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SIADH Pharmacotherapy — SCE Medical Oncology MCQ

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ModerateOncological EmergenciesSIADH PharmacotherapySCE Medical Oncology

A 65-year-old man with cancer develops syndrome of inappropriate ADH secretion (SIADH) from SCLC. His Na is 125 mmol/L. He is mildly symptomatic. Initial management with fluid restriction (1 L/day) has failed after 48 hours. What is the next pharmacological step?

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Correct answer: B — Demeclocycline or tolvaptan

SIADH management stepwise: (1) fluid restriction 1L/day; (2) if fails: demeclocycline 600-1200mg/day (onset 3-5 days) or tolvaptan 15mg/day (onset hours — requires inpatient Na monitoring due to overcorrection risk); (3) definitive: treat underlying cause (chemo for SCLC). Hypertonic saline reserved for severe/symptomatic hyponatraemia (Na <120 or seizures/reduced GCS).

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/cancer