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Pharmacological SIADH Treatment — SCE Palliative Medicine MCQ

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HardNausea & VomitingPharmacological SIADH TreatmentSCE Palliative Medicine

A 60-year-old man with advanced colorectal cancer develops hyponatraemia (Na 122 mmol/L) from SIADH. He is nauseous and confused despite fluid restriction. Which pharmacological intervention is most appropriate to relieve his nausea by addressing the underlying mechanism?

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Correct answer: C — Demeclocycline or tolvaptan to correct the SIADH-driven hyponatraemia

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

Hyponatraemia in SIADH causes nausea via neurophysiological effects of brain sodium derangement; symptomatic antiemetics (A, C, D, E) do not treat the underlying electrolyte disorder. Pharmacological correction—either with demeclocycline (licensed for SIADH in malignancy when fluid restriction fails) or tolvaptan (routinely commissioned in UK cancer-related SIADH)—addresses the cause, restores sodium levels, and thus relieves the nausea.

Reference: NHS England Clinical Commissioning Policy on tolvaptan for SIADH in cancer (2016/17); Demeclocycline SmPC, medicines.org.uk (2025). https://www.england.nhs.uk/publication/clinical-commissioning-policy-tolvaptan-for-hyponatraemia-secondary-to-the-syndrome-of-inappropriate-antidiuretic-hormone-siadh-in-patients-requiring-cancer-chemotherapy/