ESR dosimetry of irradiated ascorbic acid

Effect of gamma radiation on amlodis and its potential for radiosterilization

In the present work, radiation sensitivity of amlodis (AML) and its active ingredient Amlodipin Besylate (AML-B) were separately investigated by electron spin resonance (ESR) spectroscopy using radiolytic products induced in these drugs. Irradiation in the dose range of 2.5-25kGy did not create any ESR resonance line in AML-B, but it create five characteristic ESR resonance lines associated with more than one radical species in the case of AML. This signal is attributed to the radical species created upon irradiation of inactive ingredients such as microcrystalline cellulose and sodium starch glycolate of AML. Five resonance lines were observed to be divided into three sub groups of different characteristic behaviors associable with three different radical species. Radical species responsible from observed ESR lines were unstable at room and above room temperatures, however, they conserved their identities over a storage period of 92 days. This permitted to discriminate irradiated AML from unirradiated one. A quadratic function was found to describe best the variations of the intensities of observed resonance lines with applied radiation dose. A model based on three tentative radical species with a pyranose ring formed by the rapture of CH bonds in positions 1 and 4 was proposed to explain the observed five lines experimental ESR spectra. AML was considered not providing the characteristic features of a good dosimetric material due to its low radiation yield and relatively fast decays of the created radical species, but very low radiation sensitivity of its active ingredient, namely AML-B makes AML a good candidate for radiosterilization.

Radiation-induced effects on cefotaxime: ESR study

As an alternative to heat and gas exposure sterilization, ionizing radiation is gaining interest as sterilization process for medicinal products. Detection and dosimetry of pharmaceuticals radiosterilization is a growing concern to numerous government regulatory agencies worldwide. In this context, it is necessary to find methods distinguishing between irradiated and nonirradiated pharmaceuticals. In the absence of suitable detection methods, our attention was focused on electron spin resonance (ESR) spectrometry. A third generation cephalosporin, cefotaxime, was chosen as model; this antibiotic is a potential candidate for radiation treatment due to its thermosensitivity. While the ESR spectra of a nonirradiated sample presents no signal, a signal, dependent of the irradiation dose, is found in irradiated samples. The number of free radicals was estimated by comparing the second integral from radiosterilized samples and a diphenyl-picrylhydrazyl reference. Estimation of the number of free radicals gives 1.9 x 10(20) radicals mol(-1) at 20 kGy. From this result, the G-value (number of radicals (100eV)(-1)) could be estimated to 0.3. Aside from qualitative detection, ESR spectrometry can be used for dose estimation. When quadratic, exponential or bi-exponential functions are applied to the variation of peak to peak amplitude vs. dose, these functions correlate well with the data. However, it is important to notice that linear function correlates well with the data for doses lower than 20 kGy. Since the radiation dose selected must be always based upon the bioburden of the products and the degree of sterility required (EN 552 and ISO 11137) 25kGy could no longer be accepted as a "routine dose" for sterilizing a pharmaceutical. Doses from 6kGy (ISO 11137) could be investigated and linear regression would appear to be the least expensive route to follow. The free radicals concentration appeared to not decrease during the 57 days of storage; the number generated during the irradiation allows the detection of radiosterilized cefotaxime up to two years after irradiation.