• Matthias Rother and Ilka Rother.
• Department of Clinical Operations, X-pert Med GmbH, Graefelfing, Germany.
• J Pain Res. 2011 Jan 1; 4: 357-63.

BackgroundPain related to ultraviolet B radiation (UVR) induced sunburn is an established, simple, acute pain model. One of the major criticisms is related to the potential dermal adverse events caused by the UVR exposure. This study tried to validate the model for oral and topical drugs and to define the minimum required UVR exposure.MethodsThis subject- and observer-blinded, placebo-controlled, crossover study evaluated 600 mg oral ibuprofen (IB) and topical hydrocortisone-21-acetate (HC) twice daily (bid) in 24 healthy volunteers. Treatment started immediately after irradiation and again at 12 hours, 24 hours, and 36 hours post-UVR. Assessment of hyperalgesia to heat and signs of inflammation (erythema, skin temperature) for all areas was performed after UVR and again at 6, 12, 24, 36, and 48 hours. Subjects returned within 4-11 days to the study site for the second period of the study. As in the first period, subjects received HC at one side and topical placebo on the other side, but oral treatment was crossed-over.ResultsThe primary analysis failed to show the expected superiority of the IB-group vs the placebo group in period 1 of the study. Evaluating period 2 alone clearly showed the expected treatment effects of IB for erythema and heat pain threshold. The results were less pronounced for skin temperature. In contrast to IB vs oral placebo, there were no differences in treatment response between HC and topical placebo. UVR at all dosages induced profound erythema and reduction of heat pain threshold without causing blisters or other unexpected discomfort to the subjects. The changes were almost linear between 1 and 2 minimal erythema doses (MED), whereas the change from 2 to 3 MED was less pronounced.ConclusionUse of 2 MED in upcoming studies seems to be reasonable to limit subjects' UVB exposure. The following procedural changes are suggested: Intensified training sessions before randomization to treatmentIncrease in sample size if they are crossover studiesSimplification in design (either oral or topical treatment).

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