Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
COPD exacerbations (frequency and duration)
[53] RCT	110 people	Frequency of acute COPD exacerbations (per year) 12 months 0.79 with theophylline (100 mg twice daily) 1.70 with placebo	P = 0.047	Effect size not calculated	theophylline
[53] RCT	110 people	Duration of acute COPD exacerbations (per year) 12 months 4.58 days with theophylline (100 mg twice daily) 12.47 days with placebo	P = 0.045	Effect size not calculated	theophylline