May 22 2022

Classification of the active ingredient nitrofurantoin

Risk level in pregnancy: This medicine is classified as Category B.

Several experimental studies of reproduction in rabbits and rats at doses up to six times the human dose have revealed no impairment of fertility or harm to the fetus. However, the relevance of these findings to humans is uncertain.

There are no adequate and well controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

Nitrofurantoin crosses the placental barrier, so it is contraindicated in the last weeks of gestation, from the 38th (or earlier if delivery is imminent) until after delivery, because it may precipitate a hemolytic crisis in the newborn due to the immaturity of the enzyme system.

If the baby will be breastfed, discontinue nitrofurantoin therapy until a month after the birth.

An observational study of more than 50,000 pregnant women detected 6 cases of malformations in 83 women exposed to nitrofurantoin, which was considered not statistically significant [IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man Geneva: World Health Organization, International Agency for Research on Cancer, available at: p. V50 221]

A study of 180 120 pregnant women in the period 2004-2008 identified 1334 patients exposed to nitrofurantoin during the first trimester. There was no increased risk of malformations related controls. Taking nitrofurantoin in the last 30 days of pregnancy was associated with an increased risk of neonatal jaundice compared to controls [10.8%, OR 1.31, 95% CI: 1.02-1.70] [1] .

As with all patients, antibiotics should be prescribed to pregnant women only for appropriate indications and for the shortest time possible. During the second and third quarters, nitrofurantoin can still be used as first-line agent for the treatment and prevention of urinary tract infections caused by susceptible organisms. The prescription of this drug in the first quarter can be considered when there is no other suitable alternative antibiotics [2].

A case-control study, including 13155 cases and 4941 controls, found an association between the use of nitrofurantoin in pregnant women and birth defects in the child, such as anophthalmia or microphthalmos [OR = 3.7, 95% CI: 1.1-12.2) syndrome left ventricular hypoplasia [OR = 4.2, 95% CI: 1.9-9.1], atrial septal defects [OR = 1.9, 95% CI, 1.1-3.4) and cleft velopalatal with default or without lipstick [OR = 2.1, 95% CI: 1.2-3.9] [3].


1: Nordeng H, Lupattelli A, Rom?ren M, Koren G. Neonatal outcomes after gestational exposure to nitrofurantoin. Obstet Gynecol. 2013 Feb;121(2 Pt 1):306-13. doi: http://10.1097/AOG.0b013e31827c5f88.
2: American College of Obstetricians and Gynecologists Committee on Obstetric Practice. ACOG Committee Opinion No. 494: Sulfonamides, nitrofurantoin, and risk of birth defects. Obstet Gynecol. 2011 Jun;117(6):1484-5. doi:10.1097/AOG.0b013e3182238c57.
3: Crider KS, Cleves MA, Reefhuis J, Berry RJ, Hobbs CA, Hu DJ. Antibacterial medication use during pregnancy and risk of birth defects: National Birth Defects Prevention Study. Arch Pediatr Adolesc Med. 2009 Nov;163(11):978-85. Doi: 10.1001/archpediatrics.2009.188.

Update 18.07.2009

Meaning of category B

Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women OR Animal studies have shown an adverse effect, but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the fetus in any trimester.