Double agents. Together with its infamous partner, phentermine (right), fenfluramine is an anti-obesity drug that earned a reputation for damaging the heart valves of patients taking the drugs. This led the FDA to withdraw fenfluramine from the market.

Adult female mice (dams) were exposed to either appetite suppressant or placebo from before conception until day 15 of the 19-day gestation period. The dams and offspring were subjected to various analyses during growth and development. With regard to conception rate, maternal weight gain, duration of gestation, litter size, and sex ratio, no differences were observed between mice exposed to low or high doses of the drugs or the placebo. Studies performed on postnatal day (PND) 120 on dam and offspring hearts to determine any link between the fenfluramine compounds and irreversible pulmonary hypertension, as recently suggested in the literature, revealed that the hearts of nonpregnant and pregnant adult mice were normal regardless of drug exposure or dose. Fenfluramine and dexfenfluramine concentrations were detectable in the amniotic fluid and in fetal brain measured on gestation day 15. However, there was no difference in fetal body weight, crown rumple length, volume of amniotic fluid per fetus, and fetal brain weight between drug- and placebo-exposed mice. Additionally, offspring in both groups were tested on PND 1, 3, and 5 and showed no difference in body weight, body length, head circumference, and motor coordination.

Although no differences were noted, caution should be exercised when extrapolating these results to all stages of development. The fenfluramine compounds were found to cross the placenta and could influence organ development, which may not manifest itself until later in development. Nonetheless, this study will help clinicians counsel their patients on the potential harm of antenatal appetite suppressant exposure.