How to Prescribe Macrobid (Nitrofurantoin) for UTI
For uncomplicated cystitis in women, prescribe nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg orally twice daily for 5 days. This is a first-line recommendation with 93% clinical efficacy and minimal resistance concerns 1.
Dosing and Duration
- Standard dose: 100 mg twice daily
- Duration: 5 days for uncomplicated cystitis 1, 2, 3
- Administration: Take with food to increase bioavailability by approximately 40% 4
The 5-day regimen is equivalent in efficacy to trimethoprim-sulfamethoxazole 3-day courses (90% clinical cure for both) and superior to single-dose fosfomycin (93% vs 91% clinical efficacy, with significantly better microbiological cure: 88% vs 80%) 1. A 2018 randomized trial confirmed nitrofurantoin's superiority over fosfomycin, with 70% vs 58% clinical resolution at 28 days 5.
Renal Function Considerations
Nitrofurantoin can be used with creatinine clearance (CrCl) ≥30 mL/min, though efficacy may decrease below 60 mL/min 2, 6.
- CrCl ≥60 mL/min: Full efficacy expected; nitrofurantoin is preferred over fosfomycin (14.6% vs 20.7% failure rates) 6
- CrCl 30-60 mL/min: Use with caution; fosfomycin may be superior (16.0% vs 23.3% failure rates) 6. However, real-world data shows 69% efficacy in this range 7
- CrCl <30 mL/min: Avoid; only 2 of 8 failures in one study were attributable to renal insufficiency at this level 7
Important caveat: The traditional teaching to avoid nitrofurantoin with CrCl <60 mL/min is overly restrictive. Multiple studies demonstrate acceptable efficacy between 30-60 mL/min 6, 7, 8.
When NOT to Use Nitrofurantoin
Do not prescribe nitrofurantoin for:
- Pyelonephritis or perinephric abscesses 4
- Complicated UTIs requiring broader tissue distribution 4
- Infections with Proteus species, Serratia species, or Pseudomonas (intrinsically resistant) 4
- Pregnancy at term or during labor/delivery
- CrCl <30 mL/min
Sample Prescription
Rx: Nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg capsules
- Sig: Take 1 capsule by mouth twice daily with food for 5 days
- Disp: 10 capsules
- Indication: Acute uncomplicated cystitis
Clinical Pearls
Resistance patterns: Nitrofurantoin maintains excellent activity against common uropathogens including E. coli and Staphylococcus saprophyticus, with minimal resistance development since 1953 4, 9. Cross-resistance with other antibiotics is rare 4.
Side effects: Primarily gastrointestinal (nausea 3%, diarrhea 1%), generally mild and self-limited 1, 5. The feared pulmonary and hepatic toxicity occurs with long-term use, not short courses 10.
Urine discoloration: Warn patients that nitrofurantoin may turn urine brown 4.
Follow-up: Obtain urine culture before treatment when possible. If bacteriuria persists or recurs after treatment, select an agent with broader tissue distribution 4.
Avoid fluoroquinolones: Reserve ciprofloxacin and other fluoroquinolones for more serious infections due to collateral damage concerns, despite their high efficacy 1, 3.