a Reproduced from R. Scheuplein, J. Invest. Dermatol., 67, 672 (1976).

the drugs in Table 9.9 decrease as the number of hydroxyl groups increases, but a simple lipid/water partition coefficient is not an ideal guide, as the stratum corneum is a complex system as described above. If a substance is more soluble in the stratum corneum than in the vehicle in which it is presented, however, the concentration in the first layer of the skin may be higher than that in the vehicle. If depletion of the contact layers of the vehicle occurs, then the nature of the formulation will dictate how readily these are replenished by diffusion and, therefore, will dictate the rate of absorption.

The penetration rates of four steroids through intact abdominal autopsy skin were, in the order of their physiological activity, betamethasone 17-valerate (I) > desonide > triamcinolone acetonide (II) > hydrocortisone (III). Triamcinolone itself is five times more active systemically than hydrocortisone, but has only one-tenth of its topical activity. The acetonide of triamcinolone has a topical activity 1000 times that of the parent steroid

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