[The use of tolvaptan in a case of severe hyponatriemia in SIADH during meningitis]

Vaptans, vasopressin V2 receptor antagonists, are new drugs indicated in the treatment of Inappropriate ADH Secretion Syndrome (SIADH). We report a case of SIADH in a patient affected by AIDS. During a hospitalization for an ongoing CMV meningitis she developed a severe hyponatremia (114 mEq/L), which was initially treated with restriction of free water. When the diagnosis of SIADH was done (plasma Osmolarity 240 mOsm/kg, urinary sodium30 mEq/24 h, normal volemia, lack of hypocorticosurrenalism and hypothyroidism), tolvaptan was given at the dose of 15 mg/day. Important fluctuations of plasma Na were observed thereafter (119-143 mEq/L). The progressive reduction of the drug (to 2 mg/die) allowed a stable correction of natremia. Unconsciousness determined the impossibility of the patient to freely access to water, thus explaining the fluctuations of natremia and the difficult management of the drug. Only a posology reduction to doses lower than those available for sale allowed a stable correction of natremia.