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Biomedical subjects

W Schalla

Publications and source records attributed to W Schalla.

25 records · Page 2Linked to original sources
PubMed1979

Reversible binding of 5- and 8-methoxypsoralen to human serum proteins (albumin) and to epidermis in vitro.

Binding of the two photosensitizers, 8-methoxypsoralen (8-MOP) and 5-methoxypsoralen (5-MOP), to serum proteins and to epidermis was measured. 8-MOP binds to serum proteins with an apparent dissociation constant (Kd) of 4 x 10(-5) M. Under conditions of oral therapy, serum concentrations of the photosensitizer 2 h after administration are usually in the range of 100-1000 ng per ml serum. In this concentration range, 75-80% of the drug was found to be reversibly bound to serum proteins. 5-MOP shows a higher binding affinity to serum proteins and 98-99% of the drug is protein bound. The binding of both psoralen derivatives appears to take place mainly to serum albumin. 5-MOP and 8-MOP bind to different and non-interacting sites on serum proteins and the binding of the one has no effect on the binding of the other methoxypsoralen. Both photosensitizers bind reversibly to human epidermis. 8-MOP concentration in the epidermis is increased by ten to twenty fold compared with the equilibrium buffer. 5-MOP shows a higher binding affinity, resulting in a higher tissue concentration of the photosensitizer. As in serum, the two drugs appear to be bound in the epidermis to independent and non-interacting sites. No binding competition was found between the two methoxypsoralens and hydrocortisone, fluocinonide and acetyl salicylic acid, either in serum or in epidermis, using up to 1000 fold higher concentrations as compared with those of 5-MOP and 8-MOP.

Binding, Competitive↗
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

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↗
PubMed1977

Evidence for two distinct types of penicillinase-producing Neisseria gonorrhoeae.

Since their recognition early in 1976, penicillinase (beta-lactamase)-producing Neisseria gonorrhoeae (P.P.N.G.) have been isolated in more than 15 countries. Most strains isolated in or epidemiologically linked with the Far East are relatively resistant to tetracycline in vitro, are phenotypically wild-type or proline-dependent auxotypes, and carry a plasmid with a molecular weight of 5800 000 (5-8 X 10(6)) daltons coding for beta-lactamase production. In contrast, P.P.N.G. epidemiologically linked with West Africa are more susceptible to tetracycline, require arginine for growth, and their gene coding for beta-lactamase synthesis is contained in a smaller 3-2 X 10(6) dalton plasmid. Moreover, 43% of the Far Eastern strains, but none of those from West Africa, have an additional 24-5 X 10(6) dalton conjugative plasmid which transfers the beta-lactamase R factor(s) to other gonococci. The presence of this conjugative plasmid may explain the relatively high prevalence of P.P.N.G. in certain areas of the Far East.

Africa, Western↗
PubMed1976

Simplification of local therapy of psoriasis with 8-methoxypsoralen. Methods and initial results.

Local 8-methoxypsoralen black-light treatment was carried out on sixty-two patients. For the first time, oil was employed as a preparation base in order to increase the transparency and so the effectiveness of irradiation. Also the need for a descaling pretreatment was avoided. In investigations still being carried out, 27.5% patients showed very good improvement, 48-4% good and 24-2% unsatisfactory results of treatment. In many cases, less than fifteen irradiation sessions were necessary for clinical healing. However, to obtain a uniform pigmentation, additional irradiation proved necessary.

Erythema↗