Pharmacokinetic drug interactions between ondansetron and tamoxifen in female Sprague-Dawley rats with DMBA-induced mammary tumor.

Tamoxifen, which is used to treat breast cancer, and ondansetron, used for the treatment of chemotherapy-induced nausea, are commonly metabolized via cytochrome P450 (CYP) 2D subfamily and 3A1/2 in rats, as in humans. This study was conducted to investigate the pharmacokinetic interactions between ondansetron and tamoxifen after intravenous and oral administration of ondansetron (both 8 mg/kg) and/or tamoxifen (2 and 10 mg/kg for intravenous and oral administration, respectively), in rats bearing 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammarian tumors (DMBA rats), used as an animal model of human breast cancer. The total area under the plasma concentration-time curve, from time zero to infinity (AUC) of tamoxifen was significantly greater after both intravenous and oral administration with ondansetron, compared to that after administration of tamoxifen-alone. The hepatic and intestinal metabolism of tamoxifen in DMBA rats was inhibited by ondansetron. Taken together, the significant increase in tamoxifen AUC in DMBA rats after intravenous or oral administration with ondansetron may be attributed to non-competitive hepatic (intravenous) and competitive intestinal (oral) inhibition of CYP2D subfamily- and 3A1/2-mediated tamoxifen metabolism by ondansetron.

Effects of morin on the pharmacokinetics of etoposide in 7,12-dimethylbenz[a]anthracene-induced mammary tumors in female Sprague-Dawley rats.

Etoposide, used for the treatment of breast cancer, is mainly metabolized via hepatic cytochrome P450 (CYP) 3A4 in humans and is also a substrate for p-glycoprotein (P-gp). Morin is known to be able to modulate the activities of metabolic enzymes including CYPs and can act as a potent P-gp inhibitor. The purpose of this study was to investigate the effects of morin on the pharmacokinetics of etoposide in rats with 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors. Etoposide was administered intravenously (2 mg/kg) and orally (10 mg/kg) in control and DMBA rats without (DMBA-WOM) and with (DMBA-WM) morin (15 mg/kg). Protein and mRNA expression of CYP3A and P-gp was analyzed, and the tissue distribution of etoposide was also measured. Both protein and mRNA expression of CYP3A and P-gp was inhibited by morin in the liver, intestine and breast tumors of DMBA-WM rats. After both intravenous and oral administration of etoposide in DMBA-WM rats, the total area under the plasma concentration-time curve from time zero to infinity (AUC) of etoposide was significantly greater, and the time-averaged total body clearance (CL) of etoposide was significantly slower than those in control and DMBA-WOM rats. The amount of etoposide recovered from each tissue was significantly higher in DMBA-WM rats, especially in the breast tumor, liver and large intestine. No significant differences between control and DMBA-WOM rats were observed. Taken together, greater AUC and slower CL of etoposide in DMBA-WM rats could possibly be due to the inhibition of hepatic CYP3A (intravenous) and mainly due to the inhibition of intestinal CYP3A and P-gp (oral) by morin.

Reduced clearance of ε-acetamidocaproic acid in rats with acute renal failure induced by uranyl nitrate.

OBJECTIVES: Anti-ulcer drugs are frequently used in patients with acute renal failure (ARF). Zinc acexamate is ionized to zinc and ε-acetamidocaproic acid and free EACA exerts a potent therapeutic effect in treating gastric or duodenal ulcers with few side effects. Thus, pharmacokinetic changes in rats with acute renal failure induced by uranyl nitrate (U-ARF rats) were investigated in this study. METHODS: The in-vivo pharmacokinetics and in-vitro hepatic/intestinal metabolism of EACA were assessed using control and U-ARF rats. The mechanism of urinary excretion of EACA was further investigated in rats. KEY FINDINGS: After intravenous and oral administration of zinc acexamate to U-ARF rats, there were significant increases in the values of the area under the curve (AUC) and decreases in the values for time-averaged renal and nonrenal clearances (Cl(r) and Cl(nr) , respectively) compared with control rats. Slower Cl(nr) was partly due to a decrease in the metabolism in liver and/or intestine. Slower Cl(r) could have been due to urine flow rate-dependent timed-interval renal clearance, decrease in organic anion transporter-mediated renal excretion (drug interaction with probenecid and decrease in the relative contribution of net secretion compared with glomerular filtration in U-ARF rats) and/or impaired kidney function. CONCLUSIONS: The pharmacokinetics were significantly altered in U-ARF rats due to the changes in both the hepatic/intestinal metabolism and urinary excretion.

Effects of HMG-CoA reductase inhibitors on the pharmacokinetics of losartan and its main metabolite EXP-3174 in rats: possible role of CYP3A4 and P-gp inhibition by HMG-CoA reductase inhibitors.

The present study was designed to investigate the effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (atorvastatin, pravastatin, simvastatin) on the pharmacokinetics of losartan and its active metabolite EXP-3174 in rats. Pharmacokinetic parameters of losartan and EXP-3174 in rats were determined after oral and intravenous administration of losartan (9 mg/kg) without and with HMG-CoA reductase inhibitors (1 mg/kg). The effect of HMG-CoA reductase inhibitors on P-gp and cytochrome (CYP) 3A4 activity were also evaluated. Atorvastatin, pravastatin and simvastatin inhibited CYP3A4 activities with IC50 values of 48.0, 14.1 and 3.10 µmol/l, respectively. Simvastatin (1-10 µmol/l) enhanced the cellular uptake of rhodamine-123 in a concentration-dependent manner. The area under the plasma concentration-time curve (AUC0₋∞) and the peak plasma concentration of losartan were significantly (p < 0.05) increased by 59.6 and 45.8%, respectively, by simvastatin compared to those of control. The total body clearance (CL/F) of losartan after oral administration with simvastatin was significantly decreased (by 34.8%) compared to that of controls. Consequently, the absolute bioavailability (F) of losartan after oral administration with simvastatin was significantly increased by 59.4% compared to that of control. The metabolite-parent AUC ratio was significantly decreased by 25.7%, suggesting that metabolism of losartan was inhibited by simvastatin. In conclusion, the enhanced bioavailability of losartan might be mainly due to inhibition of P-gp in the small intestine and CYP3A subfamily-mediated metabolism of losartan in the small intestine and/or liver and to reduction of the CL/F of losartan by simvastatin.

Effects of ticlopidine on pharmacokinetics of losartan and its main metabolite EXP-3174 in rats.

AIM: Losartan and antiplatelet agent ticlopidine can be prescribed concomitantly for prevention or therapy of cardiovascular diseases. Hence, the effects of ticlopidine on the pharmacokinetics of losartan and its active metabolite EXP-3174 were evaluated in rats. METHODS: Ticlopidine (4 or 10 mg/kg po) was administered 30 min before administration of losartan (9 mg/kg po or 3 mg/kg iv). The activity of human CYP2C9 and 3A4 were measured using the CYP inhibition assay kit. The activity of P-gp was evaluated using rhodamine-123 retention assay in MCF-7/ADR cells. RESULTS: Ticlopidine (10 mg/kg) significantly increased the areas under the plasma concentration-time curves (AUCs) and peak plasma concentration (C(max)) of oral losartan (9 mg/kg), as well as the AUCs of the active metabolite EXP-3174. Ticlopidine (10 mg/kg) did not significantly change the pharmacokinetics of intravenous losartan (3 mg/kg). Ticlopidine inhibited CYP2C9 and 3A4 with IC50 values of 26.0 and 32.3 µmol/L, respectively. The relative cellular uptake of rhodamine-123 was unchanged. CONCLUSION: The significant increase in the AUC of losartan (9 mg/kg) by ticlopidine (10 mg/kg) could be attributed to the inhibition of CYP2C9- and 3A4-mediated losartan metabolism in small intestine and/or in liver. The inhibition of P-gp in small intestine and reduction of renal elimination of losartan by ticlopidine are unlikely to be causal factors.

Pharmacokinetics and first-pass metabolism of astaxanthin in rats.

Astaxanthin is a carotenoid with antioxidant, anti-cancer and anti-inflammatory properties. The pharmacokinetics of astaxanthin after its intravenous (5, 10, and 20 mg/kg) and oral (100 and 200 mg/kg) administration and its first-pass extraction ratios after its intravenous, intraportal or intragastric (20 mg/kg) administration were evaluated in rats. The pharmacokinetic parameters of astaxanthin were dose dependent after its intravenous administration, due to the saturable hepatic metabolism of astaxanthin, but dose independent after oral administration. The gastrointestinal absorption of astaxanthin followed the flip-flop model. The hepatic and gastrointestinal first-pass extraction ratios of astaxanthin were approximately 0·490 and 0·901, respectively. Astaxanthin was metabolised primarily by hepatic cytochrome P-450 1A1/2 in rats. Astaxanthin was unstable up to 4 h incubation in four rat gastric juices and up to 24 h incubation in various buffer solutions having a pH of 1-13. The tissue/plasma ratios of astaxanthin at 8 and 24 h after its oral administration (100 mg/kg) were greater than unity for all tissues studied, except in the heart, at 8 h, indicating that the rat tissues studied had high affinity for astaxanthin.

Pharmacokinetic interaction between tamoxifen and ondansetron in rats: non-competitive (hepatic) and competitive (intestinal) inhibition of tamoxifen metabolism by ondansetron via CYP2D subfamily and 3A1/2.

PURPOSE: Tamoxifen and ondansetron were commonly metabolized via rat hepatic CYP2D subfamily and 3A1/2, and ondansetron is used to treat chemotherapy-induced nausea. The purpose of this study was to report the pharmacokinetic interaction between tamoxifen and ondansetron in rats. METHODS: The pharmacokinetics of tamoxifen and ondansetron were evaluated after the intravenous and oral administration of tamoxifen, ondansetron, and both drugs together to rats. The Vmax (maximum velocity), Km (apparent Michaelis-Menten constant), CLint (intrinsic clearance), Ki (inhibition constant), and [I] (concentration of inhibitor in the liver and intestine)/Ki ratio of ondansetron were also measured. RESULTS: The AUC0-infinitys of tamoxifen were significantly greater after both intravenous and oral administration with ondansetron compared to those of tamoxifen alone. The significantly slower hepatic and intestinal CLints for the disappearance of tamoxifen with both drugs together were due to inhibition of metabolism of tamoxifen by ondansetron via CYP2D subfamily and 3A1/2. CONCLUSIONS: The significantly greater AUC0-infinity of tamoxifen after the intravenous administration of both drugs together could have possibly been attributable to a non-competitive (hepatic) inhibition of CYP2D subfamily- and 3A1/2-mediated tamoxifen metabolism by ondansetron. The significantly greater AUC0-infinity of tamoxifen after the oral administration of both drugs together could have been attributable to a competitive (intestinal) inhibition of CYP2D subfamily- and 3A1/2-mediated tamoxifen metabolism by ondansetron in addition to non-competitive inhibition in the liver.

Pharmacokinetics of oltipraz in rat models of diabetes mellitus induced by alloxan or streptozotocin.

Pharmacokinetic parameters of oltipraz were compared after intravenous (10 mg/kg) and oral (30 mg/kg) administration in rat model of diabetes mellitus induced by alloxan (rat model of DMIA) or streptozotocin (rat model of DMIS) and their respective control male Sprague-Dawley rats. In rat models of DMIA and DMIS, the expressions and mRNA levels of CYP1A2, 2B1/2, and 3A1(23) increased, and oltipraz was metabolized mainly via CYP1A1/2, 2B1/2, 2C11, 2D1, and 3A1/2 in male Sprague-Dawley rats. Hence, it would be expected that the AUC and CL values of oltipraz would be significantly smaller and faster, respectively, in rat models of diabetes. This was proven by the following results. After intravenous administration, the AUC values were significantly smaller in rat models of DMIA (40.1% decrease) and DMIS (26.0% decrease) than those in respective control rats, and this could be due to significantly faster CL values in rat models of DMIA (40.1% increase) and DMIS (26.0% increase). The faster CL could be due to increase in hepatic blood flow rate and significantly faster CL(int) in rat models of diabetes, since oltipraz is an intermediate hepatic extraction ratio drug in male Sprague-Dawley rats. After oral administration, the AUC values of oltipraz were also significantly smaller in rat models of DMIA (54.0% decrease) and DMIS (63.2% decrease). This could be due to increase in hepatic blood flow rate, significantly faster CL(int), and changes in the intestinal first-pass effect in rat models of diabetes. However, this was not due to decrease in absorption in rat models of diabetes.