The impurities in pharmaceuticals are unwanted chemicals that remain with the active pharmaceutical ingredients (APIs) or develop during formulation or upon aging of both API and formulation. The presence of these unwanted chemicals even in trace amount may influence the efficacy and safety of pharmaceutical product
Impurities is defined as an entity of drug substances or drug product that is not chemical entity defined as drug substances an excipients or other additives to drugproduct.
The control of pharmaceutical impurities is currently a critical issue to the pharmaceutical industry. 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. Potential sources and mechanisms of impurity formation are discussed for both drugs. The International Conference on Harmonization (ICH) has formulated a workable guideline regarding the control of impurities. In this review, a description of different types and origins of impurities in relation to ICH guidelines and, degradation routes, including specific examples, are presented. The article further discusses measures regarding the control of impurities in pharmaceuticals substance and drug product applications.
Impurities in pharmaceuticals are the unwanted chemicals that remain with the active pharmaceutical ingredients (APIs), or develop during formulation, or upon aging of both API and formulated APIs to medicines. The presence of these unwanted chemicals even in small amounts may influence the efficacy and safety of the pharmaceutical products.
According to ICH, an impurity in a drug substance is defined as-“any component of the new drug substance that is not the chemical entity defined as the new drug substance”. There is an ever increasing interest in impurities present in APIs recently, not only purity profile but also impurity profile has become essential as per various regulatory requirements. The presence of the unwanted chemicals, even in small amount, may influence the efficacy and safety of the pharmaceutical products.
“In the pharmaceutical world, an impurity is considered as any other organic material, besides the drug substance, or ingredients, arise out of synthesis or unwanted chemicals that remains with API’s”
The control of pharmaceutical impurities is currently a critical issue to the pharmaceutical industry. The International Conference on Harmonization (ICH) has formulated a workable guideline regarding the control of impurities.
CLASSIFICATIONS OF IMPURITIES:
Impurities have been named differently or classified as per the ICH guidelines as follows:
A] Common names
2. Degradation products
3. Interaction products
5. Penultimate intermediates
6. Related products
7. Transformation products
B] United State Pharmacopeia
The United States Pharmacopoeia (USP) classifies impurities in various sections:
1. Impurities in Official Articles
2. Ordinary Impurities
3. Organic Volatile Impurities
C] ICH Terminology
According to ICH guidelines, impurities in the drug substance produced by chemical synthesis can broadly be classified into following three categories –
1. Organic Impurities (Process and Drug related)
2. Inorganic Impurities
3. Residual Solvents
Organic impurities may arise during the manufacturing process and or storage of the drug substance may be identified or unidentified, volatile or non-volatile, and may include
1. Starting materials or intermediates
3. Degradation products
Impurities are found in API’s unless, a proper care is taken in every step involved throughout the multi-step synthesis for example; in paracetamol bulk, there is a limit test for p-aminophenol, which could be a starting material for one manufacturer or be an intermediate for the others. Impurities can also be formed by degradation of the end product during manufacturing of the bulk drugs.
The degradation of penicillin and cephalosporin are well-known examples of degradation products. The presence of a β-lactam ring as well as that of an a-amino in the C6 or C7 side chain plays a critical role in their degradation.
The primary objectives of process chemical research are the development of efficient, scalable, and safe reproducible synthetic routes to drug candidates within the developmental space and acting as a framework for commercial production in order to meet the requirement of various regulatory agencies. Therefore, assessment and control of the impurities in a drug substance and drug product are important aspects of drug development for the development team to obtain various marketing approvals. It is extremely challenging for an organic chemist to identify the impurities which are formed in very small quantities in a drug substance and wearisome if the product is nonpharmacopeial. A study describes the formation, identification, synthesis, and characterization of impurities found in the preparation of API. A study will help a synthetic organic chemist to understand the potential impurities in API synthesis and thereby obtain the pure compound.
Care to taken ensure that desired drug metabolism, safety and clinical studies are not jeopardized by inconsistent purity or impurities having potential harmful toxicological properties,
As regulatory guidelines promulgated by the International Conference on Harmonization (ICH)(1)
dictate rigorous identification of impurities at levels of 0.1%,
It is important to develop commercially viable processes for drug substance manufacture to allow greater and more affordable access in the health care sector. In regard to the process development of drug substances, it is essential to know the origin and method of control of any unwanted substances present in it. The limit should be controlled under the threshold of toxicological concern (TTC) for the purpose of ensuring safety and efficacy of the drug and to meet the requirements of various drug regulatory agencies.(2,3)
The impurities in drug substances mostly come from starting substrates, reagents, solvents, and side reactions of the synthetic route employed. Therefore, assessment and control of the undesired substances is an essential aspect of the drug development journey, with special consideration of patient health risk.(4,5)
The isolation/synthesis and characterization of process-related critical impurities (more difficult to control under the desired regulatory limits) of any drug substance in order to evaluate their origin/fate and thereafter their control strategies in the developed process as per International Council for Harmonisation (ICH) guidelines.(4)
The goal of pharmaceutical development is to develop process understanding and control which will yield procedures that consistently deliver products possessing the desired key quality attributes. To achieve this, the quality by design (QbD) paradigm has been employed in combination with process-risk assessment strategies to systematically gather knowledge through the application of sound scientific approaches.(6)
Ganzer et al. recently published an article about critical process parameters and API synthesis.(7)
The article presented an in-depth discussion of a stepwise, process risk assessment approach to facilitate the identification and understanding of critical quality attributes, process parameters, and in-process controls. The primary benefit of working within the QbD conceptual framework and employing process risk assessment strategies is the reproducible delivery of high-quality active pharmaceutical ingredient (API). However, a secondary benefit is the ability to obtain regulatory flexibility with respect to filing requirements.(8)
The control of impurities observed in an API is critical in delivering an API of high quality. Identification and understanding of the mechanism of formation of process-related impurities are critical pieces of information required for the development of control strategies. In addition, to ensure a continuing supply of API for drug product clinical manufacture, timely identification of key impurities is essential. These synthesis-related impurities and their precursors are considered as critical impurities because they directly affect the quality and impurity profile of the API. It is our practice that critical impurities be identified if practicable. Therefore, the timely identification of critical impurities becomes an integral part of process development.
There are different approaches to the identification of impurities. Described, herein, a general strategy that we have used in our laboratory, which leads to the rapid identification of impurities. To identify the structure of a low-level unknown impurity, we usually use liquid chromatography/mass spectrometry (LC/MS)/high-resolution MS (HRMS) and tandem MS (MS/MS) for molecular weight (MW) determination, elemental composition, and fragmentation patterns. On the basis of the mass spectrometric data and knowledge of the process chemistry, one or more possible structure(s) may be assigned for the impurity, with definitive structure information obtained by inspection of the HPLC retention time, UV spectrum, and MS profile of an authentic compound.
If an authentic sample is not available, the isolation of a pure sample of the impurity is undertaken for structure elucidation using NMR spectroscopy. The isolation of low-level impurities is usually conducted using preparative HPLC chromatography
- 2. Patil, G. D.; Kshirsagar, S. W.; Shinde, S. B.; Patil, P. S.; Deshpande, M. S.; Chaudhari, A. T.; Sonawane, S. P.; Maikap, G. C.; Gurjar, M. K.Identification, Synthesis, and Strategy For Minimization of Potential Impurities Observed In Raltegravir Potassium Drug Substance. Org. Process Res. Dev. 2012, 16, 1422– 1429, DOI: 10.1021/op300077m
- 3. Huang, Y.; Ye, Q.; Guo, Z.; Palaniswamy, V. A.; Grosso, J. A. Identification of Critical Process Impurities and Their Impact on Process Research and Development. Org. Process Res. Dev.2008, 12, 632– 636, DOI: 10.1021/op800067v
4. ICH Harmonised Tripartite Guideline Q3A(R): Impurities in New Drug Substances; International Conference on Harmonization: Geneva, 2002.
5. Mishra, B.; Thakur, A.; Mahata, P. P. Pharmaceutical Impurities: A Review. Int. J. Pharm. Chem.2015, 5 (7), 232– 239
6 International Conference on Harmonisation (ICH) Guidelines; Q8, Pharmaceutical Development, 2005; Q9, Quality Risk Management, 2006.
7 Ganzer, W. R.; Materna, J. A.; Mitchell, M. B.; Wall, L. K. Pharm. Technol. 2005, July 2) 1–12.
8 Nasr, M. Drug Information Association Annual Meeting, Philadelphia, PA, June 19, 2006; Pharmaceutical Quality Assessment System (PQAS) in the 21st Century, 2006.