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Randomized Controlled Trial
. 2014 Jul;134(1):56-62.
doi: 10.1016/j.jaci.2014.01.038. Epub 2014 Mar 22.

Transient receptor potential vanilloid 1 (TRPV1) antagonism in patients with refractory chronic cough: a double-blind randomized controlled trial

Saifudin Khalid  1 , Robert Murdoch  2 , Amy Newlands  2 , Kevin Smart  2 , Angela Kelsall  1 , Kimberley Holt  1 , Rachel Dockry  1 , Ashley Woodcock  1 , Jaclyn A Smith  3
Affiliations
Randomized Controlled Trial

Transient receptor potential vanilloid 1 (TRPV1) antagonism in patients with refractory chronic cough: a double-blind randomized controlled trial

Saifudin Khalid et al. J Allergy Clin Immunol. 2014 Jul.

Abstract

Background: Inhalation of capsaicin, the extract of hot chili peppers, induces coughing in both animals and human subjects through activation of transient receptor potential vanilloid 1 (TRPV1) on airway sensory nerves. Therefore the TRPV1 receptor is an attractive target for the development of antitussive agents.

Objective: We sought to assess the antitussive effect of TRPV1 antagonism in patients with refractory chronic cough.

Methods: Twenty-one subjects with refractory chronic cough (>8 weeks) attending a specialist clinic were recruited to a randomized, double-blind, placebo-controlled crossover trial assessing a TRPV1 antagonist (SB-705498). Cough reflex sensitivity to capsaicin (concentration of capsaicin inducing at least 5 coughs) and 24-hour cough frequency were coprimary end points assessed after a single dose of SB-705498 (600 mg) and matched placebo. Cough severity and urge to cough were reported on visual analog scales, and cough-specific quality of life data were also collected.

Results: Treatment with SB-705498 produced a significant improvement in cough reflex sensitivity to capsaicin at 2 hours and a borderline significant improvement at 24 hours compared with placebo (adjusted mean difference of +1.3 doubling doses at 2 hours [95% CI, +0.3 to +2.2; P = .0049] and +0.7 doubling doses at 24 hours [95% CI, +0.0 to +1.5; P = .0259]). However, 24-hour objective cough frequency was not improved compared with placebo. Patient-reported cough severity, urge to cough, and cough-specific quality of life similarly suggested no effect of SB-705498.

Conclusion: This study raises important questions about both the role of TRVP1-mediated mechanisms in patients with refractory chronic cough and also the predictive value of capsaicin challenge testing in the assessment of novel antitussive agents.

Keywords: Cough; capsaicin; cough sounds; sensory nerves; transient receptor potential vanilloid 1.

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