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Question 463
Pharmacology → General
Classification
Question
SSBAQuestion Header
An opioid-related drug has analgesic potency comparable with morphine but is not clinically useful as an analgesic because of a high incidence of dysphoria. It can displace opioid agonists from mu receptors and thereby help reverse opioid-induced respiratory depression. Which drug best fits this description?
Question Stem
Select the single best answer.
Options
A
Nalorphine
B
Pethidine
C
Fentanyl
D
Codeine
E
Tramadol
Explanation
Nalorphine as an opioid agonist-antagonist with analgesic potency comparable with morphine. Its high incidence of dysphoria limits its clinical usefulness as an analgesic. By displacing opioid agonists from mu receptors, it can help reverse opioid-induced respiratory depression; this effect does not extend to respiratory depression caused by barbiturates or benzodiazepines.
Option Validity
B) Pethidine is an opioid analgesic used in labour and can cause neonatal respiratory depression; it is not the agonist-antagonist characterised by marked dysphoria.
C) Fentanyl is an opioid used in epidural and spinal analgesia, not as the agonist-antagonist in this scenario.
D) Codeine is an opioid analgesic and does not have the agonist-antagonist profile of nalorphine.
E) Tramadol is a synthetic opioid but is not the agonist-antagonist with morphine-like analgesic potency and prominent dysphoria.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 12: Pharmacology. Analgesics, p.347.