Vinod P. Shah

A Theoretical Basis for a Biopharmaceutic Drug Classification: The Correlation of in Vitro Drug Product Dissolution and in Vivo Bioavailability

A biopharmaceutics drug classification scheme for correlating in vitro drug product dissolution and in vivo bioavailability is proposed based on recognizing that drug dissolution and gastrointestinal permeability are the fundamental parameters controlling rate and extent of drug absorption. This analysis uses a transport model and human permeability results for estimating invivo drug absorption to illustrate the primary importance of solubility and permeability on drug absorption. The fundamental parameters which define oral drug absorption in humans resulting from this analysis are discussed and used as a basis for this classification scheme. These Biopharmaceutic Drug Classes are defined as: Case 1. High solubility-high permeability drugs, Case 2. Low solubility-high permeability drugs, Case 3. High solubility-low permeability drugs, and Case 4. Low solubility-low permeability drugs. Based on this classification scheme, suggestions are made for setting standards for in vitro drug dissolution testing methodology which will correlate with the in vivo process. This methodology must be based on the physiological and physical chemical properties controlling drug absorption. This analysis points out conditions under which noin vitro-in vivo correlation may be expected e.g. rapidly dissolving low permeability drugs. Furthermore, it is suggested for example that for very rapidly dissolving high solubility drugs, e.g. 85% dissolution in less than 15 minutes, a simple one point dissolution test, is all that may be needed to insure bioavailability. For slowly dissolving drugs a dissolution profile is required with multiple time points in systems which would include low pH, physiological pH, and surfactants and the in vitro conditions should mimic the in vivo processes. This classification scheme provides a basis for establishing in vitro-in vivo correlations and for estimating the absorption of drugs based on the fundamental dissolution and permeability properties of physiologic importance.

Bioanalytical Method Validation—A Revisit with a Decade of Progress

This report is a synthesis of (1) the earlier conference on Analytical Methods Validation−Bioavailability, Bioequivalence and Pharmacokinetic Studies (Conference held in Arlington, VA, December 3–5, 1990 and the report published in Pharmaceutical Research, 9: 588-592, 1992) and (2) the workshop on “Bioanalytical Methods Validation—A Revisit with a Decade of Progress,” (Workshop held in Arlington, VA, January 12–14, 2000), sponsored by the American Association of Pharmaceutical Scientists and the U. S. Food and Drug Administration. The bioanalytical method validation workshop of January 12–14, 2000 was directed towards small molecules. A separate workshop was held in March 1–3, 2000 to discuss validation principles for macromolecules. The purpose of this report is to represent the progress in analytical methodologies over the last decade and assessment of the major agreements and issues discussed with regard to small molecules at both the conference and the workshop. The report is also intended to provide guiding principles for validation of bioanalytical methods employed in support of bioavailability, bioequivalence, and pharmacokinetic studies in man and in animals.

Dissolution Testing as a Prognostic Tool for Oral Drug Absorption: Immediate Release Dosage Forms

Dissolution tests are used for many purposes in the pharmaceutical industry: in the development of new products, for quality control and, to assist with the determination of bioequivalence. Recent regulatory developments such as the Biopharmaceutics Classification Scheme have highlighted the importance of dissolution in the regulation of post-approval changes and introduced the possibility of substituting dissolution tests for clinical studies in some cases. Therefore, there is a need to develop dissolution tests that better predict the in vivo performance of drug products. This could be achieved if the conditions in the gastrointestinal tract were successfully reconstructed in vitro. The aims of this article are, first, to clarify under which circumstances dissolution testing can be prognostic for in vivo performance, and second, to present physiological data relevant to the design of dissolution tests, particularly with respect to the composition, volume, flow rates and mixing patterns of the fluids in the gastrointestinal tract. Finally, brief comments are made in regard to the composition of in vitro dissolution media as well as the hydrodynamics and duration of the test.

Quantitative Bioanalytical Methods Validation and Implementation: Best Practices for Chromatographic and Ligand Binding Assays

AbstractThe Third AAPS/FDA Bioanalytical Workshop, entitled “Quantitative Bioanalytical Methods Validation and Implementation: Best Practices for Chromatographic and Ligand Binding Assays” was held on May 1–3, 2006 in Arlington, VA. The format of this workshop consisted of presentations on bioanalytical topics, followed by discussion sessions where these topics could be debated, with the goal of reaching consensus, or identifying subjects where addition input or clarification was required. The discussion also addressed bioanalytical validation requirements of regulatory agencies, with the purpose of clarifying expectations for regulatory submissions. The proceedings from each day were reviewed and summarized in the evening sessions among the speakers and moderators of the day. The consensus summary was presented back to the workshop on the last day and was further debated. This communication represents the distillate of the workshop proceedings and provides the summary of consensus reached and also contains the validation topics where no consensus was reached.ConclusionFor quantitative bioanalytical method validation procedure and requirements, there was a relatively good agreement between chromatographic assays and ligand-binding assays. It was realized that the quantitative and qualitative aspects of bioanalytical method validation should be reviewed and applied appropriately.1.Some of the major concerns between the 2 methodologies related to the acceptable total error for precision and accuracy determination and acceptance criteria for an analytical run. The acceptable total error for precision and accuracy for both the methodologies is less than 30. The 4–6–15 rule for accepting an analytical run by a chromatographic method remained acceptable while a 4–6–20 rule was recommended for ligand-binding methodology.2.The 3rd AAPS/FDA Bioanalytical Workshop clarified the issues related to placement of QC samples, determination of matrix effect, stability considerations, use of internal standards, and system suitability tests.3.There was a major concern and issues raised with respect to stability and reproducibility of incurred samples. This should be addressed for all analytical methods employed. It was left to the investigators to use their scientific judgment to address the issue.4.In general, the 3rd AAPS/FDA Bioanalytical Workshop provided a forum to discuss and clarify regulatory concerns regarding bioanalytical method validation issues.

Biopharmaceutics classification system: the scientific basis for biowaiver extensions.

The current BSC guidance issued by the FDA allows for biowaivers based on conservative criteria. Possible new criteria and class boundaries are proposed for additional biowaivers based on the underlying physiology of the gastrointestinal tract. The proposed changes in new class boundaries for solubility and permeability are as follows: 1. Narrow the required solubility pH range from 1.0-7.5 to 1.0-6.8. 2. Reduce the high permeability requirement from 90% to 85%. The following new criterion and potential biowaiver extension require more research: 1. Define a new intermediate permeability class boundary. 2. Allow biowaivers for highly soluble and intermediately permeable drugs in IR solid oral dosage forms with no less than 85% dissolved in 15 min in all physiologically relevant dissolution media, provided these IR products contain only known excipients that do not affect the oral drug absorption. The following areas require more extensive research: 1. Increase the dose volume for solubility classification to 500 mL. 2. Include bile salt in the solubility measurement. 3. Use the intrinsic dissolution method for solubility classification. 4. Define an intermediate solubility class for BCS Class II drugs. 5. Include surfactants in in vitro dissolution testing.

Validation of Bioanalytical Methods

Validation of bioanalytical methods used to generate data for pharmacokinetic and bioavailability studies is approached by a variety of techniques and is subject to many different methods of interpretation. This Review puts the various techniques into perspective and discusses pitfalls which may occur in interpretation of validation data. Recovery studies, standardization techniques, and selectivity/specificity are discussed with regard to the intrinsic value of various techniques that are used in validation. Models used for analytical calibration curves are explained in terms of their validity and limitations, along with a presentation of the most common ways to validate the model. Analytical sensitivity and detection limits are presented and discussed with regard to the usefulness of the various definitions. Appropriate means of testing precision and accuracy, the most important factors in assessing method quality, are presented. Stability and ruggedness testing are discussed along with a presentation of ways to assess data acceptability on a daily run basis.

AAPS-FDA workshop white paper: Microdialysis principles, application, and regulatory perspectives

Many decisions in drug development and medical practice are based on measuring blood concentrations of endogenous and exogenous molecules. Yet most biochemical and pharmacological events take place in the tissues. Also, most drugs with few notable exceptions exert their effects not within the bloodstream, but in defined target tissues into which drugs have to distribute from the central compartment. Assessing tissue drug chemistry has, thus, for long been viewed as a more rational way to provide clinically meaningful data rather than gaining information from blood samples. More specifically, it is often the extracellular (interstitial) tissue space that is most closely related to the site of action (biophase) of the drug. Currently microdialysis (μD) is the only tool available that explicitly provides data on the extracellular space. Although μD as a preclinical and clinical tool has been available for two decades, there is still uncertainty about the use of μD in drug research and development, both from a methodological and a regulatory point of view. In an attempt to reduce this uncertainty and to provide an overview of the principles and applications of μD in preclinical and clinical settings, an AAPS-FDA workshop took place in November 2005 in Nashville, TN, USA. Stakeholders from academia, industry and regulatory agencies presented their views on μD as a tool in drug research and development.

In Vitro Dissolution Profile of Water-Insoluble Drug Dosage Forms in the Presence of Surfactants

The determination of the in vitro release profile of water-insoluble drug products requires dissolution media different from those used for water-soluble drug products. Since the relevance of drug dissolution in organic solvents is questionable, we investigated the use of surfactants to determine the dissolution profiles of water-insoluble drug products. In most cases, the drug dissolution rate and extent increased as the surfactant concentration in the aqueous dissolution medium increased. Suitable dissolution profiles were obtained in the presence of sodium lauryl sulfate (SLS) for water-insoluble drug products, such as griseofulvin, carbamazepine, clofibrate, medroxyprogesterone, and cortisone acetate. These findings recommend the use of surfactants for determining the aqueous dissolution of water-insoluble drug products rather than adding organic solvents to the dissolution medium.

Bioavailability and bioequivalence: an FDA regulatory overview.

Bioavailability and/or bioequivalence studies play a key role in the drug development period for both new drug products and their generic equivalents. For both, these studies are also important in the postapproval period in the presence of certain manufacturing changes. Like many regulatory studies, the assessment of bioavailability and bioequivalence can generally be achieved by considering the following three questions. What is the primary question of the study? What are the tests that can be used to address the question? What degree of confidence is needed for the test outcome? This article reviews the regulatory science of bioavailability and bioequivalence and provides FDAs recommendations for drug sponsors who intend to establish bioavailability and/or demonstrate bioequivalence for their pharmaceutical products during the developmental process or after approval.

The Bioinequivalence of Carbamazepine Tablets with a History of Clinical Failures

The bioavailability of three lots of a generic 200-mg carbamazepine tablet, which had been withdrawn from the market, was compared to the bioavailability of one lot of the innovator product in 24 healthy volunteers. Fifty-three lots of the generic product had been recalled by the manufacturer because of concerns over reports of clinical failures for several of the lots. The three generic lots tested in this study exhibited a wide range of bioavailability, as well as large differences in the in vitro dissolution rates. The mean maximum carbamazepine plasma concentrations for two of the generic lots were only 61-74% that of the innovator product, while the third lot was 142% of the innovator. The mean areas under the plasma concentration-time curve for the three generic lots ranged from 60 to 113% that of the innovator product. The results clearly indicate a significant difference in the rate and extent of absorption of the generic products compared to the innovator, as well as among the generic lots. A good relationship was found between the in vivo parameters and the in vitro dissolution results for the four dosage forms.