Protective effect of levodropropizine against capsaicin-induced cough in allergic patients: A double-blind, placebo-controlled study

The activity of the antitussive agent levodropropizine against cough induced by inhalation of graded doses of capsaicin (1.2 to 9.6 x 10-9 M) was evaluated in a randomized, double-blind, placebo-controlled, crossover study in 12 patients with clinically stable allergic rhinitis associated with bronchial asthma in four cases. The protocol involved administration of levodropropizine (60 mg TID) or placebo for 8 consecutive days, with a washout period of at least 1 week between the two treatments. Capsaicin stimulation tests were performed at pretreatment (baseline) and on the last day of each treatment period. Two patients dropped out, one for minor side effects during placebo treatment and one who failed to return for assessment. In the 10 evaluable patients, the total number of coughs induced by capsaicin inhalation was significantly lower after levodropropizine treatment (3.6 ± 5.6) as compared to both baseline (15.4 ± 6.4) and placebo (14.1 ± 7.8). The threshold concentrations of capsaicin required to induce two coughs (D2) and five coughs (D5), respectively, were significantly increased by levodropropizine, whereas placebo had no effect. No significant changes in forced expiratory volume in 1 second or vital capacity values were observed after inhalation of capsaicin in either treatment group. Levodropropizine appeared effective in preventing capsaicin-induced cough in patients with allergic asthma or rhinitis. The mechanism underlying this effect could involve inhibition of the release and/or action of sensory neuropeptides in the upper airways.