Postmarketing surveillance in 70,898 patients treated with a triamterene/hydrochlorothiazide combination (Maxzide)

A postmarketing surveillance study on triamterene 75 mg/hydrochlorothiazide 50 mg was conducted by the Philadelphia Association of Clinical Trials on 70,898 patients. These patients received either a whole table (71% of patients) or half tablet (25.2% of patients); 61.3% of all patients continued to take the same dose throughout the 4-week study. The most frequent adverse reactions were generally nonspecific and typical of therapy with a diuretic. The withdrawal rate due to adverse events was significantly lower (p less than 0.005) with the smaller (4.4%) than with the larger (5.6%) dosage. Although not statistically significant overall, reported adverse reactions also favored a lower dose. In general, adverse reactions occurred more frequently in those taking concomitant medications. No significant difference relating to dose was detected in the percentage of initially normokalemic patients who became hyper- or hypokalemic by the end of the study. Older patients tended to achieve goal blood pressure more frequently than did younger patients. These results suggest that the potential for the development of thiazide-induced hypokalemia and other adverse effects appears to be greatly reduced by the use of a potassium-sparing agent combined with a thiazide diuretic, without incurring a greatly increased risk of hyperkalemia and without sacrificing efficacy.