Procainamide (PA) has been used safely in the third trimester of pregnancy for the treatment of ventricular tachycardia. PA crosses the human placenta. There are no reports of congenital anomalies or adverse fetal effects associated with the use of procainamide during human pregnancy. Since PA is a weak base and fetal blood is slightly more acidic than maternal, "trapping" of PA in the fetus is suspected. In one patient who was taking PA 2,000 mg orally every 6 hours, maternal and umbilical mixed blood PA levels were 6.0 and 6.4 mcg per milliliter at delivery, respectively. Corresponding values for NAPA were 9.4 and 8.7 mcg per milliliter, respectively. Without a dose change or difference in renal function, the maternal serum PA and NAPA levels 37 days postpartum were 10.3 and 8.8 mcg per milliliter, suggesting altered pharmacokinetics of PA during pregnancy.

Procainamide has been assigned to pregnancy category C by the FDA. Animal studies have not been reported. There are no controlled data in human pregnancy. Procainamide should only be given during pregnancy when benefit outweighs risk.

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Limited data from one woman who was taking procainamide (PA) 500 mg orally every 6 hours reveals that the concentrations of both PA and NAPA are lower in serum than in simultaneously collected milk specimens. The mean milk to maternal serum ratios for PA and NAPA were 4.3 and 3.8, respectively. Based on the usual therapeutic range for PA of 4 to 8 mg per liter, a regimen of 2 grams daily is estimated to result in maximal milk PA and NAPA levels of 34.4 and 30.4 mg per liter, respectively. Assuming 100% absorption and consumption of one liter per day (unlikely), the predicted plasma concentration in the nursing infant is less than 1 mg per liter.

Procainamide and N-acetylprocainamide (NAPA), an active metabolite, are excreted into and accumulate in 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.

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