Dose-response relationships of intravenous hyoscine butylbromide and atropine sulphate on heart rate in healthy volunteers.

Heart-rate responses to intravenous hyoscine butylbromide, atropine and physiological saline in cumulative dosage regimens have been recorded in six healthy subjects. Atropine sulphate induced bradycardia at low, and tachycardia at higher, dose levels whereas hyoscine butylbromide caused only tachycardia but with a flatter dose-response relationship. Exact potency ratios could not be calculated because of the differing dose-response curves. However, an approximate estimate from a comparison of equiactive doses at the upper part of the curve yielded a value less than one half that obtained from the drugs' affinity constants in guinea-pig ileum. The findings suggest that, in addition to its action as a muscarinic antagonist, hyoscine butylbromide is a ganglion blocker in man as it is in animals.