Recommended Dosage of Macrobid (Nitrofurantoin Monohydrate) for Uncomplicated UTIs
The recommended dosage of Macrobid (nitrofurantoin monohydrate) for treating uncomplicated urinary tract infections is 100 mg twice daily for 5 days, as recommended by the Infectious Diseases Society of America and European Society for Microbiology and Infectious Diseases. 1
Dosing Regimen Details
- Dosage: 100 mg twice daily
- Duration: 5 days
- Patient population: Adults with uncomplicated UTIs
Efficacy Evidence
Nitrofurantoin has demonstrated strong efficacy in treating uncomplicated UTIs:
- In a 2018 randomized clinical trial, 5-day nitrofurantoin (100 mg three times daily) achieved clinical resolution in 70% of patients compared to 58% with single-dose fosfomycin, showing a significant advantage (difference of 12%, p=0.004) 2
- Microbiological resolution was also superior with nitrofurantoin (74% vs 63%, p=0.04) 2
- Earlier research from 2002 demonstrated that nitrofurantoin (100 mg four times daily for 3 days) was significantly more effective than placebo for both symptomatic relief and bacteriological cure 3
Special Populations and Contraindications
Renal Function Considerations
- Important contraindication: Nitrofurantoin should be avoided in patients with renal impairment (GFR <30 ml/min) due to reduced efficacy and increased risk of toxicity 1
- However, some evidence suggests nitrofurantoin may still be effective in patients with moderate renal insufficiency (CrCl 30-60 ml/min) 4
Pregnancy
- Nitrofurantoin 100 mg twice daily for 5-7 days can be used in pregnant women with normal renal function 1
- Important warning: Avoid in the third trimester of pregnancy due to risk of hemolytic anemia in newborns 1
Elderly Patients
- Use with caution in elderly patients due to potential pulmonary and hepatic toxicity, though serious adverse events are rare (pulmonary toxicity 0.001%, hepatic toxicity 0.0003%) 1
Monitoring and Follow-up
- Evaluate clinical response within 48-72 hours of initiating therapy 1
- No routine follow-up urine culture is needed in patients who respond to therapy 1
- A follow-up urine culture should be performed 7 days after completing treatment to assess for persistent or recurrent bacteriuria 1
Common Side Effects
- Primarily gastrointestinal effects:
- Nausea (approximately 3% of patients)
- Diarrhea (approximately 1% of patients) 2
Clinical Pearls
- Nitrofurantoin is considered a first-line agent for uncomplicated UTIs alongside trimethoprim-sulfamethoxazole and fosfomycin 5
- While some UK guidelines recommend 3-day courses of nitrofurantoin, there is limited direct evidence supporting this shorter duration 6
- The 5-day regimen has more robust evidence supporting its efficacy 2
- Nitrofurantoin is not effective against Proteus species and other intrinsically resistant uropathogens 4
- Efficacy may be reduced in alkaline urine 4