The use of quinidine sulfate throughout pregnancy

A gravid patient was given quinidine sulfate for idiopathic ventricular tachycardia. The serum levels of quinidine remained stable throughout pregnancy. At delivery, maternal and neonatal quinidine levels were equivalent, while the level in the amniotic fluid was significantly elevated. Explanations for the latter include 1) a concentration of quinidine in amniotic fluid due to spontaneous fetal voiding and 2) the use of a nonspecific protein precipitate method to measure quinidine that is unable to differentiate quinidine from its nonfunctioning metabolites. The diffusion of quinidine into breast milk was related to the serum quinidine concentration.