Shinji Kobuchi

Effect of serum lipids on the pharmacokinetics of atazanavir in hyperlipidemic rats.

Atazanavir (ATV) has been successfully used in HIV patients with severe hyperlipidemia (HL); however, little is known about the pharmacokinetics of ATV in HL. The aim of this study was to investigate the pharmacokinetics of ATV in HL. With the increase of serum lipids, the protein binding rate in HL rats (approximately 97%) was significantly higher than that in control (approximately 87%). After intravenous (iv), oral (po) and intraportal (ip) administration of ATV at a dosage of 7 mg/kg, AUCs in HL rats were 12.41, 5.24 and 8.89 microg/mLh, respectively, and were significantly higher than those in control rats (4.09, 1.70 and 3.38 microg/mLh). Despite the decrease of distribution volume (Vd(ss)), the terminal half-life (t(1/2)) in HL tended to be shorter than in control, and hepatic distribution of ATV in HL rats was 4.8-fold increases. These results suggested that the uptake of ATV into liver might counteract the decrease of Vd(ss). On the other hand, there was no significant difference in bioavailability, and the lymphatic transport to AUC showed no statistical change. In conclusion, although the protein binding rate and AUC were significantly increased, the pharmacokinetics of ATV might be tolerated in HL.

Pharmacokinetics of clomipramine, an antidepressant, in poloxamer 407-induced hyperlipidaemic model rats.

Objective  This study was undertaken to investigate the effects of hyperlipidaemia on the pharmacokinetics of clomipramine, an antidepressant, particularly addressing the change of clomipramine distribution to plasma components in poloxamer 407‐induced hyperlipidaemia model rats.

Time-Dependent Interaction of Ritonavir in Chronic Use: The Power Balance Between Inhibition and Induction of P-Glycoprotein and Cytochrome P450 3A

Ritonavir (RTV) is not only an inhibitor but also an immunoreactive inducer of both P-glycoprotein (Pgp) and cytochrome P450 (CYP) 3A in terms of its chronic use. The aim of present study was to test the hypothesis that the power balance between inhibition effects of RTV and induced activities of Pgp and CYP3A depends on the time after last RTV treatment (TimeR) in the chronic use of RTV; rhodamine 123 (Rho) and midazolam (MDZ) were administered at predetermined TimeR to rats pretreated with RTV for 7 days. After oral administration of Rho and MDZ to rats pretreated with RTV for 7 days, the areas under the plasma concentration-time curve of Rho and MDZ were significantly altered depending on TimeR: 1.27-, 0.79-, 0.95-, and 0.11-fold increases over that of the control for Rho at TimeR = 0, 3, 9, and 24 h and 3.12-, 1.50-, 1.27-, and 0.17-fold increases over that of the control for MDZ at TimeR = 0, 3, 9, and 24 h, respectively. These results revealed the presence of the time-dependent interaction of RTV with concomitant drugs in chronic use and should be taken into account in therapeutic strategies for HIV infection.

A validated LC‐MS/MS method for the determination of canagliflozin, a sodium‐glucose co‐transporter 2 (SGLT‐2) inhibitor, in a lower volume of rat plasma: application to pharmacokinetic studies in rats

Canagliflozin is a novel, orally selective inhibitor of sodium-dependent glucose co-transporter-2 (SGLT2) for the treatment of patients with type 2 diabetes mellitus. In this study, a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative analysis of canagliflozin in a lower volume of rat plasma (0.1 mL) was established and applied to a pharmacokinetic study in rats. Following liquid-liquid extraction by tert-butyl methyl ether, chromatographic separation of canagliflozin was performed on a Quicksorb ODS (2.1 mm i.d. × 150 mm, 5 µm size) using acetonitrile-0.1% formic acid (90:10, v/v) as the mobile phase at a flow rate of 0.2 mL/min. The detection was carried out using an API 3200 triple-quadrupole mass spectrometer operating in the positive electrospray ionization mode. Selected ion monitoring transitions of m/z = 462.0 [M + NH4 ](+)  → 191.0 for canagliflozin and m/z = 451.2 [M + H](+)  → 71.0 for empagliflozin (internal standard) were obtained. The validation of the method was investigated, and it was found to be of sufficient specificity, accuracy and precision. Canagliflozin in rat plasma was stable under the analytical conditions used. This validated method was successfully applied to assess the pharmacokinetics of canagliflozin in rats using 0.1 mL rat plasma. Copyright

Therapeutic Drug Monitoring of Vancomycin in Dermal Interstitial Fluid Using Dissolving Microneedles

Objective: To design an alternative painless method for vancomycin (VCM) monitoring by withdrawing interstitial fluid (ISF) the skin using dissolving microneedles (DMNs) and possibly replace the conventional clinical blood sampling method. Methods: Male Wistar rats were anesthetized with 50 mg/kg sodium pentobarbital. Vancomycin at 5 mg/mL in saline was intravenously administered via the jugular vein. ISF was collected from a formed pore at 15, 30, 45, 60, 75, 90, and 120 min after the DMNs was removed from the skin. In addition, 0.3 mL blood samples were collected from the left femoral vein. Results: The correlation between the plasma and ISF VCM concentrations was significantly strong (r = 0.676, p < 0.05). Microscopic observation of the skin after application of the DMNs demonstrated their safety as a device for sampling ISF. Conclusion: A novel monitoring method for VCM was developed to painlessly determine concentrations in the ISF as opposed to blood sampling.

A quantitative LC–MS/MS method for determining ipragliflozin, a sodium-glucose co-transporter 2 (SGLT-2) inhibitor, and its application to a pharmacokinetic study in rats

Ipragliflozin is a highly potent and selective sodium-dependent glucose co-transporter-2 (SGLT2) inhibitor, a novel class of hypoglycemic agents. The aim of the present study was to establish a new highly sensitive and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative analysis of ipragliflozin in rat plasma and apply this method to a pharmacokinetic study in rats. Empagliflozin was used as an internal standard (I.S.) and liquid-liquid extraction was conducted using tert-butyl methyl ether. Chromatographic separation was accomplished on a Quicksorb ODS (2.1mm i.d.×150mm, 5μm in size) with acetonitrile/0.1% formic acid (90:10, v/v) at a flow rate of 0.2mL/min. An API 3200 triple quadrupole mass spectrometer operating in the positive electrospray ionization mode with multiple reaction monitoring was used to detect ipragliflozin and I.S. transitions: m/z 422.0 [M+NH4](+)→151.0 for ipragliflozin and m/z 451.2 [M+H](+)→71.0 for I.S. Inter- and intra-day accuracies and precisions were within ±15%. This validated method was successfully applied to a pharmacokinetic study of ipragliflozin in rats. This assay method may contribute to assessment of novel SGLT2 inhibitors using the rat as an animal model.

Development and validation of an LC–MS/MS method for the determination of tofogliflozin in plasma and its application to a pharmacokinetic study in rats

Tofogliflozin is a novel selective inhibitor of sodium-dependent glucose co-transporter-2 (SGLT2) and has been developed for the treatment of patients with type 2 diabetes mellitus. In this study, a highly sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitation of tofogliflozin in rat plasma was developed and validated. The detection was performed using an API 3200 triple-quadrupole mass spectrometer with selected reaction monitoring (SRM) in the positive electrospray ionization mode. The SRM transitions were m/z=387.1 [M+H](+)→267.1 for tofogliflozin and m/z=451.2 [M+H](+)→71.0 for empagliflozin (internal standard: I.S.). Chromatographic separation was performed on a Quicksorb ODS (2.1mm i.d.×150mm, 5μm size) using isocratic elution with acetonitrile/10mM ammonium acetate (50:50, v/v) as the mobile phase at a flow rate of 0.2mL/min and the total run time was 4.0min. The lower limit of quantification (LLOQ) for tofogliflozin was 0.5ng/mL with sufficient specificity, accuracy, and precision. The validated method was successfully applied to the pharmacokinetic studies of tofogliflozin in rats. This assay method could be a valuable tool for future studies including pharmacokinetic and pharmacodynamic studies of SGLT2 inhibitors.

A predictive biomarker for altered 5-fluorouracil pharmacokinetics following repeated administration in a rat model of colorectal cancer

The relationship between the plasma ratio of dihydrouracil/uracil (UH2/Ura) and hepatic dihydropyrimidine dehydrogenase (DPD) activity after repeated 5‐fluorouracil (5‐FU) treatment in rats with colorectal cancer (CRC) was investigated. Repeated intravenous 5‐FU bolus injections resulted in a significant decrease in the total clearance (CLtot) and an increased area under the curve (AUC0‐∞) in CRC rats. Furthermore, the hepatic DPD levels and the plasma ratio of UH2/Ura decreased significantly and lost their circadian rhythms in CRC rats treated repeatedly with 5‐FU, although significant circadian variation in the two parameters was observed in the control CRC rats. Moreover, a significant correlation was found between the plasma ratio of UH2/Ura and hepatic DPD activity in CRC rats untreated and treated with single or repeated 5‐FU administration (r2 = 0.865, p < 0.01). The ratio of UH2/Ura in plasma could be a predictive biomarker of the suppression of hepatic DPD levels during repeated 5‐FU‐based treatment. Furthermore, by plotting the observed pharmacokinetic parameters of 5‐FU against hepatic DPD activity levels predicted by the ratio of UH2/Ura in plasma, AUC0‐∞, CLtot and half‐life (t1/2) were closely linked to predicted hepatic DPD activity levels. These observations suggest that the factor that significantly influences the AUC0‐∞, CLtot and t1/2 of 5‐FU after single or repeated administration of 5‐FU is the hepatic DPD activity and it could be assessed by the ratio of UH2/Ura in plasma. Copyright

Effect of oxidative stress on the pharmacokinetics of clomipramine in rats treated with ferric-nitrilotriacetate.

The effect of oxidative stress (OS) on the pharmacokinetics of clomipramine (CPM), particularly addressing the change of CPM distribution to plasma components, was studied in ferric-nitrilotriacetate-induced oxidative-stress model rats (OS rats). First, CPM pharmacokinetic studies in OS rats were performed using CPM continuous infusion (17.5 μg/min/kg). Plasma concentration of CPM at a steady state in OS rats (0.20 ± 0.02 μg/mL) was significantly lower than that in control rats (0.30 ± 0.02 μg/mL). However, no difference was found in the amounts of CPM in the brains of control rats (1.67 ± 0.13 μg/g) and OS rats (1.63 ± 0.09 μg/g). Both of plasma unbound fraction and distribution to erythrocytes in OS rats were significantly higher than those of control rats. These results suggest that the lower CPM concentration in plasma in OS condition does not induce an inferior pharmacological effect.

Semi-physiological pharmacokinetic–pharmacodynamic (PK–PD) modeling and simulation of 5-fluorouracil for thrombocytopenia in rats

Abstract 1. The aim of this study was to develop a simple pharmacokinetic–pharmacodynamic (PK–PD) model that could characterize the complete time-course of alterations in platelet counts to predict the onset and degree of thrombocytopenia, which severely limits the use of the anticancer agent 5-fluorouracil (5-FU), in rats. 2. Platelet counts were measured in rats following the intravenous administration of various doses of 5-FU for 4 days to obtain data for an analysis of the PK–PD model. Our PK–PD model consisted of a two-compartment PK model, with three compartments for the PD model and 10 structural PK–PD model parameters. 3. After the 5-FU treatment, platelet counts transiently decreased to a nadir level, showed a rebound to above the baseline level before recovering to baseline levels. Nadir platelet counts and rebounds varied with the AUC0–∞ level. The final PK–PD model effectively characterized platelet count data and final PD parameters were estimated with high certainty. 4. This PK–PD model and simulation may represent a valuable tool for quantifying and predicting the complete time-course of alterations in blood cell counts, and could contribute to the development of therapeutic strategies with 5-FU and assessments of various novel anticancer agents that are difficult to examine in humans.