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Biomedical subjects

H Schaefer

Publications and source records attributed to H Schaefer.

At least 73 records · Page 4Linked to original sources
PubMed1978

8-Methoxypsoralen (8-MOP) in human skin: penetration kinetics.

Penetration kinetics of 8-methoxypsoralen (8-MOP) into human skin have been investigated under in vitro conditions. The dependence of the resulting tissue concentration on time of penetration, drug concentration in the applied preparation and vehicle composition has been studied. Tissue concentration of the drug was found to increase with time of penetration; however, in both horny layer and epidermis, this increase was followed by a significant decrease in concentration, (after 100 to 300 min), although a large amount of unpenetrated drug was present on the horny layer surface at all times. In contrast to this, 8-MOP accumulated in the lower corium and subcutis and reached concentrations higher then those found in the upper corium and epidermis. This accumulation of the drug is a consequence of the in vitro conditions and its amount is proportional to that amount that under in vivo conditions would have been taken up by the capillary system. Penetration was dependent on vehicle characteristics and was found to increase with increasing polarity of the vehicle. The penetration was found to be directly proportional to the applied concentration; however, the percentage of the drug that actually penetrated was inversely proportional to the applied concentration.

Dose-Response Relationship, Drug↗
PubMed1978

PUVA appraisal.

Explore the source record for details and available documents.

Animals↗
PubMed1978

Quantitative determination of percutaneous absorption of radiolabeled drugs in vitro and in vivo by human skin.

We have measured concentrations of about 30 drugs in the living layers of the skin under conditions which provide data which are applicable in therapeutic treatment. Since the skin is a thin organ and small amounts of drug represent high target concentrations, it is necessary to select a sensitive quantitative method; observation of the kinetics of absorption using radiolabeled drugs is the method of choice. Because of possible hazards--and legal and ethical problems--absorption studies in human skin are commonly performed in vitro. Related in vivo investigations demonstrate the relevance and the limitations of the in vitro experiments. The main hindrance against penetration of drugs is by the horny layer. The barrier-function of this layer--if it is undisturbed--may be described by a multilayer model. The reciprocal function, the reservoir function, is important for the efficiency of topical treatment; it also plays a role in determining the unique pharmacokinetics of drug absorption in the skin and percutaneous resorption. If the horny layer is injured, i.e. in diseased skin, both the barrier and the reservoir functions are disturbed. In consequence, drug concentrations in the skin--and percutaneous resorption--may be greatly enhanced, and topically applied drugs may enter preferentially into diseased areas. The form of application, such as ointment, solution, etc. influences the penetration kinetics in such a specific manner that a specific vehicle for a specific drug should always be postulated. The frequently discussed hazards of side effects due to percutaneous resorption of drugs like corticosteroids are a function of the treated area rather than of its penetration capacity. Thus the indication for local or oral treatment of severe dermatoses should be considered in terms of the affected area. The relatively frequent side effects in the skin itself which originate from unnecessarily high drug concentrations and long term treatment must also be taken into account.

Administration, Topical↗
PubMed1978

[Penetration of a non-steroidal anti-inflammatory drug into human skin in vitro and in vivo. Tissue concentrations and flow rates of p-butoxyphenylacetohydroxamic acid (author's transl)].

The penetration of p-butoxyphenylacetohydroxamic acid (BPHS; Parfenac) from a crean and an ointment into human skin in vivo and in vitro was investigated. From both preparation forms high tissue concentrations were achieved. Flow rates through the horny layer could be calculated, that from the ointment being considerably higher (3.8 . 10(-8) mol/cm2 . h) than that from the cream (7 . 10(-9) mol/cm2 . h). A control experiment in vivo proved that the in vitro data are relevant. The difference between dermal concentrations in vitro (with abolished capillary function) and that in vitro (with capillary system functioning) reflected the fast absorption of the drug by the vessels.

Administration, Topical↗
PubMed1977

Penetration, permeation, and absorption of triamcinolone acetonide in normal and psoriatic skin.

Penetration studies of radiolabelled Triamcinolone acetonide from ointment or cream preparations revealed that in cases of normal as well as psoriatic skin 70-90% of the applied substance remains on the surface. Normal horny layer stores up to 30% of the steroid. Nevertheless, a rapid penetration into the living layers of the skin is observed, whereby the epidermal concentrations reach levels between 5-10(-6) and 3-10(-5) M (mol per liter of tissue). The excretion in the urine took more than 72 h after removal of the excess of substance from the skin. In psoriatic skin, the epidermal and dermal concentrations were 3-10 times higher than in normal skin. This increase lies in the same range as the one resulting from removal of the horny layer by stripping prior to the application, as reported earlier.

Absorption↗
PubMed1977

Hydrocortisone (cortisol) concentration and penetration gradient.

Hydrocortisone (Cortisol) was incorporated into four different ointments at four concentrations (0.1% 0.3%, 1%, and 3%) and the amounts of the drug penetrating from these preparations into the different layers of excised skin were investigated. The effect of removing the horny layer on the penetration was also determined. Below a level of 1% ointments with intact horny layer and 0.3% with removed layer, a change in the ointment concentration alters the tissue concentration in the ratio 1:1. Above this level doubling of the concentration in the ointments causes an increase of tissue concentrations of only 20-50%. The removal of the horny layer increases the dermal concentrations 100 fold at each ointment concentration. Furthermore, a vasoconstriction test was performed with the different ointments. An increase in the concentrations above the 1% level failed to increase the effect on the vascular system of the skin. The in vitro and in vivo results are discussed with respect to the consequences on affected skin and the therapeutic efficacy of steroid preparations of different concentrations.

Administration, Topical↗
PubMed1976

[Penetrations kinetics and distribution of topically applied estrogens (author's transl)].

The penetration into the single layers of human skin in vitro of 17 alpha-estradiol, 17 beta-estradiol and estriol was investigated. The radiolabeled substances were incorporated into 4 standard ointments and into an alcoholic solution mixture. After application to the skin and after different penetration periods, the horny layer was taken off by adhesive tape stripping. The epidermis and the dermis were separated by slicing them down parallel to the skin surface in a freeze microtome. In each single layer, the amount of substance was determined and calculated relative to the applied quantity and in absolute concentrations (mug per tissue weight and molarity). Besides the expected dependence of the penetration on the type of ointment, there is a distinct dependence on the chemical structure: estriol penetrates considerably slower and in less concentrations into the living layers of the human skin than the estradiols. Furthermore, estriol reaches the dermis only in low concentrations so that this substance may be termed epidermotropic. 17 alpha-estriol which has only weak sexhormone properties in humans penetrates as well as the sexhormone 17 beta-estradiol.

Administration, Topical↗