Liquid chromatographic/electrospray ionization mass spectrometric identification of the oxidation end-products of metformin in aqueous solutions

Co-occurrence, toxicity, and biotransformation pathways of metformin and its intermediate product guanylurea: Current state and future prospects for enhanced biodegradation strategy

Accumulation of metformin and its biotransformation product "guanylurea" are posing an increasing concern due to their low biodegradability under natural attenuated conditions. Therefore, in this study, we reviewed the unavoidable function of metformin in human body and the route of its release in different water ecosystems. In addition, metformin and its biotransformation product guanylurea in aquatic environments caused certain toxic effects on aquatic organisms which include neurotoxicity, endocrine disruption, production of ROS, and acetylcholinesterase disturbance in aquatic organisms. Moreover, microorganisms are the first to expose and deal with the release of these contaminants, therefore, the mechanisms of biodegradation pathways of metformin and guanylurea under aerobic and anaerobic environments were studied. It has been reported that certain microbes, such as Aminobacter sp. and Pseudomonas putida can carry potential enzymatic pathways to degrade the dead-end product "guanylurea", and hence guanylurea is no longer the dead-end product of metformin. However, these microbes can easily be affected by certain geochemical cycles, therefore, we proposed certain strategies that can be helpful in the enhanced biodegradation of metformin and its biotransformation product guanylurea. A better understanding of the biodegradation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of the emerging contaminants of concern, metformin and guanylurea in the near future.

Metformin Impedes Oxidation of LDL In Vitro

Metformin is the most commonly prescribed glucose-lowering drug for the treatment of type 2 diabetes. The aim of this study was to investigate whether metformin is capable of impeding the oxidation of LDL, a crucial step in the development of endothelial dysfunction and atherosclerosis. LDL was oxidized by addition of CuCl2 in the presence of increasing concentrations of metformin. The extent of LDL oxidation was assessed by measuring lipid hydroperoxide and malondialdehyde concentrations, relative electrophoretic mobilities, and oxidation-specific immune epitopes. Cytotoxicity of oxLDL in the vascular endothelial cell line EA.hy926 was assessed using the alamarBlue viability test. Quantum chemical calculations were performed to determine free energies of reactions between metformin and radicals typical for lipid oxidation. Metformin concentration-dependently impeded the formation of lipid hydroperoxides, malondialdehyde, and oxidation-specific immune epitopes when oxidation of LDL was initiated by addition of Cu2+. The cytotoxicity of oxLDL was reduced when it was obtained under increasing concentrations of metformin. The quantum chemical calculations revealed that only the reaction of metformin with hydroxyl radicals is exergonic, whereas the reactions with hydroperoxyl radicals or superoxide radical anions are endergonic. Metformin, beside its glucose-lowering effect, might be a suitable agent to impede the development of atherosclerosis and associated CVD. This is due to its capability to impede LDL oxidation, most likely by scavenging hydroxyl radicals.

Metformin Contamination in Global Waters: Biotic and Abiotic Transformation, Byproduct Generation and Toxicity, and Evaluation as a Pharmaceutical Indicator

Metformin is the first-line antidiabetic drug and one of the most prescribed medications worldwide. Because of its ubiquitous occurrence in global waters and demonstrated ecotoxicity, metformin, as with other pharmaceuticals, has become a concerning emerging contaminant. Metformin is subject to transformation, producing numerous problematic transformation byproducts (TPs). The occurrence, removal, and toxicity of metformin have been continually reviewed; yet, a comprehensive analysis of its transformation pathways, byproduct generation, and the associated change in adverse effects is lacking. In this review, we provide a critical overview of the transformation fate of metformin during water treatments and natural processes and compile the 32 organic TPs generated from biotic and abiotic pathways. These TPs occur in aquatic systems worldwide along with metformin. Enhanced toxicity of several TPs compared to metformin has been demonstrated through organism tests and necessitates the development of complete mineralization techniques for metformin and more attention on TP monitoring. We also assess the potential of metformin to indicate overall contamination of pharmaceuticals in aquatic environments, and compared to the previously acknowledged ones, metformin is found to be a more robust or comparable indicator of such overall pharmaceutical contamination. In addition, we provide insightful avenues for future research on metformin.

NDMA formation during ozonation of metformin: Roles of ozone and hydroxyl radicals

Metformin, a high-consumed pharmaceutical for diabetes, has been reported to generate carcinogenic nitroso-dimethylamine (NDMA) during treatment of its containing wastewater. However, whether it would produce NDMA during ozonation or not is unclear, let alone discriminate roles of ozone (O₃) and hydroxyl radicals (OH). In this paper, effects of ozonation on NDMA formation from metformin were investigated, roles of O₃ and OH were also distinguished by adding tert-butyl alcohol (tBA) as OH scavenger. Moreover, various influencing factors and reaction mechanisms were demonstrated. The results indicated that NDMA could be directly formed from metformin during ozonation, the addition of OH scavenger significantly enhanced its formation (0-46.2 ng/L vs 0-139.1 ng/L). The formation of NDMA by O₃ and OH was more affected by bromide and HCO₃^- than those with only O₃; while the impacts of pH and sulphate on the latter were more notable. No matter without/with tBA in the solution, the formed NDMA during ozonation of metformin increased with raising pH (from 5 to 9) and achieved the maximum 69.6 ng/L and 235.9 ng/L at pH 9, respectively; small amount of bromide (0.1 μM) promoted NDMA production, high levels of bromide (10 μM) inhibited its formation; the existence of HCO₃^- enhanced the amounts of NDMA from 44.5 to 73.5 ng/L (raised by 65.2%) by O₃ and OH and from 102.9 to 130 ng/L with only O₃ (raised by 26.3%); with the addition of sulphate, NDMA concentration raised by 43.8% by O₃ and OH, while the value was high up to 134.6% with only O₃. Based on the result of UPLC-Q-TOF and density functional theory, the oxidation intermediates were identified and possible transformation pathways of metformin during ozonation were proposed. The findings in this paper would provide reference when treating metformin-containing water in future.

NanoUPLC-QTOF-MS/MS Determination of Major Rosuvastatin Degradation Products Generated by Gamma Radiation in Aqueous Solution

Rosuvastatin, a member of the statin family of drugs, is used to regulate high cholesterol levels in the human body. Moreover, rosuvastatin and other statins demonstrate a protective role against free radical-induced oxidative stress. Our research aimed to investigate the end-products of free radical-induced degradation of rosuvastatin. To induce the radical degradation, an aqueous solution of rosuvastatin was irradiated using different doses of gamma radiation (50-1000 Gy) under oxidative conditions. Rosuvastatin and related degradation products were separated on nanoC18 column under gradient elution, and identification was carried out on hyphenated nanoUPLC and nanoESI-QTOF mass spectrometer system. Elemental composition analysis using highly accurate mass measurements together with isotope fitting algorithm identified nine major degradation products. This is the first study of gamma radiation-induced degradation of rosuvastatin, where chemical structures, MS/MS fragmentation pathways and formation mechanisms of the resulting degradation products are detailly described. The presented results contribute to the understanding of the degradation pathway of rosuvastatin and possibly other statins under gamma radiation conditions.

Ozonation products from trace organic chemicals in municipal wastewater and from metformin: peering through the keyhole with supercritical fluid chromatography-mass spectrometry

Ozonation is an important process to further reduce the trace organic chemicals (TrOCs) in treated municipal wastewater before discharge into surface waters, and is expected to form products that are more oxidized and more polar than their parent compounds. Many of these ozonation products (OPs) are biodegradable and thus removed by post-treatment (e.g., aldehydes). Most studies on OPs of TrOCs in wastewater rely on reversed-phase liquid chromatography- mass spectrometry (RPLC-MS), which is not suited for highly polar analytes. In this study, supercritical fluid chromatography combined with high resolution MS (SFC-HRMS) was applied in comparison to the generic RPLC-HRMS to search for OPs in ozonated wastewater treatment plant effluent at pilot-scale. While comparable results were obtained from these two techniques during suspect screenings for known OPs, a total of 23 OPs were only observed by SFC-HRMS via non-targeted screening. Several SFC-only OPs were proposed as the derivatives of methoxymethylmelamines, phenolic sulfates/sulfonates, and metformin; the latter was confirmed by laboratory-scale ozonation experiments. A complete ozonation pathway of metformin, a widespread and extremely hydrophilic TrOC in aquatic environment, was elaborated based on SFC-HRMS analysis. Five of the 10 metformin OPs are reported for the first time in this study. Three different dual-media filters were compared as post-treatments, and a combination of sand/anthracite and fresh post-granular activated carbon proved most effective in OPs removal due to the additional adsorption capacity. However, six SFC-only OPs, two of which originating from metformin, appeared to be persistent during all post-treatments, raising concerns on their occurrence in drinking water sources impacted by wastewater.

The removal of metformin and other selected PPCPs from water by poly(3,4-ethylenedioxythiophene) photocatalyst

The objective of this study was to investigate the photocatalytic removal of PPCPs using poly(3,4-ethylenedioxythiophene) (PEDOT) polymer. PEDOT is a conducting polymer that exhibits excellent photocatalytic activity and was used in this study without any additives or metal co-catalysts. The PEDOT was synthesized using chemical oxidative polymerization and characterized further for composition and morphology. PEDOT, in the presence of UV irradiation, showed >99% degradation of one of the most widely prescribed antidiabetic drugs, metformin, within 60 min. The effect of varying concentration of PEDOT, pH, and light irradiance was studied to achieve maximum photocatalytic efficiency. Two major degradation products of metformin of m/z 116 and 126 were detected using triple quadrupole LC-MS/MS, while the degradation kinetics was found to be of pseudo-first-order. Results revealed that photogenerated electrons, holes, and radical species played a role in the PPCPs' degradation. When a mixture of seven PPCPs in the ultra-pure water matrix was tested, more than 99% removal was observed for most of the PPCPs within 60 min. The removal efficiency decreased in a real wastewater effluent due to the presence of dissolved organic matter; however, still, more than 50% removal was observed for majority of the studied PPCPs. The results of PEDOT reusability revealed that the reuse contributed to the drop in the conductivity and subsequent drop in the photocatalytic activity; however, a simple acid treatment was found to be effective to recoup its conductivity. PEDOT was successfully immobilized on an electrospun fiber mat to enhance its applicability.

Characterization of four major degradation products in metformin by 2D LC-QTOF/MS/MS

A two-dimensional liquid chromatography coupled with quadrupole time-of-flight mass spectrometry(2D LC-QTOF/MS/MS) method was developed for the characterization of four major degradation products in metformin under acidic, basic, oxidative and 6 months accelerated conditions. A CAPCELL PAK SCX TYPE UG80 column(5 μm, 4.6 × 150 mm) was applied using 17 g/L ammonium dihydrogen phosphate adjusted to pH 3.0 by phosphoric acid as the mobile phase at a flow rate of 1.0 mL/min in the first dimension (D1), and the collected fractions further flowed to a Waters Xbridge C18 column(5 μm, 4.6 mm × 250 mm) with a mobile phase consisting of 0.1 % formic acid and acetonitrile (95:5 v/v) at the same flow rate as the second dimension(D2). Two of the impurities were never reported as the degradation of metformin, and all the four structures, as well as the proposed fragmentation patterns were inferred in this research.

Degradation of metformin in water by TiO2-ZrO2 photocatalysis

The increasing use of pharmaceutical products also increases their release in aquatic environment. These contaminants are considered emerging pollutants, and induce adverse ecological and human health effects. The antidiabetic metformin is one example that has been detected in the aquatic environment at unusual concentrations. This fact indicates that conventional wastewater treatment is inefficient on eliminating this compound. Here we show that metformin can be effectively removed from water by photocatalysis. We found the optimised conditions for pH and concentration of catalyst on the photocatalytic process. TiO₂ and TiO₂-ZrO₂ were successful in oxidising metformin under UV radiation following a pseudo-first order kinetics. Intermediates of metformin photodegradation appeared after photocatalytic treatment. Toxicity analysis showed that the degradation products are non-toxic to Lactuca sativa seeds.

Ultraviolet photolysis of metformin: mechanisms of environmental factors, identification of intermediates, and density functional theory calculations

As a commonly used anti-diabetic drug, metformin (MEF) is frequently detected in different water bodies which pose a potential threat to human health and the ecological environment. In this study, oxidative degradation of MEF under ultraviolet (UV) light was studied, and its influencing factors, photolysis mechanism, and intermediates identification carried out as well. The results showed that the hydroxyl radical contributed 73% during the 6 h MEF photolysis process among the reactive oxygen species (ROS). In addition, triplet excited-state organic matter and singlet oxygen also played a role in the photolysis process. The reaction rates of hydroxyl radical and singlet oxygen with MEF are (6.45 ± 0.4) × 10⁹ and (5.4 ± 0.7) × 10⁶ L·(mol s)^-1, respectively. By calculating the light screening effect of environmental factors, it is found that the presence of NO₃^- and Cl^- had a greater excitation effect on ROS than the screening effect, and generally promoted the photolysis rates of MEF from 90.3 to 193.5% and from 16.1 to 80.6% during the 6-h reaction process, respectively. For bicarbonate and fulvic acid, the light screening effects were dominant and inhibited photolysis rates by 10-52% and 13-71%, respectively. The results demonstrated that the photoreactivity of environmental factors in water is the cause of the different photodegradation rates of MEF. The oxidative degradation product of MEF under UV light was detected by UPLC/Q-TOF as methylbiguanide (MBG), 2,4-diamino-1,3,5-triazine (2,4-DAT), biguanide (BGN), 1,1-dimethylguanidine (1,1-DiMBG), 4-amino-2-imino-1-methyl-1,2-dihydro-1, 3,5-triazine (4,2,1-AIMT), and 2-amino-4-methylamino-1,3,5-triazine (2,4-AMT). The result which showed that the primary sites of ∙OH attacked is consistent with that of density functional theory calculation. Graphical abstract.

Formation and occurrence of transformation products of metformin in wastewater and surface water

The aim of this work was to investigate the occurrence and fate of the antidiabetic metformin (MF) and its transformation products (TPs) in wastewater and surface water samples. New TPs of MF were approached by electrochemical degradation with a boron-doped-diamond electrode (at 1.5V for 10min). 2,4-Diamino-1,3,5-triazine (2,4-DAT), methylbiguanide (MBG), 2-amino-4-methylamino-1,3,5-triazine (2,4-AMT) and 4-amino-2-imino-1-methyl-1,2-dihydro-1,3,5-triazine (4,2,1-AIMT) were identified by hydrophilic interaction chromatography (HILIC) with quadrupole time-of-flight mass spectrometry (QTOF-MS) and accurate mass fragmentation. However, the well-known transformation product guanyl urea (GU) could not be formed electrochemically. In samples from wastewater treatment plants (WWTP), 2,4-AMT and 2,4-DAT showed an increasing trend from influents to effluents, which implies formation of the TPs during WWT. MBG is also formed by hydrolysis of MF and therefore didn't show this trend in WWTPs. Compared to GU, the concentrations of other TPs are generally three orders of magnitude lower. MBG and 2,4-DAT were also detected in surface water which was impacted by waste water, while 4,2,1-AIMT could not be detected in any sample. The concentrations of MF were in an expected range for influent (14 to 95μg/l), effluent (0.7 to 6.5μg/l), surface water (up to 234ng/l) and tap water (34ng/l). GU concentrations, however, were in one of the two investigated WWTP much higher in the influent (between 158μg/l and 2100μg/l) than in the effluent (between 26 and 810μg/l). This is a rather unexpected result which has not been reported yet. Obviously, GU has been already formed in parts of the sewer system from MF or from other biguanide compounds like antidiabetics or disinfection chemicals. Furthermore, lower concentrations of GU in the effluents than in the influents indicate degradation processes of guanyl urea in the waste water treatment.

A global perspective on the use, occurrence, fate and effects of anti-diabetic drug metformin in natural and engineered ecosystems

Metformin is the most commonly used anti-diabetic drug in the world. When consumed, this unmetabolised pharmaceutical compound is excreted by the body and eventually enters the environment through a variety of pathways. Based on its high consumption and excretion rates, high concentrations of metformin have been detected in influents of wastewater treatment plants. Metformin and its transformation product, guanylurea, are also expected to be present in other aquatic environments based on their physico-chemical properties. Not surprisingly, guanylurea has also been detected in surface water, groundwater, and drinking water. Available information on ecotoxicological effects of metformin suggests that metformin is a potential endocrine disruptor and thus further emphasising the threat this drug could pose to our environment. This review provides a comprehensive overview of metformin and critically discusses available literature data with respect to its global use/demand, occurrence, fate and ecotoxicity in treatment facilities equipped with conventional and advanced treatment technologies, and its degradation/removal mechanisms. Final section highlights the existing knowledge gaps regarding its ultimate fate under the natural and engineered ecosystems and identifies some important research areas requiring urgent attention from regulatory makers and scientific community.

Uptake, translocation and possible biodegradation of the antidiabetic agent metformin by hydroponically grown Typha latifolia

The increasing load of pharmaceutical compounds has raised concerns about their potential residues in aquatic environments and ecotoxicity. Metformin (MET), a widely prescribed antidiabetic II medicine, has been detected in high concentration in sewage and in wastewater treatment effluents. An uptake and translocation study was carried out to assess the ultimate fate of MET in phytoremediation. MET was removed from media by Typha latifolia, and the removal processes followed first order kinetics. After 28 days, the removal efficiencies were in a range of 74.0±4.1-81.1±3.3%. In roots, MET concentration was increasing during the first two weeks of the experiment but thereafter decreasing. In contrast, MET concentration was continuously increasing in rhizomes and leaves. Bioaccumulation of MET in roots was much higher than in leaves and rhizomes. As degradation product of metformin in the plant, methylbiguanide (MBG) was detected whereas guanylurea was undetectable. Moreover, MBG concentration in roots was increasing with exposure time. An enzymatic degradation experiment showed the degradation rate followed the order of MET<MBG<<guanylurea. This may explain the low concentration of MBG in plant. The findings of this study contribute to understand and evaluate the potential for phytoremediation of such kind of contaminants.

Comprehensive study of the antidiabetic drug metformin and its transformation product guanylurea in Greek wastewaters

Many pollutants such as pharmaceuticals and their transformation products (TPs) are not efficiently removed from wastewater treatment plants and enter into surface waters. The aim of this study was to investigate the occurrence and behavior of metformin, one of the most prescribed drugs worldwide, and its biological transformation product guanylurea, in eight wastewater treatment plants (WWTPs) of Greece. All WWTPs were equipped with conventional activated sludge treatment and the samples were taken from the influents and the effluents, over the four seasons of one year. The analytical method developed based on SPE followed by LC-UV/Vis-ESI/MS analysis, while positive findings were confirmed also by means of LTQ Orbitrap mass spectrometer. High polarity of both compounds led to the extraction with Oasis HLB and the use of the anionic surfactant SDS. The results showed that metformin dominated in the influents (bql-1167 ng/L), while guanylurea in the effluents (bql-627 ng/L) of the wastewater treatment plants, with Metformin/Guanylurea ratio ranging between 0.88 and 81.3 in the influents and between 0.005 and 0.78 in the effluents. Lack of a clear seasonal tendency in the occurrence and removal or formation was observed. Finally, an ecotoxicological risk assessment of metformin in effluent wastewaters took place by calculating the ratio between the environmental concentrations (MEC) and the predicted no effect concentrations (PNEC). Despite the fact that metformin presented low risk in all cases, an environmental concern is suspected for guanylurea since it is continuously released into the aquatic environment.

Fast and environmentally friendly quantitative analysis of active agents in anti-diabetic tablets by an alternative laser-induced breakdown spectroscopy (LIBS) method and comparison to a validated reversed-phase high-performance liquid chromatography (RP-HPLC) method

Laser-induced breakdown spectroscopy (LIBS) is evaluated as a potential analytic technique for rapid screening and quality control of anti-diabetic tablets. This paper proposes a simple LIBS-based method for the quantitative analysis of two active pharmaceutical ingredients (APIs): metformin (Met) and glybenclamide (Gly). In order to quantify both APIs, chlorine (Cl) concentration was estimated by employing the Cl/Br optical emission ratio, where Br was introduced as internal standard. Calibration curves were prepared, achieving linearity higher than 99%. On the other hand, for comparison to the proposed method, an isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) method was also developed for quantitative determination of the same analytes by ultraviolet (UV) detection. The chromatographic separation was achieved on a Phenomenex Hypersil C18, 250 mm × 4.6 mm, 5 μm column. The mobile phase was K(2)HPO(4)/H(3)PO(4)-CH(3)OH and flow rate was 1.0 mL min(-1). The method is linear over a range of 10-60 μg mL(-1) for Gly and 5-30 μg mL(-1) for Met and the correlation coefficients were ≥0.99. Recoveries were found to be in the range of 95-101%. Furthermore, four different commercial brands of each active agent were evaluated by both proposed LIBS and chromatographic methods and results were compared with each other. The comparison was satisfactorily validated by analysis of variance (ANOVA).

Occurrence and fate of the antidiabetic drug metformin and its metabolite guanylurea in the environment and during drinking water treatment

Metformin, an antidiabetic drug with one of the highest consumption rates of all pharmaceuticals worldwide, is biologically degraded to guanylurea in wastewater treatment plants. Due to high metformin influent concentrations of up to 100 μg/L and its high but incomplete degradation both compounds are released in considerable amounts of up to several tens of μg/L into recipient rivers. This is the first systematic study on their environmental fate and the effectiveness of treatment techniques applied in waterworks to remove metformin and guanylurea from surface water influenced raw waters. The concentrations in surface waters depend strongly on the respective wastewater burden of rivers and creeks and are typically in the range of about 1 μg/L for metformin and several μg/L for guanylurea but can reach elevated average concentrations of more than 3 and 20 μg/L, respectively. Treatment techniques applied in waterworks were investigated by an extended monitoring program in three facilities and accompanied by laboratory-scale batch tests. Flocculation and activated carbon filtration proved to be ineffective for removal of metformin and guanylurea. During ozonation and chlorination experiments with waterworks-relevant ozone and chlorine doses they were partly transformed to yet unknown compounds. The effectiveness of the treatment steps under investigation can be ordered chlorination > ozonation > activated carbon filtration > flocculation. However, most effective for removal of both compounds at the three full-scale waterworks studied proved to be an underground passage (riverbank filtration or artificial groundwater recharge). A biological degradation is most likely as sorption can be neglected. This is based on laboratory batch tests conducted with three different soil materials according to OECD guideline 106. Since such treatment steps were implemented in all three drinking water treatment plants, even traces of metformin and its metabolite guanylurea could not be detected at the end of the treatment trains. Both can only be expected in finished drinking water if surface influenced raw water is used by direct abstraction without underground passage.

Incomplete aerobic degradation of the antidiabetic drug Metformin and identification of the bacterial dead-end transformation product Guanylurea

Active pharmaceutical ingredients as well as personal care products are detected in increasing prevalence in different environmental compartments such as surface water, groundwater and soil. Still little is known about the environmental fate of these substances. The type II antidiabetic drug Metformin has already been detected in different surface waters worldwide, but concentrations were significantly lower than the corresponding predicted environmental concentration (PEC). In human and mammal metabolism so far no metabolites of Metformin have been identified, so the expected environmental concentrations should be very high. To assess the aerobic biodegradability of Metformin and the possible formation of degradation products, three Organisation of Economic Cooperation and Development (OECD) test series were performed in the present study. In the Closed Bottle test (OECD 301 D), a screening test that simulates the conditions of an environmental surface water compartment, Metformin was classified as not readily biodegradable (no biodegradation). In the Manometric Respiratory test (OEDC 301 F) working with high bacterial density, Metformin was biodegraded in one of three test bottles to 48.7% and in the toxicity control bottle to 57.5%. In the Zahn-Wellens test (OECD 302 B) using activated sludge, Metformin was biodegraded in both test vessels to an extent of 51.3% and 49.9%, respectively. Analysis of test samples by high performance liquid chromatography coupled to multiple stage mass spectrometry (HPLC-MS(n)) showed in the tests vessels were biodegradation was observed full elimination of Metformin and revealed Guanylurea (Amidinourea, Dicyandiamidine) as single and stable aerobic bacterial degradation product. In another Manometric Respiratory test Guanylurea showed no more transformation. Photodegradation of Guanylurea was also negative. A first screening in one of the greatest sewage treatment plant in southern Germany found Metformin with high concentrations (56.8 μg L⁻¹) in the influent (PEC=79.8 μg L⁻¹), but effluent concentration was much lower (0.76 μg L⁻¹) whereas Guanylurea was detected in a low influent and high effluent concentration (1.86 μg L⁻¹). These data support the experimental findings in the OECD tests and analytical results of other studies, that Metformin under aerobic conditions can bacterially be degraded to the stable dead-end transformation product Guanylurea.

Identification of pharmaceutical impurities in formulated dosage forms

Structure elucidation of pharmaceutical impurities is an important part of the drug product development process. Impurities can have unwanted pharmacological or toxicological effects that seriously impact product quality and patient safety. This review focuses on current analytical strategies for chemical and structural identification of pharmaceutical impurities. Potential sources and mechanisms of impurity formation are discussed for both drug substance and drug product applications. The utility of liquid chromatography-mass spectrometry (LC/MS) for providing structure-rich information is highlighted throughout this review. Other hyphenated analytical techniques including LC/nuclear magnetic resonance, gas chromatography/MS, and size-exclusion chromatography/chemiluminescent nitrogen detectors are also discussed, as LC/MS alone sometimes cannot reveal or confirm the final structures as required during dosage form development.

Theoretical Investigation of the Formation of a New Series of Antioxidant Depsides from the Radiolysis of Flavonoid Compounds

This paper deals with the formation of a series of antioxidant depsides obtained from flavonoid solutions irradiated with gamma rays. These reactions take place in radiolyzed alcohol solutions, a medium that is very rich in many different highly reactive species and that hosts specific reactions. We focus on the first step of those reactions, i.e., reactivity of the solute (flavonoid) with the alkoxy radicals CH(3)O(*) and CH(3)CH(2)O(*) formed in methanol and ethanol, respectively, and their carbon-centered isomers: the 1-hydroxy-methyl ((*)CH(2)OH) and the 1-hydroxy-ethyl (CH(3)(*)CHOH) radicals. Among the different flavonoid groups of molecules, only flavonols are transformed. To establish the structure-reactivity relationship that explains why the radiolytic transformation occurs only for those compounds, the process is rationalized theoretically, with Density Functional Theory calculations, taking into account the solvent effects by a Polarizable Continuum Model and a microhydrated environment (one or two water molecules surrounding the active center). The first redox reaction, occurring between the flavonol and the reactive species formed upon irradiation of the solvent, is studied in terms of (1) the O-H bond dissociation enthalpy of each OH group of the flavonoids and (2) electron abstraction from the molecule. We conclude that the reaction, initiated preferentially by the alkoxy radicals, first occurs at the 3-OH group of the flavonol. It is then followed by the formation of a peroxyl radical (after molecular oxygen or superoxide addition). The different cascades of reactions, which lead to the formation of depsides via C-ring opening, are discussed on the basis of the corresponding calculated energetic schemes.

Radical-induced oxidation of metformin

Metformin (1,1-dimethylbiguanide) is an antihyperglycaemic drug used to normalize glucose concentrations in type 2 diabetes. Furthermore, antioxidant benefits have been reported in diabetic patients treated with metformin. This work was aimed at studying the scavenging capacity of this drug against reactive oxygen species (ROS) like *OH and (O2*-)-free radicals. ROS were produced by gamma radiolysis of water. The irradiated solutions of metformin were analyzed by UV/visible absorption spectrophotometry. It has been shown that hydroxyl free radicals react with metformin in a concentration-dependent way. The maximum scavenging activity was obtained for concentrations of metformin > or = 200 micromol.L(-1), under our experimental conditions. An estimated value of 10(7) L.mol(-1).s(-1) has been determined for the second order rate constant k(*OH + metformin). Superoxide free radicals and hydrogen peroxide do not initiate any oxidation on metformin in our in vitro experiments.