The Combination of Chlorthalidone with Nifedipine Does Not Exert an Additive Antihypertensive Effect in Essential Hypertensives: A Crossover Multicenter Study

To evaluate whether the combination of nifedipine with chlorthalidone exerts an additive antihypertensive effect when compared to single-drug treatment, 66 uncomplicated essential hypertensives, whose diastolic blood pressure was > 100 and < 115 mm Hg at the end of a 1-month washout placebo period, received, according to a randomized, double-blind, crossover design, nifedipine (20 mg b.i.d.), chlorthalidone (25 mg o.d.), the two drugs combined at the same doses, and the corresponding placebo. When compared to the randomized placebo the three active treatments significantly (p < 0.001) reduced blood pressure without changing heart rate and body weight. However, blood prssure values were similarly reduced under nifedipine and the combination and were significantly lower (p < 0.05) than those under chlorthalidone. Moreover, the percentage of responders and normalized patients under nifedipine and the two drugs combined were similar and significantly (normalized, p < 0.001; responders, p < 0.02) greater than those under chlorthalidone. Under chlorthalidone and its combination with nifedipine, plasma potassium tended to decrease and blood glucose and serum uric acid were significantly (p < 0.05) increased. These data show that the combination of nifedipine with chlorthalidone does not exert any additive antihypertensive effect when compared to nifedipine alone and that this combination increases both blood glucose and serum uric acid. Taken together these findings indicate that the combination of a dihydropyridine calcium antagonist with a thiazide diuretic is devoid of any clinical significance in the treatment of uncomplicated essential hypertensives.