Positive patch test reactions to nickel sulphate are not modified by neighbouring negative fragrance patch tests. A multicenter-study by the German contact dermatitis research group.

It is tacitly assumed that a positive patch test reaction is not affected by adjacent negative tests. However, despite its fundamental importance for the interpretation of test reactions this assumption has not been proven. To test this assumption, special TRUE-test strips were prepared containing placebo, nickel sulphate and fragrance mix as the only allergens, separated by distances of 1 cm and 7 cm and blinded to the investigators. Patients were synchronously tested with two strips. Out of 493 patients tested in 6 centres, the 93 with positive reactions to nickel sulphate only were evaluated. No relevant difference was found between positive nickel reactions in the two different distances to a negative fragrance patch test. We conclude that a positive patch test reaction is not affected by adjacent negative patch tests, which therefore can be neglected for the interpretation of positive reactions.

Characterization and chemistry of imidazolidinyl urea and diazolidinyl urea.

For several decades, the cosmetic preservatives imidazolidinyl urea (IU) and diazolidinyl urea (DU) have not only been poorly characterized but have also had misleading chemical structures assigned to them. The most common trade names of IU and DU are Germall 115 and Germall II, respectively. This publication gives an insight into what these 2 well-known contact allergens consist of and their degradation patterns. Approximately, 30-40% of both products can be characterized by mixtures of allantoin (synthetic starting material), (4-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-urea (compound HU) and presumably 1-(3,4-bis-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-1,3-bis-hydroxymethyl-urea (compound BHU). A full chemical characterization of compound HU is shown. The remaining part of both IU and DU are believed to be polymers of allantoin-formaldehyde condensation products. The analytical methods used to characterize IU and DU are capillary electrophoresis and nuclear magnetic resonance and mass spectroscopy studies.

Application of confocal laser scanning microscopy in characterization of chemical enhancers in drug-in-adhesive transdermal patches.

The purpose of this study was to evaluate the application of confocal laser scanning microscopy (CLSM) in the examination of the embedment and the release characteristics of chemical permeation enhancers from transdermal drug delivery systems (TDDSs) of the "drug-in-adhesive" type. The enhancer lauric acid and a lauric acid fluorescing probe of the Bodipy type were incorporated into TDDSs consisting of an acrylic, a polyisobutylene, or a silicone polymer adhesive. Three-dimensional confocal images of the distribution were obtained before and during release into an aqueous medium. The images showed that the lauric acid fluorescing probe was homogeneously embedded in all the adhesives except for 1 polyisobutylene. The release profiles and release rate constants of the lauric acid fluorescing probe were consistent with data from a release study of lauric acid performed using conventional measurements of the released amounts. This indicated that lauric acid was distributed in a homogeneous manner. Furthermore, it was possible to illustrate the mechanics of the diffusion process inside the TDDS and compare these patterns with theoretically drawn profiles, based on Fick's law of diffusion. CLSM was demonstrated to be an excellent tool to study how enhancers are incorporated and diffuse into a TDDS.

Release of chemical permeation enhancers from drug-in-adhesive transdermal patches.

There is only limited knowledge of how chemical permeation enhancers release from transdermal drug delivery systems of the drug-in-adhesive type. In this study, the release of eight commonly known enhancers from eight types of polymer adhesives was evaluated using Franz diffusion cells. It was shown that all the enhancers released completely from the adhesives and followed a square root of time kinetic (Higuchi law). Using a statistical analysis it was shown that the release rate was more dependent on the type of enhancer than on the type of polymers. The mean release rates were in the range from 2.2 to 11.1%/ radical t for the slowest and fastest releasing enhancers, which correspond to a 50% release within 500 and 20 min, respectively. Furthermore, the release rates were inversely proportional to the cube root of the molal volumes of the enhancers and to their logarithmic partition coefficients between the polymer adhesive and the receptor fluid. It was found that the observed release rates were probably due to a high diffusion coefficient of the enhancers rather than due to an inhomogeneous embedment of the enhancers in the adhesives. The type of adhesive showed minor influence on the release rate, especially among the acrylic polymers no difference was seen. However, compared to the acrylic adhesives, the polyisobutylene adhesive showed slower release rates, while the silicone adhesive showed slightly faster release rates.