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Dexamethasone Antiemetic Mechanism — SCE Palliative Medicine MCQ

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HardNausea & VomitingDexamethasone Antiemetic MechanismSCE Palliative Medicine

A dying 78‑year‑old man with advanced lung cancer develops intractable vomiting despite morphine 30 mg, haloperidol 5 mg, and cyclizine 150 mg/24 hr in the continuous subcutaneous infusion (CSCI). The team considers adding dexamethasone as an adjuvant antiemetic. Through what mechanism does dexamethasone exert its antiemetic effect?

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Correct answer: A — The exact mechanism is unclear but likely involves reduction of peritumoral oedema, prostaglandin synthesis inhibition, decreased blood–brain barrier permeability to emetogenic substances, and direct anti‑inflammatory effects

Explanation lettering: E = shown as B · D = shown as C · C = shown as D · B = shown as E

Dexamethasone’s antiemetic effect is multifactorial and incompletely understood. Experimental studies suggest anti‑inflammatory activity, central effects at the nucleus tractus solitarius, modulation of neurotransmitter systems, HPA axis regulation, and reduction in opioid‑induced emesis. In palliative care guidance, its antiemetic action is attributed to reducing inflammatory responses with possible central effects. Distractors B, C, D, and E are incorrect—dexamethasone does not act as a dopamine blocker, prokinetic, 5‑HT₃ antagonist, nor does it stimulate tolerance via the vomiting centre.

Reference: Chu et al., The cellular mechanisms of the antiemetic action of dexamethasone…, 2014; Palliative Care Pain & Symptom Control Guidelines for Adults, NHS England, 2020