A BIOASSAY FOR TOPICAL AND SYSTEMIC EFFECT OF 3 INHALED CORTICOSTEROIDS

Background: Comparisons of relative potency for the three inhaled corticosteroids in the United States are limited to assessment of skin blanching. Objective: Development of a method for comparing relative potencies of inhaled corticosteroids for topical effect on human airway and systemic effect. Methods: With use of partial suppression of immediate response to inhaled allergen and 24-hour urinary free cortisol output, three-point dose-response curves were constructed for beclomethasone dipropionate (50 mu g/puff), triamcinolone acetonide (100 mu g/puff), and flunisolide (250 mu g/puff). A randomized, parallel, single-blind study design was used, Dosing began with one puff four times a day for flunisolide and two puffs four times a day for the others. Doses were doubled after 1 week and again after a second week. Results: Twenty-five patients completed the study. Dose-response relationships were shown for each inhaled corticosteroid for both topical and systemic effect. Dose-response curves for the three preparations were similar when response was plotted against delivered dose in micrograms. Conclusion: Within the limits of the assays, relative potencies of the three preparations appeared to be approximately equivalent for both topical and systemic effect when dose was expressed in micrograms. Relative potency per puff is therefore approximately proportional to the dose delivered. This method has potential for evaluation of relative potency of newer inhaled corticosteroids and the relative advantage of alternative delivery systems.