Thiazide diuretic dose and risk of kidney stones in older adults: a retrospective cohort study

Background — Thiazide diuretics are commonly prescribed to prevent kidney stones. However, it is unclear whether higher doses confer greater benefit.

Objective — To determine whether lower doses of thiazide diuretics confer a similar protective effect against kidney stone events as higher doses.

Design — Population-based cohort study.

Setting — Linked health administrative databases in Ontario, Canada.

Patients — Older adults newly prescribed a thiazide diuretic between 2003 and 2014 were separated into 2 groups based on daily dose: low dose (⩽12.5 mg hydrochlorothiazide /chlorthalidone, or ⩽1.25 mg indapamide) or high dose.

Measurements — The primary outcome was time to a kidney stone event, using diagnosis and procedure codes. A secondary outcome was kidney stone surgery.

Methods — An association between thiazide diuretic dose and a kidney stone event was estimated using Cox proportional hazards regression.

Results — A total of 536 of 105 239 patients (0.51%) experienced a kidney stone event. We did not detect a difference in kidney stone risk in the high-dose relative to the low-dose group (adjusted hazard ratio, 1.10; 95% confidence interval, 0.93-1.31). Results were similar when analysis was restricted to the more specific outcome of kidney stone surgery. Neither a history of prior kidney stones nor the type of thiazide diuretic modified the effect of diuretic dose on outcome.

Limitations — Patients were >65 years old and we were unable to adjust for some potential confounders such as dietary factors.

Conclusions — Lower dose thiazide diuretics appear to confer a similar protective effect as higher dose thiazides against the development of kidney stones.