Effects of antihistamines in adult asthma: a meta-analysis of clinical trials.

A meta-analysis of clinical trials of antihistamines was performed to assess the risk-benefit ratio of this therapeutic class in asthma. Double-blind randomized placebo-controlled trials assessing lung function changes under repeated use of antihistamine in adult asthma were selected, and the quality of studies was scored. Morning peak expiratory flow rate (PEFR) was the primary outcome: an effect size was computed for each study, with a 95% confidence interval (95% CI), and a mean effect size was computed, combining all studies. Effect sizes were also determined for secondary outcomes: evening PEFR, forced expiratory volume in one second (FEV1) and daily use of inhaled beta-agonists. Nineteen studies were included in the meta-analysis. Mean quality score of studies was 59.4%; asthma was generally uncontrolled at study inclusion. Altogether, 582 antihistamine-treated and 557 placebo-treated asthma patients were evaluable. Antihistamines had little effect on airway calibre (mean increase in morning PEFR: 13 L x min(-1); 95 CI: 8-18 L x min(-1)) and on use of inhaled beta-agonists (mean reduction in daily use: 0.4 doses; 95% CI: 0-0.8 doses). Sedation occurred more often with antihistamines than with placebo (p<0.001); additional side-effects were mentioned, including weight gain, altered taste, headache and dry mouth. Respiratory and systemic effects observed after repeated use of antihistamines do not support the use of these medications in the treatment of asthma; better designed studies could affect this appraisal.