Rapid attenuation of response to nifedipine in primary pulmonary hypertension.

In a 22-year-old woman with primary pulmonary hypertension resistant to all previous attempts to reduce the pulmonary vascular resistance, there was dramatic improvement after the first dose of nifedipine, 20 mg po, which was not sustained with subsequent doses. While there was a persistent reduction in systemic vascular resistance, the initial drug-related reduction in pulmonary vascular resistance was progressively attenuated with the subsequent four doses of nifedipine, 20 mg.