Cefalexin Prophylaxis for Recurrent UTI
For prophylaxis of recurrent uncomplicated UTIs in non-pregnant patients with normal renal function, use cefalexin 125-250 mg once daily at bedtime as continuous prophylaxis, or 250 mg as a single dose postcoitally if infections are temporally related to sexual activity. 1
When to Consider Antimicrobial Prophylaxis
Antimicrobial prophylaxis should only be initiated after non-antimicrobial interventions have failed, including behavioral modifications, increased fluid intake, vaginal estrogen (if postmenopausal), immunoactive prophylaxis, and methenamine hippurate. 1 The European Association of Urology provides a strong recommendation to use continuous or postcoital antimicrobial prophylaxis only when these less invasive approaches are unsuccessful. 1
Specific Cefalexin Regimens
Continuous Daily Prophylaxis
- Dosing: 125-250 mg orally once daily at bedtime 2, 3
- Duration: Typically 6-12 months with reassessment 2
- Evidence: A study of 23 women using 250 mg nightly remained infection-free for 132 months of observation (96% success rate), with no development of resistant E. coli strains. 2 Even lower doses of 125 mg nightly were equally effective as 250 mg in elderly patients. 3
Postcoital Prophylaxis
- Dosing: 250 mg orally as a single dose within 2 hours after intercourse 4
- Advantage: Uses approximately one-third the number of tablets compared to daily regimens while achieving identical efficacy 4
- Evidence: In 31 sexually active premenopausal women, postcoital cefalexin reduced UTI episodes from 127 infections (mean 6 months pre-treatment) to only 1 infection (mean 12 months during prophylaxis), a highly significant reduction. 4
Important Considerations
Choosing Between Regimens
- Postcoital prophylaxis is preferred when UTIs are clearly temporally related to sexual intercourse, offering equal efficacy with reduced antibiotic exposure 4, 5
- Continuous prophylaxis is appropriate when infections occur without clear relationship to intercourse or are frequent (≥3 UTIs per year or ≥2 in 6 months) 1
Advantages of Cefalexin for Prophylaxis
- Achieves high urinary concentrations 4
- Minimal induction of resistance in introital gram-negative flora at prophylactic doses 2
- Safe in pregnancy, making it suitable for women of childbearing age 4
- Well-tolerated with low side-effect profile 2, 3
Critical Pitfalls to Avoid
- Never treat asymptomatic bacteriuria: Treatment of ASB in patients with recurrent UTIs increases symptomatic recurrence risk (47% vs 13%; RR 3.17) and promotes antibiotic resistance. 6 ASB may actually prevent symptomatic UTIs. 6
- Confirm diagnosis with culture: Recurrent UTI should be diagnosed via urine culture before initiating prophylaxis to ensure true infection rather than confounding conditions (interstitial cystitis, overactive bladder, genitourinary syndrome of menopause). 6, 1
- Avoid surveillance cultures in asymptomatic patients: Do not perform routine urine testing in asymptomatic patients during prophylaxis. 6
Monitoring and Duration
- Counsel patients regarding possible side effects and the importance of adherence 1
- Reassess need for continued prophylaxis every 6-12 months 5
- Consider trial discontinuation after 6-12 months to determine if prophylaxis remains necessary 5
Alternative Cephalosporin Options
If cefalexin is unavailable or not tolerated, cefadroxil 500 mg twice daily for 3 days can be used for acute treatment (not prophylaxis), provided local E. coli resistance is <20%. 1