Nitrofurantoin: great for cystitis, but appropriate for everyone?

Purpose: Nitrofurantoin is now a first line treatment for cystitis due to declining susceptibilities with trimethoprim-sulfamethoxazole and quinolones. However, nitrofurantoin has important considerations when prescribing: it is contraindicated in elderly patients, patients with creatinine clearance (CrCl) <60 ml/min, and patients pregnant at term or in labor. Nitrofurantoin is available in two solid oral formulations: nitrofurantoin mono/macrocrystals and nitrofurantoin macrocrystalline, the latter being the drug on inpatient formulary. We evaluated if nitrofurantoin was prescribed appropriately to inpatients according to patient characteristics, institutional and package insert guidelines, and culture results.

Methods: This was a retrospective cohort of inpatients receiving nitrofurantoin from July 2010 through September 2010. Data collected included: patient characteristics, infection type, microbiology, treatment regimen, and appropriateness. Analyses were descriptive in nature.

Results: 54 patients were included in the study sample.  Median (IQR) age was 51 (31-66), 48 females (88.8%), median weight 78 kg (72-88), and median CrCl 76 ml/min (44-91).  Urinalysis was performed in 64.8% of patients. Only 65.7% of patients with a urinalysis had a positive result.  Nitrofurantoin was appropriately prescribed in only 11.1% of patients. Problems identified: Inappropriate formulation (43.4%), impaired renal function (31.3%), prescribing in the elderly (29.1%), pregnancy (10.4%), and resistant organisms (6.2%).

Conclusion: Patients overwhelmingly were not prescribed nitrofurantoin appropriately due to inappropriate patient selection and formulation confusion. From this data, an automatic therapeutic substitution was created to change all nitrofurantoin orders to nitrofurantoin macrocrystalline formulation. Pharmacy staff and physicians were educated on the substitution protocol and contraindications to nitrofurantoin through pharmacy staff meetings and newsletters.  Future plans are to evaluate if this change in practice resulted in a decrease in inappropriate prescribing of nitrofurantoin.