Factors Determining the Skin-Drug-Vehicle Relationship

The Importance of Scale Removing Procedures in the Treatment of Psoriasis with Tar Baths

“…Petrolatum is one of the most occlusive vehicles, and hydration of the horny layer promotes absorption, also of substances insoluble in water [5]. The object of adding salicylic acid is to increase the m acerating effect of petrolatum upon the psoriasis scales (in a con centration of 2 %, as used in the present study, this effect m ust be considered very slight).…”

“…The explanation is probably th a t other absorption-regulating factors, such as epidermal damage [4], and the concentration of the active agents on the skin surface [5] are of greater im portance than the thickness of the stratum corneum and its water-hinding ability in the treatm ent of psoriasis.…”

Biopharmaceutics: Absorption Aspects

“…Fundamental factors involved in rate and extent of percutaneous absorption are: ( a ) type of skin and whether the skin is normal, abraded, or diseased (173); (6) site of absorption-transfollicular route, transepidermal route, or both (173,174); (c) effective thickness of the skin barrier phase (174); ( d ) area to which the drug is applied (173,174); ( e ) thermodynamic activity of water in the vehicle and in the skin barrier phase (174); (g) thermodynamic activity of the drug in the vehicle (174) Shelmire (173) pointed out that the vehicle assumes more importance when the stratum corneum is intact and that differences in drug penetration attributable to the vehicle are more pronounced. On abraded or diseased skin there may be a large increase in both rate and extent of absorption of a drug in a vehicle (173).…”

“…On abraded or diseased skin there may be a large increase in both rate and extent of absorption of a drug in a vehicle (173). The site of absorption may be important since a vehicle such as petrolatum may plug the follicles and delay penetration of the drug (173). One would expect the rate of absorption to be inversely proportional to the thickness of the skin barrier (173,174).…”

“…The site of absorption may be important since a vehicle such as petrolatum may plug the follicles and delay penetration of the drug (173). One would expect the rate of absorption to be inversely proportional to the thickness of the skin barrier (173,174). Similarly, one would expect the extent of absorption to be directly proportional to the area of skin covered by the ointment, cream, or lotion (173,174).…”