THE MCKENZIE VASOCONSTRICTION ASSAY - RETHINKING ITS USE FOR INTRANASAL TOPICAL CORTICOSTEROIDS

Although the McKenzie vasoconstrictor assay (VCA) is commonly used to evaluate the potencies of topical corticosteroids, serious concerns re garding its reliability and validity for predicting the clinical effec tiveness of intranasal topical corticosteroids have been raised and sh ould be considered by clinicians when treating patients suffering from allergic rhinitis. First, the VCA measures a skin-blanching response and does not measure anti-inflammatory activity. Second, methodologic differences in study design of the VCA have undermined the reliability of the test, and many variables, including the vehicle, size and loca tion of test area, subject responsiveness, and observer subjectivity, have been shown to affect the test outcome. Discrepancies have arisen concerning the nonequivalence of generic and brand-name topical steroi ds on the VCA and testing of the same products at different time point s. Third, although it is assumed that VCA potency is correlated with c linical efficacy, this relationship has been documented only for a der matologic condition (psoriasis), not for a condition mediated by the n asal mucosa, such as allergic rhinitis. These problems indicate that t he VCA is a less than adequate model for predicting the clinical effec tiveness of intranasal topical corticosteroids.