PERCUTANEOUS ABSORPTION

THE application of preparations to the skin for cosmetic and medical purposes is as old as the history of medicine itself and references to the use of ointments, salves and pomades may be found in the early records of Babylonian and Egyptian medicine. In Roman times, drugs were sold by the “ungentarii“ who were the compounders of ointments. Galen’s formula for cold cream has persisted through the ages and, with some modification, it is still in use to-day. Although the use of ointments goes back to antiquity, their use has, until recently, been largely empirical. It is only with the advances in dermatology that there has been an appreciation of the requirements of different ointment bases for different skin conditions. Before 1948, with the exception of hydrous ointment, official ointments were made with fatty materials such as soft paraffin, anhydrous wool fat, or beeswax or combinations of these substances. It was hardly appreciated that the therapeutic usefulness of an ointment depends as much on the kind of base used as on the active medicament. To-day, there are available many different synthetic substances allowing the formulation of a wide variety of preparations for application to the skin. The clinician has, therefore, a considerable choice of bases in the prescribing of dermatological preparations and the pharmacist needs to have an expert knowledge of the properties of the different preparations. Both should understand the main principles concerned in percutaneous absorption. The percutaneous route has been used as a method of drug administration and, although of strictly limited value, may be useful in particular circumstances. With the introduction of toxic synthetic chemicals such as plasticisers in industry, and the use of highly potent insecticides in agriculture, hazards from the toxic effects after percutaneous absorption have become very real ones. The study of percutaneous absorption is of importance also in the elucidation of the normal functioning of the skin. This review describes the main factors affecting percutaneous absorption, their assessment and application in preparations used in dermatology and drug administration.