Pharmacokinetic studies sample stability

The HPLC assays for QUINs in food samples use different sample-preparation procedures and various detection modes, and some of these complete methods are applied to pharmacokinetics studies or to stability tests ... 

Mathematical models allow for considerable data compression. Data that fill many notebooks and/or tables may be summarized by means of the few parameters of a well chosen model. Plasma concentration versus time data collected during a pharmacokinetic study in many patients may be summarized using a volume of distribution term and an elimination half-life. Other models may include more parameters, but there is always a considerable compression in the information required to describe the overall results of the study. An extensive drug stability study involving many samples stored at various elevated temperatures may be summarized as a single time for 10% decomposition at room temperature. Determination of appropriate models can be a very useful method of summarizing an experimental study. 

The validated bioanalysis of rosuvastatin in human plasma by automated SPE in 96-well format with Oasis HLB material and positive-ion LC-ESI-MS-MS was reported using a [DJ-ILIS [54]. The stability of rosuvastatin and its potential conversion into the lactone due to sample pretreatment was thoroughly investigated. The method was applied in pharmacokinetic studies during clinical trials. A similar method was applied by the same group in the bioanalysis of the /V-desmethyl metabolite of rosuvastatin [55]. 

A sensitive method for quantitation of glimepiride in human plasma was established using electrospray ionization tandem mass spectrometry (ESI/MS/MS). Detection of glimepiride is accurate and precise with a quantitation limit of 0.1 ng/ml. This method was successfully applied to a pharmacokinetic study of glimepiride. No interferences of the analytes were observed because of high selectivity of the MS/MS technique. The method of Song et al. is also sufficiently sensitive, with a quantification limit lower than the minimum concentration recommended for plasma samples obtained after the administration of 2 mg glimepiride. This smdy indicates a reliable stability of... 

This is the place to start, since most often, analytical chemists are trying to help solve someone else s problem. We need to define the solute and its matrix as well as the nature of the analytical problem. For example, in the world of pharmaceuticals, there are raw material identification and purity determinations, in-process testing, dosage-form determinations, content uniformity, dissolution testing, stability studies, bioavailability, pharmacokinetics, and drug metabolism, to name a few. Each of these analytical problems has its own specific requirements. The matrix can be a raw material, granulation, tablet, capsule, solution, lotion, cream, syrup, dissolution medium, blood serum, urine, or various body tissues and fluids. Similar definitions can be described for virtually any industrial area and problem set. These definitions will help select sample preparation, separation, and detection techniques. 

Pharmacokinetics and metabolism of As(III) in APL 192 patients studied. The intermediate MMA(III) and DMA(III), were detected in most urine samples when diethyldithiocar-bomate, was added to these samples for stabilization of As species. The major urine species As(III), MMA and DMA, accounting for >95% of the total arsenic excreted in urine. On the other hand, these species accounted for 32-65% of the total arsenic, suggesting other pathways of As excretion, such as through the bile, may play an important role in removal of arsenic from the human body when challenged by high levels of As(III)... 

---