Selective serotonin reuptake inhibitors and hyponatraemia: review and proposed mechanisms in the elderly

The association between selective serotonin reuptake inhibitors (SSRIs) and hyponatraemia has been well documented, the elderly appearing to be at greatest risk. An analysis of data of hyponatraemia in the elderly using SSRIs from all published cases and from the Committee on Safety of Medicines found that the mean time to detection was about 3 weeks after commencing SSRIs. A wide range of time to detection (1-253 days) and non-specific symptoms suggest hyponatraemia is detected by chance rather than being specifically looked for. In the elderly there are physiological changes, a high prevalence of medical illnesses and concomitant drug use, which may precipitate hyponatraemia. Together with a risk of altered water regulation in psychiatric illness this may account for the particular susceptibility of the elderly to hyponatraemia whilst using SSRIs.