What is the recommended postcoital prophylaxis for urinary tract infections using Macrobid (nitrofurantoin)?

Postcoital Nitrofurantoin (Macrobid) Prescription for UTI Prophylaxis

For women with recurrent UTIs associated with sexual activity, nitrofurantoin 50-100 mg taken within 2 hours after sexual intercourse is the recommended postcoital prophylaxis regimen. 1

Prescription Details

• Medication: Nitrofurantoin (Macrobid) 100 mg capsules
• Dosage: Take 1 capsule within 2 hours after sexual intercourse
• Quantity: 30 capsules
• Refills: 2-3 (to cover 6-12 months of therapy)
• Instructions: Take one capsule with food and a full glass of water within 2 hours after sexual intercourse. Do not take more than one dose in 24 hours.

Patient Selection Criteria

Postcoital prophylaxis with nitrofurantoin is appropriate for women who:

• Have documented recurrent UTIs (≥3 UTIs in 12 months or ≥2 UTIs in 6 months) 1
• Have infections temporally related to sexual activity 1
• Have had a negative urine culture 1-2 weeks after treatment of any previous UTI 1

Evidence-Based Rationale

Nitrofurantoin is preferred for postcoital prophylaxis because:

• It has low resistance rates compared to other antibiotics 2, 3
• It has minimal impact on normal vaginal flora compared to TMP-SMX 2
• It demonstrates excellent long-term efficacy and safety profile for prophylaxis 3
• It is recommended by current guidelines as a first-line agent for UTI prophylaxis 1

Duration of Therapy

• Initial prescription should cover 6-12 months of therapy 1
• Efficacy should be assessed after this period
• Some women may require longer periods of prophylaxis to maintain benefit 1
• Clinical improvement is often maintained for at least 6 months after discontinuation 3

Monitoring and Follow-up

• No routine urine cultures needed if asymptomatic 1
• If breakthrough UTI occurs:
  • Obtain urine culture and susceptibility testing
  • Consider alternative antibiotic for prophylaxis if resistance develops
  • Assess for complicating factors

Potential Adverse Effects

• Gastrointestinal effects (nausea, vomiting) - more common with microcrystalline formulation 3
• Pulmonary reactions (rare - 0.001%) 1
• Hepatic toxicity (extremely rare - 0.0003%) 1
• Take with food to minimize GI side effects

Alternative Options

If nitrofurantoin is not tolerated or contraindicated:

• TMP-SMX 40/200 mg postcoitally 1
• Trimethoprim 100 mg postcoitally 1
• Non-antibiotic alternatives:
  • Methenamine hippurate 1g twice daily 1
  • Cranberry products (containing 36 mg proanthocyanidins) 1
  • Vaginal estrogen in postmenopausal women 1

Important Caveats

• Confirm diagnosis of recurrent UTIs before starting prophylaxis
• Ensure patient has no contraindications to nitrofurantoin (renal impairment with CrCl <60 mL/min, G6PD deficiency, pregnancy at term)
• Counsel on behavioral modifications (voiding after intercourse, adequate hydration)
• Postcoital prophylaxis is more targeted and uses less antibiotic than daily prophylaxis, potentially reducing resistance and adverse effects 1

Nitrofurantoin remains one of the most effective and well-tolerated options for postcoital prophylaxis of UTIs, with decades of evidence supporting its use and minimal development of resistance over time.