Characterization of the Role of Histamine in Children With Asthma

Asthma, a chronic disease which produces significant morbidity and mortality in children, is a significant health problem to a large segment of society. Despite considerable advances in the diagnosis and treatment of asthma over the past several years, a sizeable portion of patients do not respond to the "core" treatments. The investigators are now learning that the underlying pathophysiology of disease is different among patients with asthma therefore; treatments which are beneficial in some patient groups may be not achieve affect in other groups.

Antihistamines have been studied in the past for the treatment of asthma. These studies have shown that there may be a beneficial effect of antihistamines in patients with allergic asthma where histamine likely plays a large role in disease and treatment response. However, there is not enough evidence to include these drugs in the standard treatment of asthma.

The investigators hypothesize that histamine plays a definable, significant role in disease pathogenesis and treatment response in children with allergic asthma. The investigators plan to test this overall hypothesis through two specific aims. The first aim will characterize the relative contribution of histamine in allergic vs. non-allergic asthma. This aim will be accomplished by comparison of the microvasculature response to histamine in children with allergic asthma and children with non-allergic asthma, measured by histamine iontophoresis with laser Doppler (HILD) monitoring, to determine potential phenotype-associated differences in the pharmacodynamic response to histamine. The investigators will also investigate the role of genetic variation in the observed differences in HILD between the two groups. The second aim will characterize the pharmacodynamic response to antihistamines via HILD in children with an exaggerated histamine response compared to children with a low histamine response. This aim will be accomplished through conduct of a randomized, double-blind, placebo-controlled cross-over trial of levocetirizine (LCT) in the two groups (high histamine and low histamine) and observing the difference in antihistamine pharmacodynamics in the two groups. The investigators will also investigate the effect of pharmacokinetic variation and genetic variation in the histamine pathway on the observed pharmacodynamic drug response.