This study in the Australian and New Zealand Journal of Psychiatry sought to evaluate the incidence and mechanism of venlafaxine induced hyponatremia, which was defined as a plasma Na concentration of less than 130 mmol/L. A 17.2% incidence of hyponatremia was noted. Hyponatremia invariably developed within days of the start of therapy and was associated with failure to suppress vasopressin secretion during conditions of low osmolarity. Fluid restriction during continuation of drug treatment was effective. The authors recommend electrolyte testing in all patients over 65 within 3-5 days of starting venlafaxine.
Venlafaxine, a serotonin-norepinephrine reuptake inhibitor (SNRI), is closely related to the class of selective serotonin reuptake inhibitors (SSRI) which are known to cause hyponatremia. Should we be monitoring electrolytes in patients taking SSRIs?