Percutaneous absorption: a personal view

New formulation of chemical peeling agent: 30% salicylic acid in polyethylene glycol. Absorption and distribution of 14C-salicylic acid in polyethylene glycol applied topically to skin of hairless mice

Salicylic acid is used in chemical peeling procedures. However, they have caused many side effects, even salicylism. To achieve a salicylic acid peeling that would be safer for topical use, we recently developed a new formulation consisting of 30% salicylic acid in polyethylene glycol (PEG) vehicle. In an extension of our previous research, we studied the absorption of 30% salicylic acid labeled with 14C in PEG vehicle applied topically to the intact and damaged skin of male hairless mice. An ointment containing 3 mg salicylic acid in 10 mg vehicle was applied to both groups. In animals with intact skin, 1 h after application the plasma concentration of radioactivity was 1665.1 ng eq/ml, significantly lower than the 21437.6 ng eq/ml observed in mice with damaged skin. Microautoradiograms of intact skin showed that the level of radioactivity in the cornified cell layer was similar at 6 h after application. However, in damaged skin, the overall level of radioactivity showed a decrease by 3 h after application. In the carcasses remaining after the treated intact and damaged skin had been removed, 0.09 and 11.38% of the applied radioactivity remained, respectively. These findings confirm that 30% salicylic acid in PEG vehicle is little absorbed through the intact skin of hairless mice, and suggest that salicylism related to absorption through the skin of quantities of topically applied salicylic acid is not likely to occur in humans with intact skin during chemical peeling with this preparation. This new preparation of 30% salicylic acid in PEG vehicle is believed to be safe for application as a chemical peeling agent.

Effect of parenterally administered atropine on the percutaneous absorption of phencyclidine and methadone

The effect of parenterally administered atropine on the previously demonstrated percutaneous absorption of phencyclidine and methadone was investigated in vivo using the hairless (SKH, hr-1/hr-1) mouse as an experimental model. At both three hours and four hours following topical application of aqueous phencyclidine hydrochloride, the mean drug concentration in liver was significantly lower in mice that had received atropine sulfate by intraperitoneal injection than in mice that had received only water by this route (3 hrs: p less than 0.01; 4 hrs: p less than 0.02). Prior to three hours no statistically significant difference was noted. In contrast, parenteral administration of atropine produced no significant effect upon the percutaneous absorption of aqueous methadone hydrochloride over a four-hour period. Atropine inhibition of absorption is likely due to cutaneous dehydration, and it may be drug-specific and/or dose-related. These findings are correlated with the previously reported ethanol inhibition of percutaneous absorption. The therapeutic implications of these observations are discussed.

Ethanol inhibition of phencyclidine percutaneous absorption

The effect of parenterally administered ethanol on the percutaneous absorption of phencyclidine hydrochloride was investigated using the intact hairless (SKH, hr-1/hr-1) mouse as a model. Four hours after topical application of phencyclidine hydrochloride, the mean phencyclidine concentration (129.2 ng/g) in excised liver was significantly lower in mice that had received ethanol by intraperitoneal injection than in mice injected intraperitoneally with water (1730.1 ng/g) (p less than 0.01). When phencyclidine hydrochloride was administered by intraperitoneal injection there was no statistically significant difference between the mean concentration in liver (3442.5 ng/g) for ethanol-treated mice and that (3030.3 ng/g) for the control mice (p greater than 0.10), indicating that the observed difference was not due to enhancement of phencyclidine metabolism by ethanol. These findings suggest that ethanol inhibits the percutaneous absorption of phencyclidine hydrochloride.

Percutaneous penetration of dipyrithione in man: effect of skin color (race)

A single chemical dose of dipyrithione (2,2'-dithiobispyridine-1,1'-dioxide), 4 or 12 micrograms/cm(2) (containing 1 micro Ci of 2-6-14C material), was applied to the ventral forearm (intact skin, methyl alcohol vehicle [MeOH]), forehead (intact and stripped skin; cosmetic cream and MeOH vehicle), and scalp (intact and stripped skin; shampoo and MeOH vehicle) of human (white and black) volunteers. The urinary excretion of 14C was measured over the 7-day study period. Percutaneous penetration data were corrected for incomplete urinary recovery using data from intravenous studies (Wedig et al). The results obtained in this study suggested: (1) means from the complete analysis indicated 34% less (p less than 0.02) absorbed by blacks; (2) less was absorbed by blacks than whites when seven out of seven means were compared within groups (p less than 0.02); (3) a difference (p less than 0.03) in penetration, blacks 47% lower than whites, between a cosmetic cream vehicle vs MeOH on the forehead; (4) on the scalp (MeOH vs shampoo vehicle) more was absorbed using MeOH (p less than 0.02); (5) no evidence of a significant difference in penetration was noted when (a) the various anatomic sites were compared or (b) intact skin was compared with stripped skin.

Percutaneous absorption in experimental epidermal disease

Little is known about the absorption of topical drugs in epidermal disease associated with epidermal proliferation and altered keratinization. An abnormal hairless mouse epidermis was produced by three different methods: ultraviolet light irradiation, topical vitamin A acid and topical acetic acid. An increased epidermal thickness resulted and the in vitro percutaneous absorption of 0.1% (4-14C) hydrocortisone was found to be increased when compared with normal hairless mouse epidermis. This is evidence for defective skin barrier function in experimental epidermal disease.

Essential fatty acid deficient hairless mouse: a model of chronic epidermal hyperproliferation

Epidermal DNA synthesis has been shown to be increased approximately three-fold in hairless mice that were fed a diet deficient in essential fatty acids (EFA deficient) for 65 days, compared with animals fed a standard diet. Autoradiographic labelling indices showed a 330% increase in the EFA deficient mice over controls. The animals developed evidence of a diffuse thickening, scalping and loss of elasticity of the skin after 40 days on the EFA deficient diet. Histologically, the epiderma of the EFA deficient animals showed acanthosis, hypergranulosis, hyperkeratosis and increased intracellular epidermal spaces. Increased mitotic indices were found with Feulgen staining. This is further evidence that deficiencies of essential fatty acids are associated with disturbance of normal epidermal cell proliferation and control of keratinization. A single application of topical 0.1% betamethasone valerate to EFA deficient mice reduced the epidermal DNA synthesis to that of normal diet mice. Ten percent linoleic acid topically over 2 weeks also returned epidermal DNA synthesis to normal levels.

An animal model for screening drugs for antipsoriatic properties using hydroxyapatite to isolate DNA rapidly from the epidermis

A new, rapid, simple and accurate procedure for extracting DNA from the epidermis is described involving hydroxyapatite. This compound has an unique property of high affinity for double stranded native DNA, but none for RNA and protein. The technique has been applied to a hairless mouse model for screening systemic and topical agents for cell inhibitory properties in proliferating epidermis for potential use in the therapy of psoriasis. Mitotic counts, autoradiography and a standard chloroform procedure for isolating DNA have confirmed the results obtained using hydroxyapatite column chromatography. In addition, compounds which are known to be effective in psoriasis, have been found to be effective in the system suggesting that it should be a good predictive screen for new therapies. Of several compounds screened for topical activity, cycloheximide has been found to be very effective in the system and preliminary clinical studies confirm its efficacy in psoriasis.

An animal model for screening topical and systemic drugs for potential use in the treatment of psoriasis

A new hairless mouse model using ultraviolet light to stimulate increased epidermal cell turnover and hyperplasia and thus simulate psoriasis has been designed so that drugs may be tested both topically and systemically for possible therapeutic value in this disease. Two methods of determining drug antimitotic activity have been used, the mitotic index and the extraction of epidermal DNA and the determination of the radioactivity of the sample. Results show that 2% 5-fluorouracil in propylene glycol and 2% nitrogen mustard in water topically and cyclophosphamide systemically, which are drugs known to be effective in psoriasis, significantly reduce the mitotic index. DNA synthesis is similarly decreased by the latter two drugs. The effect of the topical agents is shown to be local and not systemic. Cyclophosphamide, which is ineffective topically in psoriasis, is ineffective in the model.