A drug used to treat lupus and malaria -- hydroxychloroquine -- reduced by half the risk of a potentially fatal heart condition in newborns who were at high risk for it.
The condition -- known as congenital heart block (CHB) -- results in a dangerously low heart rate.
"Our study shows hydroxychloroquine as the first, safe, and highly effective drug for preventing pregnant women at risk from having another child with congenital heart block," said lead author and rheumatologist Dr. Peter Izmirly, associate professor of medicine at NYU Langone Health in New York City.
Congenital heart block affects as many as 1 in 15,000 live births. About 75% of babies who survive it will require at least one pacemaker during their lifetime, and some may need a heart transplant.
CHB occurs when a pregnant woman's immune system attacks the heart of her fetus. In about half of cases, the mother has an autoimmune condition such as systemic lupus erythematosus or Sjogren's syndrome.
CHB is linked to antibodies in the mother that react with other proteins called SSA/Ro. For mothers with these antibodies, the risk of a baby with heart block is 2%, but it increases ninefold if a previous pregnancy resulted in CHB.
For newborns, a normal resting heart rate is 120 to 160 beats a minute. A heart rate below 50 beats a minute can be fatal.
This study included 54 U.S. women who previously had a newborn affected by CHB. Starting in their first trimester, the women received 400 milligrams of hydroxychloroquine a day.
Overall, 7.9% of newborns born to women taking hydroxychloroquine had CHB, compared to the historical rate of 18%, according to the study published online July 13 in the Journal of the American College of Cardiology.
Senior author Jill Buyon, director of the Division of Rheumatology at NYU Langone, said testing for anti-SSA/Ro antibodies should be considered. It is not part of a woman's normal screening during pregnancy.
"One implication of our findings is that hydroxychloroquine could be effective in preventing CHB in newborns of first-time, pregnant women with anti-SSA/Ro antibodies, which could change the way we evaluate all pregnancies regardless of a mother's health," Buyon said in an NYU news release.
The U.S. National Institutes of Health has more on congenital heart block.