Thiazide diuretics are used as initial therapy in most patients with hypertension either alone or in combination therapy with other antihypertensive drugs. There are a handful of thiazides such as: chlorathalidone, hydrochlorathiazide, metalazone, indapamide and polythiazide on the market. How do we know which one to use?
Hydrochlorthiazide (HTCZ) is the most widely used thiazide-type diuretic. But on the other hand, most recent studies showing diuretics to be effective use chlorathalidone as the selected diuretic. So should HCTZ or chlorthalidone be used in treating patients with uncomplicated hypertension?
When comparing HCTZ and chlorathalidone, the latter has a longer duration of action and it’s potency is 1.5-2 times HCTZ’s potency. An observational cohort study in Ontario, Canada, compared the risk for death or adverse cardiovascular events in patients who were newly treated with either agent from 1993-2010. The outcome of the study did not show a significant difference between chlorathalidone and HCTZ. But the study did find that more patients were being hospitalized for hypokalemia or hyponatremia in the chlorathalidone group. This can be due to the fact that both drugs were prescribed at the same starting doses of 12.5mg, 25mg or 50mg. If chlorathalidone has double the potency of HCTZ we can expect to see more adverse events of long term diuretic usage early on. Between the two thiazides studies show both have similar efficacy, but different potency, which can result in adverse side effects. Therefore when deciding which diuretic to use, maybe it is more important to consider what starting doses to give. Since both drugs are efficacious, focusing on which dose to give can prevent adverse events of a too potent diuretic. A dose of 6.25mg is a good place to start especially for older patients. Also remember to monitor electrolytes, especially potassium and magnesium, and supplement as necessary.
1) Dhalla Ia et al. Chlorthalidone versus hydrochlorathiazide for the treatment of hypertension in older adults: A population-based cohort study. Ann Intern med 2013 Mar 19;158:447.
2) Krousel-Wood M., Munter P., et al. Hypertension Control Among Newly Treated Patients Before and After the Publication of the Main ALLHAT Results and JNC 7 Guidelines. J Clin Hypertens (Greenwich). 2012; 14:277–283.
3) ALLHAT Trial Results Quick Reference. http://www.nhlbi.nih.gov/health/allhat/qckref.htm. Accessed May 20, 2013.
Posted by: Heather Nguyen PharmD. Candidate 2014