EPR study of free radicals formed in fusidic acid and neomycin under UV irradiation

Abstract

Free radicals in UV irradiated antibiotics used in dermatology were examined. Concentrations of free radicals in fusidic acid and neomycin in ointment were determined. EPR spectra of the tested antibiotics were measured by electron paramagnetic resonance spectrometer with magnetic modulation of 100 kHz and numerical acquisition system the Rapid Scan Unit. The influence of microwave powers in the range of 2.2-70 mW on the spectra was obtained. Amplitudes (A) and linewidths (∆Bpp) of the EPR spectra, were analyzed. The EPR spectra were homogeneously broadened. Fast spin-lattice relaxation processes existed in UV irradiated fusidic acid and neomycin, which EPR spectra were not saturated up to 70 mW. The influence of the time of UV irradiation on free radicals in the samples was observed. The samples were irradiated by UVA (315-400 nm) in the 30, 60, and 90 min period. Free radical concentrations in the tested antibiotics exposed to UV were proportional to the amplitudes (A) of the EPR spectra. The highest amplitudes (A) were observed for the UV irradiated antibiotics during for 60 min. Fusidic acid was characterized by higher amplitudes (A) than neomycin. Fusidic acid and neomycin in ointment used to treat bacterial infection of skin under UV irradiation may produce free radical toxic effects. The stronger photosensitivity characterized fusidic acid relatively to neomycin. EPR spectroscopy is a useful method of testing free radicals formed in antibiotics during photolysis.