Precursor to metabolite: Valproate sodium IV to 4-ene-VPA

Valproate sodium IV is converted to 4-ene-VPA by CYP2C9.

The pair

Valproate sodium IV — Intravenous valproate for seizures when oral therapy is unavailable; broad-spectrum but highly teratogenic.
4-ene-VPA — Unsaturated valproate metabolite implicated in mitochondrial dysfunction and liver toxicity; not a separate therapeutic drug.

Anything that inhibits or induces CYP2C9 shifts the balance between Valproate sodium IV and 4-ene-VPA.