Correct Answer: C. Morphine
Morphine is a mu-opioid agonist that paradoxically worsens biliary colic despite providing analgesia. The mechanism is critical: morphine causes spasm of the sphincter of Oddi (the smooth muscle sphincter controlling bile flow into the duodenum). This sphincter contraction increases intraductal pressure, which directly aggravates the pain of biliary colic rather than relieving it. While morphine does suppress pain perception centrally, the local effect on the sphincter of Oddi dominates clinically, making the overall symptom worse. This is a well-documented phenomenon in Indian clinical practice and international guidelines. NSAIDs like diclofenac and etoricoxib, by contrast, reduce prostaglandin-mediated inflammation and smooth muscle contraction without affecting the sphincter of Oddi, making them the preferred analgesics for biliary colic. Nefopam, a non-opioid analgesic, does not cause sphincter spasm. The key teaching point: opioids are contraindicated in biliary colic because their sphincter-spasm effect outweighs their analgesic benefit in this specific condition.
Why the other options are wrong
A. Diclofenac — Diclofenac is an NSAID that inhibits prostaglandin synthesis, reducing inflammation and smooth muscle contraction in the biliary system. It is the first-line analgesic for biliary colic in Indian practice (AIIMS, PGIMER protocols). NSAIDs do not cause sphincter of Oddi spasm and actually improve symptoms by reducing ductal pressure. This is the correct drug choice, not a cause of aggravation. B. Etoricoxib — Etoricoxib is a selective COX-2 inhibitor (NSAID) with similar mechanism to diclofenac—it reduces prostaglandin-mediated inflammation without sphincter spasm. Like other NSAIDs, it is safe and effective in biliary colic. The NBE trap here is pairing it with morphine to test whether students know opioids (not NSAIDs) worsen this condition. D. Nefopam — Nefopam is a non-opioid, non-NSAID analgesic that works via monoamine reuptake inhibition. It does not affect the sphincter of Oddi and does not cause biliary spasm. While less commonly used in India than NSAIDs for biliary colic, it does not aggravate symptoms. The question specifically tests knowledge of opioid-induced sphincter spasm, not nefopam's properties.
High-Yield Facts
- Morphine causes sphincter of Oddi spasm, increasing intraductal pressure and worsening biliary colic pain despite central analgesia.
- NSAIDs (diclofenac, etoricoxib) are first-line analgesics for biliary colic in Indian guidelines; they reduce prostaglandin-mediated inflammation without sphincter effects.
- Opioids are contraindicated in acute biliary colic because local sphincter spasm outweighs systemic pain relief.
- Codeine and other opioids share morphine's sphincter-spasm property; the effect is class-dependent, not drug-specific.
- Sphincter of Oddi spasm increases ductal pressure from ~20 cm H₂O to >40 cm H₂O, directly triggering pain in biliary colic.
Mnemonics
OPIOIDS WORSEN BILIARY COLIC (Memory Hook) Opioids → Oddi spasm → Outcome: worse pain. NSAIDs are the antidote. Use this when you see 'biliary colic + analgesic + worsening' — immediately think opioid. NSAID > Opioid in Biliary Colic NSAIDs reduce inflammation (good for biliary colic); opioids cause sphincter spasm (bad). In any biliary/pancreatic pain question, if opioid is an option and pain worsens, it's the answer.
NBE Trap
NBE pairs morphine (a common analgesic) with biliary colic to trap students who assume 'analgesic = symptom relief' without considering organ-specific pharmacology. The trap is cognitive: students may not know that opioids worsen this specific condition despite being analgesics elsewhere.
Clinical Pearl
In Indian emergency departments, when a patient with known cholelithiasis presents with biliary colic and an intern gives morphine, the pain paradoxically worsens within 15–30 minutes due to sphincter of Oddi spasm. Switching to IV diclofenac 75 mg or IM etoricoxib 60 mg provides relief without this complication—a critical bedside distinction that prevents iatrogenic harm.
_Reference: KD Tripathi Pharmacology Ch. 12 (Opioid Analgesics); Harrison Principles of Internal Medicine Ch. 308 (Biliary Tract Disease)_