Interpretation and prediction of the kinetics of transdermal drug delivery: oestradiol, hyoscine and timolol

A kinetic model has been used to predict the plasma concentration vs time profiles for oestradiol, hyoscine and timolol following transdermal drug delivery. Rate constants describing a drug's passage across the stratum corneum and viable epidermis are calculated from simple physicochemical parameters. When used in conjunction with the in vitro release characteristics of the topical formulation (simple vehicle or sophisticated delivery system), and with knowledge of the drug's systemic clearance, the kinetic values permit simulation of the expected plasma level profile. The theoretical predictions are consistent with published human in vivo data for each of the three compounds. This kinetic approach may be useful, therefore, in the evaluation of feasible candidates for transdermal drug delivery.