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The photochemical behaviour of amiodarone was examined in vitro in order to get more insight on the chemical reactions involved in the cutaneous phototoxicity processes. Irradiation at 300 nm of amiodarone degassed in ethanol solution leads to a photodehalogenation followed by a much slower a-cleavage reaction. Desethylamiodarone, the main metabolite of AD was found to undergo the same reaction as AD. Results of photosensitization and quenching experiments together with phosphorescence spectra indicated that the reaction proceeds via the triplet excited sta e.of-amiodarone.Radical species formed during photolysis were identified by ESR spectroscopy. CH, E HOH, HOi and an unidentified radical were detected using 5.5-dimethyl-1-pyrroline-1-oxide as spin trap. In aerated solutions, photosensitization of oxygen by amiodarone was demonstrated by adding singlet oxygen scavengers such as dimethylfuran and cholesterol. Overall, these results suggest that Type I and Type I1 mechanisms may take place in the phototoxicity of amiodarone and its metabolite. ,

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