What is the recommended dose of nitrofurantoin (macrocrystalline formulation) for treating urinary tract infections (UTIs) in pregnancy?

Nitrofurantoin Dosing for Urinary Tract Infections

The recommended dose of nitrofurantoin for treating urinary tract infections is 100 mg twice daily for 5-7 days in pregnancy with normal renal function, avoiding use in the third trimester. 1

Dosing Recommendations for Different UTI Types

Uncomplicated UTIs

• Nitrofurantoin 100 mg four times daily (qid) 2
• Alternative dosing: 100 mg twice daily for 5 days 1

Asymptomatic Bacteriuria in Pregnancy

• 100 mg twice daily for 7 days (preferred over 1-day regimen) 3
  • A 7-day regimen showed significantly better bacteriologic cure rates (86.2%) compared to a 1-day regimen (75.7%) 3

Prophylaxis for Recurrent UTIs

• 50-100 mg daily for prophylaxis 1
• 50 mg as a single post-coital dose (for UTIs related to sexual activity) 4

Important Clinical Considerations

Pregnancy-Specific Considerations

• Nitrofurantoin is appropriate for pregnant women with normal renal function 1
• Contraindications in pregnancy:
  • Should be avoided in the last three months of pregnancy (third trimester) due to risk of hemolytic anemia in newborns 1
  • Contraindicated in patients with renal impairment (GFR <30 ml/min) 1

Efficacy and Follow-up

• Follow-up urine culture should be performed 7 days after completing treatment to assess for persistent or recurrent bacteriuria 1
• No routine follow-up urine culture is needed in patients who respond to therapy 1

Alternative Options

• For patients who cannot take nitrofurantoin, consider:
  • Cefalexin 500 mg every 6 hours for 7-14 days 1
  • Cefixime 400 mg daily for 7-14 days 1
  • Amoxicillin with clavulanic acid 500 mg every 8 hours for 7-14 days 1

Treatment Duration Algorithm

1. Asymptomatic bacteriuria: 7 days 1, 3
2. Cystitis: 7-10 days 1
3. Pyelonephritis: 10-14 days (with initial IV therapy if systemic symptoms present) 1

Pitfalls and Caveats

• Nitrofurantoin has poor tissue penetration and should not be used for pyelonephritis or systemic infections
• Resistance patterns should be monitored, though nitrofurantoin has maintained relatively low resistance rates compared to other antibiotics 5
• Gastrointestinal side effects are common but typically mild
• Pulmonary reactions can occur with long-term use but are rare with short-course therapy

Remember that nitrofurantoin remains effective for UTI treatment due to its continuing safety record and lack of associated R-factor resistance compared to newer antimicrobials 5.