What is the recommended dose of Nitrofurantoin (antibiotic) for an adult patient with no significant medical history and normal renal function, diagnosed with an uncomplicated urinary tract infection (UTI)?

Nitrofurantoin Dosing for Uncomplicated UTI

For an adult patient with normal renal function and uncomplicated UTI, prescribe nitrofurantoin monohydrate/macrocrystals (Macrobid) 100 mg twice daily for 5 days in women, or 100 mg twice daily for 7 days in men. 1, 2

Standard Dosing by Sex

Women with Uncomplicated Cystitis

• Nitrofurantoin monohydrate/macrocrystals: 100 mg twice daily for 5 days 1, 2
• This represents the optimal first-line regimen recommended by both the Infectious Diseases Society of America (IDSA) and the European Association of Urology 1, 2
• Clinical cure rates range from 88-93%, with bacterial cure rates of 81-92% 1, 2
• The 5-day regimen has equivalent efficacy to trimethoprim-sulfamethoxazole (3 days) and ciprofloxacin (7 days) 1

Men with Uncomplicated UTI

• Nitrofurantoin 100 mg twice daily for 7 days minimum 3, 2
• Extend to 14 days if prostatitis cannot be excluded 3
• Note that clinical efficacy in males is substantially lower than in females (25% failure rate in males versus 10-16% in females), which should influence antibiotic selection 3

Alternative Nitrofurantoin Formulations

• Nitrofurantoin macrocrystals: 50-100 mg four times daily for 5 days 1, 2
• Nitrofurantoin macrocrystals prolonged release: 100 mg twice daily for 5 days 1, 2
• For VRE (vancomycin-resistant Enterococci) UTIs specifically: 100 mg four times daily 1

Critical Contraindications and Precautions

Renal Function Requirements

• Absolutely contraindicated if creatinine clearance <60 mL/min due to inadequate urinary drug concentrations and increased risk of peripheral neuropathy 3, 2
• This is the most common and dangerous prescribing error—always check renal function before prescribing 2
• For CrCl <60 mL/min, use alternative agents such as trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days or fosfomycin trometamol 3 g single dose 2

Clinical Situations Where Nitrofurantoin Should NOT Be Used

• Do not use if pyelonephritis is suspected—nitrofurantoin does not achieve adequate renal tissue concentrations 1, 2
• Do not use for complicated UTIs (structural/functional abnormalities, obstruction, instrumentation, pregnancy) 2
• Do not use in men with suspected prostatitis—inadequate prostatic tissue penetration 2
• Do not use for perinephric abscess 1

Efficacy Considerations

Treatment Success Rates

• Nitrofurantoin demonstrates 88-93% clinical cure rates in women with uncomplicated UTI 1, 2
• The 5-day regimen is equivalent to trimethoprim-sulfamethoxazole and ciprofloxacin when comparing appropriate duration regimens 2
• Nitrofurantoin is a first-line agent due to minimal resistance and limited collateral damage 1

Comparative Effectiveness

• Single-dose fosfomycin (3 g) shows no significant difference in clinical cure (RR 0.95) or microbiological cure (RR 0.96) compared to nitrofurantoin 4
• Nitrofurantoin is preferred over β-lactam agents (amoxicillin-clavulanate, cefpodoxime-proxetil), which are less effective as empirical first-line therapies 5

Common Adverse Effects and Safety

• Most common side effects: nausea and headache (5.6-34% of patients) 1, 2
• Serious pulmonary and hepatic toxicity are extremely rare (0.001% and 0.0003% respectively) 1
• Patients should ensure adequate hydration during treatment to prevent crystal formation 1

Follow-Up and Monitoring

When Post-Treatment Testing Is NOT Needed

• Routine post-treatment urinalysis or urine cultures are NOT indicated for asymptomatic patients 1, 2

When to Obtain Follow-Up Culture

• If symptoms do not resolve by end of treatment or recur within 2 weeks, perform urine culture with susceptibility testing 1, 2
• If retreatment is needed, assume the organism is not susceptible to the original agent and use a different antibiotic for 7 days 2

Special Populations

Pediatric Dosing

• Children ≥12 years: 100 mg twice daily for 7 days 1, 2
• Children <12 years: 5-7 mg/kg/day divided into 4 doses (maximum 100 mg/dose) for 7 days 1, 2

Patients with Diabetes

• Women with diabetes without voiding abnormalities presenting with acute cystitis should be treated similarly to women without diabetes 5