Precursor to metabolite: Meperidine to Normeperidine

Meperidine is converted to Normeperidine by CYP2B6 / CYP3A4.

The pair

Meperidine — Older opioid whose metabolite can cause seizures; serotonergic interactions add risk.
Normeperidine — Neurotoxic meperidine metabolite; accumulation, especially with renal impairment, can cause tremor and seizures.

Anything that inhibits or induces CYP2B6, CYP3A4 shifts the balance between Meperidine and Normeperidine.