Demeclocycline has been used in the management of chronic SIADH. Its mechanism of action is best described as:

• A Competitive blockade of vasopressin V2 receptors
• B Stimulation of solute-free water reabsorption through aquaporin-2 upregulation
• C Inhibition of posterior pituitary vasopressin release
• D Induction of a nephrogenic diabetes insipidus like state blocking the action of antidiuretic hormone on the collecting duct ✓

Explanation

As a tetracycline side effect, demeclocycline impairs the ability of vasopressin to promote water reabsorption in the collecting duct, essentially creating drug induced nephrogenic diabetes insipidus. This counteracts the excess antidiuretic hormone of SIADH and corrects dilutional hyponatremia. It does not block the V2 receptor competitively, which is the vaptan mechanism, nor does it affect pituitary secretion. Photosensitivity and nephrotoxicity limit its current use.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.