Two simple methods were devised for evaluation of the effectiveness of antitussive drugs. A-method: A guinea pig, to which the drug had been administered subcutaneously before 30 min., is placed in a desiccator and allowed to inhale SO2-containing air for 1 min., the animal is taken out in open air, and the number of coughing observed for 5 min. In this method, the absence of cough response was regarded as effective. B-method: A guinea pig is anesthetized lightly by intraperitoneal injection of 15mg./kg. of pentobarbital sodium and fixed in a dorsal position. The trachea is exposed and a small hole cut in it. A stimulating hair is introduced through the hole for 3cm. and a violent cough is evoked. The stimuli were given at 15, 30, 60, 90, and 120 min. after injection of a drug and when no cough occurred even to one stimulus, the drug was regarded as effective. One animal can be used several times repeatedly with an interval of 10 or more days. In both methods ED 50 was calculated by the up-and-down method. The results from these two methods gave following values of ED 50, (mg./kg.): Morphine hydrochloride, 5.90 (A-method), 6.40 (B-method); codeine phosphate, 14.4 (A-method), 18.4 (B-method).
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Takagi et al. (1960) studied this question.