Safety of Macrobid (Nitrofurantoin) with Creatinine of 0.61
Macrobid (nitrofurantoin) is safe to use in a patient with a creatinine clearance of 0.61 mg/dL, as this value indicates normal renal function.
Understanding Nitrofurantoin and Renal Function
- Nitrofurantoin has historically been contraindicated in patients with creatinine clearance (CrCl) <60 mL/min due to concerns about decreased efficacy and increased risk of adverse effects 1
- The contraindication was included in product information packets between 1988 and 2003, with the cutoff changing from 40 mL/min to 60 mL/min during this period 2
- The primary concerns with using nitrofurantoin in renal impairment include:
Interpretation of Creatinine Value of 0.61
- A serum creatinine of 0.61 mg/dL indicates normal renal function in most adults 4
- To accurately assess renal function, the creatinine value should be used to calculate creatinine clearance using the Cockcroft-Gault formula, which takes into account age, weight, and gender 4
- Even without the calculation, a creatinine value of 0.61 mg/dL is well within normal range and would correspond to a creatinine clearance well above 60 mL/min in most adults 4
Recent Evidence on Nitrofurantoin in Mild-Moderate Renal Impairment
- More recent studies have challenged the strict cutoff of 60 mL/min for nitrofurantoin use 2, 5
- A 2017 study found nitrofurantoin to be highly effective in patients with CrCl between 30-60 mL/min, with treatment failures primarily related to resistant organisms rather than renal function 5
- A 2015 population-based study of older women (median eGFR 38 mL/min) found that mild or moderate reductions in eGFR did not justify avoidance of nitrofurantoin 6
- However, significant renal impairment (CrCl <30 mL/min) remains associated with treatment failure 5
Risk of Adverse Events
- Pulmonary adverse events leading to hospitalization were significantly increased (HR 4.1) in patients with renal impairment (<50 mL/min/1.73 m²) 7
- Peripheral neuropathy risk increases with renal impairment, prolonged treatment, and in patients with anemia, diabetes, vitamin B deficiency, or electrolyte imbalances 1, 3
- The FDA label specifically notes that "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 1
Conclusion
- With a creatinine of 0.61 mg/dL indicating normal renal function, Macrobid (nitrofurantoin) can be safely prescribed at standard dosing 1, 2
- Monitor for early signs of adverse effects, particularly in patients with other risk factors for peripheral neuropathy or pulmonary reactions 1
- If the patient has other conditions that might affect renal function or increase risk of adverse effects (diabetes, anemia, vitamin B deficiency), closer monitoring may be warranted 1, 3