Skin tests methodology

Organisation of Economic Cooperation and Development, Skin Sensitisation Testing Methodological Considerations, Tech. Rep. No. 78, Paris, 1999. 

Testing Methodology of Preoperative Skin Preparation and Surgical Scrub as Over-the-Counter Drugs... 

Skin testing with vancomycin and teicoplanin has not been well studied and the procedure remains to be validated with both positive and negative predictive values unknown. Skin test results, and particularly details of drug concentrations used and methodologies employed, are hard to find in the vancomycin-teicoplanin literature on adverse reactions. In a case study of vancomycin anaphylaxis followed by successful desensitization, intradermal skin tests with the drug were positive at a concentration of 0.1 pg/ml. Control subjects showed positive responses at concentrations of 10 pg/ml or greater. A loss of skin test reactivity to vancomycin has been demonstrated in one case study after successful desensitization to the drug. 

IgE antibodies to iodinated contrast media have not been consistently and convincingly demonstrated. This raises doubts about patient selection (that is, the degree of severity of patient reactions) and the adequacy and appropriateness of the present IgE test methodologies. Challenge tests with contrast media, rarely employed and refused by most patients, are valuable for the identification of tolerated skin test-negative agents. 

A large number of different test methodologies has been developed for such a purpose. The selection of the methodology will depend on the objective of the test, the type of product to be tested, the type of skin alteration the investigator wants to follow, the already available safety information about the product, and so forth. 

With the development of milder and milder surfactants or surfactant-based products, methods to evaluate the irritation or nonirritation potential of those materials evolved toward more sensitivity. That is why several testing methodologies have been developed to investigate faint interactions of surfactants with the upper layers of the skin which do not induce any visible alteration of the surface of the skin but some slight, invisible changes. Several of these methods were recently reviewed [75]. Briefly, they are as follows. 

Besides the development of new testing methodologies, the way to evaluate skin reactions has also undergone continual evolution. For the past 20 years, more objective and quantitative instrumental measurements have been developed and have improved in their sensitivity and reliability. They are used to measure skin color, barrier function, surface hydration, relief, oiliness, and so on. Specific tests investigating faint changes due to the interaction of surfactants with the stratum comeum have also been described in this section and help in comparing the effect of different products or surfactants applied to skin in close-to-realistic conditions. 

Methodology to assess skin penetration, deposition, and metabolism needs to be further advanced. The LLNA needs to be further developed with a view to testing of aqueous solutions, preparations, and complex mixtures. The effects of irritant activity in the LLNA should be further explored. It is recommended that nonradioactive active forms of the LLNA, or LLNA-type assays that use reduced amounts of radioactivity, get more attention. 

The two standards specify slightly different tests and follow different methodologies. The USP Class VI test method consists of acute systemic (over the tissue), intracutaneous (under the skin), and muscle implantation (in the muscle) tests. Establishing a USP Class VI rating has little bearing on whether the product will win approval from the Food and Drug Administration (FDA). The Class VI rating merely states that the products exhibit a low level of toxicity under the test conditions. 

In addition to skin-prick testing, Wilkinson and Beck used ammoniated latex for diagnosing delayed-type allergy to NRL. Of 822 patients, 16 (1.9%) demonstrated positive cutaneous reactions to latex. Six were SPT-positive, five were both SPT and patch-test positive and five were only patch-test positive. Patch testing with latex will be an important methodology in the future in diagnosing delayed-type eczematous reactions to NRL, but proper test materials not containing rubber chemicals are first needed (Wilkinson and Beck 1996). 

In a more recent study, an increase of the skin microcirculatory patterns (skin temperature and blood flow/velocity in the skin capillaries) consequent to application of pure soluble collagen has been reported. These effects were related by the authors to a shortterm inhibition of the transepidermal water loss, causing indirect uptake of excess water by the biopolymers in the dermis and consequent increase of elasticity and pulsation efficacy of the small blood vessels (83). These tests are largely heterogeneous and the results obtained not comparable, being based on different exposure and evaluation methodologies however, all studies report only short-term moisturizing effects. 

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