Disposition and pharmacodynamics of methamphetamine in pregnant sheep.

To determine the placental transfer of methamphetamine, its subsequent fetal disposition, and its hemodynamic effects, we administered methamphetamine intravenously to 15 pregnant ewes 3 days after placement of maternal and fetal vascular catheters. Methamphetamine crossed the placenta within 30 seconds of its administration. Although the ewes had higher peak concentrations, the fetuses' longer elimination half-life ultimately led to higher fetal than maternal methamphetamine concentrations. The ratio of fetal tissue to plasma drug concentration 2 hours after administration was highest in the lung, followed by the placenta, kidney, intestine, liver, brain, and heart. Methamphetamine caused a 54% to 63% rise in maternal blood pressure, a 20% to 37% increase in fetal blood pressure, and a drop in fetal oxyhemoglobin saturation and arterial pH. We conclude that methamphetamine, in doses at or below what is commonly abused, has effects that could be detrimental to the health of the mother and her fetus.