[A case of venlafaxine-induced syndrome of inappropriate ADH secretion (SIADH) - treatment with tolvaptan].

History And Admission Findings: A 74-year-old woman with known COPD was admitted to hospital because of dyspnoa. Clinical and laboratory tests showed an acute pulmonary infection which was treated with antibiotics. Additionally she was found to have a moderately severe episode of depression for which she had the preceding three weeks been treated with venlafaxine, a selective serotonin re-uptake inhibitor. During the subsequent days she gradually developed a hyponatremia with serum sodium levels down to 108 mmol/l.

Investigations: After excluding common causes of hyponatremia such as a cerebral or pulmonal malignancy or endocrine disorders by computed thomography and laboratory tests, a venlafaxine induced syndrome of inappropriate ADH secretion (SIADH) was assumed to be the cause of the hyponatremia.

Treatment And Course: As neither discontinuation of venlafaxine nor strict fluid restriction led to a rise in the natrium level and the patient had a generalized seizure, oral treatment with the tolavaptan, a vasopressin-2-receptor antagonist, was initiated. This resulted within 48 hours in a rise of the sodium level to 131 mmol/l and there were no further seizures.

Conclusion: Hyponatremia is a relatively common side effect of medical treatment with SSRI or SSNRI in elderly patients. The therapy of choice in case of a hyponatremia due to a SIADH is to discontinue the antidepressive drugs and institute strict fluid restriction. Tolvaptan has recently emerged as a promising new therapeutic option for SIADH.