PHENYTOIN and PHENOBARBITONE PLASMA CLEARANCE DURING PREGNANCY

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Abstract
In a retrospective investigation the plasma level of phenytoin (DPH) and phenobarbitone (PB) was studied in 23 epileptics during pregnancy and in the non-pregnant state to elucidate the possible influence of pregnancy on drug metabolism, and to correlate changes in seizure frequency to plasma clearance. The plasma clearance was expressed as the ratio between dose in mg per 24 hours, and the plasma level in mg per liter. In all the patients, plasma clearance of DPH increased during pregnancy with interindividual differences. Within a few months after the delivery most patients had DPH plasma clearance in the same range as before pregnancy. The change in PB plasma clearance was insignificant. The increase in seizure frequency seemed to be correlated to the increased DPH plasma clearance. The DPH plasma levels should be monitored once a month during pregnancy and after delivery, until the previous plasma clearance rate is reached, to adjust the plasma levels to within the therapeutic range. It might then be possible to prevent the increased seizure frequency seen in 45% of pregnant epileptics.