Antihypertensive effect of tiapamil, a calcium antagonist. Double-blind placebo crossover study

The antihypertensive effects of intravenously and orally administered tiapamil and placebo were compared in 6 male patients (60 +/- 5 years: mean +/- SD) with mild essential hypertension (WHO classification Stage I) in a randomized double-blind crossover procedure. In the intravenous study, 1 mg/kg loading dose of tiapamil (or placebo) was followed by 50 micrograms/kg/min tiapamil or placebo over 2 h. In the oral study, the patients received placebo or approximately 6 mg/kg tiapamil. Blood pressure (BP) was determined by the Hawksley Random Zero Sphygmomanometer. Heart rate (HR) and P-R interval were derived from ECGs. Statistical significance was assessed by the paired Student's test. While intravenously administered placebo transiently increased both BP and HR, intravenous tiapamil significantly (p less than or equal to 0.05) lowered both variables. The P-R interval was also transiently but significantly (p less than or equal to 0.05) increased by intravenous tiapamil. Similarly, orally administered tiapamil showed an antihypertensive effect which was not observed with placebo. Neither HR nor P-R interval was influenced by oral tiapamil. The results suggest that tiapamil is an effective but short-acting antihypertensive agent.