The main objective of this study is the examination of cough reflex sensitivity via inhalational challenge and can demonstrate pharmacological end points. The effect of dextromethorphan, butamirate and placebo on capsaicin-induced cough in healthy participants were compared.

A placebo-controlled, randomized and a six-way crossover study was conducted to assess the effect of four doses of butamirate, dextromethrophan 30 mg, and placebo on incremental capsaicin challenges that were performed at baseline and 2, 4, 6, 8, 12 and 24 hours following the dosing. Plasma butamirate metabolites were analysed to assess the pharmacokinetic and pharmacodynamic associations.

Thirty-four participants (i.e., 13 males, average age 25 years) completed the study. Cough sensitivity reduced from baseline in all study arms. Dextromethorphan was superior to placebo. Butamirate did not show any significant activity with maximum attenuation even at the 45 mg dose. No apparent association between pharmacodynamic and pharmacokinetic parameters for butamirate.

The study established that the dextromethorphan weakens the capsaicin challenge thus confirming its broad activity upon the cough reflex for the first time.

Source: Faruqi S, Wright C, Thompson R, Morice AH. A randomized placebo controlled trial to evaluate the effects of butamirate and dextromethorphan on capsaicin induced cough in healthy volunteers. Br J Clin Pharmacol. 2014 Dec;78(6):1272-80.