What antibiotics can be used to prevent urinary tract infections (UTIs) after intercourse?

Post-Coital Antibiotics for UTI Prevention

For women with recurrent UTIs associated with sexual activity, low-dose antibiotics taken within 2 hours of intercourse are recommended as an effective prophylactic strategy. 1

First-Line Antibiotic Options for Post-Coital Prophylaxis

The following antibiotics are preferred for post-coital prophylaxis:

• Nitrofurantoin 50-100 mg - First-line option with low resistance rates
• Trimethoprim-sulfamethoxazole (TMP-SMX) 40/200 mg - Effective but consider local resistance patterns
• Trimethoprim 100 mg - Alternative when TMP-SMX is contraindicated

These medications should be taken as a single dose within 2 hours of sexual intercourse 1.

Clinical Decision Algorithm

1. Confirm diagnosis of recurrent UTIs (defined as ≥3 UTIs in 12 months or ≥2 in 6 months)
2. Establish temporal relationship between UTIs and sexual activity
3. Rule out complicating factors requiring additional evaluation:
   • Structural abnormalities of urinary tract
   • Neurogenic bladder
   • Immunosuppression
   • Nephrolithiasis
   • Recent surgery
4. Implement behavioral modifications first:
   • Voiding after intercourse
   • Adequate hydration
   • Avoiding prolonged urine retention
   • Avoiding sequential anal and vaginal intercourse
5. Initiate post-coital antibiotic prophylaxis if UTIs continue despite behavioral changes

Evidence for Efficacy

Post-coital antibiotic prophylaxis has been shown to significantly reduce UTI recurrence rates compared to placebo 1, 2. One study demonstrated that patients taking prophylactic antibiotics after sexual intercourse had significantly fewer infections (19) during treatment periods compared to when not taking prophylaxis (90) 3.

The AUA/CUA/SUFU guidelines support this approach, noting that post-coital prophylaxis is associated with decreased risk of adverse events compared to daily prophylaxis while maintaining efficacy 1.

Antibiotic Selection Considerations

• Nitrofurantoin is preferred due to low resistance rates, though it carries rare but serious risks of pulmonary and hepatic toxicity (0.001% and 0.0003%, respectively) 1
• TMP-SMX is effective but should be avoided in the first and third trimesters of pregnancy 4, 5
• Fluoroquinolones should be restricted due to risk of adverse effects and to promote antimicrobial stewardship 4

Duration of Therapy

The recommended duration for antibiotic prophylaxis is typically 6-12 months 1. After this period, consider reassessment to determine if continued prophylaxis is necessary.

Important Caveats and Pitfalls

1. Confirm eradication of previous UTI with a negative urine culture 1-2 weeks after treatment before starting prophylaxis 1

2. Discuss risks and benefits with patients, including potential adverse effects such as:

   • Gastrointestinal disturbances
   • Skin rash
   • Vaginal candidiasis
   • Risk of antimicrobial resistance

3. Consider non-antibiotic alternatives for patients concerned about antibiotic use:

   • Methenamine hippurate (1 gram twice daily)
   • Lactobacillus-containing probiotics
   • Cranberry products (though evidence is limited) 1, 4

4. Monitor for breakthrough infections and reassess antibiotic choice if they occur, considering local resistance patterns

5. Avoid prolonged antibiotic courses (>5 days) for acute UTI treatment as this increases risk of resistance without improving outcomes 1

By following this approach, post-coital antibiotic prophylaxis can reduce UTI recurrence by approximately 90% in appropriate candidates 6, significantly improving quality of life and reducing morbidity associated with recurrent UTIs.