Pharmacokinetics and Bioequivalence of Methotrexate in Human Plasma Studied by Liquid Chromatography-Mass Spectrometry (LC-MS)

Pharmacokinetic Simulation and Area under the Curve Estimation of Drugs Subject to Enterohepatic Circulation

Enterohepatic circulation (EHC) is a complex process where drugs undergo secretion and reabsorption from the intestinal lumen multiple times, resulting in pharmacokinetic profiles with multiple peaks. The impact of EHC on area under the curve (AUC) has been a topic of extensive debate, questioning the suitability of conventional AUC estimation methods. Moreover, a universal model for accurately estimating AUC in EHC scenarios is lacking. To address this gap, we conducted a simulation study evaluating five empirical models under various sampling strategies to assess their performance in AUC estimation. Our results identify the most suitable model for EHC scenarios and underscore the critical role of meal-based sampling strategies in accurate AUC estimation. Additionally, we demonstrate that while the trapezoidal method performs comparably to other models with a large number of samples, alternative models are essential when sample numbers are limited. These findings not only illuminate how EHC influences AUC but also pave the way for the application of empirical models in real-world drug studies.

LC-MS/MS method for screening of intoxication and drug adherence of angiotensin-converting enzyme inhibitors in plasma

Aim: Intentional and accidental drug intoxication as well as medication adherence require sensitive and reliable analytical screening methods. Such methods are often lacking in children and adults, therefore, a reliable analytical method has been developed by using low plasma volume. Materials & methods: Sample preparation from plasma was achieved by solid-phase extraction process. LC-MS in positive ion mode was performed using X-select CSH™ C18 column. The mobile phase consisted of water and acetonitrile acidified with 1% formic acid using a gradient method with total run time of 10 min. Results: The method showed repeatability for all analytes. The linearity range from 0.78 to 100 ng/ml per analyte was established with recoveries ≥87% and matrix effect for all analytes was within guideline limits. Conclusion: The screening method was successfully validated for monitoring of intoxication and medication adherence of ten analytes in 50 μl residual plasma samples of children and adults.

Liquid chromatographic methods for the therapeutic drug monitoring of methotrexate as clinical decision support for personalized medicine: A brief review

Methotrexate (MTX) is an antifolate drug used for several diseases. Depending on the disease, MTX can be administered at low dose (LDMTX) in some autoimmune diseases, like rheumatoid arthritis, or at high dose (HDMTX) in some cancers, such as acute lymphoblastic leukemia. After absorption, MTX is metabolized in the liver to 7-hydroxymethotrexate and in the intestine to 2,4-diamino-N10-methylpteroic acid (DAMPA). Moreover, inside red blood cells, MTX is converted to active metabolites, MTX polyglutamates (MTXPGs), contributing to its pharmacodynamics. Owing to its narrow therapeutic range, and inter- and intra-patient variability, either noneffectiveness and/or toxicity may occur. Because of the existence of a relationship between drug therapeutic outcome and its systemic concentration, therapeutic drug monitoring (TDM) may ensure the effectiveness and safety of MTX use. In order to monitor the optimization of patient clinical response profile, several analytical methods have been described for TDM in biological samples. These include liquid chromatography (LC) coupled with ultraviolet detection, fluorescence detection or mass spectrometry, each one presenting advantages and drawbacks. This paper reviews the most commonly used techniques for sample preparation and critically discusses the current LC methods applied for the TDM of MTX in biological samples, at LDMTX and HDMTX.