Pharmacokinetic modeling and simulation of subcutaneous and intravenous IgG dosing in patients with primary immunodeficiency diseases.

A population pharmacokinetic (PK) model for comparing the PK of subcutaneously administered immunoglobulin G (IgG) replacement therapy (SCIG) with Gamunex-C 10% or SCIG 20% formulations in patients with primary immunodeficiency diseases was developed using data from 3 clinical trials (N = 95, 69.5% adults, 30.5% <18 years) of intravenous IG (IVIG) 10% and SCIG 10% or SCIG 20%. Serum IgG exposure following switches from IVIG 10% every 3 or 4 weeks to biweekly SCIG 20% (dose adjustment factor 1.0 or 1.37) and from weekly SCIG 20% to biweekly SCIG 20% or SCIG 20% 2-7 times/week was simulated. The PK of IVIG 10% and SCIG 20% were adequately described by a 2-compartment model with first-order absorption rate constant of exogenous IgG from an SC depot compartment into the central compartment and first-order elimination from the central compartment. Switching from IVIG 10% every 4 weeks to biweekly SCIG 20% produced similar serum IgG exposure, with lower peak and higher trough serum IgG concentrations. Switching from IVIG 10% every 3 or 4 weeks to weekly and biweekly SCIG 20% yielded comparable IgG exposure and clinically effective trough IgG concentrations.

GSSG/GSH ratios in cryopreserved rat and human hepatocytes as a biomarker for drug induced oxidative stress.

The formation of reactive oxygen species (ROS) could cause cellular damage and eventually lead to apoptosis and necrosis. The ratio between oxidized glutathione and reduced glutathione (GSSG-to-GSH ratio) has been used as an important in vitro and in vivo biomarker of the redox balance in the cell and consequently of cellular oxidative stress. This paper optimizes a LC-MS/MS method for the simultaneous determination of GSH and GSSG. The proposed method is based on the derivatization of reduced GSH using iodoacetic acid (IAA) in order to prevent its rapid oxidation to GSSG during sample preparation. The optimized analytical method was applied to evaluate the effect of different pharmaceutical agents on GSSG-to-GSH ratio in cryopreserved rat and human hepatocytes in culture. Hepatocyte viabilities were also determined at the same time by using the WST-1 assay as a direct measurement of cell mitochondrial respiration. The results obtained demonstrate that cryopreserved rat and human hepatocytes in culture are reliable in vitro models for the evaluation of cellular oxidative stress. In addition, the GSSG-to-GSH ratio measurements could be a biomarker of hepatotoxicity providing similar results to those of cytotoxicity assay.

Determination of S-containing drug metabolites from in vitro and in vivo metabolism studies by using LC-ICP/MS.

Recently, liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP/MS) has been introduced to deal with some applications in the field of pharmaceutical, biomedical, and clinical analysis. In the case of drug research, the number of drugs and their metabolites containing detectable elements is quite limited. In this paper, LC-ICP/MS has been demonstrated to be suitable for the determination of S-containing drugs and their metabolites. In order to minimize the interference of polyatomic oxygen (m/z 32), the indirect detection of S, by means of the SO(+) ion (m/z 48), was optimized. For quantification purposes, it has been encountered that the percentage of organic solvent in the mobile phase strongly affects the sensitivity. Here, corrective strategies based on calibration curves established at different solvent concentrations (solvent-zone quantification) and post-column gradient compensation have been proposed to circumvent sensitivity variations. Results obtained have shown that suitable calibration models have been built for any compound regardless of the solvent percentage at which it is eluted from the chromatographic column. To prove the applicability of this methodology, the metabolism of ethacrynic acid and tiotropium bromide has been studied in vitro and in vivo. In the first case, ethacrynic acid does not contain S in its structure, however, the major route of metabolism for this compound consists of the formation of glutathione adduct and its further degradation. In the second case, tiotropium bromide contains two S atoms in its structure.

In vitro liver metabolism of aclidinium bromide in preclinical animal species and humans: identification of the human enzymes involved in its oxidative metabolism.

The metabolism of aclidinium bromide, a novel long-acting antimuscarinic drug for the maintenance treatment of chronic obstructive pulmonary disorder, has been investigated in liver microsomes and hepatocytes of mice, rats, rabbits, dogs, and humans. Due to the rapid hydrolysis of this ester compound, two distinct radiolabeled forms of aclidinium were studied. The main biotransformation route of aclidinium was the hydrolytic cleavage of the ester moiety, resulting in the formation of the alcohol metabolite (M2, LAS34823) and carboxylic acid metabolite (m3, LAS34850), which mainly occurred non-enzymatically. By comparison, the oxidative metabolism was substantially lower and the metabolite profiles were similar across all five species examined. Aclidinium was metabolized oxidatively to four minor primary metabolites that were identified as monohydroxylated derivatives of aclidinium at the phenyl (M4) and glycolyl (m6 and m7) moieties of the molecule. The NADPH-dependent metabolite m4 involved the loss of one of the thiophene rings of aclidinium. Incubations with human recombinant P450 isoforms and inhibition studies with selective chemical inhibitors and antibodies of human P450 enzymes demonstrated that the oxidative metabolism of aclidinium is primarily mediated by CYP3A4 and CYP2D6. Additionally, up to eight secondary metabolites were also characterized, involving further hydrolysis, oxidation, or glucuronidation of the primary metabolites. Also, the liver oxidative metabolism of the alcohol metabolite (LAS34823) resulted in the production of one hydroxylated metabolite (M1) mediated by human CYP2D6, whereas the acid metabolite (LAS34850) was not metabolized enzymatically, although a minor non-enzymatic and NADPH-dependent reduction was observed.