Simultaneous determination of furosemide and carbamazepine in biological matrices by solvent bar microextraction combined with HPLC-DAD and central composite design CCD

A sensitive and simple sample pretreatment method based on a two-phase solvent bar microextraction SBME technique coupled with HPLC-DAD was developed for simultaneous extraction and determination of trace amounts of furosemide and carbamazepine in human urine and plasma samples. The significance of operational factors on carbamazepine and furosemide extraction efficiency % (EE%) was screened using full factorial design (FFD) while central composite design (CCD) was used to model the entire process. A quadratic model was found convenient to correlate the extraction EE% of selected drugs with dominant experimental factors. A Pareto chart was also used to examine the importance of factors on drugs' EE%. The analytical performance of the method in urine and plasma samples demonstrated good linearity R² ˃ 0.992 with detection limits ranging from 4.2 to 10.9 μg L^-1 , and extraction recovery ˃ 89.45% for both drugs in urine and plasma samples. A comparison against published methods was also studied and the results revealed that the developed method exhibits a confident sensitivity, feasible operation, and simple analysis for both drugs. Finally, the practicability of the validated SBME-HPLC-DAD method was demonstrated by successfully applying it to the analysis of furosemide, and carbamazepine in real patient urine samples.

Metabolism and Pharmacokinetics of SP-8356, a Novel (1S)-(-)-Verbenone Derivative, in Rats and Dogs and Its Implications in Humans

(1S,5R)-4-((E)-3,4-dihydroxy-5-methoxystryryl)-6,6-dimethylbicylco[3.1.1]hept-3-en-2-one (SP-8356) is a novel (1S)-(−)-verbenone derivative that is currently in preclinical development for the treatment of ischemic stroke and atherosclerosis. This report aimed at characterization of the metabolism and pharmacokinetic properties of SP-8356. Following intravenous dose in rats and dogs, plasma concentrations of SP-8356 declined rapidly with high clearance (CL) and short half-life; after oral administration in both species, its plasma levels were below the quantitation limit. Fourteen circulating metabolites, formed by mono-oxygenation, demethylation, glucuronidation, catechol O-methylation, sulfation and oxidation (bioactivation) followed by glutathione (GSH) conjugation, were tentatively identified in both species. Urinary excretion of SP-8356 appeared to be minimal in rats, compared to its metabolites. GSH conjugate of SP-8356 was also formed during incubation with rat liver S9 fraction consistent with oxidative bioactivation; this bioactivation was almost completely inhibited by the cofactors for glucuronidation, sulfation and methylation, indicating that it may be abolished by competing metabolic reactions in the body. The human pharmacokinetics of SP-8356 was predicted to be similar to that of the animals based on the current in vitro metabolic stability results. In summary, rapid phase II metabolism appears to be mainly responsible for its suboptimal pharmacokinetics, such as high CL and low oral absorption. Because of competing metabolic reactions, potential safety risks related to SP-8356 bioactivation may be low.

The application of control charts in regulated bioanalysis for monitoring long-term reproducibility

In regulated bioanalysis, the acceptance of results is batch-wise. When during clinical development derived pharmacokinetic or pharmacodynamic results from different studies will be combined or compared, it is recommendable to monitor the long-term reproducibility of bioanalytical assays. Long-term reproducibility can be evaluated by control charts generated from control samples included in each batch. We present a methodology for the implementation, construction and evaluation of control charts next to the regular batch acceptance of bioanalytical results. Decision rules can be set up for a statistical evaluation of the results. Violation of a decision rule may lead to a root-cause investigation and corrective actions to improve assay robustness. Three examples of control charts, for pharmacokinetic and pharmacodynamic analytes are presented.

Therapeutic drug management of linezolid: a missed opportunity for clinicians?

Some studies have shown that adjustments to the linezolid dose guided by therapeutic drug monitoring (TDM) can reduce interindividual variability in drug exposure and improve linezolid tolerability. In this study, 6 years of linezolid TDM, a diagnostic service for our hospital and others in the Milan (Italy) area, is described. Samples were collected immediately before the morning dose intake (trough concentrations) in steady-state conditions. Linezolid concentrations were quantified by a validated high-performance liquid chromatography (HPLC) method. Four hundred linezolid trough concentrations from 220 patients were collected. A 20-fold variability in linezolid levels was observed. Positive and significant correlations between linezolid trough concentrations and patient age (r = 0.325, P <0.01) or serum creatinine (r = 0.511, P <0.01) were found. A progressive increase in linezolid concentrations with time was observed in a subgroup of patients with more than one TDM assessment. Elderly patients, especially those aged >80 years and with impaired renal function, are at a higher risk of overexposure to linezolid. Despite the observed progressive increase in linezolid concentrations over time, most physicians did not change the drug dose according to the TDM results, even in the presence of frank overexposure to linezolid.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.