Two Common Antibiotics Linked to Birth Defects

It is very important during pregnancy to know which medications cross the placental barrier and can affect your child. Not all medications are created equal, and some can do more harm than good. Antibiotics are good example. Recently a surprising link between two common antibiotics, used to treat urinary tract infections, and birth defects.

Bacterial infections themselves can cause many problems for both mother and fetus if they are left unchecked, so expectant mothers shouldn’t avoid antibiotics entirely. Instead, women should discuss their choices of antibiotics with their doctors.

A new study provided the first large analysis of the use of antibiotics during pregnancy. The study found that mother of babies that had birth defects were more likely than mothers who had healthy babies to report taking two types of antibiotics during their pregnancy: urinary germicides which are called nitrofurantoins (brand names Macrobid and Furadantin) and sulfa drugs (brand names Bactrim and Thiosulfil Forte). However, this was the first time an association had been found between urinary tract treatments and birth defects, said lead author Krista Crider, who is a geneticist with the Centers for Disease Control and Prevention, which funded the research for the study. “Additional studies are going to need to be done to confirm these findings.”

Used for many decades already, the antibiotics in question predate the Food and Drug Administration and its requirements for very rigorous testing for safety. The FDA now grades all medications for safety to the fetus based on research, however, rigorous studies are lacking in so many cases that no antibiotics get the highest grade of an “A.” Sulfa drugs are the oldest antibiotics to be used and some animal studies have been conducted which found no harm during pregnancy. Nitrofurantoins have also been previously viewed to be safe by doctors to treat urinary tract infections during pregnancy. The most-prescribed antibiotics during early pregnancy, penicillins, appear to be the safest of the bunch.

Dr. Susan Mehnert-Kay, who is a family practice doctor in Tulsa, Oklahoma, who has also written about diagnosing and managing urinary tract infections, said that the new research is “very interesting” and would cause her to reconsider her antibiotic choices during early pregnancy. Dr. Michael Katz, from the March of Dimes, said that the study is very important because it looked at the drugs that have been used for decades without large studies of their safety in women who are pregnant. “Some physicians are not as attuned to this as they ought to be, so patients have the right to ask questions,” Katz stated.

The researchers analyzed the data from more than 13,000 mothers whose infants had birth defects and approximately 5,000 women who lived in the same regions that had babies who were healthy. The women were interviewed over the phone from six weeks to two years after their pregnancies. The mothers who remembered taking antibiotics during the month before they conceived through the first three months of their pregnancy were identified as exposed to the antibiotics.

The authors did acknowledge that the women’s memories could have been faulty, which is considered a substantial weakness in the study. Approximately one-third of the women who did take the antibiotics could not remember the specific type of medication they took. It is also unclear whether the birth defects were actually caused by the medications or by the underlying infections that were being treated, Crider said.

Birth defects that have been linked to sulfa drugs included rare heart and brain problems and shortened limbs. Those that were linked to nitrofurantoins included cleft palate and heart problems. The medications seemed to double or even triple the risk, depending on the type of defect. Crider said, “These defects are rare. Even with a threefold increase in risk, the risk for the individual is still quite low.” Anencephaly, which is a fatal brain problem linked to sulfa drugs, affects about 1 in 10,000 births in the United States. Cleft palate occurs in approximately 20 per 10,000 births.

Sandy Walsh, who is a spokeswoman for the FDA, said that the FDA recommends that women who are pregnant discuss medications with their doctors. The agency has also proposed changes to prescription drug labels that would require more complete information for women that are of childbearing age, women who are pregnant, and mothers who are breastfeeding, Walsh stated.