Electron spin resonance studies of some irradiated pharmaceuticals

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.

Gamma irradiation effect on some asthma drugs: EPR detection of radiosterilization

Among many sterilization methods, radiosterilization is a preferred method in the pharmaceutical industry because of its advantages. However, the detection of radiosterilization of drugs is a growing concern for many government regulatory agencies around the world because of changes in the drug's structure because of exposure to radiation. Electron Paramagnetic Resonance (EPR) proved to be a very sensitive technique to discriminate between irradiated and nonirradiated drugs and detect radicals for days even to years. In this study, the focus is on the detection of radiosterilization of irradiated three asthma drugs (Airfix, Ventolin and Prednol) by using EPR spectroscopy. Regarding the commercial aspects of drugs, it was found that radicals can be detected at least 2 y after irradiation. Therefore, paramagnetic centers formed by the effect of radiation in the samples were determined and the stability of these centers was examined for 2 y by performing the fading study.

Limitations in predicting radiation-induced pharmaceutical instability during long-duration spaceflight

As human spaceflight seeks to expand beyond low-Earth orbit, NASA and its international partners face numerous challenges related to ensuring the safety of their astronauts, including the need to provide a safe and effective pharmacy for long-duration spaceflight. Historical missions have relied upon frequent resupply of onboard pharmaceuticals; as a result, there has been little study into the effects of long-term exposure of pharmaceuticals to the space environment. Of particular concern are the long-term effects of space radiation on drug stability, especially as missions venture away from the protective proximity of the Earth. Here we highlight the risk of space radiation to pharmaceuticals during exploration spaceflight, identifying the limitations of current understanding. We further seek to identify ways in which these limitations could be addressed through dedicated research efforts aimed toward the rapid development of an effective pharmacy for future spaceflight endeavors.

An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution

The effects of γ-radiation sterilization on the parenteral excipient l-histidine were analysed by means of EPR spectroscopy. The irradiation process was found to induce the formation of a deamination radical which was persistent in the solid state. The nature and reactivity of the radicals following dissolution in water was evaluated using spin-trapping EPR experiments. The deamination radical was found to regenerate in solution in the presence of trace metals, potentially leading to radical induced degradation reactions occurring up to an hour after the dissolution process. Understanding this process is significant for the improved design of parental pharmaceutical formulations in which unwanted radical reactions after γ-radiation sterilization could lead to degradation of active ingredients.

Free radicals properties of gamma-irradiated penicillin-derived antibiotics: piperacillin, ampicillin, and crystalline penicillin

The aim of this work was to determine the concentrations and properties of free radicals in piperacillin, ampicillin, and crystalline penicillin after gamma irradiation. The radicals were studied by electron paramagnetic resonance (EPR) spectroscopy using an X-band spectrometer (9.3 GHz). Gamma irradiation was performed at a dose of 25 kGy. One- and two-exponential functions were fitted to the experimental data, in order to assess the influence of the antibiotics' storage time on the measured EPR lines. After gamma irradiation, complex EPR lines were recorded confirming the presence of a large number of free radicals formed during the irradiation. For all tested antibiotics, concentrations of free radicals and parameters of EPR spectra changed with storage time. The results obtained demonstrate that concentration of free radicals and other spectroscopic parameters can be used to select the optimal parameters of radiation sterilization of β-lactam antibiotics. The most important parameters are the constants τ (τ (1(A),(I)) and τ (2(A),(I))) and K (K (0(A),(I)), K (1(A),(I)), K (2(A),(I))) of the exponential functions that describe free radicals decay during samples storage.

The effects of gamma irradiation on diclofenac sodium, liposome and niosome ingredients for rheumatoid arthritis

The use of gamma rays for the sterilization of pharmaceutical raw materials and dosage forms is an alternative method for sterilization. However, one of the major problems of the radiosterilization is the production of new radiolytic products during the irradiation process. Therefore, the principal problem in radiosterilization is to determine and to characterize these physical and chemical changes originating from high-energy radiation. Parenteral drug delivery systems were prepared and in vitro characterization, biodistribution and treatment studies were done in our previous studies. Drug delivery systems (liposomes, niosomes, lipogelosomes and niogelosomes) encapsulating diclofenac sodium (DFNa) were prepared for the treatment of rheumatoid arthritis (RA). This work complies information about the studies developed in order to find out if gamma radiation could be applied as a sterilization method to DFNa, and the raw materials as dimyristoyl phosphatidylcholine (DMPC), surfactant I [polyglyceryl-3-cethyl ether (SUR I)], dicethyl phosphate (DCP) and cholesterol (CHOL) that are used to prepare those systems. The raw materials were irradiated with different radiation doses (5, 10, 25 and 50 kGy) and physicochemical changes (organoleptic properties pH, UV and melting point), microbiological evaluation [sterility assurance level (SAL), sterility and pyrogen test] and electron spin resonance (ESR) characteristics were studied at normal (25 °C, 60% relative humidity) and accelerated (40 °C, 75% relative humidity) stability test conditions.

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.

Spectroscopic, kinetic and dosimetric features of the radical species produced after radiodegradation of solid triclosan

In the present work, spectroscopic, kinetic and dosimetric features of the radicalic intermediates produced after gamma irradiation at room temperature of solid triclosan (2,4,4-trichloro-2-hydroxydiphenyl ether; TCS) were investigated by means of electron spin resonance spectroscopy (ESR) at various temperatures. The same material was also irradiated with UV light, and an ESR spectrum very similar to that obtained for gamma-irradiated TCS, was recorded. The ESR spectrum of TCS is characterized by an unresolved doublet with resonance lines split into other doublets. An evaluation technique based on variations of four assigned peak-to-peak amplitudes and signal intensity was adopted, to monitor the evolution of the spectrum under different experimental conditions. Radicals of one type were proposed to be created upon irradiation exhibiting decays via intra-track and inter-track recombination reactions with activation energies of 43 +/- 2 and 139 +/- 6 kJ/mol, respectively. A radical exhibiting axial g anisotropy and interacting with two un-equivalent protons was found to describe the experimental spectrum well. The sensitivity of TCS to gamma radiation was high (G = 0.12) suggesting TCS to be a suitable dosimetric material in measuring normal and accidental radiation doses in the range of (1-25 kGy).

The effect of ionizing radiation of 1,4-dihydropyridine derivatives in the solid state

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate the gamma-radiation damage in the crystalline powder form of nine calcium channel blockers from the 1,4-dihydropyridine derivatives, which are in clinical use for treatment of arteria hypertension and ischemic heart disease. EPR studies have been carried out, showing the influence of irradiation and storage parameters on the nature and concentration of the free radicals trapped. EPR spectra of isardipine and felodipine showed single EPR line. EPR spectra of nifedipine, nisoldipine, nitrendipine, nimodipine, nicardipine and nilvadipine reveal a broad anisotropic signal of hyperfine interaction. No EPR signal was observed from amlodipine.

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.

Spectroscopic features of radiolytic intermediates induced in gamma irradiated sulfatiazole: an ESR study

Sulfonamides are used as active ingredients in different drugs to treat infections caused by bacteria. Sulfatiazole (STZ) is one of the commonly used sulfonamides as antibacterial agent in drugs, which constitute potential candidates for radiosterilization. However, the crucial point in this respect is to monitor the amount and characteristic features of the radiolytic intermediates produced after irradiation. Electron spin resonance (ESR) spectroscopy is extensively used for this purpose due to its high sensitivity toward intermediates exhibiting radicalic nature. Thus, the aim of the present work is to investigate the spectroscopic and kinetic features of the species having unpaired electrons induced in gamma irradiated STZ at room and different temperatures in the dose range of 5-50kGy using ESR spectroscopy. Spectra of irradiated STZ consisted of many resonance peaks in the studied dose and temperature ranges. Heights of the peaks measured with respect to the base line were used to monitor microwave, temperature, time-dependent features of the radical species contributing to the experimental ESR spectra. Four tentative species of different spectroscopic and structural features assigned as A, B, C and D were found well explaining the experimental ESR spectra of gamma irradiated STZ. Comparison between the principal IR bands of unirradiated and gamma irradiated samples showed no detectable changes and appearance of new bands.

Investigation of radiosterilization and dosimetric features of sulfacetamide sodium

In the present work, the spectroscopic and kinetic features of the radical species induced in gamma-irradiated sulfacetamide-sodium (SS) was studied at room and at different temperatures in the dose range of 5-50kGy by electron spin resonance (ESR) technique with the aim of investigating the possibility of radiosterilization and dosimetric features of SS. A model consisting of four radical species of different spectroscopic features denoted as I-IV was found to describe best whole experimental data derived throughout the present work. These species were quite stable at room temperature but relatively unstable above room temperature. Heights of the characteristic resonance peaks measured with respect to the base line were considered to monitor microwave, temperature, time dependent and kinetic features of the radical species contributing to ESR spectrum. Collected experimental data were used to characterize the radical species responsible from ESR spectra through simulation calculations. Possible changes in the IR bands of gamma irradiated SS was also investigated by FT-IR technique, but no definite difference was observed between unirradiated and irradiated IR spectra of SS. As in other sulfonamides, radiation yield of solid SS was found to be very low (G </= 0.1), therefore basing on this result it was concluded that SS and SS containing drugs could, safely, be sterilized by radiation and that SS did not exhibit good dosimetric features.

ESR investigation of gamma irradiated sulbactam sodium

In the present work, radiolysis of gamma irradiated sulbactam sodium (SS) was investigated through detailed ESR studies performed at low and at high temperatures on the radiolytic products induced in this drug after gamma irradiation in the dose range of 3-15 kGy. While unirradiated SS presented no ESR signal, irradiated SS exhibited an ESR spectrum with many resonance peaks. Variations of the spectrum pattern and of the intensities of resonance peaks with microwave power, applied radiation dose, storage time and temperature were followed. A radical with unpaired electron localised on the carbon atom of five membered ring directly attached to two CH(3) groups and SO(2)(-) ionic radical called as species A and B, respectively, were found to be produced after gamma radiolysis of SS. The characteristic spectral and kinetic features of these species were determined by spectrum simulation calculation and by curve fitting techniques using experimental signal intensity data as input. Although, species A was fairly unstable at room and especially at high temperatures, species B were observed to be relatively stable even at high temperatures having activation energies of E(A) (+/-4)kJ/mol and E(B) (+/-3)kJ/mol, respectively, at room temperature. Four different mathematical functions were tried to explore the dosimetric features of SS and a linear function of applied dose described best the dose-response data obtained for stable species, that is, radical B, in the dose range of 0-10 kGy. An accuracy of 4% in the dose measurements was concluded to be achievable through back-projection dose calculations if SS were used as a dosimetric material.

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

This article describes a simple preliminary test to determine whether a drug is sufficiently radioresistant to withstand radiosterilization. The test is based on the electron spin resonance (ESR) detection of radicals produced after irradiation of a solid-state drug, assuming that these radicals are the precursors of the final products detected after dissolution of the drug. A calibration curve has therefore been established by measuring ESR spectra of l-alanine irradiated at different doses. The response factor to quantify the radicals is the normalized double integration (DI) of the whole first-derivative ESR spectrum. The curve gives the relationship between the normalized DI and the number of radicals. Eight beta blockers have been chosen and their radical yield determined. This is the first time that several different drugs of the same pharmacological group have been studied and compared. The results obtained are similar for seven of the eight beta blockers; the mean G value (excepted for nadolol) is 3 x 10(-9) mol/J. This means that beta blockers are radioresistant. The two most radiosensitive drugs (nadolol and esmolol hydrochloride) were also studied by high-performance liquid chromatography (HPLC). No significant loss of the active compound was detected, which confirms this radioresistant property. Moreover, no change in color or smell was observed. Using ESR and HPLC, beta blockers were identified as potential candidates for radiosterilization.

Detection of free radicals in gamma-irradiated seasnail hard tissues by electron paramagnetic resonance

Gamma-irradiated seasnail (from family of Helix lukortium) hard tissues (CaCO3) were investigated by electron paramagnetic resonance (EPR) at room temperature. The radicals produced by gamma-irradiation in seasnail were attributed to orthorhombic C*O2-, freely rotating C*O2-, orthorhombic C*O3-, axial C*O3-, and axial C*O3(3-) free radicals. Unirradiated seasnail hard tissues also feature Mn2+ ions in their EPR spectra. The hyperfine values were determined for the 13C nucleus in the orthorhombic C*O2- and axial C*O3(3-) free radicals and for the manganese impurity ions. The g values of all the free radicals have been measured. The results were compared with the literature data for similar defects.

Electron paramagnetic resonance of some gamma-irradiated drugs

Some drugs, used mainly in treatment of some neurological diseases and hypertension were exposed to gamma-irradiation, and the samples were investigated by electron paramagnetic resonance (EPR). The observed spectra were interpreted in terms of some type of alkyl and amine radical fragments. The spectra were computer simulated and the g values of the radicals and the hyperfine structure constants of the free electron with nearby protons were determined. The species were found to be stable at room temperature for more than a year. The samples were found to display no EPR signal without irradiation.

Kinetics of the radicals induced in gamma-irradiated naproxen sodium and apranax. Applicability of ESR technique to monitor radiosterilization of naproxen sodium-containing drugs

In the present work the spectroscopic and kinetic features of the radicals induced in gamma-irradiated naproxen sodium (NS) and apranax (AP) tablet are investigated at room and different temperatures in the dose range of 2.5-25 kGy by electron spin resonance technique (ESR). Radiation produces two different radicals (I, II) in NS quite stable at room temperature but relatively unstable above room temperature, giving rise to a broad singlet centered at g = 2.0057. Dose-response and decay curves associated with the broad singlet were found to follow bi-exponentials. Information concerning the saturation decay rates and activation energies were obtained through the characteristics of these exponentials. Similar calculations were also performed for AP, which contains 550 mg NS as active ingredient, and the applicability of ESR technique for monitoring radiosterilization of AP was discussed.

Electron paramagnetic resonance of radicals induced in drugs and excipients by radiation or mechanical treatments

Radiation as well as mechanical treatments induced in drugs and excipients radicals, which can be studied by electron paramagnetic resonance. A special attention is pointed about the use of electron paramagnetic resonance (EPR) to bring the proof whether or not a drug has been irradiated or not. We also discuss of other methods (thermoluminescence (TL), gas phase chromatography (GPC)) which can be used to bring the same proof in case of irradiated drugs, excipients and cosmetic products.