Nitrofurantoin is Low-Risk in Pregnancy

The teratogenic potential of nitrofurantoin is low, according to the results of a large, population-based study conducted in Norway.¹
   
Nitrofurantoin, which is a pregnancy category B drug, is an antibiotic commonly used to treat urinary tract infections, but it also may be used to combat other types of bacterial infections. In pregnancy, nitrofurantoin should be prescribed only when need has been clearly established and for the shortest effective duration.^2,3 The goal of this recent study was to estimate whether increased malformation rates resulted from exposure to nitrofurantoin in the first trimester.¹ Also, researchers estimated whether the rates of adverse pregnancy outcomes and perinatal complications were increased in women who used nitrofurantoin during pregnancy.¹
   
Of 180,120 pregnant women, 5794 (3.2%) filled prescriptions for nitrofurantoin while they were pregnant. About 1334 (0.7%) prescriptions were filled during the first trimester and 979 (0.5%) were filled in the last 4 weeks of pregnancy. The pregnancy outcomes of women who filled a prescription for nitrofurantoin were compared with those of a disease comparison group comprised of women who were dispensed pivmecillinam, a prodrug of mecillinam not available in the United States, and unexposed women, explained the study authors.¹
   
The rate of major malformations in the group of women who filled a prescription for nitrofurantoin in the first trimester was lower than that for the disease control group (2.3% vs 2.8%, respectively). In addition, there was no increased risk of secondary adverse pregnancy outcomes in women who were dispensed nitrofurantoin in the first trimester when compared with those in women in the disease comparison group. However, neonatal jaundice occurred more often in the group dispensed nitrofurantoin in the last 30 days of pregnancy compared with unexposed women (10.8% vs 8.1%, respectively). Overall, these results suggest that the teratogenic potential of nitrofurantoin is low, concluded the study authors.
   
In some advisements, the use of nitrofurantoin is contraindicated near term (38 to 42 weeks’ gestation) and during labor and delivery because of the potential for the induction of hemolytic anemia in the neonate, which is caused by low levels of red blood cell glutathione. However, the American College of Obstetricians and Gynecologists (ACOG) currently advises that nitrofurantoin can be used as a first-line agent for the prevention and treatment of urinary tract infections and other infections caused by susceptible organisms in the second and third trimesters.^2,3 ACOG’s current opinion is that allowing infections to remain untreated in a pregnant woman because of concerns about possible adverse effects associated with nitrofurantoin is unadvisable, because doing so can lead to other more serious maternal and fetal complications.³

Pertinent Points:
- Nitrofurantoin dispensed in the first trimester was not associated with an increased risk of major malformations.
- Dispensing nitrofurantoin in the last 30 days before delivery increased the risk of neonatal jaundice.
- The overall teratogenic potential of nitrofurantoin is low.
 

References:

1. Nordeng H, Lupattelli A, Romoren M, Koren G. Neonatal outcomes after gestational exposure to nitrofurantoin. Obstet Gynecol. 2013;121(pt 1):306-313.
2. Nitrofurantoin pregnancy warnings. Available at: http://www.drugs.com/pregnancy/nitrofurantoin.html. Accessed May 24, 2013.
3. Committee opinion no. 494: sulfonamides, nitrofurantoin, and risk of birth defects. Obstet Gynecol. 2011;117:1484-1485.