Quantitative clinical metabolite

While this article presents and concentrates on examples of the common and routine use of mass spectrometry in the diagnosis of metabolic disease, many other applications are important in the identification and quantitation of metabolites in other areas of clinical medicine. 

Clinical Trials Human PK and metabolite Identification and quantitation Yes Medium to high... 

The synthesis of adrenal steroids and major excreted metabolites is illustrated in Fig. 5.3.1. Little secreted steroid product is excreted unchanged and most of the catabolism takes place in the liver, although cortisol metabolism by the kidney is clinically important and microbial metabolism in the gut can be quantitatively significant. The major metabolic transformations of hormonal steroids and precursors are detailed by Makin [54] and summarized in Fig. 5.3.2. GC-MS steroid profiling is the technique of choice for measurement of important urinary constituents. 

In clinical chemistry, interpretation of the data can be quite simple or complex. In the case of MS/MS applications pertaining to a single analyte, all that is needed is the intensity value from the mass of a peak of interest and its internal standard. Viewing of a spectrum is not necessary. For profile methods such as full-scan acylcarni-tines, amino acids, or other compound families, the interpretation is more complex. With multiple related components, calculation of the concentration of many key metabolites is required. The system generally has multiple internal standards, external standards, or both. In addition to the concentration calculations, examination of a profile is often best achieved by viewing the spectra together with the quantitative information. 

Ramanathan, R., Zhong, R., Blumenkrantz, N., Chowdhury, S. K., and Alton, K. B. (2007d). Quantitative assessment of metabolites early in the clinical program Potential for using LC-Nanospray-MS. Eastern Analytical Symposium and Exposition, Somerset, NJ. 

The use of SRM methods for quantitative bioanalysis represents increased dimensions of mass spectrometry analysis. SRM methods that use APCI-LC/MS/MS for the quantitative analysis of an antipsychotic agent, clozapine, in human plasma were described by Dear and co-workers (Dear et al., 1998). Preclinical development studies of clozapine in rats and dogs used HPLC with fluorescence detection (FLD). With this method, a better limit of quantitation (LOQ) of 1 ng/mL was obtained. As the compound moved into the clinical stages of development, a more sensitive method of analysis was required to obtain rapid metabolic information in support of drug safety evaluation studies. A standard LC/MS/MS method is used for the quantitative analysis of clozapine (I) and four metabolites (II-V) in human plasma (Figure 6.34). 

In vitro studies can only give a limited, mechanistic picture of biotransformation in animals or humans. The quantitative importance of each individual metabolite can only be assessed in vivo. Also, samples collected from in vivo studies give rise to comprehensive metabolite identification work (Watt et al. 2003 Clarke et al. 2001) which is also required from a regulatory point of view (Baillie et al. 2002). Due to the labour-intense nature of these studies and the need of applying radiolabeled compounds in order to get a complete picture of biotransformation these studies are performed at a later stage of development during preclinical and clinical phase. 

The quantitative determination of analytes in biological matrices such as blood, urine, etc. is called bioanalysis. Regulatory authorities and International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidance requires that the concentration-time profiles of drugs and/or metabolites in man or in animals are studied so their respective pharmacokinetics can be calculated and used as a basis for the evaluation of pre-clinical (especially toxicological) and clinical studies. 

---