Nifedipine Pregnancy and Breastfeeding Warnings
Nifedipine Pregnancy Warnings
Nifedipine has been used safely in humans for treatment of preeclampsia and preterm labor. Data from the Michigan Medicaid Birth Defects Study failed to reveal an association between the use of nifedipine and congenital abnormalities (written communication, Franz Rosa, MD, Food and Drug Administration, 1994). This study was a retrospective study of 229,101 completed pregnancies between 1985 and 1992, of which 37 were exposed to the drug at any time during pregnancy. Of these pregnancies, two total birth defects and one cardiovascular birth defect were observed. The incidence of these birth defects did not achieve statistical significance. There were no observations of cleft palate, spina bifida, polydactyly, limb reduction, or hypospadias. These data do not support an association between nifedipine and birth defects. In uncontrolled studies of pregnant women with severe hypertension who were given nifedipine, the drug caused a significant reduction in systemic blood pressure without adversely affecting the expected course of pregnancy. While these pregnancies were complicated, no complications or adverse outcomes were attributed to nifedipine. There were no cases of uterine relaxation, although the high Cesarean section rate and the long and variable intervals between antenatal nifedipine administration and delivery made it impossible to assess the impact of the drug on the progress of labor. In a placebo-controlled study of 30 pregnant women with preeclampsia, nifedipine caused significant reductions in maternal systemic blood pressure without causing significant changes in fetal heart rates or the systolic to diastolic ratio of the umbilical artery. A retrospective review of 78 women with first-trimester exposure to calcium channel blockers (CCBs) (44%, or 34 were taking nifedipine) revealed no increase in major malformations compared with a control group matched for maternal age and smoking. This review suggests that CCBs do not represent a major teratogenic risk. A case in which a 36-year-old primipara with primary pulmonary hypertension (PPH), who received nifedipine SL 180 mg per day (with digoxin and heparin) has been reported. Pelvic ultrasonography and fetal heart monitoring were normal until gestation week 36, when oligohydramnios was detected. Labor was induced, and a healthy 2,485 g infant was delivered vaginally. The authors attributed the good outcome in this case and in other cases of PPH to the use of nifedipine. They do acknowledge, however, that the effects of nifedipine on the fetus remain largely unknown. Nifedipine has been used as a tocolytic agent because of its ability to cause uterine relaxation. Some studies have shown it to be as effective as and safer than either terbutaline or magnesium sulfate in the management of preterm labor. The pharmacokinetics of nifedipine have been elucidated in the immediate postpartum period in patients with preeclampsia. Because of the increased plasma clearance of nifedipine in these patients, dosing every three to four hours may be necessary to achieve adequate antihypertensive control. Due to in vitro evidence that nifedipine can arrest sperm motility, the drug has been considered as a male contraceptive device.
Nifedipine has been assigned to pregnancy category C by the FDA. Animal studies have revealed evidence of teratogenicity, embryotoxicity, placentotoxicity, and fetotoxicity. On a mg/kg or mg/m2 basis, some of the doses associated with these various effects were higher than the maximum recommended human dose and some were lower, but all were within an order of magnitude of it. Small, controlled, but unblinded studies in humans and cases reports have revealed decreased maternal blood pressure and decreased uterine artery perfusion pressure associated with nifedipine. Uterine blood flow was maintained due to vasodilation in these studies. A specific prenatal risk has not been identified from the available clinical evidence; however, an increase in prenatal asphyxia, caesarean delivery, prematurity, and intrauterine growth retardation have been reported. Perinatal deaths and decreased birth weights have been associated with the use of nifedipine in other human clinical studies, but other antihypertensive agents were also used, making implication of nifedipine alone difficult. Reversible reduction in the ability of human sperm obtained from a limited number of infertile men receiving recommended doses of nifedipine to bind to and fertilize an ovum in vitro has been reported. Nifedipine is only recommended for use during pregnancy when benefit outweighs risk.
Nifedipine Breastfeeding Warnings
Nifedipine is excreted into human milk. The manufacturer recommends that due to the potential for serious adverse reactions in nursing infants, a decision should be made to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Data reveal the milk nifedipine concentrations represent about 5% of a therapeutic dose and pose little risk to a nursing infant. Delaying breast-feeding 3 to 4 hours after a dose significantly decreases the amount of nifedipine to which a nursing infant may potentially be exposed.
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