Comparative potency of atropine sulphate and glycopyrrolate on heart rate in man

Disagreement as to the effect of glycopyrrolate and atropine sulphate at various dosages on heart rate has been reported in the literature. Of particular interest is the question of whether small doses of glycopyrrolate cause bradycardia. Three groups of subjects were studied. The QRS complexes of the electrocardiogram were continuously recorded on a microcomputer. Group 1 consisted of 10 healthy volunteers who were given two doses of atropine sulphate 1.25 micrograms kg-1 and glycopyrrolate 0.75 micrograms kg-1, in random order at two different times, i.v. Monitoring continued until heart rate returned to baseline. Group 2 consisted of 24 women, ASA class I or II, scheduled for gynaecological operations. Each patient received fractionated i.v. doses of either atropine sulphate 2.5, 2.5 and 5 micrograms kg-1 or glycopyrrolate 1.5, 1.5 and 3.0 micrograms kg-1 at 3-min intervals. Heart rate was measured continuously for 1 h before drug injection and for 10 min after the last dose. Group 3 consisted of six volunteers given both drugs in the same dose and time schedule as Group 2, but heart rate was monitored for 180 min after the last dose. In Group 1, the incidence of bradycardia and increases in heart rate after the first dose were statistically significant for both atropine sulphate and glycopyrrolate when compared with baseline values. In Group 2, both drugs significantly increased the heart rate and had similar times to peak effect. In Group 3, bradycardia occurred only with atropine sulphate. Increases in heart rate, peak heart rate and duration of action were similar with both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)