Psychotropics and hyponatraemia

Hyponatraemia and selective serotonin re-uptake inhibitors in elderly patients

Hyponatraemia (serum sodium arbitrarily defined as less than 135 mmol/L) is an increasingly recognised adverse effect of selective serotonin re-uptake inhibitors (SSRIs). Its precise prevalence and incidence in the elderly are hard to determine because of confounding factors including other prescribed medications and medical conditions. Although hyponatraemia has been reported with all SSRIs and venlafaxine, most studies are small, retrospective, limited by confounding variables or are individual case reports. The risk of developing hyponatraemia while on an SSRI seems to increase with age, female, sex, previous history of hyponatraemia and the concomitant use of other medications known to include hyponatraemia. The sodium concentrations of most patients with SSRI associated hyponatraemia return to normal within days to weeks of SSRI withdrawal. A few cases of SSRI rechallenge indicate that hyponatraemia may sometimes be a transient effect with tolerance developing over time. There is an urgent need for controlled, rigorous studies to confirm the extent of the association between SSRIs and hyponatraemia. Older drugs such as tricyclic antidepressants also need systematic study. It remains quite unclear whether any specific SSRI or venlafaxine has a stronger association with hyponatraemia than any other antidepressant drug.

Selective serotonin reuptake inhibitors: a review of efficacy and tolerability in depression

Selective serotonin reuptake inhibitors (SSRIs) are now generally regarded as effective and better tolerated alternatives to tricyclic antidepressants (TCAs) for the treatment of depression. SSRIs also seem to be as well tolerated as moclobemide, mirtazapine, venlafaxine, reboxetine and nefazodone and show comparable efficacy. Minor differences have been observed between some SSRIs and some of the newer antidepressants but these findings are far from conclusive. Widespread use of the SSRIs has highlighted some unforseen adverse effects associated with SSRIs, namely hyponatraemia, EPSE and sexual dysfunction. Overall, differences in efficacy and tolerability between individual SSRIs are small and clinically insignificant.

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.