A patient with SIADH remains hyponatremic despite fluid restriction and demeclocycline is initiated. Demeclocycline corrects hyponatremia by which mechanism?

• A Blocking V2 receptors in the collecting duct
• B Inhibiting ADH synthesis in the hypothalamus
• C Promoting free water excretion via osmotic diuresis
• D Inducing nephrogenic diabetes insipidus by reducing collecting duct responsiveness to ADH ✓

Explanation

Demeclocycline, a tetracycline antibiotic, induces nephrogenic diabetes insipidus by interfering with ADH signaling in the collecting duct, reducing aquaporin-2 expression and water reabsorption. This makes the kidney resistant to ADH, promoting free water excretion. It was historically used for SIADH but has been largely replaced by vaptans like tolvaptan. It does not block V2 receptors directly or inhibit ADH synthesis.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.