Normeperidine

What it isThe N-demethylated metabolite of meperidine — not an analgesic, but a neurotoxin.

Why it mattersIt is the reason meperidine fell out of favor: accumulation causes tremor, myoclonus, and seizures, especially with renal impairment or repeated dosing.

What it changesThe toxicity is not opioid-receptor mediated, so naloxone does not reverse it — stopping the drug is the treatment.