Influence of e-beam irradiation on sulfamethoxazole in solid state.

The effects of ionizing radiation generated by a beam of electrons, in that doses varied from 25-800 kGy, on the physico-chemical properties of sulfamethoxazole (SMX) in solid state have been studied at room temperature and in the air atmosphere. The changes appearing after the irradiation were detected and evaluated by the spectroscopic methods (UV, IR, MS, EPR), chromatography (TLC and HPLC) and SEM, XRD and DSC. Already the lowest dose of 25 kGy was found to change the color of SMX from white to pale cream; such change became more intense with our increasing the irradiation dose. Products of radiodegradation and decreases in the drug content were detected by TLC and HPLC only after irradiation with 400 kGy. Since the SMX radiolysis products (sulfanilamide and sulfanilic acid) are colorless compounds, it is supposed that the color results from trapping of free radicals in the crystal lattice; the concentration of free radicals was 1.04 × 10(15) spin/g. Our results indicate that the radiolysis of SMX in the solid state caused by e-beams involves breaking of the S-N and N-C bonds. The mean radiolytic yield of this process is G((-SMX)) = 1.89 × 10(-7) mol/J, whereas the yield of formation of the two products of radiolysis is close and equal to 2.18 × 10(-8) mol/J (sulfanilamide) and 2.13 × 10(-8) mol/J (sulfanilic acid).