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

Keflex (Cephalexin) Dosing for Uncomplicated UTI

For uncomplicated urinary tract infections in adults, the recommended dosing of Keflex (cephalexin) is 500 mg orally every 12 hours for 7-14 days. 1, 2, 3

Dosing Recommendations

• According to the FDA label, the usual adult dose for uncomplicated cystitis is 500 mg every 12 hours, with therapy continued for 7 to 14 days 1
• Recent evidence supports that twice-daily (BID) dosing is as effective as four-times-daily (QID) dosing for uncomplicated UTIs, with no significant difference in treatment failure rates (BID 12.7% vs QID 17%, p=0.343) 2
• A 2025 study comparing cephalexin 500 mg twice daily versus four times daily for UTIs diagnosed in the emergency department found no statistically significant difference in treatment failure rates (18.7% vs 15.0%, p=0.465) 3

Patient-Specific Considerations

• For more severe infections or those caused by less susceptible organisms, larger doses may be needed 1
• If daily doses greater than 4 g are required, parenteral cephalosporins should be considered 1
• Beta-lactams (including cephalexin) are generally considered alternative rather than first-line agents for uncomplicated UTIs due to:
  • Inferior efficacy compared to other UTI antimicrobials 4
  • More adverse effects compared to first-line agents 4

Duration of Therapy

• Cystitis therapy with cephalexin should be continued for 7 to 14 days 1
• This duration is consistent with general recommendations for beta-lactam antibiotics in UTI treatment 4

Clinical Pearls and Caveats

• Beta-lactams like cephalexin should be used with caution for uncomplicated cystitis and considered alternative antimicrobials rather than first-line therapy 4
• Twice-daily dosing may improve patient adherence compared to four-times-daily dosing without compromising effectiveness 2, 3
• Local antimicrobial susceptibility patterns should be considered when selecting empiric therapy for UTIs 4
• For patients with complicated UTIs, treatment failure rates may be higher (27.3% with BID dosing vs 30.3% with QID dosing) 3

Alternative Regimens for Uncomplicated UTIs

• First-line options (preferred over cephalexin) include:

  • Nitrofurantoin 100 mg PO every 12 hours for 5 days 4
  • Trimethoprim-sulfamethoxazole 160/800 mg (one double-strength tablet) twice daily for 3 days (if local resistance is <20%) 4
  • Fosfomycin 3 g PO single dose 4

• Fluoroquinolones are highly efficacious but should be reserved for important uses other than acute cystitis due to their propensity for collateral damage 4