Validation of Impurity Methods, Part I

626 LCGC NORTH AMERICA VOLUME 21 NUMBER 7 JULY 2003 www.chromatographyonline.com Validation Viewpoint John D. Orr, Ira S. Krull, and Michael E. Swartz This column is the first installment in a two-part series reviewing International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and U.S. Food and Drug Administration (FDA) impurity method validation guidelines. In the first part, the authors discuss background information such as policy and laboratory controls that pertain to validation. The second part will address the specifics of ICH and FDA guidelines for impurity method validation components such as specificity, linearity, and reproducibility. Ira S. Krull and Michael E. Swartz Validation Viewpoint Editors Validation of Impurity Methods, Part I This column is the first in a two-part series that will review impurity method validation guidelines provided by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and the U.S. Food and Drug Administration (FDA). To facilitate successful and consistent performance of method validation work and to provide the highest level of protection to patients who rely upon medicines, ICH and FDA have written many guidance documents to be used by scientists in the pharmaceutical industry. Documents from ICH are available on its web site at http://www.ich.org/, and FDA documents can be found on its web site at http://www.fda.gov/cder/ guidance/index.htm. It is useful to understand the mission of ICH and how ICH and FDA relate to each other. A description of the role of ICH, as paraphrased from http://www. ich.org/ich4.html, is ICH comprises regulatory authorities of Europe, Japan, and the United States and experts from the pharmaceutical industry in the three regions. The purpose of ICH is to make recommendations for ways to achieve greater harmonization in the interpretation and application of technical guidelines and requirements for drug registration to reduce the need for duplicate testing performed during the research and development of new medicines. The ultimate goal is a more economical use of human, animal, and material resources; the elimination of unnecessary delay in the global development and availability of new medicines; and the maintenance of safeguards on quality, safety and efficacy, and regulatory obligations to protect public health. The ICH guidance document formation process proceeds in a stepwise fashion (see http://www.ich.org/ich4.html for details about this process), including development of scientific consensus through discussions between regulatory and industry experts; wide consultation of the draft consensus documents, through normal regulatory channels, before a harmonized text is adopted; and commitment by regulatory parties to implement ICH harmonized texts. After a guideline has been finalized by ICH, it is implemented by the regulatory agencies from regions composing ICH (the European Union, Japan, and the United States). Guidelines adopted by FDA in the United States appear in the Federal Register. FDA produces guidance documents and, as paraphrased from the FDA guidance document web site (http://www.fda.gov/ cder/guidance/), Guidance documents represent the Agency s current thinking on a particular subject. They do not create or confer any rights for or on any person and do not operate to bind FDA or the public. An alternative approach may be used if such approach satisfies the requirements of the applicable statute, regulations, or both. The first part of this Validation Viewpoint series contains an overview of both FDA and ICH guidelines, including topics such as method validation background, validation policy, laboratory controls, types of analytical procedures to be validated, classification of impurities, validation documentation, and reporting impurity content of active pharmaceutical ingredient (also known as drug substance, bulk drug substance, or bulk active) batches. The second part of this series will address specific validation components such as specificity, linearity, and reproducibility. ICH and FDA guidelines contain a great deal of detailed information about validation, and analysts should refer to them to gain a full understanding of this subject (1 4). Validation discussed in this Validation Viewpoint series pertains to validation of high perfor-

628 LCGC NORTH AMERICA VOLUME 21 NUMBER 7 JULY 2003 www.chromatographyonline.com mance liquid chromatography (HPLC) methods for assessing organic impurity levels in active pharmaceutical ingredients. To ensure that the data from impurity methods are reliable (precise and accurate), pharmaceutical companies are expected to validate impurity methods for the active pharmaceutical ingredient and latter-stage key synthetic intermediates. Method Validation Background Validation policy: Pharmaceutical companies should have an overall validation policy, part of which describes their approach to validating analytical methods (5). A company s validation policy typically is stipulated in a standard operating procedure. A separate standard operating procedure for the validation of analytical procedures also should be available. This standard operating procedure should define the validation extent and the assay attributes to be validated for methods for synthetic intermediates (at different phases of the chemical process) and for the active pharmaceutical ingredient. This standard operating procedure also should contain information regarding the degree of validation required at different stages of the drug development process (that is, phase I, II, and III clinical trials). ICH recommends that all active pharmaceutical ingredient analytical methods be validated (5) unless the method used already is included in a relevant pharmacopeia, such as the United States Pharmacopeia National Formulary (USP NF [6]) or a recognized standard reference. Tests for inorganic compounds, for example, can be found in the USP NF; however, HPLC impurity assays for new active pharmaceutical ingredients in development must be created. After an assay has been developed and researchers have confidence in the utility of the method under the conditions in which samples will be analyzed, the assay validation (per ICH and FDA guidelines) can begin. However, before assay validation begins, laboratory controls and standard operating procedures should be in place to ensure that analysts will obtain reliable data from the validation experiments. Laboratory controls: To properly and confidently validate analytical methods, laboratory controls and standard operating procedures must be in place (7). A laboratory must have adequate space for personnel and instrumentation. Conditions within the laboratory should be conducive to proper experimentation and testing and should ensure personnel safety. These conditions include adequate bench space, glassware and equipment storage space, sink access, fume hoods, waste solvent and sample disposal facilitation equipment, proper laboratory ventilation and climate control, instrument power supply, and building services such as house vacuum, nitrogen, air, and helium when it is used for HPLC solvent degassing. For safety, a laboratory must have proper egress, ideally with multiple exits in the case of emergencies, safety eye wash stations; a safety shower; fire suppression equipment; and emergency power shutoff. Laboratory workers should consider ventilation to HPLC waste solvent collection containers, HPLC solvent reservoirs, and sample vial disposal containers to minimize their exposure to noxious fumes. Furthermore, proper laboratory controls include reagents and standards properly labeled with expiration dates. Mobile phases used in HPLC systems should be labeled properly with the mobile-phase composition, the preparation and expiration dates, and the name of the researcher who prepared it. The company policy related to the conditions above should be stipulated in a standard operating procedure. The validation of impurity methods should occur on appropriately qualified instruments. We recommend that instrument manufacturers or other highly qualified technical personnel be employed to qualify analytical instruments on a regular basis, as stipulated in a company-authored standard operating procedure. Yearly instrument qualification is a relatively standard frequency; however, if an instrument becomes subject to a move or major repair, researchers must consider either partial or complete requalification to ensure that the instrument operates within specifications. Instruments used for validation work should have a record of daily operation that includes date of use, analyst names, and methods or mobile phases passed through the instrument. One strategy to ensure less problematic HPLC instrument operation is to assign each HPLC instrument to a specific researcher who has responsibility for its proper operation. In our experience, this strategy results in a sense of ownership for an instrument s proper operation, limits uncontrolled instrument access, and results in fewer instrument malfunctions. Additional details about laboratory controls are available in ICH and FDA guidelines. Having the proper laboratory controls in place will ensure reliable validation, which in turn will result in reliable analytical data. Types of analytical procedures to be validated: ICH guidelines address the types of analytical procedures to be validated (3). The four most common types of analytical procedures are identification tests such as comparisons of HPLC retention times or IR spectra of a test sample and an authentic reference standard, quantitative tests such as HPLC impurity assays for levels of impurities, limit tests such as gas chromatography (GC) of residual solvents and heavy metals assays for the control of impurities, and quantitative tests such as wt % HPLC assays for the active moiety in the active pharmaceutical ingredient. We will discuss only one item from this list quantitative tests for levels of impurities. Classification of impurities: Active pharmaceutical ingredient batches comprise a number of substances. For chemically manufactured active pharmaceutical ingredients, the major component is the active pharmaceutical ingredient itself; however, if the active pharmaceutical ingredient is a salt, the counterion also will compose a significant portion of the batch. Other substances or impurities from various sources commonly are present at different levels. Table I is a list of classes, examples, and typical origins of impurities. The ICH guidance for impurities in drug substances was accepted by FDA in 2000, and it provides a comprehensive view of what types of impurities to expect, how to test for them (in general), how to list them in specifications, and how to qualify their biological safety (8). These impurities can be organic, inorganic, or solvent-related compounds. The nature of the active pharmaceutical ingredient and the impurities present influence the choice of analytical procedures used in the quantification of impurity levels. Organic impurities can come from the chemical process or can arise during storage (9). These impurities might include starting materials, byproducts, intermediates, degradation products, reagents, ligands, and catalysts. The impurities might or might not be identified, might or might not be volatile, and might or might not have UVabsorption properties similar to the active pharmaceutical ingredient. Because many organic impurities found in active pharmaceutical ingredients are amenable to HPLC analysis, many impurity methods use this

630 LCGC NORTH AMERICA VOLUME 21 NUMBER 7 JULY 2003 www.chromatographyonline.com technique coupled with UV detection. As mentioned above, impurities and active pharmaceutical ingredients do not all absorb UV light equally, so the selection of detection wavelength is important. An understanding of the UV light absorptive properties of the organic impurities and the active pharmaceutical ingredient is very helpful. Some organic impurities or active pharmaceutical ingredients, however, do not absorb UV light appreciably. In these cases, researchers should use HPLC coupled with alternate methods of detection. Techniques such as evaporative light-scattering, refractive index, mass spectrometry, fluorescence, and various other element-specific detection are available. Each detection technique has its own advantages and limitations. Knowledge of the nature of the active pharmaceutical ingredient and its impurities is very helpful when selecting the appropriate impurity analytical technique. The application of this knowledge will better ensure the development of precise and accurate impurity methods. As mentioned above, when the active pharmaceutical ingredient is produced as a salt and the counterion is inorganic, the major inorganic component of the batch is the counterion. Minor inorganic impurities typically are present in active pharmaceutical ingredients and must be controlled. Inorganic impurities that can result from the manufacturing process usually are known and identified. They include reagents, ligands, catalysts, heavy or other residual metals, inorganic salts, and other materials such as filter aids. Inorganic impurities normally are detected using procedures found in pharmacopeias or other standard references (8). Alternative procedures used to detect inorganic impurities not listed in the general literature should be validated. Based upon their knowledge of the manufacturing process, analysts can determine which Table I: Classification of impurities Impurity Type Examples Typical Origin inorganic impurities might be present in the active pharmaceutical ingredient. Known metals used as catalysts, for example, should be controlled during the manufacturing process if possible. If the desired degree of removal is not achieved before active pharmaceutical ingredient isolation, then the metal levels in the active pharmaceutical ingredient must be determined. Typical techniques for this determination include atomic absorption spectroscopy and inductively coupled plasma emission spectroscopy. To quantify levels of other inorganic impurities in an active pharmaceutical ingredient of unknown nature, researchers typically use a residue-onignition technique (10). Active pharmaceutical ingredient batches typically are harvested or isolated from a solvent or a mixture of solvents. Solvents used in the active pharmaceutical ingredient synthesis generally are of known toxicity. Residual solvents are considered impurities and are listed in three classifications: classes 1, 2, and 3 in the ICH guideline on residual solvents (11). Class 1 solvents are to be avoided. They include known or strongly suspected human carcinogens and environmental hazards such as carbon tetrachloride and benzene. The use of class 2 solvents should be limited; they are not genotoxic carcinogens, but they possibly cause irreversible toxicities such as neurotoxicity and teratogenicity. Acetonitrile and methylene chloride are class 2 solvents. Class 3 solvents have low toxic potential and include substances such as ethanol, whose permissible daily limit allows for active pharmaceutical ingredients that contain 0.5% ethanol. Capillary GC typically is used to quantify levels of residual solvents in active pharmaceutical ingredients. The USP NF lists an excellent method for these analyses (12). Validation documentation: Validation begins with the preparation of a validation protocol that should be reviewed and Organic Starting materials; by-products; Chemical process; degradants may intermediates; degradants; come from active pharmaceutical reagents; ligands ingredient Inorganic Reagents; ligands; catalysts; Chemical process; processing residual metals; inorganic salts; equipment; processing aids filter aids (such as filter aids) Solvent Reaction solvents; API isolation Chemical reaction; crystallization; solvents; chromatographic precipitation; extraction or partition; solvents chromatographic purification approved by the appropriate departments such as analytical chemistry, quality control, and quality assurance (5). The validation protocol should describe the test method, assay attributes to be validated, exactly how the assay attributes will be validated (that is, descriptions of how test samples will be prepared and analyzed), and validation results acceptance criteria (that is, limit of quantitation must be 0.05% or greater). The validation report should cross-reference the validation protocol, describe the results obtained, and present the conclusions made, including the passing or failing of predetermined acceptance criteria. Furthermore, deviations from the validation protocol should be documented and justified, as well. The HPLC impurity method report (also called the HPLC impurity method standard operating procedure) should be attached to the validation protocol. It should describe exactly how to execute the test method and should include a list of instrumentation, including acceptable instrument manufacturers and models; HPLC column description, including manufacturer, model, and packing lot numbers if lot-to-lot column variability is a concern; a list of the reagents and solvents for use, including the grade and manufacturer; the exact sample preparation instructions, including blank, reference standard, system suitability, and test samples; and a description of the instrument operating conditions (sample injection volume, flow rate, gradient parameters and column reequilibration time, detection wavelength, and run time), injection sequence, instructions for calculating system-suitability and test sample analysis results, system-suitability acceptance criteria, and figures of sample and blank chromatograms that clearly indicate how to integrate each impurity peak. The HPLC impurity method report also can be attached to the validation report, if desired. Although it is not required by ICH or FDA, having HPLC impurity method reports reviewed and approved by an analyst and supervisor in the department to which the method will be transferred is advantageous. The value of this review is that the method recipients have an early opportunity to review and provide constructive feedback about the method well

632 LCGC NORTH AMERICA VOLUME 21 NUMBER 7 JULY 2003 www.chromatographyonline.com before it is ever transferred to their department. This process has a significant and positive effect on method transfer, which is an important task. Reporting the impurity content of active pharmaceutical ingredient batches: After an HPLC impurity method has been validated successfully and the validation report has been written and approved, the method is suitable for use to analyze clinical active pharmaceutical ingredient batches. ICH guidelines address the reporting of impurity content in active pharmaceutical ingredient batches (8). Table II: Impurity reporting thresholds (14) Organic impurity levels typically are determined by an HPLC impurity assay. Patients must be protected from exposure to significant levels of impurities with toxicities that have not been qualified through biological testing. If the toxicology lot is manufactured separately, as is often the case, from any of the clinical lots (Phase I, II, or III), then the clinical lot impurity profile must be compared with that of the toxicology lot. This step is needed to ensure that patients are not exposed to unacceptable levels of unqualified impurities. Maximum Reporting Daily Dose* Threshold Identification Qualification (g/day) (%) Threshold Threshold 2 0.05 0.10% or 1.0 mg per day# 0.15% or 1.0 mg per day# 2 0.03 0.05% 0.05% * The amount of drug substance administered per day. Higher reporting thresholds should be scientifically justified. Lower thresholds can be appropriate if the impurity is unusually toxic. Impurities greater than this threshold must be identified by a new drug application filing. Impurities greater than this threshold must have their safety qualified by toxicology testing. # Whichever is lower. It is important to understand acceptable means of reporting active pharmaceutical ingredient batch impurity levels, because this information can be used to determine if an active pharmaceutical ingredient batch intended for clinical use is acceptable. Impurities are classified in the impurity profile by HPLC retention time (or retention time relative to the active pharmaceutical ingredient) and structure (if known). Quantitative results should be presented numerically. Individual impurities and total impurity levels greater than 1% should be reported to one decimal place; for example, 1.4%. On the other hand, impurities present at levels less than 1% should be reported to two decimal places; for example, 0.23% and 0.07%. Results should be rounded using conventional rules as described in ICH (8) and USP (13) guidelines. ICH guidelines state that all impurities at a level greater than the reporting threshold should be summed and reported as total impurities (8). Table II lists information about impurity reporting thresholds (14). The specifications for active pharmaceutical ingredients at the new drug application (NDA) stage should include a list of impurities to be controlled, based upon those observed in active pharmaceutical ingredient batches manufactured with the proposed commercial process. The structures of these impurities could be known or unknown (8). By the time of new drug application filing, researchers should propose a rationale for impurity limits based upon appropriate safety (toxicology) or human clinical studies (8). Conclusion We have discussed ICH and FDA guidelines related to the background information about impurity method validation. We reviewed information regarding validation policy, laboratory controls, types of analytical procedures to be validated, impurity classification, validation documentation, and reporting impurity content of active pharmaceutical ingredient batches. A better understanding of the above topics will be of value when performing method validation. More in-depth information can be found on ICH and FDA web sites. In the second part of this series, we will provide a review and discussion of ICH and FDA guidelines for validation components. We will discuss validation topics such as specificity and selectivity; linearity; range; accuracy; precision, including

www.chromatographyonline.com repeatability, intermediate precision, and reproducibility; recovery; detection and quantitation limits; robustness; systemsuitability specifications and tests; samplesolution stability; stability-indicating assays; and analysis of stereoisomeric drugs. Editors Note The views and opinions expressed in this Validation Viewpoint column are those of the authors, John D. Orr, Ira S. Krull, and Michael E. Swartz, and do not necessarily reflect the views and opinions of Eisai Research Institute (nor of its parent company, Eisai Co., Ltd., nor any of its subsidiaries), Northeastern University, or Waters Corp. References (1) Draft Guidance for Industry: Analytical Procedures and Methods Validation (U.S. Department of Health and Human Services, U.S. Food and Drug Administration, Center for Drug Evaluation and Research, Center for Biologics Division of Research, Rockville, Maryland, August 2000). (2) ICH Q2B Validation of Analytical Procedures: Methodology Geneva, Switzerland, May 1997). (3) ICH Q2A Text on Validation of Analytical Procedures Geneva, Switzerland, March 1995). (4) Reviewer Guidance: Validation of Chromatographic Methods (U.S. Department of Health and Human Services, U.S. Food and Drug Administration, Center for Drug Evaluation and Research, Rockville, Maryland, November 1994). (5) ICH Q7A Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use, Geneva, Switzerland, November 2000). (6) United States Pharmacopeia 26 National Formulary 21 (United States Pharmacopeial Convention, Inc., Rockville, Maryland, 2002). (7) L. Huber, in Validation and Qualification in Analytical Laboratories (Interpharm/CRC Press, Boca Raton, Florida, 1998). (8) ICH Q3A(R) Impurities in New Drug Substances of Pharmaceuticals for Human Use, Geneva, Switzerland, February 2002). (9) O. Repič, in Principles of Process Research and Development in the Pharmaceutical Industry (John Wiley & Sons, Inc., New York, 1998), pp. 1 54. (10) United States Pharmacopeia 24 National Formulary pp. 1862. (11) ICH Q3C Impurities: Guideline for Residual Solvents Geneva, Switzerland, July 1997). (12) United States Pharmacopeia 24 National Formulary pp. 1877 1878. (13) United States Pharmacopeia 24 National Formulary pp. 3 4. (14) ICH Q3A(R) Impurities in New Drug Substances of Pharmaceuticals for Human Use, Geneva, Switzerland, February 2002), attachment 1, pp. 8. John D. Orr is director of analytical chemistry at Eisai Research Institute, 100 Federal Street, Andover, MA 01810, e-mail john_orr@ eisai.com. Ira S. Krull Validation Viewpoint co-editor Ira S. Krull is an associate professor of chemistry at Northeastern University in Boston, Massachusetts, and a member of LCGC s editorial advisory board. Michael E. Swartz Validation Viewpoint co-editor Michael E. Swartz is a principal scientist at Waters Corp., Milford, Massachusetts, and a member of LCGC s editorial advisory board. The columnists regret that time constraints prevent them from responding to individual reader queries. However, readers are welcome to submit specific questions and problems, which the columnists may address in future columns. Direct correspondence about this column to Validation Viewpoint, LCGC, 859 Willamette Street, Eugene, OR 97401, e-mail lcgcedit@lcgcmag.com. JULY 2003 LCGC NORTH AMERICA VOLUME 21 NUMBER 7 633