(RxWiki News) Women at risk for having a second preemie may be taking the only drug on the market to prevent early birth. If so, they should be cautious about taking other prescription medications.
The drug called 17-OHPC (marketed as Makena) is routinely given to women at risk for giving birth early.
"Avoid taking other medications with 17-OHPC unless a doctor advises otherwise."
But one of the body's enzymes, called CY3A4, which is responsible for processing 17-OHPC, also processes many other prescription drugs, including commonly used asthma, antidepressant and antifungal medications.
Researchers led by Dr. Courtney Cuppett, working in Maternal Fetal Medicine at the Magee-Womens Hospital at the University of Pittsburgh, wanted to see if other medications might interfere with 17-OHPC.
It would be unethical to test different drugs on pregnant women taking 17-OHPC, so Cuppett and her colleagues conducted their study in the laboratory.
They added 17-OHPC to parts of human cells and tested the concentration of 17-OHPC when it was left alone to metabolize or when 25 different other medications were added to the mix that the researchers knew used the CY3A4 enzyme as well.
Of the 25 drugs tested, 13 of them negatively affected the ability of 17-OHPC to metabolize. Four of the drugs reduced 17-OHPC's effectiveness by more than 80 percent.
The four drugs causing the highest decrease in effectiveness were the acid reflux drug Nexium, the asthma drug Singulair, and two antivirals for HIV: Viracept and Norvir.
"Over half of the drugs inhibited 17-OHPC metabolism by 50 percent or more," Cuppett said. "This indicates that prescription medications may indeed affect 17-OHPC metabolism."
Among the drugs interfering with 50 to 80 percent of 17-OHPC's effectiveness were the antifungal drugs Diflucan, Sporanox and Vfend as well as the antidepressants Zoloft, Desyrel and Oleptro. The antipsychotic Haldol and the immunosuppressant drugs Hecoria and Prograf were also in that group.
This means that doctors may have to adjust the dosage of 17-OHPC women take if they are taking other medications at the same time.
"17-OHPC is currently given weekly via injection from 16 weeks until 36 weeks," said Dr. Kevin Gordon, M.D., an obstetrician and gynecologist in Arlington, Texas, who was not involved with this study.
"This is a very important study that may dramatically affect the practice patterns of obstetricians since preterm birth currently accounts for 12 percent of all U.S. deliveries," Gordon told dailyRx.
Further study is required to determine whether 17-OHPC might impact the effectiveness of other drugs taken at the same time.
The study was presented February 9 at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Dallas, TX.
The study was funded by an Obstetric-Fetal Pharmacology Research Units Network grant from the National Institute of Child Health and Human Development. Financial disclosures of the authors were unavailable.