Dantrolene in pregnancy: lack of adverse effects on the fetus and newborn infant.

Twenty malignant hyperthermia-susceptible pregnant patients were given dantrolene sodium orally for 5 days before delivery and 3 days after delivery. When cesarean section was necessary, triggering agents were avoided. No patient had a malignant hyperthermia reaction. No adverse effect of dantrolene sodium was detected by extensive testing of the fetus and neonate. The maternal predelivery dantrolene level was correlated with the noenatal cord blood dantrolene level (r = 0.837). The mean maternal predelivery dantrolene level was 0.99 +/- 0.5 microgram/ml, and the mean neonatal cord blood dantrolene level 0.68 +/- 0.3 microgram/ml. The time from the last dose of dantrolene to delivery was correlated with both the maternal dantrolene level and the neonatal cord blood level (r = 0.65). The half-life of dantrolene in the neonatal circulation was 20 hours. The controversy of oral dantrolene prophylaxis and the implications of this study with regard to further investigation are discussed.