Influence of lung function on course of disease and response to antibiotic therapy in adult primary care patients with acute cough: a post hoc analysis of patients enrolled in a prospective multicentre study

BACKGROUND: In acute cough patients, impaired lung function as present in chronic lung conditions like asthma and chronic obstructive pulmonary disease (COPD) are often thought to negatively influence course of disease, but clear evidence is lacking. AIMS: To investigate the influence of lung function abnormalities on course of disease and response to antibiotic therapy in primary care patients with acute cough. METHODS: A total of 3,104 patients with acute cough (⩽28 days) were included in a prospective observational study with a within-nested trial, of which 2,427 underwent spirometry 28–35 days after inclusion. Influence of the lung function abnormalities fixed obstruction (forced expiratory volume in 1 s (FEV(1))/forced vital capacity (FVC) ratio <0.7) and bronchodilator responsiveness (FEV(1) increase of ⩾12% or 200 ml after 400 μg salbutamol) on symptom severity, duration and worsening were evaluated using uni- and multivariable regression models. Antibiotic use was defined as the reported use of antibiotics ⩾5 days in the first week. Interaction terms were calculated to investigate modifying effects of lung function on antibiotic effect. RESULTS: The only significant association was the effect of severe airway obstruction on symptom severity on days 2–4 (difference=0.31, 95% confidence interval (CI)=0.03–0.60, P=0.03). No evidence of a differential effect of lung function on the effect of antibiotics was found. Prior use of inhaled steroids was associated with a 30% slower resolution of symptoms rated ‘moderately bad’ or worse (hazard ratio=0.75, 95% CI=0.63–0.90, P=0.00). CONCLUSIONS: In adult patients with acute cough, lung function abnormalities were neither significantly associated with course of disease nor did they modify the effect of antibiotics.