Pharmacodynamic modeling of cough responses to capsaicin inhalation calls into question the utility of the C5 end point

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• 作者：Emma C.Y. Hilton ; Paul G. Baverel ; Ashley Woodcock ; Piet H. Van Der Graaf ; Jaclyn A. Smith
• 关键词：Capsaicin ; cough ; challenge ; human ; model ; nonlinear ; reflex ; response ; sensitivity
• 刊名：Journal of Allergy and Clinical Immunology
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：132
• 期：4
• 页码：847-855.e5
• 全文大小：1833 K

文摘

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Background

Inhaled capsaicin elicits cough reproducibly in human subjects and is widely used in the study of cough and antitussive therapies. However, the traditional end points C2 and C5 (the concentrations of capsaicin inducing at least 2 or 5 coughs, respectively) display extensive overlap between health and disease and therefore might not best reflect clinically relevant mechanisms.

Objectives

We sought to investigate capsaicin dose responses in different disease groups.

Methods

Two novel capsaicin cough challenges were compared in patients with chronic cough (CC; n?= 20), asthmatic patients (n?= 18), and healthy volunteers (HVs; n?= 20). Increasing doubling doses of capsaicin (0.48-1000 ¦Ìmol/L, 4 inhalations per dose) were administered in challenge 1, whereas the order of the doses was randomized in challenge 2. A?nonlinear mixed-effects model compared dose-response parameters by disease group and sex. Parameters were also correlated with objective cough frequency.

Results

The model classified subjects based on maximum cough response evoked by any concentration of capsaicin (E_max) and the capsaicin dose inducing half-maximal response (ED₅₀). HVs and asthmatic patients were not statistically different for either parameter and therefore combined for analysis (mean ED₅₀, 38.6 ¦Ìmol/L [relative SE, 28 % ]; mean E_max, 4.5 coughs [relative SE, 11 % ]). Compared with HVs/asthmatic patients, patients with CC had lower ED₅₀ values (14.7 ¦Ìmol/L [relative SE, 28 % ], P?= .008) and higher E_max values (8.6 coughs [relative SE, 11 % ], P?< .0001). E_max values highly correlated with 24-hour cough frequency (r?= 0.71, P?< .001) and were 37 % higher in female compared with male subjects, regardless of disease group (P?< .001).

Conclusions

Nonlinear mixed-effects modeling demonstrates that maximal capsaicin cough responses better discriminate health from disease and predict spontaneous cough frequency and therefore provide important insights into the mechanisms underlying CC.