Triamterene, a new potassium-sparing pteridine diuretic was found to have a weaker saluretic effect than the benzothiadiazines in nonedematous patients. However, a combination of 50 mg of triamterene plus 25 mg of hydrochlorothiazide, while continuing to prevent potassium loss, exhibited saluretic potency equivalent to 50 mg of hydrochlorothiazide alone. In 32 hypertensive outpatients, crossover therapeutic trials revealed that the combination just mentioned was as effective in controlling blood pressure as full doses of hydrochlorothiazide alone, whereas hypokalemia was prevented. No toxic effects, attributable to triamterene, were detected during the course of these studies.
William C. Heath, Edward D. Freis. Triamterene with Hydrochlorothiazide in the Treatment of Hypertension. JAMA. 1963;186(2):119–122. doi:10.1001/jama.1963.03710020039012