Do Antidepressants Lower the Prevalence of Lithium-associated Hypernatremia in the Elderly? A Retrospective Study

BACKGROUND Clinically important measures of lithium-induced nephrogenic diabetes insipidus (NDI) such as hypernatremia have not been well-studied. This is especially relevant for the elderly who, in comparison to younger adults, may become symptomatic and require hospitalization with relatively small elevations in sodium levels. We hypothesized that antidepressant use, which has been associated with the syndrome of inappropriate antidiuretic hormone secretion, has a protective effect against lithium-associated hypernatremia in the elderly. METHODS Retrospective cohort study of 55 geriatric psychiatry outpatients followed at tertiary-care hospitals. Patients using lithium and antidepressants were compared with those using lithium alone for prevalence rates of hypernatremia during a 15-year observational period. RESULTS The prevalence of hypernatremia was less in patients who had concurrent use of lithium and antidepressants, as compared to lithium alone 3/35 (8.6%) vs. 8/20 (40%), OR 0.14, p = .011. CONCLUSIONS Our results suggest that elderly lithium patients are less likely to develop hypernatremia if they are taking antidepressants concurrently. Whether antidepressants may be useful in the prevention of lithium-associated hypernatremia should be assessed in future prospective observational or treatment studies.