A comparison of some atropine-like drugs in man, with particular reference to their end-organ specificity.

Atropine, methanthelinium, propantheline, oxyphenonium, hyoscine, and hyoscine methylbromide have been compared in man. After graded subcutaneous doses of these drugs simultaneous observations were made on the heart rate, salivary secretion, pupil size, near point of accommodation, micturition, and palmar sweating. This permitted a quantitative assessment of any differential effects of the drugs on the different end-organs.Small doses which depressed salivary secretion and palmar sweating did not necessarily accelerate the heart or slow micturition. Atropine and hyoscine, which are tertiary amines, had a greater effect than the other (quaternary) drugs on the iris and the ciliary muscle, compared with the effects on the other end-organs studied. This difference may be related to the fact that quaternary compounds penetrate cellular membranes with difficulty.The time course of the drug effects differed for different end-organs. The changes in heart rate, salivary secretion, and sweating began and ended sooner than those affecting accommodation and the pupil. As the dose of a drug was increased, the peak effect on the heart rate and salivary secretion tended to occur sooner, but the peak effect on the iris and ciliary muscle always occurred later. It is suggested that the aqueous humour may be acting as a reservoir for the drugs. After methanthelinium, all the drug effects began sooner and reached their peak sooner than after the other drugs.