PERSORPTION 119 hair follicle likewise are points of entry especially for fat soluble substances. In certain regions such as in the armpits the apocrine glands also open into the hair follicles and offer additional pathways (15). It is essential for good persorption to assure prolonged contact with the substance in an easily spread ointment base or lotion (16). Rubbing and pressure would certainly force more material into the skin openings. Washing the skin to remove sebum and other matter, including the "acid mantle" (17) that might interfere with the application, usually affords more rapid persorption. For deep fungal infection it is useful at times to remove the upper layers by abrasion (18) or with scotch tape (19) before administering the topical drug or it may be necessary to soften the keratin layer with alkaline solutions, or with organic solvents. Breaking the sulfide linkages in the keratin layer with reducing agents may also prove useful (8). Low concentration of salicylic acid softens the outer structures while higher strengths damage the tissue (20). Damaged epidermal tissue increases passage by permitting material to enter the blood and lymph vessels of the dermis directly (21). During persorption tests on intact skin, therefore, the investigator must exercise utmost care in preventing skin damage during cleaning or shaving the skin. Damage also changes the negative charge on the outside of the skin which usually repels anions. The methods of determining persorption merit consideration for by these means it is possible to compare drugs and drug vehicles, and obtain other pertinent data necessary to establish good therapeutic action. It is well to remember that experiments on laboratory animals do not always give the same results as are obtained with humans (22). Known amounts of ointments or solutions in enclosed containers or compresses (23) have been applied to the skin for various periods of time the difference between the original and final amounts represents the amount going into the skin. However, this quantity may remain in the epidermis without exhibiting persorption, or a part will go into the skin orifices with immediate persorp- tion, or produce a depot effect by liberating material gradually into the dermis. This difference may also be determined by extraction, but again this need not indicate persorption. Excretion of inuncted material or its derivatives in feces, urine, or breath or identification in tissues or organs proves persorption. The depth of percutaneous penetration has recently been investigated by means of radioactive (24) and fluorescent (25) ma- terials. By the former method autoradiograms give pictures of the tissues containing the test material at different depths, at various time intervals. Hydrocortisone appears to pass generally through the epidermis, and not preferentially through the hair follicles. However, radioactive chemicals with short wave emission may indicate a deeper penetration than actually obtained. The fluorescent method shows that oleic acid is very easily petsorbed it indicates that linoleates and oleates may be especially valu-

1:20 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS able for persorptive purposes. _rn vitro tests with isolated skin tissue may prove useful in certain instances (26). The prevention of cutaneous disturbances has also been used to estimate percutaneous penetration. Thus, histamine solutions applied to the skin either directly or by iontophoresis, produce the usual response however, antihistamine preparations when applied to the skin may interfere with or prevent this action (27). Incidentally, iontophoresis is an excellent method for enabling certain ions to pass the epidermal barrier. Usually it is more applicable with cations applied at the anode it was used over fifty years ago for introducing the iodide ion into the neck for the successful treatment of deficiency goiter. Histamine, because of its biological importance, has been widely tested for percutaneous absorption. The base will penetrate from most solutions and ointments, but it is such a potent drug that only very •small quantities are needed to elicit vascular responses. The salts of histamine are less easily petsorbed. An attempt was made to inunct "48-80" (28), a potent histamine liberator, into the skin of several species of animals. A water washable ointment containing 1 per cent of "48-80" was rubbed vigorously into the skin of the backs of a rabbit, rat, guinea pig and dog from which the hair had been removed with an electric clipper. No cutaneous effects or temperature changes were observed in any of the animals, and no drop in blood pressure was found in the dog. Later a 1 per cent aqueous solution was applied on the same regions with still no effects except for a slight blister on the dog, possibly due only to the rubbing. Administered intravenously, 25 to 50 micrograms of "48-80" will produce a 50 per cent reduction in the dog's blood pressure. Thus the above data indicate that a polymer (formaldehyde' with N-methylhomoanisylamine) of large molec- ular weight (about 471 or more), will not rapidly pass the epidermal mem- brane barrier and reach the mast cells where much of the skin histamine is located. In order to determine the persorption of chlorocyclizine hydrochloride from a water washable ointment* the amount of drug actually found in the blood was biologically measured (29). This was accomplished by taking blood samples from the inuncted dog at various time intervals and deter- mining the inhibition of histamine induced contractions of the isolated guinea pig ileum following the addition of plasma samples to the tissue bath. During this procedure it was discovered that an appreciable amount of chlorocyclizine became bound in the plasma and did not exhibit full activity in this type of assay. Control samples of standards in plasma were thus made necessary in order to evaluate the actual amount passing through the skin and found in the blood. * Supplied as "Perazil" brand Chlorcyclizine Hydrochloride Cream, Burroughs Wellcome & Co. (U.S.A.), Inc., Tuckahoe, N.Y.