We evaluated single and chronic dosing effects of modern H₁-antihistamine, levocetirizine (LEV), given at the usual clinically recommended dose, on the primary outcome of AMP bronchoprovocation.

15 atopic asthmatics were randomized in double-blind, cross-over fashion to receive for 1 week either LEV 5mg or placebo (PL). There was a 1-week washout period prior to each randomized treatment. AMP PC₂₀ was measured after each washout at baseline and at 4–6 hours following first and last doses of each randomized treatment.

Baseline mean (SEM) values after washout prior to each randomized treatment comparing LEV vs. PL were not significantly different for pre-challenge FEV₁ (% predicted): 83 (4) vs. 82 (4), or AMP PC₂₀ (mg/ml): 45 (24) vs. 45 (22). Pre-challenge FEV₁ for LEV vs. PL was not significantly different following first dose: 86 (4) vs. 82 (4), or last dose: 85 (4) vs. 83 (4). There were significant improvements (p<0.05) in AMP PC₂₀ comparing LEV vs. PL following first dose: 123 (73) vs. 48 (24); a 1.4 doubling dilution difference (95%CI: 0.8–1.9), and last dose: 53 (29) vs. 127 (74); a 1.2 doubling dilution difference (95%CI: 0.5–2.0). AMP PC₂₀ also improved (p<0.05) following first and last doses of LEV but not PL, compared to respective baseline values, with no difference in bronchoprotection between first and last doses.

Single and chronic dosing with LEV conferred similar improvements in AMP bronchial hyperresponsiveness, which was unrelated to pre-challenge airway caliber. Further studies are indicated to evaluate longer-term effects of LEV on asthma exacerbations.