British Journal of Dermatology (1983) IO9> Supplement 25, 111-113. Kinetics of UV-erythema in normal subjects W.RUPP, M.BADIAN, E.DAGROSA, F.GANSHORN, M. LUCENA, W.PETRI AND W.SITTIG Medical Department, Clinical Pharmacology, Hoechst AG, D-6230 Frankfurt/Main 80, F,R,G, SUMMARY In the expandingfieldof clinical dermatopharmacology we standardized an erythema model for testing drugs with effects on UV-induced infiammation in normal male Caucasian subjects. Using a light source with fibre-optic transmission and precise radiation characteristics, some of the shortcomings of conventional UV-application could be overcome. The radiation geometry during the various experiments was kept constant by a tube, permitting a defined area of exposure. Up to eight skin areas of the backs of normal volunteers were radiated with 86-2% UV-A and 13 8% UV-B. After exclusion of hyporeactive and hyperreactive subjects a good intrasubject reproducibility was obtained repeatedly over at least 3 months. According to the definition of bioavailability, our method allows the measurement of the rate and extent of UV-induced erythema. This model has been used for testing topical steroids, non-steroidal antiphlogistics in a variety of pharmaceutical formulations. In clinical dermatopharmacology there is a need for quantitative, reliable and reproducible measurements of the anti-infiammatory effects of new entities. Therefore, we were asked to develop an objective screening method to evaluate optimum pharmaceutical formulations in the context of onset and duration of the anti-infiammatory action of topically and systematically administered drugs (Schalla & Schaefer, 1982; Dagrosa et al., 1981). We used the Dermafiex® UV-table model, which was primarily developed for diagnostic and therapeutic purposes (e.g. photoallergy and treatment of psoriasis) (Stuttgen et al., 1981). The radiation intensity was 10 mW/cm UV-A at 430 nm and i-6 mW/cm UV-B at 360 nm wavelength (Willis & Cylus, 1977). The Dermafiex® light source allows precise radiation characteristics through fibre-optic transmission of the light to the area of the skin under investigation. The geometry of irradiation was standardized using a 25-mm tube without filter. In the inner circle of 5 mm diameter, the light intensity reached its maximum (10 mW UV-A and i-6 mW UV-B) (Fig. i). In thirteen volunteers the exposure time was increased in steps from 10 to 60 sec in order to find the minimum erythema dose (m.e.d.), which was approximately 20 sec in normal subjects Correspondence: Dr Werner Rupp, Medical Department, Clinical Pharmacology, Hoechst AG, P,O, Box 800320, 6230 Frankfurt am Main 80, F,R,G, III