What is the dose of Cephalexin (Cephalexin) for urinary tract infection (UTI)?

Cephalexin Dosing for Urinary Tract Infections

For uncomplicated UTIs, prescribe cephalexin 500 mg twice daily for 3 days in women, or 500 mg every 12 hours for 7-14 days for cystitis, as this dosing is equally effective to four-times-daily regimens while improving adherence. 1, 2

Standard Dosing Regimens

Uncomplicated Cystitis in Women

• Cephalexin 500 mg twice daily (every 12 hours) for 3 days is the recommended alternative regimen when first-line agents cannot be used and local E. coli resistance is <20% 3
• The FDA label supports 500 mg every 12 hours for uncomplicated cystitis in patients over 15 years of age, with therapy continued for 7-14 days 1
• Recent evidence demonstrates that twice-daily dosing (500 mg BID) achieves equivalent clinical success rates (81-87%) compared to four-times-daily dosing, with no difference in treatment failure 2, 4, 5

Uncomplicated Cystitis in Men

• Cephalexin is not specifically recommended in current European guidelines for men with uncomplicated UTI, as trimethoprim-sulfamethoxazole or fluoroquinolones are preferred for the standard 7-day course 3
• If cephalexin is used based on susceptibility testing, the FDA-approved dosing would be 500 mg every 12 hours for 7-14 days 1

General Adult Dosing Range

• The FDA-approved adult dosage ranges from 1-4 grams daily in divided doses 1
• For more severe infections or less susceptible organisms, larger doses may be needed, but if >4 grams daily is required, parenteral cephalosporins should be considered 1

Key Clinical Considerations

Twice-Daily vs Four-Times-Daily Dosing

• Multiple recent studies confirm that 500 mg twice daily is non-inferior to 500 mg four times daily for uncomplicated UTIs 2, 4, 5, 6
• Treatment failure rates are comparable: 12.7% (BID) vs 17% (QID) in one study, and 18.7% (BID) vs 15% (QID) in another 2, 5
• Twice-daily dosing improves patient adherence and reduces cost without compromising effectiveness 2, 5

Duration of Therapy

• 3-day courses are recommended by European guidelines for uncomplicated cystitis in women when cephalosporins are used as alternatives 3
• The FDA label specifies 7-14 days for cystitis therapy 1
• In practice, shorter courses (3-5 days) of twice-daily dosing appear safe and effective based on recent evidence 4

When Cephalexin is Appropriate

• Cephalexin should be used as an alternative agent when first-line options (fosfomycin, nitrofurantoin, pivmecillinam) cannot be used 3
• Only use when local E. coli resistance to cephalosporins is <20% 3
• Cephalexin has excellent bioavailability and urinary penetration, making it suitable for UTI treatment 2

Common Pitfalls to Avoid

• Do not use cephalexin for pyelonephritis or upper tract infections - it is not recommended for these more severe infections where fluoroquinolones or parenteral agents are preferred 7, 8
• Avoid four-times-daily dosing when twice-daily is equally effective - this unnecessarily burdens patients and reduces adherence 2, 5
• Do not prescribe cephalexin as first-line empiric therapy - it should be reserved as an alternative when resistance patterns support its use 3
• Routine post-treatment cultures are not indicated for asymptomatic patients 3

Special Populations

Pediatric Dosing

• The usual pediatric dose is 25-50 mg/kg/day in divided doses 1
• For streptococcal pharyngitis and skin infections in children >1 year, the total daily dose may be divided every 12 hours 1

Treatment Failure Management

• If symptoms do not resolve by end of treatment or recur within 2 weeks, obtain urine culture and susceptibility testing 3
• Assume the organism is not susceptible to cephalexin and retreat with a 7-day regimen using another agent 3