ABSTRACT

INTRODUCTION Dosing strategies for topical and regional products applied to the skin are poorly defined and developed. For example, dose is usually expressed as the percentage concentration of the drug in a topical formulation. In fact, clearly, the dose applied is a multiple of the concentration of drug in the formulation, times the amount of formulation applied per area of skin. Also topical bioavailability, the ratio of dose absorbed to dose applied, is most usually in the range of 0.01 of 0.02 (1-2%), exceptionally up to 0.10 (10%), and, not infrequently, as little as 0.001 (0.1%). Thus, percentage dose absorbed is low, “99% is wasted” (1), and dose absorbed is poorly correlated to dose applied. Finally, dose intervals are based on consumer habits, which are derived from oral drug usage, and in general have little basis in science.