What is the recommended dosage of Nitrofurantoin (Nitrofurantoin Monohydrate/Macrocrystals) for an elderly man with a urinary tract infection (UTI) and potential Impaired renal function?

Nitrofurantoin Dosing for UTI in Elderly Men

For an elderly man with uncomplicated UTI and preserved renal function (CrCl ≥60 mL/min), prescribe nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 7 days; however, nitrofurantoin is contraindicated if CrCl <60 mL/min, and alternative antibiotics must be used. 1, 2, 3

Critical First Step: Assess Renal Function

Before prescribing nitrofurantoin to any elderly patient, you must check renal function:

• Nitrofurantoin is contraindicated when creatinine clearance is <60 mL/min due to inadequate urinary drug concentrations and increased risk of toxicity, including peripheral neuropathy 2, 3
• Expert consensus from geriatric clinical pharmacists specifically recommends not using nitrofurantoin in older adults with CrCl <30 mL/min 4
• This is the most common and dangerous prescribing error with nitrofurantoin 3

Dosing Algorithm Based on Renal Function

If CrCl ≥60 mL/min:

• Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 7 days 1, 3
• Men require 7 days of treatment (not the 5-day regimen used in women) based on limited observational data 3
• Clinical cure rates of 88-93% can be expected 1, 2

If CrCl 30-60 mL/min:

• Avoid nitrofurantoin per FDA labeling and major guidelines 2, 3
• Consider trimethoprim-sulfamethoxazole 160/800 mg twice daily for 7 days if local resistance <20% 2, 3
• Alternative: fosfomycin trometamol 3 g single dose 2, 3
• Reserve fluoroquinolones (ciprofloxacin) for more invasive infections due to resistance concerns 2

If CrCl <30 mL/min:

• Nitrofurantoin is absolutely contraindicated 4, 2
• Use trimethoprim-sulfamethoxazole or fosfomycin as above 2

Important Nuances in the Evidence

There is a notable controversy in the literature regarding nitrofurantoin use in renal impairment:

• Recent research challenges the strict CrCl <60 mL/min contraindication: A 2018 population-based study of 116,945 older patients found that nitrofurantoin was not associated with increased adverse outcomes in patients with eGFR <60 mL/min, and was actually associated with lower odds of AKI hospitalization compared to trimethoprim 5
• A 2017 hospital study showed nitrofurantoin was effective in 69% of patients with CrCl <60 mL/min, with failures primarily occurring only when CrCl <30 mL/min 6
• A 2015 Canadian study found similar treatment failure rates with nitrofurantoin regardless of renal function, questioning whether mild-moderate renal impairment justifies avoidance 7

However, despite this emerging research, current FDA labeling and all major guidelines (IDSA, European Association of Urology, American College of Physicians) maintain the CrCl <60 mL/min contraindication 2, 3. In clinical practice, you must follow the FDA contraindication and guideline recommendations.

Common Pitfalls to Avoid

• Never prescribe nitrofurantoin without checking renal function first - this is the most dangerous error 3
• Do not use nitrofurantoin for complicated UTIs or suspected pyelonephritis - it does not achieve adequate tissue concentrations 1
• Do not use for perinephric abscess 1
• Be aware that nausea and headache occur in 5.6-34% of patients 1, 3
• Monitor for peripheral neuropathy, pulmonary reactions, and hepatotoxicity, especially in patients with borderline renal function 2

Follow-Up Recommendations

• Do not order routine post-treatment cultures if the patient is asymptomatic 3
• If symptoms persist or recur within 2 weeks, obtain urine culture with susceptibility testing 3
• If retreatment is needed, assume resistance to the original agent and use a different antibiotic for 7 days 3