Lack of Contribution of Multidrug Resistance-associated Protein and Organic Anion-transporting Polypeptide to Pharmacokinetics of Regorafenib, a Novel Multi-Kinase Inhibitor, in Rats.

We investigated whether hepatic multidrug resistance-associated protein 2 (ABCC2) is involved in the hepatobiliary excretion of regorafenib, a novel multi-kinase inhibitor, using Sprague-Dawley (SD) rats and Eisai hyperbilirubinemic rats (EHBR) lacking the efflux transporter ABCC2. The involvement of organic anion-transporting polypeptide 1 (OATP1; OATP in humans) and OATP2 in the hepatic uptake of regorafenib and their protein levels in the liver were also investigated in the two rat groups. When regorafenib (5 mg/kg) was administered intravenously, the plasma concentrations of regorafenib were higher in EHBR than those in SD rats. However, the slope of the plasma concentration-time curves was the same for the two groups. Although the apparent biliary clearance of regorafenib in EHBR was lower than that of SD rats, no significant difference in the biliary excretion rate was observed between them, suggesting that regorafenib is not a substrate for ABCC2 and is not excreted into bile by ABCC2. It was also found that the contribution of biliary excretion to the systemic elimination of regorafenib is small. The protein-binding profiles of regorafenib were found to be linear in both rat groups. The binding potency, which was very high in both rat groups (>99.5%), was significantly higher in EHBR than that in SD rats. No significant differences in the plasma concentrations of unbound regorafenib were observed between the two rat groups, suggesting that the differences observed in the pharmacokinetic behaviors of regorafenib between the two rat groups were due to differences in protein-binding. When the protein levels of hepatic OATP1 and OATP2 were measured by immunoblot analysis, the expression of both transporters in EHBR was less than 40% of that in SD rats. The present results suggest that regorafenib is not a substrate for OATP1 and OATP2. These findings suggest the possibility that ABCC2-mediated hepatobiliary excretion and OATP1/OATP2-mediated hepatic uptake do not play important roles in the disposition of regorafenib.

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.

Mechanism of drug interaction between a Kampo medicine, byakkokaninjinto, and tetracycline in rats.

We have previously reported that concomitant oral administration of the Kampo medicine, byakkokaninjinto (TJ-34), in extract granules, reduced the plasma concentrations of tetracycline (TC) and ciprofloxacin in humans, which might be the result of forming a chelate with Ca(2+). In the present study, we investigated the effect of a chelating agent, ethylenediaminetetraacetic acid (EDTA), on the plasma concentration-time profiles of TC after coadministration of TJ-34 dried extract and TC in rats to clarify whether metal ions contained in the TJ-34 dried extract contribute to this interaction. TJ-34 dried extract significantly reduced the plasma concentration of TC. The values of maximum concentration (C (max)), area under the plasma concentration-time curve and percentage of urinary recovery (f (e)) of TC were reduced to 42%, 40%, and 45%, respectively. On the other hand, treatment with EDTA significantly counteracted the effect of TJ-34 dried extract to reduce absorption of TC, indicating that metal ions mainly account for the interaction. Next, we investigated the effect of staggered administration of TJ-34 dried extract and TC to avoid the drug interaction between them. Administration of TJ-34 dried extract 2 h before TC had no effect on plasma concentrations and pharmacokinetic parameters of TC. These results provide a precise mechanism of the interaction TJ-34 and TC, suggesting a safe and effective dosage regimen to coadminister TJ-34 and TC in clinical use.

Panipenem does not alter the pharmacokinetics of the active metabolite of irinotecan SN-38 and inactive metabolite SN-38 glucuronide (SN-38G) in rats.

The present study has investigated the effect of panipenem, a widely used antibiotic, on the pharmacokinetics of an active metabolite of irinotecan (CPT-11), 7-ethyl-10-hydroxy-camptothecin (SN-38) and SN-38 glucuronide (SN-38G) produced by uridine-diphosphate glucuronosyltransferase (UGT) 1A isoform-mediated glucuronidation in rats. Rats received a 1 h infusion with panipenem at a loading dose of 10 mg/kg and a maintenance dose of 15 mg/min/kg once a day for 5 days. When the effect of pretreatment with panipenem on glucuronidation activities of substrates for hepatic UGT1A isoforms was investigated using substrates 4-methylumbelliferone (4MU), estradiol and SN-38, the rate of 4MU glucuronide formation was significantly increased, but that of estradiol glucuronide formation was unchanged. However, the rate of SN-38G formation showed a tendency to increase. One hour after the final infusion of panipenem or saline, SN-38 (2 mg/kg) was administered intravenously in rats with or without bile duct cannulation. Pretreatment with panipenem had no effect on the plasma concentration-time curves and biliary excretion of SN-38 and SN-38G in rats with and without bile duct cannulation. There were also no significant differences in the relative extent of glucuronidation of SN-38 to SN-38G (AUC(2 h, SN-38G)/AUC(2 h, SN-38)) between panipenem-treated and untreated rats. These findings suggest that pretreatment with panipenem does not alter the pharmacokinetics of SN-38 and SN-38G, suggesting the possibility that panipenem can be used safely for cancer patients undergoing irinotecan chemotherapy.

Long-lasting impairment of associative learning is correlated with a dysfunction of N-methyl-D-aspartate-extracellular signaling-regulated kinase signaling in mice after withdrawal from repeated administration of phencyclidine.

In humans, the administration of phencyclidine causes schizophrenic-like symptoms that persist for several weeks after withdrawal from phencyclidine use. We demonstrated here that mice pretreated with phencyclidine (10 mg/kg/day s.c. for 14 days) showed an enduring impairment of associative in a Pavlovian fear conditioning 8 days after cessation of phencyclidine treatment. Extracellular signaling-regulated kinase (ERK) was transiently activated in the amygdalae and hippocampi of saline-treated mice after conditioning. In the phencyclidine-treated mice, the basal level of ERK activation was elevated in the hippocampus, whereas the activation was impaired in the amygdala and hippocampus after conditioning. Exogenous N-methyl-D-aspartate (NMDA), glycine, and spermidine-induced ERK activation was not observed in slices of hippocampus and amygdala prepared from phencyclidine-treated mice. Repeated olanzapine (3 mg/kg/day p.o. for 7 days), but not haloperidol (1 mg/kg/day p.o. for 7 days), treatment reversed the impairment of associative learning and of fear conditioning-induced ERK activation in repeated phencyclidine-treated mice. Our findings suggest an involvement of abnormal ERK signaling via NMDA receptors in repeated phencyclidine treatment-induced cognitive dysfunction. Furthermore, our phencyclidine-treated mice would be a useful model for studying the effect of antipsychotics on cognitive dysfunction in schizophrenia.