Nineteen randomised, placebo-controlled trials, with a total of 1,680 patients, were included.
The quality assessment delivered a total score ranging from 42 to 76%, with a mean score of 59%. Significant flaws were detected in all sections of the quality scoring.
The mean effect sizes for antihistamines versus placebos were.
for morning PEFR (15 studies), 0.13 (95% CI: 0.08, 0.18);
for evening PEFR (14 studies), 0.12 (95% CI: 0.08, 0.16);
for FEV1 (10 studies), 0.03 (95% CI: 0.01, 0.25); and
for inhaled beta-agonists (12 studies), 0.13 (95% CI: 0.01, 0.25), which corresponded to a reduction in daily use of 0.4 doses (95% CI: 0, 0.8).
The studies were homogeneous for the measurement of morning PEFR (Q=9.82, p=0.78) and for daily use of inhaled bronchodilators (Q=5.49, p=0.91). The incidence of sedation was significantly higher in antihistamine studies compared with placebo, although the studies were found to be heterogeneous for this variable (p<0.001). None of the sensitivity analyses had a significant impact on the overall result in terms of morning PEFR.