Effect of oral mexiletine on the cough response to capsaicin and tartaric acid

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Abstract
BACKGROUND The effect of the orally active local anaesthetic mexiletine on the cough response to two different tussive agents, a C-fibre ending stimulator capsaicin and a chemostimulant tartaric acid, was examined in normal subjects. METHODS The cough threshold, defined as the lowest concentration of capsaicin (C5-CP) or tartaric acid (C5-TA) causing five or more coughs, and histamine induced bronchoconstriction were measured three hours after a single oral dose of 300 mg mexiletine or placebo in 14 normal subjects. RESULTS Mexiletene in a mean (SE) serum concentration of 0.99 (0.04) μg/ml significantly increased C5-TA from a geometric mean (SE) of 32.0 (1.27) mg/ml with placebo to 49.9 (1.34) mg/ml, but C5-CP did not differ significantly between treatment with mexiletine (12.2 (1.33) μM) and placebo (14.9 (1.23) μM). CONCLUSIONS These results suggest that the cough response to capsaicin and tartaric acid may be mediated in part via different neural pathways.