Assessing Efficacy of Therapy for Cough

Subjective assessments of cough

In clinical practice and also in clinical trials, one of the quickest and easiest methods for documenting cough severity is to use either a numerical scoring system or visual analog scale.

Cough reflex sensitivity testing

The inhalation of irritant substances (capsaicin, citric acid, distilled water) in increasing concentrations can be used as a measure of the sensitivity of a subject's cough reflex.¹⁰ Capsaicin is the most commonly used agent and has been shown to be safe,¹¹ and it has good long- and short-term reproducibility.¹² Additionally, studies have used these challenges to demonstrate the effect of several drugs on cough reflex sensitivity.13, 14, 15, 16 Although in the past variability in challenge

Objective cough counting

With the development of portable digital sound recording devices, it has become possible to make high-quality acoustic cough recordings from patients over 24-hour periods to quantify coughing. Cough is under considerable conscious control. Therefore, monitoring cough in an unobtrusive manner, while patients go about their usual activities, is far more likely to give an accurate measure of the symptom, than making assessments in laboratory conditions over shorter periods of time, where placebo

Health-related quality of life

Health-related quality of life refers to an individual's physical, emotional, and social well-being, and their ability to perform day-to-day tasks. The recent development of cough-specific quality-of-life tools now allows quantification of the disruption caused by coughing, and it generally is accepted that the burden of cough can be considered to fall into physical, psychological, and social domains.

Three cough quality-of-life tools are in current use, the Cough Quality of Life Questionnaire

Selecting patient groups for testing cough therapies

When deciding the type of patients in whom an antitussive drug might be tested, there are several important considerations. Obviously, the mechanism of action of the drug, if specific to a particular condition, may dictate the population recruited; however, if a drug is expected to suppress cough generally, then some patient groups may have advantages over others. There is always a concern that cough should not be suppressed in subjects with a productive cough because of the theoretical risk of

Clinical trial design

As with any clinical trial, double-blind randomized controlled trials are required to assess the effects of a novel antitussive over placebo responses. Crossover designs have the advantage of requiring smaller numbers of patients than a parallel design but may not be truly blind if the drug in question has significant adverse effects that patients may be able to detect. One solution to unblinding of treatments by adverse effects is to include an additional study arm/treatment period with a

Summary

In conclusion, the development of objective cough monitoring systems and cough-specific quality-of-life measures will revolutionize the testing of novel antitussive agents. A combination of both objective and subjective measures is required to fully assess responses to therapy, and hopefully these will facilitate the development of efficacious treatments.