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Biomedical subjects

R D McDowall

Publications and source records attributed to R D McDowall.

At least 19 recordsLinked to original sources
PubMed1998

Validation of bioanalytical chromatographic methods.

A strategy is discussed for the validation of chromatographic methods that are developed to quantify drugs in biological matrices. Both the validation terminology and the hypothesis testing are briefly reviewed. The emphasis is on the design of the experiments required to allow a reliable conclusion about acceptance or rejection of the bioanalytical method. In particular, it is explained how to evaluate the calibration line, devise experiments to estimate precision and bias and how to determine the stability of the analyte between the time of the sample collection and the analysis of the processed sample.

Algorithms↗
PubMed1995

Practical computer validation for pharmaceutical laboratories.

Computer validation should address the scientific correctness of the application software, the business objectives of the organisation, and the concerns of regulatory agencies. It is a balance between a practical and cost effective system that must develop the confidence that the system is under control. This paper gives an overview of computer validation from the following perspectives. What is computer validation? Why can a computer system not be completely validated? Why and how should computer systems be validated? The principles outlined in this paper should be adapted to a specific system on a case by case basis depending on its scope and complexity.

Chemistry, Pharmaceutical↗
PubMed1994

An analysis of the Washington Conference Report on bioanalytical method validation.

The Washington Conference Report on bioanalytical method validation is analysed with respect to the requirements for precision and accuracy. It is shown that if the requirements are interpreted too literally, this could lead to disappointment in practice. A better approach is to separate the total measurement error into its constant (bias) and random (precision) components. To ensure that 95% of all methods fall within the acceptance interval of +/- 15% around the true value, would require, for example, the bias to be < or = 8% and the method precision to be < or = 8% relative standard deviation (RSD; n = 5).

Chemistry Techniques, Analytical↗
PubMed1993

The development of a strategy for the implementation of automation in a bioanalytical laboratory.

Laboratory automation is equipment, instrumentation, software and techniques that are classified into four groups: instrument automation; communications; data to information conversion; and information management. This new definition is necessary to understand the role that automation can play in achieving the aims and objectives of a laboratory within its organization. To undertake automation projects effectively, a laboratory automation strategy is outlined which requires an intimate knowledge of an organization and the target environment to implement individual automation projects.

Automation↗
PubMed1990

Two systems for the automated analysis of drugs in biological fluids using high-performance liquid chromatography.

This paper describes two fully automated assays. One for zaprinast, a cGMP specific phosphodiesterase inhibitor, which uses the Gilson-Advanced Automated Sample Processor combination, and the other for an H+/K+ ATPase inhibitor and its sulphone metabolite, which uses direct injection. Both assays were developed to support pharmacokinetic studies at therapeutic doses in small animals as well as in man. Plasma or serum (20-200 microliters) is placed directly into an autosampler and all subsequent manipulations are performed mechanically.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1990

Method validation in the bioanalytical laboratory.

Bioanalytical methods, based on a variety of physico-chemical and biological techniques such as chromatography, immunoassay and mass spectrometry, must be validated prior to and during use to engender confidence in the results generated. The fundamental criteria for assessing the reliability and overall performance of a bioanalytical method are: the evaluation of drug and analyte stability, selectivity, limits of quantification and detection, accuracy, precision, linearity and recovery. The extent to which a method is validated is dependent on its prospective use, the number of samples to be assayed and the use to which the data are put. Specific analytical techniques may require additional validation such as antibody-binding characteristics, peak purity determination, evaluation of matrix effects or structural confirmation of the analyte. Ideally each assay should be cross-validated with a method utilizing a highly specific detector such as a mass spectrometer. Once in use, the performance of the method should be monitored using quality control standards. If a method is set up in another laboratory, the performance of that assay should be monitored with quality control standards sent from the originating laboratory.

Chemistry, Pharmaceutical↗
PubMed1989

Sample preparation for biomedical analysis.

A review of sample preparation techniques for biomedical analysis is presented. Firstly, sample preparation techniques can be divided into unit operations which can be classified into four groups: release of the analyte from the matrix, removal of endogenous material, liquid handling procedures and the enhancement of selectivity and sensitivity. The concept of unit operations gives an analyst a tool with which to evaluate critically any method for preparing a sample for analysis. Secondly, the major techniques of sample preparation (protein precipitation, liquid-liquid extraction, liquid-solid extraction and high-performance liquid chromatography, HPLC) are discussed and their advantages and disadvantages presented. Thirdly, the rationale for the automation of sample preparation is reviewed; in general liquid-solid extraction and HPLC are the best techniques for automation. The means by which this can be effected (either flexible or dedicated automation) is discussed. Finally, techniques such as supercritical fluid extraction, micellar liquid chromatography, microwave energy and immunoextraction which may be applied to biomedical sample preparation are evaluated briefly.

Chemistry Techniques, Analytical↗
PubMed1989

Analysis of 2-cyano-1-methyl-3-[4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin-3-yl phenyl]guanidine in dog plasma by liquid-solid extraction and reversed-phase high-performance liquid chromatography.

A method for the determination of 2-cyano-1-methyl-3-[4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin- 3- yl)phenyl]guanidine (SK&F94836, 1) in plasma is presented. The method involves liquid-solid extraction of the drug by C18 cassettes, with subsequent elution by an AASP LC module for determination by HPLC with UV detection. The assay is rapid, precise, accurate, and specific. The between-day CV values over the concentration range 50-500 ng/mL are 4% or less; this rises to 8% at 25 ng/mL. The corresponding between-day bias is less than 1% over the same range of concentrations. The limit of quantification is 25 ng/mL and the assay can be used for measuring 1 in samples from preclinical studies following either oral or intravenous administration of the compound.

Administration, Oral↗
PubMed1989

Sample preparation for the HPLC analysis of drugs in biological fluids.

Sample preparation for the analysis of drugs in biological fluids consists of a number of unit operations that are used for (i) release of the drug from a conjugate or biological matrix; (ii) removal of endogenous compounds that could interfere with the assay; and (iii) techniques for liquid handling. The trends in sample preparation that have occurred over the past 10 years in the authors' laboratory are discussed. In general, there has been a move from the traditional liquid-liquid extraction to methods using bonded-silica which permit rapid throughput and efficient extraction. Automation of sample preparation has seen further gains in productivity; however, the present generation of equipment lack the control and communication systems that are essential for the development of the automated integrated laboratory of the future.

Automation↗
PubMed1988

Laboratory Information Management Systems--part I. Concepts.

The purpose of this analytical survey is to give a summary of some of the main design features that can be incorporated into a Laboratory Information Management System (LIMS), in the context of the total automation of the laboratory. Additionally it will give potential purchasers of such systems some essential background knowledge and a summary of our experiences. The survey is presented in two parts: the first covers the features and the possible concepts that could be used in a LIMS system. This is followed in the second part by an outline of the stages of acquisition, validation and benefits of such a system. Together the two articles provide the information required to aid the design and installation of a LIMS. This first section deals with the possible features that a laboratory could include when contemplating the installation of such a system: the basic tools that are required for a LIMS, the database and the computer equipment are discussed. This is followed by the interfacing of analytical instruments and central versus distributed processor philosophy. The various screen formats available and the use of bar codes as a means of identifying samples and for rapid data entry into the computer system are discussed.

Journal Article↗
PubMed1988

Laboratory Information Management Systems--part II. Implementation.

In this, the second of two articles on Laboratory Information Management Systems (LIMS), the stages of the acquisition of a system are discussed. First, the laboratory automation strategy is developed leading to the writing of the requirements specification sent to prospective suppliers. The next step, in conjunction with the chosen supplier, is to write the functional and systems specifications from which the LIMS will be tailored. Once installed the LIMS must be validated and in the event of hardware or software changes, should undergo partial or full re-validation. The education and training of users, and operational considerations are presented before concluding with possible developments of LIMS in the future.

Journal Article↗
PubMed1988

The analysis of SK&F 94120, a novel inotropic agent, and its four metabolites by isolation on C18 AASP cassettes followed by high-performance liquid chromatography.

A selective and specific assay for SK&F 94120 [5-(4-acetamidophenyl)pyrazin-2(1H)-one] and its four metabolites in plasma has been developed. The method incorporates a single liquid-solid extraction step using C18 Analytichem Automated Sample Processor (AASP) cassettes. This is followed by successive elutions of the solid phase with two mobile phases of increasing acetonitrile content, by an AASP liquid chromatography module. A mobile phase containing 10% acetonitrile elutes a glucuronide metabolite from the cartridge which is then chromatographed and quantified intact. A second mobile phase, containing 20% acetonitrile, is then used to elute the unchanged drug and the three other metabolites from the same cartridge. The assay shows good accuracy and precision (less than 10% for all analytes) and is able to determine SK&F 94120 and its metabolites in plasma at concentrations between 0.05 and 1.00 mg l(-1).

Journal Article↗
PubMed1988

Laboratory Information Management Systems in practice.

To maximize the benefits of a LIMS, the system must be integrated with the analytical instrumentation in the laboratory. This provides on-line data capture or transfer of results for matching with the corresponding sample records held within the database, which reduces transcription error checking and ensures data integrity. Furthermore, the LIMS must be integrated with existing corporate systems to ensure efficient use of resources and to avoid the development of parallel systems.

Journal Article↗
PubMed1986

Analysis of 5-(4-acetamidophenyl)pyrazin-2(1H)-one (SK&F 94120) in plasma with an Analytichem automated sample processor liquid chromatography module.

A selective and specific assay for 5-(4-acetamidophenyl)pyrazin-2(1H)-one (SK&F 94120), a novel inotropic agent, has been developed. The method incorporates a liquid-solid extraction step with a C18 Analytichem automated sample processor (AASP) cassette, which consists of ten miniature extraction columns. The cassette is then loaded into the AASP auto injector, ready for automated liquid chromatography with UV detection. The AASP consists of a high-pressure sealing chamber which encapsulates each column. The high-performance liquid chromatographic mobile phase is directed through the chamber, and the analytes are eluted onto the analytical column for subsequent separation and measurement. The assay is sufficiently accurate and precise to determine SK&F 94120 at concentrations as low as 0.5 mg/l. The mean coefficient of variation for the concentration range 0.5-10.0 mg/l was 2% with a bias of +/- 1%. The assay has been used for pharmacokinetic and bioavailability studies in several species, including rat, dog, and cynomolgus monkey.

Animals↗
PubMed1986

Liquid-solid sample preparation in drug analysis.

This article compares liquid-solid extraction (LSE) with the more conventional liquid-liquid extraction (LLE) for the preparation of biological samples for assay. The commercially available manual LSE methods, Sep-Pak and Bond Elut, as well as the automated instruments Prep and Analytichem Automated Sample Processor (AASP), are reviewed. Using examples from the literature and the authors' own experiences a practical guide is given to the advantages and disadvantages of LSE.

Journal Article↗
PubMed1986

Recent advances in pharmaceutical chemistry--review II. Histamine H2-receptor antagonists.

The concept of histamine receptors is outlined and the rationale for the synthesis of H2-antagonists presented. Structure-activity relationships among these compounds are described and aspects of absorption, distribution and elimination discussed with particular reference to cimetidine and ranitidine. Oxmetidine, lupitidine and loxtidine are also considered. Methods for the analysis of these drugs in body fluids are presented followed by a discussion of their toxicology. Volunteer and patient studies are also surveyed.

Animals↗
PubMed1984

High-performance liquid chromatographic determination of oxmetidine in human plasma: comparison of liquid-liquid and liquid-solid extraction techniques.

A preliminary liquid-solid sample preparation scheme (LSE) for the HPLC determination of oxmetidine in human plasma is compared with the existing liquid-liquid extraction. The LSE method shows great practical advantages, such as ease of preparation, saving of time, and smaller sample volumes, but needs to be investigated further with respect to robustness and the removal of an endogenous compound that interfered with the quantitation of oxmetidine at low concentrations.

Chromatography, High Pressure Liquid↗