What is the recommended dosing of cephalexin (Keflex) for a urinary tract infection (UTI)?

Cephalexin (Keflex) Dosing for Urinary Tract Infections

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

Adult Dosing Recommendations

Uncomplicated UTIs:

• Standard dose: 500 mg orally every 12 hours for 7-14 days 1
• Alternative dosing: 250 mg orally every 6 hours 1

Complicated UTIs:

• Higher doses may be needed: 500 mg orally every 6 hours 1
• For severe infections: Consider doses up to 4g daily in divided doses 1
• If daily doses greater than 4g are required, consider parenteral cephalosporins 1

Treatment Duration

• 7-14 days is the recommended duration for cystitis therapy 1
• Recent research suggests that 5-7 days of therapy may be effective for uncomplicated UTIs 2, 3

Pediatric Dosing for UTIs

• Standard dose: 25-50 mg/kg/day divided into 4 doses 1
• For severe infections: Dosage may be doubled 1
• Weight-based dosing examples:
  • 10 kg (22 lb): 125-250 mg (½-1 tsp of 125 mg/5 mL) four times daily
  • 20 kg (44 lb): 250-500 mg (1-2 tsp of 125 mg/5 mL) four times daily
  • 40 kg (88 lb): 500-1000 mg (2-4 tsp of 125 mg/5 mL) four times daily

Clinical Considerations

Efficacy of Twice-Daily Dosing

• Recent research shows that twice-daily dosing (500 mg BID) is as effective as four-times-daily dosing for uncomplicated UTIs 2
• Clinical success rates were comparable between twice-daily (87.3%) and four-times-daily (83%) regimens 2
• Twice-daily dosing may improve patient adherence without compromising efficacy 2, 3

Antimicrobial Stewardship

• For multidrug-resistant organisms causing UTIs, consider alternative agents based on susceptibility testing 4
• For complicated UTIs caused by carbapenem-resistant Enterobacterales, consider newer agents like ceftazidime/avibactam or aminoglycosides 4

Common Pitfalls and Caveats

1. Local resistance patterns: Always consider local E. coli susceptibility patterns when prescribing cephalexin for empiric UTI treatment
2. Dosing frequency: While FDA labeling suggests four-times-daily dosing, recent evidence supports twice-daily dosing for uncomplicated UTIs
3. Duration: Don't treat uncomplicated UTIs for less than 7 days with cephalexin
4. Severe infections: Don't use oral therapy for patients who appear toxic or cannot tolerate oral intake - consider parenteral therapy initially

Special Populations

• For patients with renal impairment: Consider dose adjustment based on creatinine clearance
• For pregnant patients: Cephalexin is generally considered safe in pregnancy (FDA Category B)

By following these dosing recommendations for cephalexin in UTIs, you can optimize treatment outcomes while promoting antimicrobial stewardship.