Phenytoin hypersensitivity reaction

Phenytoin hypersensitivity reaction:

- inherited enzyme def of epoxide hydroxylase. Phenytoin is aromatic.

- cutaneous reaction seen after 1 - 3 wks.

- Fever, diffuse erythematous purpuric, non-blanchable, cutaneous eruption.

- leukocytosis, hepatitis, nephritis.

Tx: stop phenytoin, start gluco-corticoids.

Valproic acid (non-aromatic) is safe. Cross reactivity with other drugs (aromatic) like carbamazepine, phenobarbital, felbamate.