Comparison of biomarker and chromatographic analytical approaches to pharmacokinetic study of sitagliptin.

The pharmacokinetic profiling of active compounds is necessary for drug development and application. Approaches to a pharmacokinetic study based on biological markers are alternatives to traditional approaches based on chromatographic methods. The aim of the study was to compare two analytical approaches to pharmacokinetics investigation for an example of sitagliptin in rabbits after one dose oral administration. The method for sitagliptin quantification in rabbit plasma samples based on a correlation between its concentration and dipeptidyl peptidase IV activity was proposed, validated, and applied. The high-performance liquid chromatography (HPLC)-ultraviolet (UV) method was also validated and applied for the same sample analysis. The plasma pharmacokinetics of sitagliptin after oral administration to the rabbits in one dose was characterized after two analytical assays. The close values of the main pharmacokinetic parameters were obtained after two approaches. The nontraditional approach based on correlation of special marker activity and active substance concentration appears to be more sensitive than HPLC-UV. Thus, the sitagliptin concentrations determined by biomarker assay were higher than the lower limit of quantification (LLOQ) for a longer period (more timepoints) than after the HPLC-UV assay. This feature may influence the values of some calculated concentration-dependent (area under the curve [AUC]0-t , etc.) and time-dependent parameters (mean residence time [MRT], T1/2 , etc.). The values of Tmax obtained by the two approaches were similar and adequate for oral drug administration that confirms the correctness of biomarker selection for pharmacokinetics assessment. The obtained results on the example of sitagliptin confirms that the biomarker approach is adequate and applicable for a pharmacokinetics study. Similar approaches may be effective for individual compounds and complex mixtures when it is difficult or impossible to analyze them traditionally by chromatographic methods.

Pharmacokinetics and Tissue Disposition of Nanosystem-Entrapped Betulin After Endotracheal Administration to Rats.

BACKGROUND AND OBJECTIVES: Betulin is a triterpene extracted from the cork layer of the outer bark of Betula spp. It has a wide spectrum of pharmacological activities, including being lung protective; however, its bioavailability is low. To increase its bioavailability, betulin was entrapped in a nanosystem (BN). In this study, we investigated the pharmacokinetics and tissue distribution of nanosystem-entrapped betulin after single dose endotracheal administration to rats. METHOD: Betulin was nanosystem-entrapped using a solvent exchange technique. The surface morphology and size of the nanosystem were characterized by transmission electron microscopy and dynamic light scattering. The plasma and tissue concentrations of betulin were determined using a validated high-performance liquid chromatography method. RESULTS: The highest concentration of betulin was found in lungs and liver, and the lowest in the heart. Betulin did not penetrate highly vascularized tissues or tissue with an average degree of vascularization, nor did it cross the blood-brain barrier. Tissue availability in the lungs was 1.3 times higher for BN than for free betulin. Betulin was detected in the bloodstream at 15 min after administration of BN compared with only at 1 h after administration of free betulin. Penetration of betulin in the liver tissue was characterized by a high degree of intensity both for BN and free betulin. Betulin in the heart tissue was detected in much smaller quantities than in the liver. CONCLUSION: Entrapment of betulin in nanosystem form shows promise as a novel strategy in the treatment of pulmonary diseases.

Determination and pharmacokinetic study of taxifolin in rabbit plasma by high-performance liquid chromatography.

Taxifolin has been widely used in the treatment of cerebral infarction and sequelae, cerebral thrombus, coronary heart disease and angina pectoris. A reliable sensitive reversed-phase high-performance liquid chromatography (RP-HPLC) method with UV detection for the pharmacokinetic study of taxifolin in rabbit plasma after enzymatic hydrolysis was developed and validated for the first time. Taxifolin, with biochanin A as the internal standard, was extracted from plasma samples by liquid/liquid extraction after hydrolysis with beta-glucuronidase and sulfatase. Chromatographic separation was conducted on a Luna C18 column (4.6 mm x 150 mm, 5 microm particle size) and pre-column (2.0 mm, the same sorbent). Two-step linear gradient elution with acetonitrile and 0.03% water solution of trifluoroacetic acid as mobile phase at a flow rate of 1.0 ml/min was used. The UV detector is set at 290 nm. The elution time for taxifolin and biochanin A was approximately 7.9 and 18.3 min, respectively. The calibration curve of taxifolin was linear (r > 0.9997) over the range of 0.03-5.0 microg/ml in rabbit plasma. The limit of detection (LOD) and limit of quantification (LOQ) for taxifolin were 0.03 and 0.11 microg/ml, respectively. The present method was successfully applied for the estimation of the pharmacokinetic parameters of taxifolin following intravenous and oral administration of lipid solution to rabbits. The absolute bioavailability of taxifolin after oral administration of lipid solution was 36%.

Determination of icariin in rat plasma by reverse-phase high-performance liquid chromatography after oral administration of a lipid-based suspension of Epimedium koreanum extract.

A simple, specific and sensitive method for quantitative determination of icariin in rat plasma using reverse-phase high-performance liquid chromatography with UV-detection was developed and applied to an animal study of a lipid-based suspension of the Epimedium koreanum extract in rats. Rutin was selected as the internal standard and methanol was found to be the best solvent for extraction of icariin from the plasma. Linearity was observed between 0.030 and 100 microg/mL (r > 0.99). The extraction recoveries of icariin and rutin were approximately 75 and 80%, respectively, in plasma. The intra- and inter-day coefficients of variation were less than 5%. The limit of detection was 6 ng/mL and the limit of quantification was 18 ng/mL.