Antipyrine disposition in relation to lowered anticonvulsant plasma level during pregnancy

The authors studied antipyrine disposition before and after delivery in 4 epileptic women whose anticonvulsant plasma level per dosage ratio was lowered during pregnancy, and compared the results to those found in nonpregnant women undergoing antiepileptic treatment (N = 6) and healthy women (N = 6). The antipyrine clearance at term (0.53 +/- 0.11 ml/min/kg, mean +/- SD) was lower than it was early during puerperium (0.70 +/- 0.14 ml/min/kg, P less than .05) and approximately 3 months after delivery (1.14 +/- 0.26 ml/min/kg, P less than .01). The antipyrine clearance in nonpregnant epileptics (1.17 +/- 0.44 ml/min/kg) was comparable to that found 3 months after delivery, whereas it was significantly (P less than .01) higher than that found in healthy women (0.47 +/- 0.02 ml/min/kg). These observations suggest that the fall during pregnancy of anticonvulsant plasma concentrations relative to dosage is not attributable to the enhanced oxidative process of hepatic drug metabolism.