Contribution of plasma proteins, albumin and alpha 1-acid glycoprotein, to pharmacokinetics of a multi-targeted receptor tyrosine kinase inhibitor, sunitinib, in analbuminemic rats.

The present study investigated the role of the major plasma proteins, albumin and α1-acid glycoprotein (AAG), in the pharmacokinetics of sunitinib using Sprague-Dawley (SD) rats and analbuminemic rats with considerably low concentration of albumin established from SD rats. When sunitinib (3 mg/kg) was administered intravenously, the plasma concentrations of sunitinib at the early-distribution phase were significantly lower in analbuminemic rats than those in SD rats. The corresponding pharmacokinetic parameters of systemic clearance and volume of distribution at steady-state of sunitinib were significantly larger in analbuminemic rats (2.17 l/h/kg and 3.94 l/kg, respectively) than those in SD rats (1.26 l/h/kg and 2.37 l/kg, respectively). In in vitro protein-binding experiments using an equilibrium dialysis method, the binding profiles of sunitinib in SD and analbuminemic rats were linear, and the unbound fraction in analbuminemic rats (0.110) was significantly larger than that of SD rats (0.062). However, no significant differences in the unbound plasma concentration-time curves and pharmacokinetic parameters of sunitinib were observed between SD and analbuminemic rats. Protein-binding profiles of sunitinib to human serum albumin and AAG showed concentration independency and the binding potency was 65.3% and 33.7%, respectively. These results suggest that AAG has a low affinity for sunitinib and that the contribution of AAG to plasma protein-binding of sunitinib is relatively low compared to albumin. The present study suggests that the increased systemic clearance of sunitinib in analbuminemic rats might be due to an increase in the volume of distribution at steady-state, which could be due to the significant increase in the unbound fraction of sunitinib due to the low concentration of albumin.

A simple liquid chromatography-tandem mass spectrometry method for determination of plasma fentanyl concentration in rats and patients with cancer pain.

A fentanyl patch is widely used for the treatment of cancer pain. Its few adverse effects include constipation and drowsiness. The absorption volume of transdermally applied fentanyl may differ according to its site of application and variability in patch adhesion. Since fentanyl is predominantly metabolized by the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 in the liver, its concentration may vary in cases of physiologically reduced CYP3A4 activity in the liver (liver disease and aging) or on co-administration of drugs. The clinical significance of measuring plasma concentration of fentanyl is high, but conventional methods require complicated processes such as solid-phase extraction and liquid-liquid extraction before the sample is injected into an HPLC system. In this study, a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for determining plasma fentanyl concentrations by deproteinization with acetonitrile. A recovery test was conducted using an absolute calibration curve to confirm the method's linearity and inter- and intra-day reproducibility. The required plasma volume for detection was reduced from 1 mL in the conventional method to 20 µL in the present study, and a good calibration curve was obtained in the concentration range from 0.05 to 5 ng/mL. These findings suggest that the method for sample preparation and quantification developed in this study are appropriate for measuring fentanyl concentration in human plasma in clinical settings.

Evaluation of safety in clinical use of generic paclitaxel [NK] for injection.

PURPOSE: The introduction of generic drugs is a favored strategy in reducing medical costs, but some clinicians are often reluctant to use them because of lack of information with regard to their side effects. Generic paclitaxel [NK] differs from the proprietary version, Taxol®, in containing added citric acid and a more pure form of castor oil. However, little information exists regarding the effects of these additives on adverse events such as vascular pain, phlebitis, hypersensitivity and hepatic dysfunction. To compensate for this lack of information and to validate the safety of using generic paclitaxel, we investigated adverse events in response to generic paclitaxel [NK]. METHODS: Our investigation focused on patients treated with both the proprietary formulation (Taxol® for injection) and the generic version(paclitaxel [NK] for injection)sequentially from April 2008 to March 2009. Adverse events were investigated retrospectively. RESULTS: Incidence of vascular pain, phlebitis and hypersensitivity was similar to that with the original product. Although the expression of some liver enzymes was slightly increased and some gastrointestinal events were reduced following generic paclitaxel [NK] treatment there was no statistically significant difference. The profiles of other adverse events were not significantly different. CONCLUSION: Increased vascular pain and phlebitis, predicted due to low pH conditions caused by citric acid, were not observed. Similarly, the pure castor oil included in generic paclitaxel [NK] did not influence hypersensitivity and hepatic function. We found no significant differences in our study of proprietary and generic paclitaxel [NK]. Thus, clinicians have no reason for prejudice against using generic paclitaxel [NK] on the basis of increased risk of side effects.