Despite the widespread use of meperidine as an analgesic, its potential
for producing delirium has been overlooked. Six cases demonstrating
meperidine-induced behavioral toxicity are reported. Toxicity was more
likely when meperidine was combined with cimetidine or drugs having
anticholinergic activity. Discontinuation of meperidine and substitution of
morphine for analgesia were usually successful in treating the delirium.
Physostigmine reversed the delirium in one patient. The authors suggest
that the delirium results from the excessive anticholinergic activity of
meperidine or its only active metabolite, normeperidine.