Meperidine (Demerol), also called pethidine, was the first synthetic opioid. Since it is synthetic, you would not refer to it as an opiate. Eduardo Fraifeld, MD opined that Demerol is “toxic and sedating” and “should not be used at all”. Withdrawal symptoms are worse than with morphine. Meperidine should not be used for chronic pain. Its use for acute pain should be reserved for those allergic to first-line opioids. Oral administration is not advised due to extremely poor bioavailability. The usual route of administration is intramuscular (IM). It is not available for intravenous (IV) administration. Duration of action is very short, about 3 hours.
Meperidine is distinguished from other opioids by its serotonergic properties, caused by 5-HT reuptake inhibition. Meperidine was involved in a high-profile death from serotonin syndrome in 1984, which killed an 18-year-old college student named Libby Zion. The reaction occurred when meperidine was added to the MAOI phenelzine (Nardil).
Opioids, meperidine excluded, are potent pupillary constrictors. Due to meperidine’s serotonergic and anticholinergic effects, it can cause dilation of pupils in some individuals. Withdrawal from meperidine manifests with dilated pupils like the other opioids. It is more likely than other opioids to cause seizures with overdose.
Although primarily a mu opioid receptor agonist, meperidine has more affinity for the kappa receptor than morphine, making meperidine more likely to cause dysphoria, hallucinations, and dissociation.
The metabolite of meperidine (normeperidine) is neurotoxic and may accumulate in cases of renal or hepatic impairment.