Effect of omalizumab on adenosine 5′-monophosphate responsiveness in subjects with allergic asthma

Background: The objective of this study was to evaluate the effects of omalizumab on bronchoconstriction induced by methacholine and adenosine 5'-monophosphate (AMP). Methods: Thirty-four subjects with mild to moderate allergic asthma were randomized to receive placebo (n = 16) or omalizumab ( n = 18) subcutaneously during 12 weeks. Airway responsiveness to AMP was measured at baseline and after 4 and 12 weeks of treatment, whereas the response to methacholine was measured at baseline and after 12 weeks of treatment. Results: After 4 weeks of treatment, the increase in AMP PC20 ( provocative concentration required to produce a 20% fall in FEV1) was significantly greater in the omalizumab group than in the placebo group, the mean difference in the change between the groups being 1.52 doubling concentrations (95% CI, 0.25 - 2.79, p = 0.02). Compared with baseline, the mean AMP PC 20 values at 12 weeks were increased by 1.91 doubling concentrations with omalizumab ( p < 0.001) and 1.01 doubling concentrations with placebo ( p = 0.16), but changes were not significantly different between the treatment groups. Changes in methacholine PC20 values were not significantly different between the omalizumab and placebo groups. Conclusions: In subjects with allergic asthma, omalizumab reduces the response to AMP without decreasing the response to methacholine. These findings are consistent with the conclusion that the contribution of IgE to the development of AMP bronchoconstriction is more important than their role in the induction of methacholine hyperresponsiveness. Copyright (C) 2006 S. Karger AG, Basel.