MTX Concentration (mtx + concentration)

Distribution by Scientific Domains

Selected Abstracts

High dose methotrexate population pharmacokinetics and Bayesian estimation in patients with lymphoid malignancy

Ye Min
Abstract The purpose of present study was to develop a population pharmacokinetic model of high dose methotrexate (HD-MTX) infusion in patients with lymphoid malignancy, to investigate the biological and clinical covariates related to the drug distribution and elimination. It is also the purpose to propose a limited sampling strategy (LSS) for the estimation of the time above the threshold (0.2,molL,1). A total 82 patients with lymphoid malignancy were involved in the study. A pharmacokinetic model was developed using nonlinear mixed-effect model. The influence of demographic characteristics, biological factors, and concurrent administration were investigated. The final predictive performance was validated by bootstrap and cross-validation. Bayesian estimation was evaluated. The pharmacokinetics of HD-MTX was described by a two-compartment model. The pharmacokinetic parameters and the inter-individual variability were as follows: the clearance CL, 7.45,Lh,1 (inter-individual variability 50.6%), the volume of the central and peripheral compartment V1, 25.9,L (22.5%), V2, 9.23,L (97.8%), respectively, and the intercompartmental clearance Q, 0.333,Lh,1 (70.4%). The influence of serum creatinine on CL and weight on V1 was retained in the final model. The protocol involved one sampling time at 44,h after the start of the infusion, allowing one to predict the time at which the MTX concentration reached the expected threshold (0.2,molL,1). Serum creatinine and weight showed significant influence on methotrexate CL and V1, respectively. Furthermore, a Bayesian estimation based on the covariates and 44,h sample was developed, allowing prediction of the individual methotrexate pharmacokinetic parameters and the time to 0.2,molL,1. Copyright 2009 John Wiley & Sons, Ltd. [source]

Mechanisms of unintended amino acid sequence changes in recombinant monoclonal antibodies expressed in Chinese Hamster Ovary (CHO) cells

Donglin Guo
Abstract An amino acid sequence variant is defined as an unintended amino acid sequence change and contributes to product heterogeneity. Recombinant monoclonal antibodies (MAbs) are primarily expressed from Chinese Hamster Ovary (CHO) cells using stably transfected production cell lines. Selections and amplifications with reagents such as methotrexate (MTX) are often required to achieve high producing stable cell lines. Since MTX is often used to generate high producing cell lines, we investigated the genomic mutation rates of the hypoxanthine,guanine phosphoribosyltransferase (HGPRT or HPRT) gene using a 6-thioguanine (6-TG) assay under various concentrations of MTX selection in CHO cells. Our results show that the 6-TG resistance increased as the MTX concentration increased during stable cell line development. We also investigated low levels of sequence variants observed in two stable cell lines expressing different MAbs. Our data show that the replacement of serine at position 167 by arginine (S167R) in the light chain of antibody A (MAb-A) was due to a genomic nucleotide sequence change whereas the replacement of serine at position 63 by asparagine (S63N) in the heavy chain of antibody B (MAb-B) was likely due to translational misincorporation. This mistranslation is codon specific since S63N mistranslation is not detectable when the S63 AGC codon is changed to a TCC or TCT codon. Our results demonstrate that both a genomic nucleotide change and translational misincorporation can lead to low levels of sequence variants and mistranslation of serine to asparagine can be eliminated by substituting the TCC or TCT codon for the S63 AGC codon without impacting antibody productivity. Biotechnol. Bioeng. 2010;107: 163,171. 2010 Wiley Periodicals, Inc. [source]

Methotrexate loaded poly(l -lactic acid) microspheres for intra-articular delivery of methotrexate to the joint

Linda S. Liang
Abstract A controlled release delivery system that localizes methotrexate (MTX) in the synovial joint is needed to treat inflammation in rheumatoid arthritis (RA). The purpose of this work was to develop and characterize MTX loaded poly(l -lactic acid) (PLLA) microspheres and evaluate in vivo tolerability and MTX plasma concentrations following intra-articular injection into healthy rabbits. MTX loaded PLLA (2 kg/mole) microspheres were prepared using the solvent evaporation method and characterized in terms of size, molecular weight, thermal properties, and release rates into phosphate buffered saline (PBS) (pH 7.4) at 37C. Biocompatibility was evaluated by observing the swelling of the joints of the rabbits and histological analysis following the injection of the microspheres. MTX concentrations in the plasma and urine samples of rabbits were evaluated by high-performance liquid chromatography (HPLC). MTX loaded microspheres showed a rapid burst phase followed by a slow release phase. MTX loaded and control microspheres were biocompatible and plasma concentrations of MTX were tenfold higher in rabbits injected intra-articularly with free MTX than MTX microspheres. MTX microspheres may retain the drug in the joint by reducing clearance from the joint into the blood. 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93: 943,956, 2004 [source]

Methotrexate catabolism to 7-hydroxymethotrexate in rheumatoid arthritis alters drug efficacy and retention and is reduced by folic acid supplementation

Joseph E. Baggott
Objective To assess the catabolism of methotrexate (MTX) to 7-hydroxy-MTX (7-OH-MTX) in patients with rheumatoid arthritis as well as the effect of folic acid and folinic acid on this catabolism. Methods Urinary excretion of MTX and its catabolite, 7-OH-MTX, was measured in 2 24-hour urine specimens collected after MTX therapy. Urine samples were collected from patients after the sixth and seventh weekly doses of MTX. MTX and 7-OH-MTX concentrations were determined by high-performance liquid chromatography mass spectrometry. Swelling and pain/tenderness indices were used to measure symptoms before and at 6 and 7 weeks of therapy. Patients received either folic acid or folinic acid supplements (1 mg/day) from week 6 to week 7. Results Folic acid inhibited aldehyde oxidase (AO), the enzyme that produces 7-OH-MTX, but folinic acid did not. Excretion of 7-OH-MTX (determined as a percentage of the dose of MTX or as mg 7-OH-MTX/gm creatinine) was not normally distributed (n = 39). Patients with marked improvement in swelling and pain/tenderness indices had a lower mean 7-OH-MTX excretion level (P < 0.05). Patients who received folic acid supplements had decreased 7-OH-MTX excretion (P = 0.03). Relatively high 7-OH-MTX excretion was correlated with relatively high MTX excretion and with relatively low MTX retention in vivo (P < 0.05) (n = 35). Conclusion Our findings of a non-normal distribution of 7-OH-MTX excretion suggest that there are at least 2 phenotypes for this catabolism. Decreased 7-OH-MTX formation suggests folic acid inhibition of AO and a better clinical response, while increased 7-OH-MTX formation may interfere with MTX polyglutamylation and binding to enzymes and, therefore, may increase MTX excretion and decrease MTX retention and efficacy in vivo. [source]