Comparative actions of hydralazine, nifedipine and amrinone in primary pulmonary hypertension.

The effects of 3 types of vasoactive agents, hydralazine, nifedipine and amrinone, were evaluated in 7 patients with primary pulmonary hypertension (PPH). Hemodynamic values were measured before and after drug administration in every patient. All drugs increased cardiac output and reduced both systemic and pulmonary resistance in the patients studied. Only nifedipine significantly reduced pulmonary artery (PA) pressure (6 +/- 5 mm Hg). In addition, it decreased pulmonary resistance to a greater degree than systemic resistance in 2 of the 7 patients, suggesting that nifedipine can cause selective pulmonary vasodilation in some patients. Hydralazine appeared to increase cardiac output and stroke volume by reducing systemic resistance. There was no evidence of direct pulmonary vasodilating effects; it decreased systemic resistance more than pulmonary resistance in every case. The increase in cardiac output from amrinone was secondary to a decrease in systemic arterial pressure with reflex tachycardia; stroke volume was unchanged. Amrinone had little pulmonary effect in all but 1 patient, in whom it substantially reduced PA pressure and pulmonary resistance. The mechanism of action of these 3 drugs in PPH differs. Nifedipine holds the most promise as an effective pulmonary vasodilator. A study of the effects of long-term administration of nifedipine in PPH is warranted.