Induction of delta-aminolaevulinic acid synthase in leucocytes of patients on phenytoin therapy--comparison with changes in rat hepatic tissue.

1 In rats daily phenytoin (DPH) administration resulted in an increase in hepatic cytochrome P450 content. The rise in cytochrome P450 was associated with a temporary increase in the acitvity of hepatic delta-aminolaevulinic acid (ALA) synthase. 2 In patients newly commenced on DPH anticonvulsant therapy the activity of ALA synthase in peripheral leucocytes showed a marked temporary increase during the first 10 days of therapy. 3 These findings suggest that DPH induces a haem-requiring eenzyme system in peripheral leucocytes as well as in hepatic tissue.