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.

Group 1 will begin with active Levocetirizine(LCT) 0.5 mg/ml oral solution for 5-8 days. This arm will then undergo a 3-7 day washout period at which point crossover will occur and placebo will be provided for 5-8 days.

Group 2 will begin with placebo oral solution for 5-8 days. This arm will then undergo a 3-7 day washout period at which point crossover will occur and active Levocetirizine(LCT) 0.5 mg/ml will be provided for 5-8 days.

Subjects in two arms, will be enrolled in a classical, randomized, double blind, crossover, placebo controlled trial of Levocetirizine(LCT) with determination of the PD response to LCT as determined by suppression of histamine microvasculature response via HILD.

The investigators will compare the response to histamine via histamine iontophoresis with laser doppler monitoring (measured in flux units on a continuous scale)between subjects with allergic asthma compared to subjects with non-allergic asthma.

Inclusion Criteria: children age 7-17 years old with the diagnosis of allergic asthma or non-allergic asthma (n=102 Exclusion Criteria: history of immunodeficiency, mastocytosis chronic abnormal conditions of the skin, liver or kidney neoplastic disease movement or neurologic disorders active eczema on the forearms at the time of study history of a previous anaphylactic episode evidence of pregnancy (by urinary hCG) or lactation at the time of the study