Determination of radical yields in solid-state drugs as one technique to identify drugs that will withstand radiosterilization: radioresistance of beta blockers

The long-term stability of solid-state oral pharmaceuticals exposed to simulated intravehicular space radiation

Pharmaceutical products brought for space missions must remain effective and safe throughout the mission. Previous NASA experiments suggest that radiation exposure could threaten drug stability during long-duration space missions. The Exploration Medical Capability (ExMC) Element has evaluated this possibility by exposing four medications to simulated Galactic Cosmic Radiation (GCRSim) at the NASA Space Radiation Laboratory followed by a three-year storage period. The solid oral drug products Acetaminophen, Amoxicillin, Ibuprofen, and Promethazine were used. Identical lots of each medication were assigned to four experimental groups: the non-irradiated Johnson Space Center control group, the non-irradiated traveling control group, the irradiation group I (GRSim, 0.5 Gy), and the irradiation group II (GCRSim, 1.0 Gy). Drug products were assessed for active pharmaceutical ingredient, degradation impurities, and dissolution 2, 18, and 34 months after irradiation. All samples show comparable degradation, revealing that GCR exposure does not facilitate the degradation of the drugs.

The Use of Multi-frequency EPR Techniques to Identify the Radicals Produced in Irradiated β-Blockers

The identification of radicals trapped in irradiated drugs can be very intricate. A multi-frequency electron paramagnetic resonance (EPR) study is proposed to resolve this problem. The Q-band (ca. 34 GHz) comparison with X-band (ca. 9 GHz) did not show significant differences for the four beta-blockers studied (atenolol, esmolol, nadolol and propranolol). The use of a higher frequency (285 GHz) was required. It enabled us to determine the g-tensor values of the radicals present in atenolol and esmolol, respectively, g1 = 2.0086, g2 = 2.0059 and g3 = 2.0021 and g1 = 2.0066, g2 = 2.0044 and g3 = 2.0021. The latter was assigned as a phenoxyl radical, which can not be the case for the former. Therefore, radicals produced in esmolol may result from a more complex mechanism than the abstraction followed by the diffusion of an H atom inside the solid. In addition, two molecules as similar as atenolol and esmolol hydrochloride do not contain the same radicals after irradiation. These two conclusions drawn from the EPR results on beta-blockers show clearly the importance of continuing the investigations on radiolytic mechanisms in solid-state drugs.

Electron Beam and Gamma Radiolysis of Solid-State Metoclopramide

PURPOSE

Study the radiolysis of solid-state metoclopramide hydrochloride at various absorbed doses. Elucidate the structure of the degradation products to gain information on the radiolysis mechanisms.

METHODS

Solid-state metoclopramide samples were irradiated at several doses with gamma rays and high-energy electrons to evaluate the influence of the dose rate. High-performance liquid chromatography with a diode array detector was used to measure the chemical potency as a function of the absorbed dose and to quantify the degradation products. The characterization of degradation products was performed by liquid chromatography/atmospheric pressure chemical ionization/tandem mass spectrometry.

RESULTS

The degradation of solid-state metoclopramide after irradiation was negligible. No qualitative or quantitative differences were observed between gamma and electron beam irradiations (no dose rate effect). Four degradation products that were similar to metoclopramide were detected in trace levels (below 0.1% of the drug concentration) and were not unique to irradiation because they were found in lower amounts in unirradiated metoclopramide. The major degradation product formed after radiation was due to the loss of the chlorine atom from the metoclopramide molecule.

CONCLUSION

Solid-state metoclopramide is radioresistant from a chemical point of view and therefore could be a suitable candidate for radiosterilization studies by either gamma rays or high-energy electrons.

Attempts at Correlation of the Radiolytic Species of Irradiated Solid-State Captopril Studied by Multi-frequency EPR and HPLC

The purpose of this study was to provide insight into the processes that occur after the irradiation of solid-state drugs. Electron paramagnetic resonance (EPR) experiments were performed at two different frequencies, X-band (about 9.5 GHz) and Q-band (about 34 GHz), to identify the radicals present in irradiated captopril. The results confirmed that an irradiated drug can trap several main radicals. Moreover, the radical composition varied as a function of the treatment. In addition, non-volatile final products were studied by liquid chromatography coupled to UV and to mass spectrometry (LC-MS). The variation of the radical composition did not influence the profile of the final products; this appears to indicate that, in the case of captopril, the trapped radicals observed by EPR are not the main precursors of the final products. Finally, high-performance liquid chromatography data appear to indicate that radiosterilization of captopril is feasible.