Capsaicin inhalation cough challenge is one of the most important methods evaluating cough and is acknowledged not only in pharmacological, but also in scientific studies and clinical practice. However, it is not popular in Poland. The aim of the study was then introduction of capsaicin challenge into clinical and scientific practice, evaluation of cough threshold in healthy volunteers and assessment of the test reproducibility and safety.
Material and methods: Thirty healthy volunteers (18 women) were included. Cough was induced by inhalation of capsaicin aerosol in doubling concentrations (0.49-1000 microM), using single breath method and a compressed air-driven nebulizer controlled by a breath activated dosimeter. Cough was counted for 10 s after each inhalation to assess the capsaicin concentration evoking at least 2 (C2) and 5 coughs (C5). The reproducibility of cough challenge results was assessed on the ground of two tests performed in an at least 10 day interval.
Results: Basing on the previously published literature, we introduced the capsaicin inhalation cough challenge into clinical practice. No difference between cough threshold among men and women was observed. A negative correlation between the age of the subjects and log C2 value was found (r = -0.44, p = 0.025). Reproducibility of cough challenge was assessed in 14 subjects and no significant differences between log C2 and log C5 in both tests were observed. Correlation coefficient for log C2 and C5 was r = 0.89, p = 0.0000 and r = 0.79, p = 0.001, respectively. There was a better reproducibility of log C2 (kappa 0.654, SEM = 0.10) than C5 (kappa 0.420, SEM = 0.13). The most common symptom reported by the patients during the capsaicin challenge was throat irritation. No serious adverse events were observed.
Conclusions: Access to previously published medical literature allows to introduce the capsaicin inhalation cough challenge into clinical practice. The test is safe, shows good tolerability and reproducibility of the results.