Chronotropic effects of atropine sulfate and methscopolamine bromide in normal subjects and patients undergoing cardiac catheterization.

: The increase in heart rate caused by intravenous injections of atropine sulfate (AS) and methscopolamine bromide (MSB) were compared in 12 healthy volunteers. AS, 200 micrograms, or MSB, 100 micrograms, were injected every 3 min for five doses on successive days. Mean heart rate from the second and fifth injections of MSB was significantly greater than after corresponding injections of atropine. The ratio of equivalent doses of MSB and AS was found to be 1:3. Three subjects with AS and four subjects with MSB exhibited reduced heart rates after the first injection. Excellent correlation of plasma atropine concentrations and heart rate increase were obtained in two volunteers (correlation coefficient, r = 0.84). In the second study, AS, 180 micrograms, and MSB, 60 micrograms, were compared in 20 patients undergoing cardiac catheterization and coronary arteriography. Both drugs produced equivalent increments in heart rate. MSB produced a more predictable dose response than AS. Side effects were similar with both drugs when equivalent doses were used. This study confirms previous investigations that MSB can be titrated by intravenous injections to increase heart rate to desired levels. Absence of central nervous system stimulation by MSB suggests that it may be more appropriate for use in patients with myocardial infarction.