Risk Summary 

Available data on the use of zoledronic acid in pregnant women are insufficient to inform a drug-associated risk of adverse maternal or fetal outcomes. Discontinue zoledronic acid when pregnancy is recognized. 

In animal reproduction studies, daily subcutaneous administration of zoledronic acid to pregnant rats during organogenesis resulted in increases in fetal skeletal, visceral, and external malformations, decreases in postimplantation survival, and decreases in viable fetuses and fetal weight starting at doses equivalent to 2 times the recommended human 5 mg intravenous dose (based on AUC). Subcutaneous administration of zoledronic acid to rabbits during organogenesis did not cause adverse fetal effects at up to 0.4 times the human 5 mg intravenous dose (based on body surface area, mg/m2), but resulted in maternal mortality and abortion associated with hypocalcemia starting at doses equivalent to 0.04 times the human 5 mg intravenous dose. Subcutaneous dosing of female rats from before mating through gestation and lactation and allowed to deliver caused maternal dystocia and periparturient mortality, increases in stillbirths and neonatal deaths, and reduced pup body weight starting at doses equivalent to 0.1 times the human 5 mg intravenous dose (based on AUC). (see Data).

Bisphosphonates are incorporated into the bone matrix, from which they are gradually released over a period of years. The amount of bisphosphonate incorporated into adult bone, and available for release into the systemic circulation is directly related to the dose and duration of bisphosphonate use. Consequently, based on the mechanism of action of bisphosphonates, there is a potential risk of fetal harm, predominantly skeletal, if a woman becomes pregnant after completing a course of bisphosphonate therapy. The impact of variables such as time between cessation of bisphosphonate therapy to conception, the particular bisphosphonate used, and the route of administration (intravenous versus oral) on the risk has not been studied. 

The estimated background risk of major birth defects and miscarriage for the indicated populations is unknown. All pregnancies have a background risk of birth defects, loss, or other adverse outcomes. In the U.S. general population, the estimated background risks of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Data

Animal Data

In pregnant rats given daily subcutaneous doses of zoledronic acid of 0.1, 0.2, or 0.4 mg/kg during organogenesis, fetal skeletal, visceral, and external malformations, increases in pre-and post-implantation loss, and decreases in viable fetuses and fetal weight were observed at 0.2 and 0.4 mg/kg/day (equivalent to 2 and 4 times the human 5 mg intravenous dose, based on AUC).

Adverse fetal skeletal effects at 0.4 mg/kg/day (4 times the human 5 mg dose) included unossified or incompletely ossified bones, thickened, curved or shortened bones, wavy ribs, and shortened jaw. Other adverse fetal effects at this dose included reduced lens, rudimentary cerebellum, reduction or absence of liver lobes, reduction of lung lobes, vessel dilation, cleft palate, and edema. Skeletal variations were observed in all groups starting at 0.1 mg/kg/day (1.2 times the human 5 mg dose). Signs of maternal toxicity including reduced body weight and food consumption were observed at 0.4 mg/kg/day (4 times the human 5 mg dose).

In pregnant rabbits given daily subcutaneous doses of zoledronic acid of 0.01, 0.03, or 0.1 mg/kg during gestation no adverse fetal effects were observed up to 0.1 mg/kg/day (0.4 times the human 5 mg intravenous dose, based on body surface area, mg/m2). Maternal mortality and abortion were observed in all dose groups (starting at 0.04 times the human 5 mg dose). Adverse maternal effects were associated with drug-induced hypocalcemia. 

In female rats given daily subcutaneous doses of 0.01, 0.03, or 0.1 mg/kg, beginning 15 days before mating and continuing through gestation, parturition and lactation, dystocia and periparturient mortality were observed in pregnant rats allowed to deliver starting at 0.01 mg/kg/day (0.1 times the human 5 mg intravenous dose, based on AUC). Also, there was an increase in stillbirths and a decrease in neonate survival starting at 0.03 mg/kg/day (0.3 times the human 5 mg dose), while the number of viable newborns and pup body weight on postnatal Day 7 were decreased at 0.1 mg/kg/day (equivalent to the human 5 mg dose). Maternal and neonatal deaths were considered related to drug-induced periparturient hypocalcemia.