first-line agents 4

First-line agents for uncomplicated UTIs include:

• Nitrofurantoin (100 mg twice daily for 5 days)
• Fosfomycin (3 g single dose)
• Trimethoprim-sulfamethoxazole (if local resistance <20%)

Efficacy Considerations

While twice-daily dosing of cephalexin (500 mg) has been shown to be as effective as four-times-daily dosing for uncomplicated UTIs 2, some studies suggest that higher doses may be beneficial in certain situations:

• A study found that 1 g twice daily for 10 days was effective for chronic UTIs 5
• Single-dose therapy with 3 g of cephalexin has shown efficacy in younger patients but less so in those over 40 years of age 6

Common Pitfalls to Avoid

1. Inadequate duration: Ensure a full 7-day course is completed to prevent treatment failure and recurrence
2. Using cephalexin as first-line therapy: Remember that nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole are preferred first-line agents when appropriate
3. Not considering local resistance patterns: Check local antibiotic susceptibility data before prescribing
4. Not adjusting for renal function: Patients with impaired renal function require dose adjustment

Monitoring

• Clinical improvement should occur within 48-72 hours
• Routine post-treatment cultures are not necessary in patients whose symptoms resolve
• Consider follow-up cultures for patients whose symptoms persist or recur within 2 weeks of treatment

By following these evidence-based recommendations for cephalexin dosing in uncomplicated UTIs, clinicians can provide effective treatment while minimizing the risk of treatment failure and antibiotic resistance.