Macrobid (Nitrofurantoin) is Contraindicated at eGFR 17
Nitrofurantoin should NOT be used in patients with an eGFR of 17 mL/min/1.73 m² and must be discontinued immediately if currently prescribed. This represents stage 4 chronic kidney disease with severe renal impairment, well below the safety threshold for this medication.
Guideline-Based Contraindication
- The American College of Physicians explicitly recommends that nitrofurantoin should be avoided and discontinued in patients with an eGFR persistently below 45 mL/min/1.73 m² 1
- An eGFR of 17 falls into CKD stage 4 (severe GFR decrease, 15-29 mL/min/1.73 m²), which is far below this cutoff 2
- Expert consensus from nephrology, geriatric, and primary care pharmacists identified nitrofurantoin as one of the top medications that should be avoided in individuals with eGFR below 30 mL/min 3
Why This Matters: Safety and Efficacy Concerns
Dual problem at this level of renal function:
- Inadequate urinary drug concentrations: Nitrofurantoin requires adequate renal excretion to achieve therapeutic urinary concentrations. At eGFR <30 mL/min, insufficient drug reaches the urine to effectively treat urinary tract infections 4
- Increased systemic toxicity risk: Reduced renal clearance leads to drug accumulation in the bloodstream, increasing the risk of serious adverse effects including pulmonary toxicity, peripheral neuropathy, and hepatotoxicity, particularly with any prolonged exposure 4, 5
Clinical Evidence Supporting This Recommendation
- A large retrospective cohort study of 116,945 older patients demonstrated that while nitrofurantoin was not associated with increased adverse outcomes at eGFR 45-59 mL/min, the study specifically excluded patients with more severe renal impairment, highlighting the lack of safety data at lower eGFR levels 6
- Historical pharmacokinetic data showed minimal urinary drug recovery in patients with creatinine clearance below 60 mL/min, with even less at lower levels of renal function 4
- Dosing errors with nitrofurantoin in advanced CKD (stages 4-5) are exceedingly common in clinical practice, with the drug being inappropriately prescribed despite contraindication 5
Alternative Antibiotic Selection
For UTI treatment at eGFR 17, consider:
- Fluoroquinolones with dose adjustment: Ciprofloxacin requires dose reduction in severe renal impairment but remains an option with appropriate monitoring 7, 3
- Beta-lactam antibiotics: Many can be dose-adjusted for severe renal impairment
- Trimethoprim-sulfamethoxazole: Can be used with dose adjustment, though monitoring is essential
Critical Monitoring Consideration
- The European Society of Cardiology emphasizes using the CKD-EPI equation for accurate eGFR estimation rather than relying solely on serum creatinine, which may appear falsely normal in older patients with reduced muscle mass 1, 2
- Renal function should be monitored regularly when prescribing any renally-cleared antibiotic in this population 1
Common Pitfall to Avoid
Do not confuse the historical 60 mL/min cutoff with current evidence-based recommendations. While older product labeling cited 60 mL/min as a contraindication, current expert consensus places the threshold at 45 mL/min 1. However, at eGFR 17, this distinction is academic—the patient is well below any acceptable threshold for nitrofurantoin use.