Assessment of the antitussive effect of vadocaine hydrochloride using citric acid-induced cough in healthy volunteers.

Vadocaine hydrochloride (2',4'-dimethyl-6'-methoxy-3-(2-methylpiperidyl)propionanilide+ ++ hydrochloride, OR K-242-HCl; INN: vadocaine) is a novel compound with potent antitussive and local anaesthetic action. The antitussive profile of this compound was evaluated in 40 healthy volunteers in double-blind, placebo-controlled cross-over study design using inhaled citric acid a cough inducer. In Part I, vadocaine was compared in 20 healthy volunteers at two dose levels (10 and 30 mg) with codeine phosphate (50 mg) and a placebo. In part II, vadocaine (30 mg) and a placebo were compared in 20 healthy volunteers. In Part I, no statistically significant differences were found between the 3 compounds tested. However, statistically significant rises from the pre-dose value in the cough threshold stimulus level were observed following 10 and 30 mg doses of vadocaine. Neither codeine phosphate nor the placebo produced any statistically significant change in the cough threshold stimulus level. In Part II, vadocaine at a dose of 30 mg dose was found to be a potent antitussive with a statistically significant difference (p less than 0.0001) as compared with the placebo. The maximum cough threshold stimulus level was achieved 2 h after administration and was 72.6% higher than at pre-dose. With the placebo the cough threshold stimulus level also rose to some extent after 4 h, although the change was not statistically significant. The use of inhaled citric acid in graded concentrations for induction of the cough response was found to be a reliable method when the baseline cough threshold stimulus level is maintained within narrow limits throughout the entire study population.