Reduced risk for hospitalization due to hyponatraemia in lithium treated patients: A Swedish population-based case–control study

BACKGROUND: Many drugs used in psychiatry have been reported to cause hyponatraemia. However, lithium may be an exception due to its potential for causing nephrogenic diabetes insipidus, but clinical data are largely absent. The objective of this investigation was to study the association between lithium therapy and hospitalization due to hyponatraemia. METHODS: This study was a register-based case–control investigation of the general Swedish population. Patients hospitalized with a principal diagnosis of hyponatraemia (n=11,213) were compared with matched controls (n=44,801). Analyses using multivariable logistic regression adjusting for co-medication, diseases, previous hospitalizations and socioeconomic factors were deployed to calculate the association between severe hyponatraemia and the use of lithium. Additionally, newly initiated (⩽90 days) and ongoing lithium therapy was studied separately. RESULTS: Compared with controls, the unadjusted odds ratio (OR) (95% confidence interval (CI)) for hospitalization due to hyponatraemia was 1.07 (0.70–1.59) for lithium. However, after adjustment for confounding factors the risk was reduced (adjusted OR: 0.53 (0.31–0.87)). Newly initiated lithium therapy was not significantly associated with hyponatraemia (adjusted OR 0.73 (0.35–5.38)). In contrast, for ongoing therapy the corresponding adjusted OR was significantly reduced (adjusted OR: 0.52 (0.30–0.87)). CONCLUSIONS: A marked inverse association was found between ongoing lithium therapy and hospitalization due to hyponatraemia.