Introduction Acute cough is a common illness with more than 12 million episodes each year in the UK. More than £100 million is spent on over-the-counter cough medicines annually, despite limited evidence to support their efficacy. The optimal cough assessment outcome parameter for clinical evaluation of anti-tussive drugs is not known. We investigated the natural course of acute cough with objective and subjective cough assessment tools.
Methods 32 healthy subjects with acute cough due to upper respiratory tract infection (median (IQR) age 30 (32–35) years, 63% female, mean (SEM) duration of cough 4.2 (0.4) days) were recruited for evaluation. Subjects taking anti-tussives were excluded. Assessments of cough severity included objective 24-h ambulatory cough frequency monitoring with the Leicester Cough Monitor, health related quality of life (HRQOL) with the Leicester Cough Questionnaire-Acute (LCQ) and cough severity visual analogue scale (VAS). Assessments were performed at baseline (day 1) and then 4 and 8 days later. Global rating of change questionnaires were completed by patients at each follow-up to assess change in cough severity and determine minimal important difference.
Results At baseline, the median (IQR) LCQ score was 14.7 (10.9–18.3) and mean (SEM) cough VAS was 48 (4) mm, consistent with a severe cough associated with significant impairment in HRQOL. Geometric mean (logSD) 24-h cough frequency (CF24) at baseline was 15.0 (0.4) coughs/hr, and at days 5 and 9 were 8.7 (0.5) and 3.4 (0.7) coughs/hr respectively. At day 5, 3 subjects reported no change, 9 mild, 14 moderate and 6 large change in their cough severity. At day 9, 6 subjects reported mild, 5 moderate and 20 large change in cough severity. The minimal important difference on day 5 for the LCQ was 2.0, VAS 17 mm and CF24 54% change from baseline.
Conclusions Acute cough is associated with a significant cough frequency and impairment in HRQOL. We suggest clinical trials of anti-tussive drugs should incorporate objective and subjective cough assessment outcome measures. Anti-tussive drugs need to demonstrate a considerable reduction in cough frequency (>54% over a 4-day interval) to establish clinically important efficacy.