Eighteen randomised controlled trials (RCTs) were included in the review (n=1,161 participants). Sample sizes ranged from 10 to 854.
Theophylline demonstrated a significant improvement over placebo for trough forced expiratory volume in one second (weighted mean difference 0.108 L, 95% confidence interval (CI): 0.05 to 0.16; 10 RCTs, n=704 patients), trough forced vital capacity (weighted mean difference 0.186 L, 95% CI: 0.04 to 0.34; six RCTs, n=166 patients), peak forced expiratory volume in one second (weighted mean difference 0.096 L, 95% CI: 0.04 to 0.15; 12 RCTs, n=800 patients), and peak forced vital capacity (weighted mean difference 0.242 L, 95% CI: 0.11 to 0.37;10 RCTs, n=358 patients).