ABSTRACT
In the Food and Drug Administration (FDA) criteria for evaluations of bioavail-
ability (1), it is stated that for drugs not intended to be absorbed into the
bloodstream, measurements should reflect the rate and extent to which the active
molecule “becomes available at the site of action.” The defined target tissue toward
which topical drug therapy is aimed can be the stratum corneum (SC), the deeper
epidermis or the dermis. Current FDA requirements for bioequivalence determina-
tion of topical drug products are dependent on the pharmacological class of the
dosage form. For glucocorticoid dosage forms, a blanching assay procedure using a
chromameter is recommended. For all other topical drug products, a draft guidance
describing dermatopharmacokinetic methodology was published but later with-
drawn by FDA. As a result, currently comparative clinical trials are required for
bioequivalence determination between test and reference topical drug products.
