Which drug is a mu opioid receptor agonist that is about 1/8 as potent as morphine and known by the trade name Demerol?

• A. Meperidine
• B. Hydrocodone
• C. Etorphine
• D. Carfentanil

Answer: (A)

Meperidine is a mu opioid receptor agonist, a synthetic analgesic known by the trade name Demerol. Its analgesic potency is about one-eighth that of morphine, so you’d need roughly eight times as much meperidine to achieve the same effect as morphine. This explains why it’s the correct choice for a Demerol reference. Meperidine has some distinctive pharmacology: a relatively short duration of action, and antimuscarinic effects that can cause tachycardia and pupil dilation; it also tends to cause less histamine release than morphine, which can influence side effects. A notable caveat is its metabolite normeperidine, which can accumulate and provoke CNS excitation or seizures in renal impairment or with high or prolonged dosing. In contrast, the other options are either far more potent opioids used in different contexts (extremely potent fentanyl-like agents) or are not associated with the Demerol brand.