The recent CMAJ teaching case report by Aneez Mohamed and colleagues elegantly details an important complication of treatment with nitrofurantoin,1 which might have occurred even if the patient had not been pregnant. However, the complication should have been avoided in this case, given that nitrofurantoin use is contraindicated in pregnant patients in whom labour is potentially imminent.
Nitrofurantoin is commonly used to treat urinary tract infections in pregnancy.2 Animal model studies have not demonstrated an obvious problem with fetal exposure to this antibiotic.3 The authors of a meta-analysis of studies in humans did not find evidence of harmful effects in pregnancy, but they were cautious about drawing conclusions because of the small amount of data available.4
Nitrofurantoin use in pregnancy continues to be of concern for several reasons. This antibiotic can affect glutathione reductase activity and hence can cause hemolytic anemia (analogous to the problems it causes in patients with glucose-6-phosphate dehydrogenase deficiency). Newborns and fetuses are apparently susceptible to this effect on glutathione reductase activity and hemolytic crises have been documented in these patients.5,6 Other evidence links craniosynostosis to fetal exposure to nitrofurantoin and drugs with similar chemical structures.7,8
The US Food and Drug Administration continues to list nitrofurantoin as a Category B drug (probably safe). The Canadian Compendium of Pharmaceuticals and Specialties (2007) continues to state that nitrofurantoin use is contraindicated in pregnancy when patients are close to delivery;9 until further data are available, it would be prudent to follow this guideline.