Drugs quantification

Column size is another important consideration. For equipment designed for most routine laboratory HPLC situations the relative sensitivity of APTelectrospray instruments is better at low flow rates (0.2-0.8 mL/min) whereas the relative sensitivity of APCI instruments is enhanced at high flow rates (0.5-2 mL/min). As a result, small columns are appropriate for API-electrospray/MS and, if only one or two compounds of interest are found in a particular sample, high-resolution separations are not necessary. For APTelectrospray analysis of complex samples, 150 mm x 4.1 mml.D., 3 pm columns (flow 0.5-1.0 mL/min) are usually sufficient. For drug quantification involving analysis of single or low numbers of compounds, small columns such as 30 mm x 2.1 mm I.D., 3.5 pm columns (flow rate 0.2-0.4 mL/min) provide sufficient separation and a saving in both column cost and solvent utilization. The reduced injection volume required for the small columns often results in better resolution and increased sensitivity. 

Maurer HH (2005) Advances in analytical toxicology the current role of liquid chromatography-mass spectrometry in drug quantification in blood and oral fluid. Anal Bioanal Chem 381 (1) 110-118. doi 10.1007/s00216-004-2774-z... 

To improve upon the approach employed by King et al. [164], Li et al. [327] used SRM-triggered information-dependent acquisition (IDA) to acquire both parent drug quantification data and qualitative metabolite MS/MS data. To validate the IDA approach, Li et al. [327] tested both the conventional triple quadrupole mode as well as in the ion trap mode and showed that the cycle time improved from 2.78 to 1.14 s with the IDA approach. The longer cycle time in the triple quadrupole mode of operation would have resulted in possibly missing some the metabolites. 

Saerens L, Dierickx L et al (2011). Raman spectroscopy for the in-line polymer-drug quantification and solid state characterization during a pharmaceutical hot-melt extrusion process. Eur J Pharm Biopharm 77 158-163... 

The work by Hammett and Taft in the 1950s had been dedicated to the separation and quantification of steric and electronic influences on chemical reactivity. Building on this, from 1964 onwards Hansch started to quantify the steric, electrostatic, and hydrophobic effects and their influences on a variety of properties, not least on the biological activity of drugs. In 1964, the Free-Wilson analysis was introduced to relate biological activity to the presence or absence of certain substructures in a molecule. 

Nikolai LN, McClure EL, MacLeod SL, Wong CS (2006) Stereoisomer quantification of the Beta-blocker drugs atenolol, metoprolol, and propranolol in wastewaters by chiral high-performance liquid chromatography-tandem mass spectrometry. J Chromatogr A 1131 103-109... 

A knowledge of the metabolic fate of a particular drug, both in terms of the identification and quantification of the metabolites, is necessary not only to ensure that its use will not cause more problems than the medical condition it is designed to alleviate but, from the drug company s perspective, to facilitate the design of more effective drugs. 

Since endosulfan is a cytochrome P450-dependent monooxygenase inducer, the quantification of specific enzyme activities (e.g., aminopyrine-A -demethylase, aniline hydroxylase) may indicate that exposure to endosulfan has occurred (Agarwal et al. 1978). Because numerous chemicals and drugs found at hazardous waste sites and elsewhere also induce hepatic enzymes, these measurements are nonspecific and are not necessarily an indicator solely of endosulfan exposure. However, these enzyme levels can be useful indicators of exposure, together with the detection of endosulfan isomers or the sulfate metabolite in the tissues or excreta. 

The aim of the analysis of cannabinoids in plants is to discriminate between the phenotypes (drug-type/fiber-type). Quantification of cannabinoids in plant material is needed if it will be used in medicinal appHcations, e.g., in C. sativa extracts. The ratio between A9-THC and CBN can be used for the determination of the age of stored marijuana samples [84]. 

In a traditional, two-way cross-over study, blood samples are taken at predetermined times (e.g., 0.5, 1, 1.5, 3, 6, 9, 12, 24, and 36 hours after dosing). The samples are assayed for drug (and if necessary metabolites). Fortunately, analytical methods, especially HPLC, are now available that make the quantification of many drugs in blood or serum convenient, rapid, and relatively inexpensive. The method selected should normally have an acceptance precision so that concentrations of drug of one tenth Cmax can be reliably quantified. 

Proponents of the clinical mirror theory of bioequivalence would like to see increased emphasis placed on quantification of pharmacodynamic values. In some instance we can readily identify how reliable and relevant pharmacodynamic values can be measured. For example, for an antihypertensive drug, measurement of blood pressure changes can be conveniently, inexpensively and objectively determined. However, for other types of drug (e.g., antidepressants) it is not easy to conceive any simple pharmacodynamic attributes that could be readily determined. 

Analytical methods available for the quantification of drugs in body fluids have developed rapidly in recent... 

Also, if conversion of drug to active metabolite shows significant departure from linear pharmacokinetics, it is possible that small differences in the rate of absorption of the parent drug (even within the 80-125% range for log transformed data) could result in clinically significant differences in the concentration/ time profiles for the active metabolite. When reliable data indicate that this situation may exist, a requirement of quantification of active metabolites in a bioequivalency study would seem to be fully justified. 

Another circumstance in which there may be generally compelling reasons to require quantification of active metabolites is when a controlled-release drug-delivery system is used for a drug that has an active metabolite. Some of the papers that consider the topics of bioequivalency testing for drugs with long half-lives or active metabolites are listed in the references section of this chapter [12-17]. 

Obviously, if the clinical mirror approach to bioequivalency testing gains momentum, we may expect to see more quantification of clinical response in bioequivalency studies. In some instances pharmacodynamic parameters that are amenable to precise quantification are easily identified. Thus, if we are working with an antihypertensive drug, measurement of blood pressure using an electronic sphygnomanometer is an obvious option. However, for many drugs there is no simple way to quantify pharmacodynamic response. In some cases we may have to rely, to some extent at least, on patient diaries [41]. Such techniques are open to criticism of subjectivity and imprecision. 

There are special problems in bioequivalency determinations when conventional pharmacokinetic studies are not possible. For example, when drugs are administered intranasally for direct treatment of receptors in the nasal mucosa, the concentration of drug in plasma may be below the limit of quantification. In such cases we are forced to attempt measurement of clinical response. The subjectivity and/or low precision of this type of study can be a serious problem. 

Huber, J.F.K., Kenndler, E., Reich, G. (1979). Quantification of the information content of multi-dimensional gas chromatography and low resolution mass spectrometry in the identification of doping drugs. J. Chromatogr. 172, 15-30. 

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