Thiazide-related hyponatraemia is not rare, and its incidence increases with age and number of medical comorbidities.

Although thiazide-induced hyponatraemia traditionally has been considered to be very uncommon, clinical experience suggests otherwise. In a retrospective cohort, investigators used a Danish national registry to assess the frequency of new hyponatraemia (Na level, below 130 mmol/L) among patients who initiated antihypertensive therapy with a thiazide diuretic or a combined thiazide-renin-angiotensin system (RAS) inhibitor. The control group was patients who initiated either a calcium-channel blocker or a RAS inhibitor alone. Two-year cumulative incidence outcomes were reported.

Incidence of hyponatraemia was significantly higher among 50,000 patients who initiated antihypertensive therapy with thiazide diuretics or combined thiazide-RAS inhibitors than among 130,000 control patients who initiated nonthiazide antihypertensives (about 3.5% vs about 2.0%). Hospitalisation with hyponatraemia also was significantly more common in patients who took thiazides than in control patients (about 2.5% vs about 1.5%). Hyponatraemia was more common in patients with three or more medical comorbidities (more than 10%) and in patients older than 60 years. Risk increased progressively with age (incidence for patients in their 60s, 70s and 80s: 4%, 6% and more than 10%, respectively). 

Comment: This study confirms what many of us have observed clinically: hyponatraemia occurs somewhat frequently in patients who take thiazide diuretics, and it occurs more commonly as patients age. These researchers only examined a two-year interval after thiazide initiation, but my colleagues and I occasionally have seen long-term thiazide users who developed hyponatraemia after years of having normal serum sodium levels. Patients who use thiazides probably deserve laboratory monitoring, and this study might make us think twice before starting a thiazide in a patient with advanced age or multiple medical comorbidities.

Daniel D. Dressler, MD, MSc, MHM, FACP, Professor of Medicine, Emory University School of Medicine, Atlanta, USA.

Andersson NW, et al. Cumulative incidence of thiazide-induced hyponatremia: a population-based cohort study. Ann Intern Med 2023 Dec 19; e-pub (https://doi. org/10.7326/M23-1989).

This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine, Hospital Medicine, Cardiology.