New Bioanalytical Methods

Decisions must be made about the method based on the quality of the data produced, and quality criteria must be established. This task is not trivial, since new guidance documents are continually produced to determine whether an analytical 

Bianalytical Chemistry, by Susan R. Mikkelsen and Eduardo Corton ISBN 0-471-54447-7 Copyright 2004 John Wiley Sons, Inc. 

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Electrochemical detection has matured considerably in recent years and is routinely used by many laboratories, often for a very specific biomedical application. The most popular applications include acetylcholine, serotonin, catecholamines, thiols and disulfides, phenols, aromatic amines, macrocycUc antibiotics, ascorbic acid, nitro compounds, hydroxylamines, and carbohydrates. As the last century concluded, it is fair to say that many applications for which LC-EC would be an obvious choice are now pursued with LC-MS-MS. This only became practical in the 1990s and is clearly a more general method applicable to a wider variety of substances. In a similar fashion, LC-MS-MS has also largely supplanted LC-F for new bioanalytical methods. Nevertheless, there remain a number of key applications for these more traditional detectors known for their selectivity (and therefore excellent detection limits). 

The development of a single enantiomer as a new active substance should be described in the same manner as for any other new chemical entity. Studies should be carried out with the single enantiomer, but if development began with the race-mate then these studies may also be taken into account. Chiral conversion should be considered early on so that enantiospecific bioanalytical methods may be developed. These methods should be described in chemistry and pharmacy part of the dossier. If the opposite enantiomer is formed in vivo, then it should be evaluated in the same way as other metabolites. For endogenous human chiral compounds, enantiospecific analysis may not be necessary. The enantiomeric purity of the active ingredient used in preclinical and clinical studies should be stated. 

It is important to keep in mind that safety assessment is only one of many components involved in the discovery and development of new pharmaceuticals. The entire process has become enormously expensive, and completing the transit of a new drug from discovery to market has to be as efficient and expeditious a process as possible. Even the narrow part of this process (safety assessment) is dependent on many separate efforts. Compounds must be made, analytical and bioanalytical methods developed, and dosage formulations developed, to name a few. One needs only to refer to Beyer (1978), Hamner (1982), Matoren (1984), Sneader (1986) (a good short overview), Zbinden, (1992) or Spilker (1994) for more details on this entire process and all of its components. 

Compliance with the FDA guidance can be considered a minimum requirement to test the performance of a bioanalytical method. Due to the fact that the validation process should simulate closely sample analysis, the real and decisive final test for a validated method will always be the sample analysis itself. It is possible that even if it passes all the validation criteria, a bioanalytical method may not be reliable for the analysis of actual samples. This undesirable situation could happen when actual samples (in vivo samples) contain new interferences not present in the spiked samples (in vitro samples) due to a metabolic process and/or other biotransformations. For this reason, bioanalytical laboratories could decide to use more stringent criteria and procedures and/or use actual sample during the method development to further guarantee the validity of the validated methods. 

Full Validation. Full validation is important when developing and implementing a bioanalytical method for the first time, for a new drug entity, and if metabolites are added to an existing assay for quantification. 

The TDM of TKIs is thus likely to become a very rapidly evolving field, with new targeted anticancer agents approved at a regular pace. Further developments for the TDM of several new TKIs are therefore anticipated to occur within the next few years. In that context, not only a facilitated access to powerful mass spectrometry instruments, but also the availability of robust methodologies for TKIs and tamox-ifen/metabolites analysis is a necessity for academic hospital centers that provide TDM service for targeted anticancer therapy. In particular, bioanalytical methods... 

The link between specific transition metals and various disease processes has prompted research interest into new and more effective bioanalytical methods to determine transition metals in physiological fluids. Traditionally clinical chemistry laboratories have used atomic absorption spectrophotometric (AAS) techniques to determine transition metals in physiological fluids. Although both low and high serum levels of various transition metals such as copper, iron and also zinc have been associated with various disease processes, the exact mechanisms underlying many of these conditions are still not completely understood. The following subsections describe some of the most prominent and best understood conditions associated with increased or decreased blood plasma levels of transition metals. 

Powell ML, Unger SE. Bioanalytical methods challenges and opportunities in drug development. In Applications of Pharmacokinetic Principles in Drug Development. Krishna R, ed. 2004. Kluwer Academic/Plenum Publishers, New York. pp. 21-52. 

Mass spectrometry-based bioanalytical methods play an important role in the entire process of searching new medicines to improve the quality of human life. High-performance liquid chromatography coupled to a tandem mass spectrometer (HPLC-MS/MS) has become the standard tool for the determination of pharmaceuticals in various in vitro and in vivo samples stemming from drug discovery and development experiments [1-5], However, the major disadvantage of the HPLC-MS/ MS technique is that it does not readily provide information on the distribution of the administrated drug and its metabolites. 

Cotton et al. Already in their preliminary work, the authors explored the potentialities and goals of the SERRS technique for possible applications to bioanalytical problems. The first possibility is enhanced sensitivity for the RR scattering of scarce materials. A second possibility can be added specifically to redox-active chromophores in proteins. Indeed, this new spectroelectrochemical method permits the simultaneous study of an electrochemical reaction in a biological system in conjunction with a specific measurement of subtile variations in the vibrational spectrum of the chromophores. Another striking feature of the SERRS spectroscopy is that fluorescence of the adsorbate can be completely quenched by the metal surface which generates a high-quality Raman spectrum Another common application of SERRS spectroscopy is the study of the adsorption behaviour and conformation of biomolecules at the metal/electrolyte interface. 

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