Luisa Valvo

Gamma irradiation effects on poly(dl-lactictide-co-glycolide) microspheres

Gamma radiation treatment plays an increasingly important role in the sterilization/sanitization of pharmaceutical products. However, irradiation may affect the stability of the product and thus its safety of use. We investigated the influence of ionizing radiation on modified release microparticulate drug delivery systems made of two types of polylactide-co-glycolide copolymers (PLG): RG 503 and RG 503H; these polymers have identical molecular weights but different chemical structures. The effect of gamma radiation on polymer stability of the raw polymers (P) and related microspheres (Ms) was evaluated. Samples were irradiated at different irradiation doses (5, 15 and 25 kGy) using 60Co as radiation source. The microspheres were prepared using the spray drying technique. Degradation of PLG and related microspheres was evaluated during six months in terms of average molecular weight (Mw) loss by gel permeation chromatography (GPC) and variation in glass transition temperature (Tg) using differential calorimetry (DSC). The presence of free radicals in the product was tested by electron paramagnetic resonance (EPR). Both P and Ms showed a trend in decreasing their Mw at time 0 as a function of irradiation dose. For RG503 the decay in Mw is always negligible for doses below 15 kGy while it is about 10% for 25 kGy. After 150 days Mw decay was 25% in the microspheres and 20% in the raw polymer. It was not possible to evaluate the radiation effect, at different storage times, for RG503H because this polymer resulted to be unstable even in the regular storage conditions without being irradiated. The concentration of radiation-induced free radicals was higher in RG 503H (both P and Ms) and they were more stable than the free radicals species observed in the case of polymer RG 503. Alterations and/or production of new radicals were observed on exposure of RG 503H microspheres to the light. Radiolytic degradation of RG 503 under vacuum is characterized by a prevalence of the chain scission events leading to a decrease of Mw. Some crosslinking can occur mainly in the post irradiation stage through the decay and coupling of the hydrogen abstraction radicals. A hydroperoxydative cycle, whose mechanism is suggested, is generated in the presence of oxygen.

Gamma irradiation effects on stability of poly(lactide-co-glycolide) microspheres containing clonazepam.

This work was aimed at evaluating the effects of gamma irradiation on the stability of microspheres made of a poly(lactide-co-glycolide) copolymer (PLGA) and loaded with 15% w/w of clonazepam (CLO). The influence of CLO on PLGA radiolysis mechanisms and the identification of possible irradiation markers were also investigated. Microspheres were prepared by means of a spray-drying method. gamma Irradiation was carried out either under vacuum or in air, at a dose of 25 kGy, by using a 60Co source. The stability of CLO loaded microspheres was evaluated over a 6-month period on the basis of drug content and dissolution profile. Radiolysis mechanisms were investigated by using electronic paramagnetic resonance (EPR) analysis. The microspheres irradiated under vacuum were stable over the considered period of time. After irradiation in air, CLO release rate increased by approximately 10%, and did not change further in the following period of storage. The EPR analysis showed some radicals arising from both the polymeric matrix and the active ingredient. Polymer/CLO spin transfer reactions suggest that CLO had a radio-stabilising effect on the polymeric matrix. In the loaded microspheres, the intensity in time of the CLO radical signal is sufficient for its possible use as irradiation marker.

Poly(lactide-co-glycolide) microspheres containing bupivacaine: comparison between gamma and beta irradiation effects.

The beta- and gamma-irradiation effects on stability of microspheres made of poly(lactide-co-glycolide) 50:50 copolymer (PLGA) containing bupivacaine (BU) were studied. Microspheres containing 10, 25, and 40% w/w, respectively, of BU were prepared by spray drying and irradiated in air with beta- and gamma-irradiation at a dose of 25 kGy. Morphology (atomic force microscopy, particle-size analysis), physico-chemical characteristics (DSC and FT-IR spectroscopy), drug content and in vitro dissolution profile of microspheres were all determined; the stability of irradiated microspheres was evaluated over a 9-month period. The decrease of BU content in gamma-irradiated microspheres was almost always constant independent of the amount of BU per sample, therefore it was in inverse proportion to drug loading (range between 5 and 15%). BU release rate increased immediately after irradiation and increased slightly until 90 days of storage. As far as beta-irradiated microspheres are concerned, BU content decreased in a significant way (approximately 3%) only in microspheres containing 10% w/w of BU. Immediately after irradiation, drug release rate in beta-irradiated microspheres increased less than in the corresponding gamma-irradiated microspheres, and it did not change further over the following storage period. BU-loaded microspheres have been shown to be more stable against beta- than gamma-irradiation. AFM revealed that the surface roughness of the irradiated microspheres increases depending on irradiation. As such, if a parameter is quantifiable, it is proposed as a marker of degradation due to ionizing radiation.

Medicines informal market in Congo, Burundi and Angola: counterfeit and sub-standard antimalarials

BackgroundThe presence of counterfeits and sub-standards in African medicines market is a dramatic problem that causes many deaths each year. The increase of the phenomenon of pharmaceutical counterfeiting is due to the rise of the illegal market and to the impossibility to purchase branded high cost medicines.MethodsIn this paper the results of a quality control on antimalarial tablet samples purchased in the informal market in Congo, Burundi and Angola are reported. The quality control consisted in the assay of active substance by means of validated liquid chromatographic methods, uniformity of mass determination, disintegration and dissolution tests. Moreover, a general evaluation on label and packaging characteristics was performed.ResultsThe results obtained on thirty antimalarial tablet samples containing chloroquine, quinine, mefloquine, sulphadoxine and pyrimethamine showed the presence of different kinds of problems: a general problem concerning the packaging (loose tablets, packaging without Producer name, Producer Country and sometimes without expiry date); low content of active substance (in one sample); different, non-declared, active substance (in one sample); sub-standard technological properties and very low dissolution profiles (in about 50% of samples). This last property could affect the bioavailability and bioequivalence in comparison with branded products and could be related to the use of different excipients in formulation or bad storage conditions.ConclusionThis paper evidences that the most common quality problem in the analysed samples appears to be the low dissolution profile. Here it is remarked that the presence of the right active substance in the right quantity is not a sufficient condition for a good quality drug. Dissolution test is not less important in a quality control and often evidences in vitro possible differences in therapeutic efficacy among drugs with the same active content. Dissolution profile can be dramatically affected by the choice of excipients in the oral solid formulation and, in many cases, is out of specifications due to the absence of formulation studies by producers of developing countries.

ESR identification of irradiated antibiotics: cephalosporins

Abstract The ESR technique was tested as a tool to detect antibiotics irradiated for sterilization purposes. Thirteen different cephalosporins, each commercially available, were given a sterilization dose of 25 kGy and then studied by ESR. For 12 out of the 13 samples tested, a specific radiation-induced signal was detected whose time stability allows identification tests. For one cephalosporin (cefaclor), the same signal is present in the irradiated and unirradiated samples. However, identification is still possible due to the high radiation-induced radical concentration and favorable signal time stability.

Simultaneous determination of zidovudine and nevirapine in human plasma by RP-LC.

A simple method for the simultaneous determination of zidovudine and nevirapine in human plasma by reversed-phase liquid chromatography with UV detection at 265 nm was developed. A solid-liquid extraction procedure with internal standard was applied to the samples prior to analysis. The system requires a Zorbax SB-C18 column, 250 x 4.6 mm I.D. and a mobile phase composed of potassium dihydrogen phosphate (10 mM; pH 6.5)-acetonitrile (83:17, v/v). Peak-areas are linear; correlation coefficients are better than 0.999; both inter- and intra-day accuracy and precision are lower than 15%. Extraction recoveries are higher than 90% for both zidovudine and nevirapine. The method proposed was employed to determine the levels of the two retroviral drugs in plasma from HIV infected human subjects.

Determination of oxidized and reduced glutathione in pharmaceuticals by reversed-phase high-performance liquid chromatography with dual electrochemical detection

Abstract A sensitive and rapid reversed-phase HPLC method with electrochemical detection was developed for the analysis of glutathione in pharmaceutical preparations. The separation was achieved on an LC 18-DB (100×4.6 mm I.D.; 5 μm particle size) column. The mobile phase consisted of 0.1% (v/v) trifluoroacetic acid and acetonitrile (98:2, v/v). The effluent was monitored with dual electrochemical detection (applied potentials: E 1 =+0.450 V; E 2 =+0.750 V) in order to check simultaneously the declared amount of reduced glutathione and to quantify the related impurity oxidized glutathione. Limits of detection of 0.60 and 0.15 ng were achieved for the reduced and oxidized form, respectively. The method was validated and applied to the analysis of five commercial preparations containing reduced glutathione.

RP-HPLC study of the degradation of diclofenac and piroxicam in the presence of hydroxyl radicals

The effect of hydroxyl radical attack on two non-steroidal anti-inflammatory drugs (NSAIDs) was studied in vitro. Diclofenac and piroxicam were analysed by RP-HPLC after reaction with OH* free radicals to detect newly formed oxidation and/or degradation products. OH* free radicals were obtained by means of ferrous sulphate and ascorbic acid mixtures. During the reaction the mixtures were exposed to irradiation by a tungsten lamp to obtain an increased and more reproducible formation of hydroxyl radicals. The chromatographic profiles showed the formation of several new peaks for both diclofenac and piroxicam due to the presence of a number of degradation/oxidation products formed in the presence of OH* radicals.

Development of a simple liquid chromatographic method with UV and mass spectrometric detection for the separation of substances related to amoxicillin sodium

Abstract The development of a selective method for the separation and identification of amoxicillin sodium-related substances is described. It is based on reversed-phase liquid chromatography followed either by UV detection (LC–UV) or by mass spectrometry (LC–MS). Mass detection was carried out by an atmospheric pressure ionization source and ionspray interface. Flow injection analyses–MS gave positive-ion mass spectra exhibiting abundant peaks due to their protonated molecules without significant fragmentation. The protonated molecules were used for selected ion monitoring LC–MS analyses. The method allowed the resolution of 13 available potential impurities from amoxicillin and from each other. Its applicability to an MS detector also permits a rapid identification of the impurities in the lack of the corresponding reference substances.

Gamma radiation induced effects on cefuroxime and cefotaxime. Investigation on degradation and syn-anti isomerization

The effects of gamna irradiation on cefuroxime and cefotaxime were studied. Degradation products and long-lived free radicals were investigated as a function of radiation dose. The formation of new impurities was evidenced by HPLC in both the compounds. A valuable increase of the pre-existent impurities, anti-isomer included, was found only in cefuroxime. ESR measurements put in evidence the presence of ganma radiation induced long-lived free radicals. Moreover, the influence of gamma irradiation on syn-anti isomerization was evaluated in comparison with the photoisomerization induced by ultraviolet light exposition on powder samples.