Todd Zelesky

Degradation and Impurity Analysis for Pharmaceutical Drug Candidates

Abstract The objective of this chapter is to give guidance with degradation and impurity structure elucidation for pharmaceutical drug candidates. Stress testing knowledge is provided as guidance in developing and executing forced degradation experiments. Impurity and degradant structure elucidation is a collaborative effort involving the degradation chemist, analytical chemist, process chemist, and/or formulator, as well as the isolation chemist, mass spectrometry and NMR experts. Updates in this second addition include: (1) the use of quality by design (QbD) model as applied to stress testing practices, expanded oxidative experimental analysis, and expanded information on predictive programs. (2) The impact of supercritical fluid chromatography as a tool for impurity isolations, along with expanded information on process workflow. (3) Mass spectrometry: additional examples and a section on the use of accurate mass information in the role of structure elucidation. (4) Expansion on the use of NMR as applied to structure characterization and elucidation. (5) In‐depth case studies that illustrate collaborative efforts made between disciplines, as well as the impact that new technologies have on the structure elucidation process.

A practical application of two in silico systems for identification of potentially mutagenic impurities

The International Conference on Harmonization (ICH) M7 guidance for the assessment and control of DNA reactive impurities in pharmaceutical products includes the use of in silico prediction systems as part of the hazard identification and risk assessment strategy. This is the first internationally agreed guidance document to include the use of these types of approaches. The guideline requires the use of two complementary approaches, an expert rule-based method and a statistical algorithm. In addition, the guidance states that the output from these computer-based assessments can be reviewed using expert knowledge to provide additional support or resolve conflicting predictions. This approach is designed to maximize the sensitivity for correctly identifying DNA reactive compounds while providing a framework to reduce the number of compounds that need to be synthesized, purified and subsequently tested in an Ames assay. Using a data set of 801 chemicals and pharmaceutical intermediates, we have examined the relative predictive performances of some popular commercial in silico systems that are in common use across the pharmaceutical industry. The overall accuracy of each of these systems was fairly comparable ranging from 68% to 73%; however, the sensitivity of each system (i.e. how many Ames positive compounds are correctly identified) varied much more dramatically from 48% to 68%. We have explored how these systems can be combined under the ICH M7 guidance to enhance the detection of DNA reactive molecules. Finally, using four smaller sets of molecules, we have explored the value of expert knowledge in the review process, especially in cases where the two systems disagreed on their predictions, and the need for care when evaluating the predictions for large data sets.

Use of Activated Carbon in Packaging to Attenuate Formaldehyde-Induced and Formic Acid–Induced Degradation and Reduce Gelatin Cross-Linking in Solid Dosage Forms

Formaldehyde and formic acid are reactive impurities found in commonly used excipients and can be responsible for limiting drug product shelf-life. Described here is the use of activated carbon in drug product packaging to attenuate formaldehyde-induced and formic acid-induced drug degradation in tablets and cross-linking in hard gelatin capsules. Several pharmaceutical products with known or potential vulnerabilities to formaldehyde-induced or formic acid-induced degradation or gelatin cross-linking were subjected to accelerated stability challenges in the presence and absence of activated carbon. The effects of time and storage conditions were determined. For all of the products studied, activated carbon attenuated drug degradation or gelatin cross-linking. This novel use of activated carbon in pharmaceutical packaging may be useful for enhancing the chemical stability of drug products or the dissolution stability of gelatin-containing dosage forms and may allow for the 1) extension of a drug products shelf-life when the limiting attribute is a degradation product induced by a reactive impurity, 2) marketing of a drug product in hotter and more humid climatic zones than currently supported without the use of activated carbon, and 3) enhanced dissolution stability of products that are vulnerable to gelatin cross-linking.

Electrochemical oxidation coupled with liquid chromatography and mass spectrometry to study the oxidative stability of active pharmaceutical ingredients in solution: A comparison of off-line and on-line approaches

Stability studies of pharmaceutical drug products and pharmaceutical active substances are important to research and development in order to fully understand and maintain product quality and safety throughout its shelf-life. Oxidative forced degradation studies are among the different types of stability studies performed by the pharmaceutical industry in order to understand the intrinsic stability of drug molecules. We have been comparing the use of electrochemistry as an alternative oxidative forced degradation method to traditional forced degradation and accelerated stability studies. Using the electrochemical degradation approach the substrate oxidation takes place in a commercially available electrochemical cell and the effluent of the cell can be either a) directly infused into the mass spectrometer or b) injected in a chromatographic column for separation of the different products formed prior to the mass spectrometry analysis. To enable the study of large numbers of different experimental conditions and molecules we developed a new dual pump automated electrochemical screening platform. This system used a HPLC pump and autosampler to load and wash the electrochemical cell and deliver the oxidized sample plug to a second injection loop. This system enabled the automatic sequential analyses of large numbers of different solutions under varied experimental conditions without need for operator intervention during the run sequence. Here we describe the system and evaluate its performance using a test molecule with well characterized stability and compare results to those obtained using an off-line electrochemistry approach.

The application of electrochemistry to pharmaceutical stability testing--comparison with in silico prediction and chemical forced degradation approaches.

The aim of this study was to evaluate the use of electrochemistry to generate oxidative degradation products of a model pharmaceutical compound. The compound was oxidized at different potentials using an electrochemical flow-cell fitted with a glassy carbon working electrode, a Pd/H2 reference electrode and a titanium auxiliary electrode. The oxidative products formed were identified and structurally characterized by LC-ESI-MS/MS using a high resolution Q-TOF mass spectrometer. Results from electrochemical oxidation using electrolytes of different pH were compared to those from chemical oxidation and from accelerated stability studies. Additionally, oxidative degradation products predicted using an in silico commercially available software were compared to those obtained from the various experimental methods. The electrochemical approach proved to be useful as an oxidative stress test as all of the final oxidation products observed under accelerated stability studies could be generated; previously reported reactive intermediate species were not observed most likely because the electrochemical mechanism differs from the oxidative pathway followed under accelerated stability conditions. In comparison to chemical degradation tests electrochemical degradation has the advantage of being much faster and does not require the use of strong oxidizing agents. Moreover, it enables the study of different operating parameters in short periods of time and optimisation of the reaction conditions (pH and applied potential) to achieve different oxidative products mixtures. This technique may prove useful as a stress test condition for the generation of oxidative degradation products and may help accelerate structure elucidation and development of stability indicating analytical methods.

Artifactual degradation of secondary amine-containing drugs during accelerated stability testing when saturated sodium nitrite solutions are used for humidity control

Graphical abstract Figure. No caption available. HighlightsSecondary amines are susceptible to artifactual nitrosative degradation.Mechanism involves volatilization of nitric oxide from saturated NaNO2 solution.NaNO2 solutions should be avoided for humidity control during stability testing. ABSTRACT Accelerated stability studies of pharmaceutical products are commonly conducted at various combinations of temperature and relative humidity (RH). The RH of the sample environment can be controlled to set points using humidity‐controlled stability chambers or via storage of the sample in a closed container in the presence of a saturated aqueous salt solution. Herein we report an unexpected N‐nitrosation reaction that occurs upon storage of carvedilol‐ or propranolol‐excipient blends in a stability chamber in the presence of saturated sodium nitrite (NaNO2) solution to control relative humidity (˜60% RH). In both cases, the major products were identified as the corresponding N‐nitroso derivatives of the secondary amine drugs based on mass spectrometry, UV–vis and retention time. These degradation products were not observed upon storage of the samples at the same temperature and humidity but in the presence of saturated potassium iodide (KI) solution (˜60% RH) for humidity control. The levels of the N‐nitrosamine derivatives varied with the pH of various NaNO2 batches. The presence of volatile NOx species in the headspace of a container containing saturated NaNO2 solution was confirmed via the Griess assay. The process for formation of the N‐nitrosamine derivatives is proposed to involve volatilization of nitric oxide (NO) from aqueous nitrite solution into the headspace of the container followed by diffusion into the solid drug‐excipient blend and subsequent reaction of NOx with the secondary amine.