Pharmaceutical Forced Degradation (Stress Testing) Endpoints: A Scientific Rationale and Industry Perspective.

Forced degradation (i.e., stress testing) of small molecule drug substances and products is a critical part of the drug development process, providing insight into the intrinsic stability of a drug that is foundational to the development and validation of stability-indicating analytical methods. There is a lack of clarity in the scientific literature and regulatory guidance as to what constitutes an "appropriate" endpoint to a set of stress experiments. That is, there is no clear agreement regarding how to determine if a sample has been sufficiently stressed. Notably, it is unclear what represents a suitable justification for declaring a drug substance (DS) or drug product (DP) "stable" to a specific forced degradation condition. To address these concerns and to ensure all pharmaceutically-relevant, potential degradation pathways have been suitably evaluated, we introduce a two-endpoint classification designation supported by experimental data. These two endpoints are 1) a % total degradation target outcome (e.g., for "reactive" drugs) or, 2) a specified amount of stress, even in the absence of any degradation (e.g., for "stable" drugs). These recommended endpoints are based on a review of the scientific literature, regulatory guidance, and a forced degradation data set from ten global pharmaceutical companies. The experimental data set, derived from the Campbell et al. (2022) benchmarking study,1 provides justification for the recommendations. Herein we provide a single source reference for small molecule DS and DP forced degradation stress conditions and endpoint best practices to support regulatory submissions (e.g., marketing applications). Application of these forced degradation conditions and endpoints, as part of a well-designed, comprehensive and a sufficiently rigorous study plan that includes both the DS and DP, provides comprehensive coverage of pharmaceutically-relevant degradation and avoids unreasonably extreme stress conditions and drastic endpoint recommendations sometimes found in the literature.

Assessing the Relevance of Solution Phase Stress Testing of Solid Dosage Form Drug Products: A Cross-Industry Benchmarking Study.

Stress testing (also known as forced degradation) of pharmaceutical products has long been recognized as a critical part of the drug development process, providing foundational information related to intrinsic stability characteristics and to the development of stability-indicating analytical methods. A benchmarking study was undertaken by nine pharmaceutical companies and the Brazilian Health Regulatory Agency (Agência Nacional de Vigilância Sanitária, or ANVISA) with a goal of understanding the utility of various stress testing conditions for producing pharmaceutically-relevant chemical degradation of drugs. Special consideration was given to determining whether solution phase stress testing of solid drug products produced degradation products that were both unique when compared to other stress conditions and relevant to the formal drug product stability data. The results from studies of 62 solid dosage form drug products were compiled.  A total of 387 degradation products were reported as being observed in stress testing studies, along with 173 degradation products observed in accelerated and/or long-term stability studies for the 62 drug products.  Among these, 25 of the stress testing degradation products were unique to the solution phase stress testing of the drug products; however, none of these unique degradation products were relevant to the formal stability data. The relevant degradation products were sufficiently accounted for by stress testing studies that included only drug substance stressing (in solution and in the solid state) and drug product stressing (in the solid state). Based on these results, it is the opinion of the authors that for solid dosage form drug products, well-designed stress testing studies need not include solution phase stress testing of the drug product in order to be comprehensive.

The Degradation Chemistry of Prasugrel Hydrochloride: Part 1-Drug Substance.

Prasugrel hydrochloride is the active ingredient in Effient™, a thienopyridine platelet inhibitor. An extensive study of the degradation chemistry of prasugrel hydrochloride (LY640315 hydrochloride) has been carried out on the drug substance (part I) and on the drug product (part II, future article) using a multidimensional approach including hydrolytic, oxidative, and photolytic stressing, computational chemistry, HPLC analysis, and structure elucidation by various spectroscopic techniques. The major degradation products formed from the drug substance under the various stress conditions have been isolated and structures unambiguously determined, and the pathways leading to these products have been proposed. Fourteen new (not previously disclosed) products were discovered and characterized, in addition to 4 degradation products that had been previously identified in the literature. The pathways indicate that prasugrel is susceptible to hydrolysis, autoxidation (both radical-initiated and single-electron mediated), and peroxide-mediated oxidation; in solution, prasugrel is susceptible to photodegradation.

Degradation Rate Observations as a Function of Drug Load in Solid-State Drug Products.

Degradation rates of solid-state drug products generally increase as the drug load decreases. A model for quantifying this effect based on surface area ratios is proposed here. This model relates the degradation rate to an estimate of the proportion of drug substance in contact with the excipient, and that the drug substance in contact with excipients degrades more quickly. Degradation data from previously published case studies and from 5 new case studies were found to be consistent with our proposed model; our model performed better than similar previously published models. It was also found that the relationship between degradation rate and drug load is largely independent of the temperature and humidity conditions, suggesting that drug load solely affects the pre-exponential factor of the Arrhenius equation and does not significantly affect the activation energy of the degradation process. A second method for calculating the proportion of the drug substance surface in contact with the excipient surface is presented in the Supplementary Material. Fundamentally, the 2 methods are very similar and provide almost identical fits to the experimental data.

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

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.

Mechanistic Studies of the N-formylation of Edivoxetine, a Secondary Amine-Containing Drug, in a Solid Oral Dosage Form.

Edivoxetine (LY2216684 HCl), although a chemically stable drug substance, has shown the tendency to degrade in the presence of carbohydrates that are commonly used tablet excipients, especially at high excipient:drug ratios. The major degradation product has been identified as N-formyl edivoxetine. Experimental evidence including solution and solid-state investigations, is consistent with the N-formylation degradation pathway resulting from a direct reaction of edivoxetine with (1) formic acid (generated from decomposition of microcrystalline cellulose or residual glucose) and (2) the reducing sugar ends (aldehydic carbons) of either residual glucose or the microcrystalline cellulose polymer. Results of labeling experiments indicate that the primary source of the formyl group is the C1 position from reducing sugars. Presence of water or moisture accelerates this degradation pathway. Investigations in solid and solution states support that the glucose Amadori Rearrangement Product does not appear to be a direct intermediate leading to N-formyl degradation of edivoxetine, and oxygen does not appear to play a significant role. Solution-phase studies, developed to rapidly assess propensity of amines toward Maillard reactivity and formylation, were extended to show comparative behavior with example systems. The cyclic amine systems, such as edivoxetine, showed the highest propensity toward these side reactions.

Determination of the Degradation Chemistry of the Antitumor Agent Pemetrexed Disodium.

Stress-testing (forced degradation) studies have been conducted on pemetrexed disodium heptahydrate (1) (LY231514·2Na·7H2O) drug substance in order to identify its likely degradation products and establish its degradation pathways. Solid samples of the drug substance were stressed under various conditions of heat, humidity, and light, and solutions of the drug substance were stressed under various conditions of heat, light, oxidation, and over a wide pH range (1-13). The stressed samples were analyzed using a gradient elution reversed-phase HPLC method. The 7 major degradation products detected in the stress-testing studies were isolated, and the structures were elucidated via spectroscopic characterization. The structures of the degradation products and their proposed mechanisms of formation indicate that 1 degrades via 2 main pathways: oxidation and hydrolysis. Of the 7 identified degradation products, 6 are proposed to result from oxidation and 1 from hydrolysis.

Implications of In-Use Photostability: Proposed Guidance for Photostability Testing and Labeling to Support the Administration of Photosensitive Pharmaceutical Products, Part 3. Oral Drug Products.

The ICH Q1B guidance and additional clarifying manuscripts provide the essential information needed to conduct photostability testing for pharmaceutical drug products in the context of manufacturing, packaging, and storage. As the previous 2 papers in this series highlight for drug products administered by injection (part 1) and drug products administered via topical application (part 2), there remains a paucity of guidance and methodological approaches to conducting photostability testing to ensure effective product administration. Part 3 in the series is presented here to provide a similar approach and commentary for photostability testing for oral drug products. The approach taken, as was done previously, is to examine "worst case" photoexposure scenarios in combination with ICH-defined light sources to derive a set of practical experimental approaches to support the safe and effective administration of photosensitive oral drug products.

Formation of copper(I) from trace levels of copper(II) as an artifactual impurity in the HPLC analysis of olanzapine.

An analytical artifact peak appearing to be an impurity was observed intermittently among several laboratories performing HPLC analyses of olanzapine drug substance and formulation samples. The artifact peak was identified as Cu(I) that was formed from the reaction of trace amounts of Cu(II) with olanzapine in the sample solution. Unlike Cu(II), Cu(I) was retained under the ion-pairing HPLC conditions used for analysis. A reaction mechanism was postulated whereby Cu(II) present in the sample solution oxidizes olanzapine to a radical-cation, resulting in formation of Cu(I) and three oxidation products of olanzapine including a previously unknown oxidation product that was identified as hydroxy-olanzapine. Acetonitrile in the sample solution was necessary for the reaction to occur. As little as 100 ppb Cu(II) in the sample solution produced a Cu(I) peak, that by peak area, corresponded to about 0.1% relative to the olanzapine peak. The hydroxy-olanzapine oxidation product was also detectable, but the relative peak area was much smaller. To prevent formation of the Cu(I) artifact peak, EDTA was added to the sample solvent to complex any trace Cu(II) that might be present. The addition of EDTA was shown to prevent Cu(I) formation when Cu(II) was present at levels of 4ppm in the sample solution.

Artifacts Generated During Azoalkane Peroxy Radical Oxidative Stress Testing of Pharmaceuticals Containing Primary and Secondary Amines.

We report artifactual degradation of pharmaceutical compounds containing primary and secondary amines during peroxy radical-mediated oxidative stress carried out using azoalkane initiators. Two degradation products were detected when model drug compounds dissolved in methanol/water were heated to 40°C with radical initiators such as 2,2'-azobis(2-methylpropionitrile) (AIBN). The primary artifact was identified as an α-aminonitrile generated from the reaction of the amine group of the model drug with formaldehyde and hydrogen cyanide, generated as byproducts of the stress reaction. A minor artifact was generated from the reaction between the amine group and isocyanic acid, also a byproduct of the stress reaction. We report the effects of pH, initiator/drug molar ratio, and type of azoalkane initiator on the formation of these artifacts. Mass spectrometry and nuclear magnetic resonance were used for structure elucidation, whereas mechanistic studies, including stable isotope labeling experiments, cyanide analysis, and experiments exploring the effects of butylated hydroxyanisole addition, were employed to support the degradation pathways.

Implications of In-Use Photostability: Proposed Guidance for Photostability Testing and Labeling to Support the Administration of Photosensitive Pharmaceutical Products, Part 2: Topical Drug Product.

Although essential guidance to cover the photostability testing of pharmaceuticals for manufacturing and storage is well-established, there continues to be a significant gap in guidance regarding testing to support the effective administration of photosensitive drug products. Continuing from Part 1, (Baertschi SW, Clapham D, Foti C, Jansen PJ, Kristensen S, Reed RA, Templeton AC, Tønnesen HH. 2013. J Pharm Sci 102:3888-3899) where the focus was drug products administered by injection, this commentary proposes guidance for testing topical drug products in order to support administration. As with the previous commentary, the approach taken is to examine "worst case" photoexposure scenarios in comparison with ICH testing conditions to provide practical guidance for the safe and effective administration of photosensitive topical drug products.

In silico prediction of pharmaceutical degradation pathways: a benchmarking study.

Zeneth is a new software application capable of predicting degradation products derived from small molecule active pharmaceutical ingredients. This study was aimed at understanding the current status of Zeneth's predictive capabilities and assessing gaps in predictivity. Using data from 27 small molecule drug substances from five pharmaceutical companies, the evolution of Zeneth predictions through knowledge base development since 2009 was evaluated. The experimentally observed degradation products from forced degradation, accelerated, and long-term stability studies were compared to Zeneth predictions. Steady progress in predictive performance was observed as the knowledge bases grew and were refined. Over the course of the development covered within this evaluation, the ability of Zeneth to predict experimentally observed degradants increased from 31% to 54%. In particular, gaps in predictivity were noted in the areas of epimerizations, N-dealkylation of N-alkylheteroaromatic compounds, photochemical decarboxylations, and electrocyclic reactions. The results of this study show that knowledge base development efforts have increased the ability of Zeneth to predict relevant degradation products and aid pharmaceutical research. This study has also provided valuable information to help guide further improvements to Zeneth and its knowledge base.

Investigation of the mechanism of racemization of litronesib in aqueous solution: unexpected base-catalyzed inversion of a fully substituted carbon chiral center.

Mitosis inhibitor (R)-litronesib (LY2523355) is a 1,3,4-thiadiazoline-bearing phenyl and N-(2-ethylamino)ethanesulfonamido-methyl substituents on tetrahedral C5. Chiral instability has been observed at pH 6 and above with the rate of racemization increasing with pH. A positively charged trigonal intermediate is inferred from the fact that p-methoxy substituent on the phenyl accelerated racemization, whereas a p-trifluoromethyl substituent had the opposite effect. Racemization is proposed to occur through a relay mechanism involving intramolecular deprotonation of the sulfonamide by the side chain amino group and attack of the sulfonamide anion on C5, cleaving the C5S bond, to form an aziridine; heterolytic dissociation of the aziridine yields an ylide. This pathway is supported by (1) a crystal structure providing evidence for a hydrogen bond between the sulfonamide NH and the amino group, (2) effects of substituents on the rate of racemization, and (3) computational studies. This racemization mechanism results from neighboring group effects in this densely functionalized molecule. Of particular novelty is the involvement of the side-chain secondary amino group, which overcomes the weak acidity of the sulfonamide by anchimeric assistance.

On-column nitrosation of amines observed in liquid chromatography impurity separations employing ammonium hydroxide and acetonitrile as mobile phase.

The availability of high performance liquid chromatography (HPLC) columns capable of operation at pH values up to 12 has allowed a greater selectivity space to be explored for method development in pharmaceutical analysis. Ammonium hydroxide is of particular value in the mobile phase because it is compatible with direct interfacing to electrospray mass spectrometers. This paper reports an unexpected N-nitrosation reaction that occurs with analytes containing primary and secondary amines when ammonium hydroxide is used to achieve the high pH and acetonitrile is used as the organic modifier. The nitrosation reaction has generality. It has been observed on multiple columns from different vendors and with multiple amine-containing analytes. Ammonia was established to be the source of the nitroso nitrogen. The stainless steel column frit and metal ablated from the frit have been shown to be the sites of the reactions. The process is initiated by removal of the chromium oxide protective film from the stainless steel by acetonitrile. It is hypothesized that the highly active, freshly exposed metals catalyze room temperature oxidation of ammonia to NO but that the actual nitrosating agent is likely N(2)O(3).

Implications of in-use photostability: proposed guidance for photostability testing and labeling to support the administration of photosensitive pharmaceutical products, part 1: drug products administered by injection.

Basic guidance on the photostability testing of pharmaceuticals, designed to cover manufacturing and storage over shelf life, has long been established within ICH Q1(ICH,B(10) , but the guideline does not cover the photostability of drugs during or after administration (i.e., under conditions of use). To date, there has been a paucity of guidance covering the additional testing that would be of value during the clinical preparation and use of products. This commentary suggests a systematic approach, based on realistic "worst case" photoexposure scenarios and the existing ICH Option 1 and 2 light sources, to provide valuable data to pharmaceutical manufacturers and compounding pharmacists for the safe and effective use of photosensitive injection products.

The assessment of impurities for genotoxic potential and subsequent control in drug substance and drug product.

The strategies implemented at Eli Lilly and Company to address European Medicines Agency and US Food and Drug Administration requirements governing the control of genotoxic impurities (GTIs) are presented. These strategies were developed to provide understanding with regard to the risk and potential liabilities that could be associated with developmental and marketed compounds. The strategies systematize the assessment of impurities for genotoxic potential, addressing both actual and potential impurities. Timing of activities is designed to minimize impact to development timelines while building a data package sufficient to either discharge the risk of potential GTI formation or support the implementation of a specification necessary for long-term control. This article presents the background associated with GTI control, the types of impurities that should be assessed, and the actions to be taken when an impurity is found to be genotoxic. A systematic approach to define potential degradation products derived from stress-testing studies is outlined with a proposal to perform a genotoxic risk assessment on these impurities. Finally, an Arrhenius-based strategy is proposed for a rapid assessment of the likelihood of potential degradation impurities to form in the commercial drug product formulation. Importantly, this article makes a proposal for discharging the risk of a potential GTI with supporting data.

A critical assessment of the ICH guideline on photostability testing of new drug substances and products (Q1B): Recommendation for revision.

The ICH guideline on photostability (ICH Topic Q1B) was published in November 1996 and has been implemented in all three regions (US, EU, and Japan). The guideline describes a useful basic protocol for testing of new drug substances and associated drug products for manufacturing, storage, and distribution, but it does not cover the photostability of drugs under conditions of patient use. The pharmaceutical industry now has considerable experience in designing and carrying out photostability studies within the context of this guideline, and issues have been identified that would benefit from the revision process. The purpose of this commentary is to accomplish the following: (i) highlight issues proposed for consideration in the ICH revision process, (ii) offer a rationale for why these issues may compromise the design of a testing protocol and/or the results of the testing program, and (iii) provide recommendations for clarification of the guideline.

Isolation, identification, and synthesis of two oxidative degradation products of olanzapine (LY170053) in solid oral formulations.

Two impurities found in both stressed and aged solid-state formulations of olanzapine have been identified as (Z)-1,3-dihydro-4-(4-methyl-1-piperazinyl)-2-(2-oxopropylidene)-2H-1,5-benzodiazepin-2-one (1) and (Z)-1-[1,2-dihydro-4-(4-methyl-1-piperazinyl)-2-thioxo-3H-1,5-benzodiazepin-3-ylidene]propan-2-one (2). The structures indicate that the two impurities are degradation products resulting from oxidation of the thiophene ring of olanzapine. The impurities were isolated by preparative HPLC from a thermally stressed formulation, and characterized by UV, IR, MS, and NMR. A synthetic preparation of compounds 1 and 2 by reaction of olanzapine with the singlet oxygen mimic 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) is presented. The structure of 2 was also determined by single-crystal X-ray diffraction analysis. A degradation pathway for the formation of 1 and 2 is proposed.