THE QUANTITATIVE EVALUATION OF SPASMOLYTIC DRUGS IN VITRO

¹ Sterling-Winthrop Research Institute, Rensselaer, N.Y.

An experimental procedure is described for using the Magnus-type excised organ preparation for comparison of the spasmolytic potency of compounds under test against standardized spasms induced by fixed doses of barium, histamine or acetylcholine. The proportion of preparations giving a positive response at different dose levels is changed to straight line functions by using probit and log-dose transformations. From these the ED₅₀ and ratios of activity can be readily determined by conventional methods.

Use of the symbol pD is proposed to express the concentrations required for a standard effect. This value is the logarithm of the reciprocal of the concentration of the active drug or, expressed alternatively, the log of the degree of dilution. It thus is entirely comparable to the term pH, now widely accepted as a convenient means of expressing otherwise unwieldy numerical values of hydrogen ion concentration.

This general assay procedure may be readily adapted to quantitating the responses of any smooth muscled organ to tonic or depressant drugs by appropriate choice of the standard and test agents.