Changes in Primidone/Phenobarbitone Ratio During Pregnancy and the Puerperium

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Abstract
Plasma concentrations of primidone and its metabolite phenobarbitone were monitored in 9 pregnant epileptic patients treated with primidone (and in 3 cases other antiepileptic drugs) given at constant doses throughout pregnancy and the Puerperium. Phenobarbitone plasma concentrations were monitored in another 6 patients given phenobarbitone itself. A trend towards increasing primidone plasma concentrations during the second quarter of pregnancy was evident in all patients, with a concomitant significant decrease in primidone-derived phenobarbitone plasma concentrations. A trend towards a lowering of plasma concentrations of phenobarbitone administered as such was confirmed. These results suggest the usefulness of a careful monitoring of primidone and primidone-derived phenobarbitone during pregnancy and the Puerperium. Discrepancies of findings with primidone and phenobarbitone are discussed in view of the possible mechanism involved.