Dose-dependent inhibition of the hemodynamic response to dipyridamole by caffeine

We investigated the effects of the adenosine antagonist caffeine on the hemodynamic response to dipyridamole infusion (0.4 mg/kg for 4 minutes). According to a randomized, placebo-controlled double-blind protocol, eight normotensive volunteers each participated in five tests: placebo after placebo, dipyridamole after placebo, and dipyridamole after 1, 2, and 4 mg/kg caffeine. Infusion of caffeine alone (4 mg/kg) induced an increase in mean arterial pressure of 6.1 +/- 0.5 mm Hg versus 1.5 +/- 0.9 mm Hg after placebo (p less than 0.05). Infusion of dipyridamole alone exerted a characteristic hemodynamic response with an increase in systolic blood pressure (+8.4 +/- 2.4 mm Hg), pulse pressure (+7.0 +/- 2.4 mm Hg), heart rate (+25.7 +/- 3.8 beats/min) and calculated rate-pressure product (+3419 mm Hg x beats per minute), all being significantly different from the changes induced by placebo. Caffeine induced a dose-dependent attenuation of the response to dipyridamole, with a significant negative correlation between the dose of caffeine on the one hand (0, 1, 2, and 4 mg/kg) and the dipyridamole-induced increments in systolic blood pressure (r = -0.53), pulse pressure (r = -0.50), heart rate (r = -0.95), and rate-pressure product (r = -0.93) on the other hand. We conclude that caffeine attenuates the hemodynamic response to dipyridamole infusion in humans in a dose-dependent fashion. Because of the wide-spread use of caffeine, this pharmacologic interaction may be of clinical importance, for example, in the diagnostic use of dipyridamole in thallium-201 myocardial imaging.