Plasma verapamil levels and exercise performance

Our study in 10 patients with stable, exercise‐related angina under a double‐blind, placebo‐controlled protocol correlated plasma verapamil levels after single oral doses of 120 and 240 mg and exercise performance. Plasma verapamil levels peaked at 2 hr in seven patients and 4 hr in three patients and declined thereafter, with a mean plasma t½ of 3.22 and 4.54 hr after the 120‐ and 240‐mg dose. Despite the relatively short t½s, total exercise duration and time to onset of angina and S‐T segment depression were longer than placebo values for 4 hr after the 120‐mg dose and for 8 hr after the 240‐mg dose. Percentage increase in treadmill time and log of plasma verapamil levels correlated. All patients with plasma levels above 100 ng/ml had at least a 50% increase in exercise duration. Thus measurement of plasma verapamil levels are useful in patients who fail to respond to a dose of verapamil. If the level is below 100 ng/ml, increasing the dose of verapamil may improve response. Clinical Pharmacology and Therapeutics (1984) 36, 25–32; doi: 10.1038/clpt.1984.134