Ionizing Radiation Used in Drug Sterilization, Characterization of Radical Intermediates by Electron Spin Resonance (ESR) Analyses

In this study, the feasibility of radiation sterilization of drugs/drug raw materials is investigated by using Electron Spin Resonance (ESR) spectroscopy. Experimental data and their theoretical correspondings are presented for Sulfanilamide (SA), Sulfafur‐ azole (SFZ), Sulfatiazole (STZ), Sulfacetamide Sodium (SS), Sulfamethazine (SMH), Butylated Hydroxyanisole (BHA), and Albendazole (ALB). Unirradiated samples exhibited no ESR signal whereas the irradiated samples showed ESR spectra consisting of different number of resonance lines indicating that radiolytic intermedi‐ ates were produced upon irradiation. Increase in the absorbed dose did not create any pattern change in the ESR spectra of these samples. The results of ESR microwave power studies indicated that saturation is observed to be faster for the studies held below room temperatures. Low radiation yield (G=0.1-0.5) calculated by ESR data for the gamma-irradiated samples showed that these materials can not be used as sensitive dosimetric materials. No significant differences were observed between FTIR spectra of the unirradiated and irradiated samples and this result is considered to be in agreement with the relatively small G value derived from ESR studies. The decay rates of the ESR peak heights of the samples irradiated at different doses and stored at normal and stability conditions were found to be independent of the irradiation doses. The contributing radical species were determined to decay with different decay characteristics and the decay rates but decaying faster at stability conditions. The discrimination of the samples irradiated at even a low absorbed dose from unirradi‐ ated samples was possible for a long storage time after irradiation. Cooling the sample temperature down to room temperature did not create any pattern change in the ESR © 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. spectra of irradiated samples except slight reversible increases in the peak heights and at high temperatures irreversible decreases in the peaks heights were observed. Annealing studies indicated that the decay rates of the radical species at high temperatures were higher than the decay rates at low temperatures and the decay activation energies for the radical species were calculated by using Arrhenius plots. Spectrum simulation calculations were also performed and it was concluded that, the molecular ionic fragments and ionic radicals were the main responsible units from the resonance lines of ESR spectra of the gamma-irradiated sulfanomides such as SA, SFZ, STZ, SS, and SMH. Besides these two radical species, some other radical types were also likely produced after irradiation in STZ, SS, and SMH. Besides these two radical species, some other radical types were also likely produced after irradiation in STZ, SS and SMH. As for BHA and ALB, again two other type radical species were believed to produce upon irradiation. Basing on the derived experimental and theoretical data it was concluded that SA, SFZ, STZ, SS, SMH, BHA, and ALB could be safely sterilized by gamma radiation up to permitted drug sterilization radiation doses without causing high amount of molecular damages upon irradiation, and ESR spectroscopy could be used as a potential technique in monitoring the radiosteriliza‐ tion of the drugs, drug raw materials, and drug delivery systems containg present samples as active ingredient.