Abstract
INTRODUCTION: Asthma exacerbations spike in the spring and autumn months, yet the seasonal variation of asthma symptoms and lung function is poorly studied. METHODS: Seasonal variation of lung function, rescue medication use and patient-reported symptoms was evaluated by post hoc analyses of the Phase III lebrikizumab (anti-IL-13) LAVOLTA I and II studies in 2148 subjects with uncontrolled asthma. Lung function measurements (prebronchodilator FEV(1), forced vital capacity (FVC) and peak expiratory flow (PEF)), rescue medication use and Standardised Asthma Quality of Life Questionnaire (AQLQ(S)) were measured every 4 weeks over 52 weeks. By-month estimates normalised by hemispheric season were based on mixed-effect models with repeated measures (MMRM), adjusted by study stratification factors as covariates when appropriate. The dependency of clinical outcomes with seasonal variability was assessed by employing linear contrasts comparing hemisphere normalised December versus July group means from an MMRM regression and presented as the difference in means (adjusted 95% CI). RESULTS: FEV(1), FVC and PEF, rescue medication use and AQLQ(S) progressively worsened towards winter, unlike spring and autumn surges in asthma exacerbations. The December versus July mean differences were: (1) PEF=-6.5 (-8.7 to -4.2) L/min, 2) prebronchodilator FEV(1)=-42 (-57 to -27) mL, (3) FVC=-41 (-59 to -23) mL and (4) AQLQ(S)=-0.15 (-0.19 to -0.1) units. Among AQLQ questions, discomfort or distress related to cough was most variable with respect to season (-0.33 (-0.42 to -0.24) units). DISCUSSION: Interpretation of interventional studies biased by seasonal exposures may be confounded by seasonal variability. TRIALS REGISTRATION NUMBERS: NCT01867125 and NCT01868061.