From the FDA Drug Label
Conditions such as renal impairment (creatinine clearance under 60 mL per minute or clinically significant elevated serum creatinine)... may increase the possibility of peripheral neuropathy
- Renal Impairment: The patient has a Glomerular Filtration Rate (GFR) of 50, which indicates renal impairment.
- Nitrofurantoin Use: The drug label warns that renal impairment, specifically creatinine clearance under 60 mL per minute, may increase the risk of peripheral neuropathy. The FDA drug label does not provide a clear answer on the safety of using Macrobid (nitrofurantoin) in a patient with a GFR of 50, but it does indicate that renal impairment may increase the risk of certain adverse effects 1.
From the Research
Macrobid (nitrofurantoin) can be used with caution in a patient with a GFR of 50 mL/min, as the most recent and highest quality study suggests that renal function should be considered in the clinical decision-making for cystitis treatment, and nitrofurantoin may still be effective and reasonably safe in moderate renal impairment. The standard dosing for Macrobid is 100 mg twice daily for 5-7 days for uncomplicated urinary tract infections. No dosage adjustment is typically needed at this level of renal function, but monitoring for side effects is important, as the concern with using nitrofurantoin in renal impairment is twofold: reduced efficacy because the drug requires adequate renal concentration to be effective against urinary pathogens, and increased risk of toxicity (particularly pulmonary and neurological) due to higher systemic drug levels when elimination is impaired, as noted in studies such as 2. Patients should be monitored for symptoms such as shortness of breath, cough, fever, or peripheral neuropathy. Alternative antibiotics may be preferable if the patient has other risk factors for nitrofurantoin toxicity or if treatment is needed for longer than 7 days.
Some key points to consider when using Macrobid in patients with impaired renal function include:
- The presence of mild or moderate reductions in estimated glomerular filtration rate does not necessarily justify avoidance of nitrofurantoin, as suggested by 3
- The effectiveness of nitrofurantoin may be reduced in patients with severe renal impairment, but it may still be effective in moderate renal impairment, as noted in 2
- Monitoring for side effects and adjusting the treatment plan as needed is crucial when using Macrobid in patients with impaired renal function
- Alternative antibiotics, such as fosfomycin or trimethoprim, may be preferable in certain cases, depending on the patient's specific situation and renal function, as discussed in 2.
Overall, the decision to use Macrobid in a patient with a GFR of 50 mL/min should be made on a case-by-case basis, taking into account the patient's individual needs and circumstances, and considering the potential benefits and risks of the medication, as informed by studies such as 4, 3, and 2.