Stability behaviour of antiretroviral drugs and their combinations. 5: Characterization of novel degradation products of abacavir sulfate by mass and nuclear magnetic resonance spectrometry

Comparison of Chemical and Electrochemical Approaches to Abacavir Oxidative Stability Testing

A novel electrochemical approach using two different electrode materials, platinum and boron-doped diamond (BDD), was employed to study the oxidative stability of the drug abacavir. Abacavir samples were subjected to oxidation and subsequently analysed using chromatography with mass detection. The type and amount of degradation products were evaluated, and results were compared with traditional chemical oxidation using 3% hydrogen peroxide. The effect of pH on the rate of degradation and the formation of degradation products were also investigated. In general, both approaches led to the same two degradation products, identified using mass spectrometry, and characterised by 319.20 and m/z 247.19. Similar results were obtained on a large-surface platinum electrode at a potential of +1.15 V and a BDD disc electrode at +4.0 V. Degradation of 20% of abacavir, the rate required for pharmaceutical stability studies, took only a few minutes compared to hours required for oxidation with hydrogen peroxide. Measurements further showed that electrochemical oxidation in ammonium acetate on both types of electrodes is strongly pHdependent. The fastest oxidation was achieved at pH 9. The pH also affects the composition of the products, which are formed in different proportions depending on the pH of the electrolyte.

Characterization of stress degradation products of nintedanib by UPLC, UHPLC-Q-TOF/MS/MS and NMR: Evidence of a degradation product with a structure alert for mutagenicity

Nintedanib is an anti-cancer drug used for the treatment of idiopathic pulmonary fibrosis and non-small cell lung cancer. The purpose of this study was to explore its degradation chemistry under various stress conditions recommended in ICH guidelines Q1A R(2). The drug was subjected to hydrolytic, photolytic, thermal and oxidative (H₂O₂, AIBN, FeCl₃ and FeSO₄) stress conditions. The degradation products formed in stressed solutions were successfully separated on an ACQUITY UPLC CSH C18 (2.1 × 100 mm, 1.7 μm) column, using a gradient UPLC-PDA method, developed with acetonitrile:methanol (90:10) and 0.1 % formic acid (pH 3.0) as the mobile phase. The drug proved to be labile to acidic, neutral and alkaline hydrolytic, and H₂O₂/AIBN oxidative conditions. It was stable to photolytic and thermal stress conditions, and even in oxidative reaction solutions containing FeCl₃ or FeSO₄. Additionally, the drug exhibited instability when its powder with added sodium bicarbonate was stored at 40 °C/75 % RH for 3 months. In total, nine degradation products (DPs 1-9) were formed. To characterize them, a comprehensive mass fragmentation pathway of the drug was first established using UHPLC-Q-TOF/MS/MS data. Similarly, the mass studies were then carried out on the stressed samples using the developed UPLC method. All the degradation products were primarily characterized through comparison of their mass fragmentation profiles with that of the drug. To confirm the structure in one case (DP 3), additional nuclear magnetic resonance (NMR) studies were carried out on the isolated product. Subsequently, mechanisms for their formation were laid down. A significant finding was the formation of a degradation product upon acid hydrolysis having a free aromatic amine moiety, which is considered as a structural alert for mutagenicity. Furthermore, the physicochemical and ADMET properties of the drug and its degradation products were predicted using ADMET predictor™ software.

Stability behaviour of antiretroviral drugs and their combinations. 11: Characterization of interaction products of zidovudine and efavirenz, and evaluation of their anti HIV-1 activity, and physiochemical and ADMET properties

Zidovudine (ZDV) and efavirenz (EFV), which belong to two separate classes of antiretroviral drugs, viz., NRTI and NNRTI, respectively, were subjected to different stability test conditions alone and in solid mixtures to evaluate possibility of interaction among them. The exposed samples were analyzed by high performance liquid chromatography (HPLC) using a C18 column and a PDA detector. Two new peaks were observed in the sample in which 50 μl CH₃CN was added to increase the contact among the drugs, and which was subjected in open beaker to accelerated stability test condition of 40 °C/75%RH for 15 d. Subsequently, liquid chromatography-high resolution mass spectrometric (LC-HRMS) studies were carried out to obtain their accurate mass. The products were also isolated, and subjected to ¹H, ¹³C, DEPT-135, COSY, HSQC and HMBC nuclear magnetic resonance (NMR) studies. The collective information allowed their structural characterization as isomeric cycloaddition products of the two drugs. As these were novel compounds, they were subjected to testing for cytotoxicity and in vitro anti-HIV-1 activity against primary isolates HIV-1_UG070 (X4, subtype D) and HIV-1_VB59 (R5, subtype C) in TZM-bl cell line. The two were found to show weak activity against the standard drugs. The reason was sought through molecular docking studies, which highlighted that it was perhaps their comparative bigger molecular size than the drugs of both classes used currently in HIV therapy. Being previously unknown molecules, their in silico physicochemical and ADMET properties were also evaluated using ADMET Predictor™ and TOPKAT software.

Reverse Transcriptase Inhibitors Nanosystems Designed for Drug Stability and Controlled Delivery

An in-depth analysis of nanotechnology applications for the improvement of solubility, distribution, bioavailability and stability of reverse transcriptase inhibitors is reported. Current clinically used nucleoside and non-nucleoside agents, included in combination therapies, were examined in the present survey, as drugs belonging to these classes are the major component of highly active antiretroviral treatments. The inclusion of such agents into supramolecular vesicular systems, such as liposomes, niosomes and lipid solid NPs, overcomes several drawbacks related to the action of these drugs, including drug instability and unfavorable pharmacokinetics. Overall results reported in the literature show that the performances of these drugs could be significantly improved by inclusion into nanosystems.

Stability behavior of antiretroviral drugs and their combinations. 7: Comparative degradation pathways of lamivudine and emtricitabine and explanation to their differential degradation behavior by density functional theory

The interest in this study was to establish comparative degradation behavior of lamivudine (3TC) and emtricitabine (FTC) under solution and solid state stress conditions. Structurally, the two drugs differ only in terms of additional fluorine at 5 position in FTC. Along with the known degradation products of both the drugs, one additional degradation product was observed in each case, which was characterized by mass spectrometry. Both the drugs degraded via the same route, but at a differential rate in acid, base and oxidative stress conditions. The variable rate of degradation in acid and base conditions was justified by the application of density functional theory (DFT).