What are the doses of Nitrofurantoin (macrocrystals) for urinary tract infections?

Nitrofurantoin Macrocrystal Dosing for Urinary Tract Infections

For uncomplicated urinary tract infections in adults, nitrofurantoin macrocrystals should be dosed at 100 mg twice daily for 5 days. 1, 2

Adult Dosing Regimens

Acute Uncomplicated Cystitis

• First-line treatment for women:
  • Nitrofurantoin macrocrystals: 50-100 mg four times daily for 5 days 1
  • Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days 1
  • Nitrofurantoin macrocrystals prolonged release: 100 mg twice daily for 5 days 1

Alternative Dosing According to FDA Label

• 50 to 100 mg four times daily (with food to improve absorption and tolerance) 2
• Treatment should continue for at least one week or for at least 3 days after sterility of urine is obtained 2

Long-term Suppressive Therapy

• For adults: 50 to 100 mg at bedtime 2, 3
• Studies have shown that 50 mg of macrocrystalline nitrofurantoin once daily at bedtime is effective for prophylaxis with fewer side effects than twice-daily dosing 3

Pediatric Dosing

• 5 to 7 mg/kg of body weight per 24 hours, given in four divided doses 2
• For long-term suppressive therapy: doses as low as 1 mg/kg per 24 hours, given in a single dose or two divided doses 2
• Contraindicated in infants under one month of age 2

Clinical Considerations

Efficacy

• Clinical cure rates with nitrofurantoin range from 88% to 93% 1
• Bacterial cure rates range from 81% to 92% 1
• The 5-day regimen of nitrofurantoin monohydrate/macrocrystals (100 mg twice daily) is equivalent in clinical and microbiological cure rates to trimethoprim-sulfamethoxazole (160/800 mg twice daily for 3 days) 1

Administration

• Should be given with food to improve drug absorption and tolerance 2
• For uncomplicated cystitis, the 5-day regimen is recommended based on clinical evidence 1

Monitoring

• If symptoms do not resolve by the end of treatment or recur within 2 weeks, a urine culture and antimicrobial susceptibility testing should be performed 1
• Continued infection indicates the need for reevaluation of therapy 2

Cautions

• Long-term therapy carries risks (see warnings in product labeling) 2
• Nausea is more common with microcrystalline formulations compared to macrocrystalline formulations 3
• Patients over 65 years do not report more adverse events than younger patients 3

Formulation Differences

• Macrocrystalline nitrofurantoin (Macrodantin) has better tolerability with fewer gastrointestinal side effects compared to microcrystalline formulations 3
• The monohydrate/macrocrystals formulation allows for twice-daily dosing rather than four times daily dosing 1

Remember that nitrofurantoin is only effective for lower urinary tract infections and should not be used for pyelonephritis or systemic infections due to inadequate tissue and serum concentrations.