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Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.

Thomapyrin has been on the German market as analgesic for the past 50 years. It is the prescription-free preparation with the highest sales there. This is an occasion to survey current state of scientific knowledge concerning combination analgesics with acetyl salicylic acid, paracetamol and caffeine. For the assessment and registration of fixed preparations authorities of different European countries and also USA have defined special criteria. Analgesic preparations must agree with these defined criteria. The importance of these combination analgesics in pain therapy is described with the respect to the latest scientific results. Combination analgesics represent an important area of self-medication by the patient. The properties of the active substances alone and in combination are set forth, with respect to pharmacokinetics and efficacy. The experimental and especially clinical results clearly show a broader spectrum of action in consequence of the different modes of action of the individual active substances. Analgesic action is 1.4 fold higher owing to added caffeine. The fixed combination of active substances does not change the profile of side effects. The conclusion is that combination analgesics such as Thomapyrine show a positive benefit/risk ratio. Furthermore such combination analgesics are appropriate for self-medications and suited to combat pain of different kinds.