Radiosterilization dosimetry of vitamins: an ESR study

Abstract

Purpose: As an alternative to heat and gas exposure sterilization, ionizing radiation is gaining interest as a sterilization process for medicinal products. Detection and dosimetry of pharmaceutical radiosterilization is a growing concern for numerous government regulatory agencies world-wide. Materials and methods : Equations to describe the ESR curves versus the dose and storage time were developed using mathematical procedures. For this investigation six vitamins (riboflavin, biotin, thiamine mononitrate, thiamine hydrochloride, folic acid and pyridoxine) were chosen as models. Results : The yield of free radicals is in the range 1.7 1018-7.3 1019 radicalsmol-1 (G values from 0.0003 to 0.025 mu mol J-1). Apart from qualitative detection, ESR spectrometry can be used for dose estimation; when an exponential function is applied to the variation of peak-to-peak amplitude on dose, the function correlates well with the data. Tests were carried out to investigate whether storage has an effect on the concentration of free radicals. In order to estimate the time limit of detection, decay curves were modelled using a bi-exponential function. From this, the time limit from the irradiation (25 kGy) for identification of irradiated vitamins by ESR was evaluated. In the commercial drug market, radicals should be detected for up to 2 years after irradiation; this probably will be the case for the vitamins studied, with the exception of folic acid and pyridoxine. Conclusion : The detection method based on ESR dosimetry seems promising. ESR dosimetry requires only small samples, and minimal time and effort for sample preparation; the measurement is non-destructive.