Modulation of the immediate allergic wheal reaction in the skin by drugs inhibiting the effects of leukotriene C4 and prostaglandin D2

Mechanisms of action that contribute to efficacy of omalizumab in chronic spontaneous urticaria

The monoclonal anti-immunoglobulin E (IgE) antibody, omalizumab, was the first drug approved for use in patients with chronic idiopathic/spontaneous urticaria (CIU/CSU) who remain symptomatic despite H₁ -antihistamine treatment. Omalizumab binds to free IgE, which lowers free IgE levels and causes FcεRI receptors on basophils and mast cells to be downregulated. It has been shown to improve symptoms of CIU/CSU, but its mechanism of action is not currently understood. Potential mechanisms in CIU/CSU include reducing mast cell releasability, reversing basopenia and improving basophil IgE receptor function, reducing activity of IgG autoantibodies against FcεRI and IgE, reducing activity of IgE autoantibodies against an antigen or autoantigen that has yet to be definitively identified, reducing the activity of intrinsically 'abnormal' IgE, and decreasing in vitro coagulation abnormalities associated with disease activity. However, none of these theories alone or in combination fully account for the pattern of symptom improvement seen with omalizumab therapy, and therefore, no one mechanism is likely to be the definitive mechanism of action. Additional research is needed to further clarify the involvement of omalizumab in relieving symptoms associated with the complex, multifactorial pathogenesis of CIU/CSU.

Itraconazole and rifampin alter significantly the disposition and antihistamine effect of ebastine and its metabolites in healthy participants

The present study was performed to elucidate the effects of itraconazole and rifampin on the pharmacokinetics and pharmacodynamics of ebastine, a nonsedative H1 receptor antagonist. In a 3-way crossover sequential design with 2-week washouts, 10 healthy participants were pretreated with itraconazole for 6 days, rifampin for 10 days, or neither. After oral administration of 20 mg ebastine, blood and urine samples were collected for 72 and 24 hours, respectively, and histamine-induced wheal and flare reactions were measured to assess the antihistamine response for 12 hours. Itraconazole pretreatment decreased the oral clearance of ebastine to 10% (P < .001) and increased the AUC(infinity) of the active metabolite, carebastine, by 3-fold (P < .001). On the other hand, rifampin pretreatment decreased the AUC(infinity) of carebastine to 15% (P < .001), with an enormous reduction in the oral bioavailability of ebastine and significantly reduced histamine-induced skin reactions. From these results, the disposition of ebastine and carebastine seems to be significantly altered by coadministration of itraconazole or rifampin. The antihistamine response after ebastine dosing would be decreased following rifampin pretreatments.

The effects of montelukast on intradermal wheal and flare

OBJECTIVE

We sought to determine the effect of montelukast, a leukotriene receptor antagonist, on intradermal skin testing. Study design and setting We conducted a prospective, randomized, double-blind, placebo-controlled study in a university setting.

METHODS

After a 1-week washout of allergy pharmacotherapy, intradermal skin testing was performed on 23 atopic subjects. Whealing size was measured 20 minutes after injection. Subjects then began a 1-week regimen of daily loratadine, montelukast, or placebo. At 1 week, subjects again underwent intradermal skin testing. The change in wheal size was then calculated from baseline.

RESULTS

A significant difference (P < 0.05) between the montelukast and loratadine groups in suppression of intradermal whealing at 1 week was observed. No significant difference was noted between the montelukast and placebo subjects.

CONCLUSIONS

Montelukast demonstrated no significant suppression of skin whealing after antigen challenge over placebo.

SIGNIFICANCE

Montelukast does not need to be discontinued before intradermal allergy testing.