Pharmacokinetic and pharmacodynamic interaction between nifedipine and metformin in rats: competitive inhibition for metabolism of nifedipine and metformin by each other via CYP isozymes.

It has been reported that hypertension exponentially increases in the patients with type 2 diabetes mellitus. Thus, this study was performed to investigate the pharmacokinetic and pharmacodynamic interactions between nifedipine and metformin, since both drugs were commonly metabolized via hepatic CYP2C and 3A subfamilies in rats. Nifedipine (3 mg/kg) and metformin (100 mg/kg) were simultaneously administered intravenously or orally to rats. Concentrations (I) of each drug in the liver and intestine, maximum velocity (V(max)), Michaelis-Menten constant (K(m)), and intrinsic clearance (CL(int)) for the disappearance of each drug, apparent inhibition constant (K(i)) and [I]/K(i) ratios of each drug in liver and intestine were determined. Also the metabolism of each drug in rat and human CYPs and blood pressure were also measured. After the simultaneous single intravenous administration of both drugs together, the AUCs of each drug were significantly greater than that in each drug alone due to the competitive inhibition for the metabolism of nifedipine by metformin via hepatic CYP3A1/2 and of metformin by nifedipine via hepatic CYP2C6 and 3A1/2. After the simultaneous single oral administration of both drugs, the significantly greater AUCs of each drug than that in each drug alone could have mainly been due to the competitive inhibition for the metabolism of nifedipine and metformin by each other via intestinal CYP3A1/2 in addition to competitive inhibition for the hepatic metabolism of each drug as same as the intravenous study.

Pharmacokinetics of mirodenafil and its two metabolites, SK3541 and SK3544, in spontaneously or DOCA-salt-induced hypertensive rats.

Hypertension is the most common comorbidity and major risk factor in patients with erectile dysfunction. The pharmacokinetics of mirodenafil, used for the treatment of erectile dysfunction, after the intravenous and oral administration (20 mg/kg) to 6-week-old rats (with blood pressure within the normotensive range) and 16-week-old spontaneously hypertensive rats (SHRs) and their age-matched control normotensive Kyoto-Wistar (KW) rats, and 16-week-old deoxycorticosterone acetate-salt-induced hypertensive rats (DOCA-salt rats) and their age-matched control Sprague-Dawley (SD) rats were compared. It was found that time-averaged renal clearance (Cl(r)) was of minor importance and that time-averaged non-renal clearance (Cl(nr)) was dominant. In both 6- and 16-week-old SHRs, the Cl(nr)s and areas under the curve (AUCs) of intravenous mirodenafil were significantly smaller and greater than those of the controls, but in 16-week-old DOCA-salt rats, they were comparable to the controls. Although the AUC of oral mirodenafil in 16-week-old SHRs was comparable to the controls, the Cl(nr)s (or total body clearances, Cls) of intravenous mirodenafil and intestinal intrinsic clearances were significantly smaller than the controls and comparable to the controls for both 6- and 16-week-old SHRs, unlike in the 16-week-old DOCA-salt rats. The above data suggest that the significantly smaller Cl(nr) and greater AUC of intravenous mirodenafil and comparable AUC of oral mirodenafil in 16-week-old SHR could be due to the hereditary characteristics of SHRs, and not due to the hypertensive state itself.

Dose-dependent pharmacokinetics of SP-8203 in rats.

The pharmacokinetics of SP-8203, a potential protective agent for the treatment of cerebral infarction, were evaluated after its intravenous (10, 20 and 30 mg/kg) and oral (10, 20, 30 and 100 mg/kg) administration in rats. After the intravenous administration of SP-8203, the AUCs of SP-8203 were dose-dependent; the dose-normalized AUCs were significantly greater with increasing doses. After the oral administration of SP-8203, plasma concentrations of SP-8203 were much lower than those after intravenous administration. This could be due to considerable hepatic and intestinal metabolism and the high percent of the dose recovered from the gastrointestinal tract (including its contents and feces) at 24 h as unchanged drug.

Effects of cytochrome P450 inducers and inhibitors on the pharmacokinetics of intravenous furosemide in rats: involvement of CYP2C11, 2E1, 3A1 and 3A2 in furosemide metabolism.

OBJECTIVES: It has been reported that the non-renal clearance of furosemide was significantly faster in rats pretreated with phenobarbital but was not altered in rats pretreated with 3-methylcholanthrene. However, no studies on other cytochrome P450 (CYP) isozymes have yet been reported in rats. METHOD: Furosemide 20 mg/kg was administered intravenously to rats pretreated with various CYP inducers--3-methylcholanthrene, orphenadrine citrate and isoniazid, inducers of CYP1A1/2, 2B1/2 and 2E1, respectively, in rats--and inhibitors--SKF-525A (a non-specific inhibitor of CYP isozymes), sulfaphenazole, cimetidine, quinine hydrochloride and troleandomycin, inhibitors of CYP2C6, 2C11, 2D and 3A1/2, respectively, in rats. KEY FINDINGS: The non-renal clearance of furosemide was significantly faster (55.9% increase) in rats pretreated with isoniazid, but slower in those pretreated with cimetidine or troleandomycin (38.5% and 22.7% decreases, respectively), than controls. After incubation of furosemide with baculovirus-infected insect cells expressing CYP2C11, 2E1, 3A1 or 3A2, furosemide was metabolized via CYP2C11, 2E1, 3A1 and 3A2. CONCLUSIONS: These findings could help explain possible pharmacokinetic changes of furosemide in various rat disease models (where CYP2C11, 2E1, 3A1 and/or CYP3A2 are altered) and drug-drug interactions between furosemide and other drugs (mainly metabolized via CYP2C11, 2E1, 3A1 and/or 3A2).

Faster clearance of omeprazole in mutant Nagase analbuminemic rats: possible roles of increased protein expression of hepatic CYP1A2 and lower plasma protein binding.

It is well known that there are various changes in the expression of hepatic and intestinal CYPs in mutant Nagase analbuminemic rats (NARs). It has been reported that the protein expression of hepatic CYP1A2 was increased, whereas that of hepatic CYP3A1 was not altered, and it was also found that the protein expression of the intestinal CYP1A subfamily significantly increased in NARs from our other study. In addition, in this study additional information about CYP changes in NARs was obtained; the protein expression of the hepatic CYP2D subfamily was not altered, but that of the intestinal CYP3A subfamily increased in NARs. Because omeprazole is metabolized via hepatic CYP1A1/2, 2D1, 3A1/2 in rats, it could be expected that the pharmacokinetics of omeprazole would be altered in NARs. After intravenous administration of omeprazole to NARs, the Cl(nr) was significantly faster than in the controls (110 versus 46.6 ml/min/kg), and this could be due to an increase in hepatic metabolism caused by a greater hepatic CYP1A2 level in addition to greater free fractions of the drug in NARs. After oral administration of omeprazole to NARs, the AUC was also significantly smaller (80.1% decrease) and F was decreased in NARs. This could be primarily due to increased hepatic and intestinal metabolism caused by greater hepatic CYP1A2 and intestinal CYP1A and 3A levels. In particular, the smaller F could mainly result from greater hepatic and intestinal first-pass effect in NARs than in the controls.

Ipriflavone pharmacokinetics in mutant Nagase analbuminemic rats.

Ipriflavone, a derivative of naturally occurring isoflavones, was primarily metabolized in rats via hepatic CYP1A1/2 and 2C11. Protein and mRNA expression of CYP1A2 in the liver, reported to be increased in mutant Nagase analbuminemic rats (NARs), should influence the pharmacokinetic parameters of ipriflavone. In this study, the contribution of hepatic CYP2C11 and intestinal CYP1A protein to the metabolism and the pharmacokinetic parameters of ipriflavone were examined after intravenous (20 mg/kg) and oral (200 mg/kg) administration to male Sprague-Dawley (control) rats and NARs. There was no change in the protein expression of hepatic CYP2C11. By contrast, CYP1A protein of the intestine increased by almost 100%. After the intravenous administration of ipriflavone to NARs, the Cl(nr) and AUC were unchanged, suggesting that the contribution of the increase in protein expression and mRNA level of hepatic CYP1A2 to hepatic metabolism of the drug in NARs seemed to be almost negligible. However, after the oral administration of ipriflavone to NARs, the AUC was significantly lower than that in the control rats (53.0% decrease), possibly due to the increased intestinal CYP1A that resulted in increased intestinal metabolism and decreased gastrointestinal absorption of ipriflavone in NARs.

Dose-dependent pharmacokinetics and first-pass effects of mirodenafil, a new erectogenic, in rats.

The pharmacokinetics of mirodenafil and its two metabolites, SK3541 and SK3544, after intravenous (5, 10, 20 and 50 mg/kg) and oral (10, 20 and 50 mg/kg) administration of mirodenafil, and the first-pass effect of mirodenafil after intravenous, oral, intraportal, intragastric and intraduodenal (20 mg/kg) administration of mirodenafil were evaluated in rats. The pharmacokinetics of mirodenafil and SK3541 were dose-dependent after both intravenous and oral administration of mirodenafil due to the saturable hepatic metabolism of mirodenafil. After oral administration of mirodenafil, approximately 2.59% of the oral dose was not absorbed, the F value was approximately 29.4%, and the hepatic and gastrointestinal first-pass effects of mirodenafil were approximately 21.4% and 54.3% of the oral dose, respectively. The low F value of mirodenafil in rats was mainly due to considerable hepatic and gastrointestinal first-pass effects in rats. The equilibrium plasma-to-blood cell partition ratios of mirodenafil were independent of the initial blood mirodenafil concentrations of 1-10 microg/ml; the mean values were 1.08-1.21. The plasma binding values of mirodenafil to rat plasma was 87.8%.

Time-dependent effects of Klebsiella pneumoniae endotoxin on the pharmacokinetics of chlorzoxazone and its main metabolite, 6-hydroxychlorzoxazone, in rats: restoration of the parameters in 96 hour in KPLPS rats to control levels.

It has been reported that chlorzoxazone (CZX) was primarily metabolized via hepatic Cyp2e1 to form 6-hydroxychlorzoxazone (OH-CZX) in rats, and the activity of aniline hydroxylase (a Cyp2e1 marker) in the liver was significantly decreased in rats at 24 h after pretreatment with lipopolysaccharide derived from Klebsiella pneumoniae (24 h KPLPS rats), whereas the levels were not changed at 2 h and 96 h in the KPLPS rats. Thus, the time-dependent pharmacokinetic parameters of CZX and OH-CZX were evaluated after the intravenous administration of CZX (20 mg/kg) to control rats, and the 2 h, 24 h and 96 h KPLPS rats along with the time-dependent changes in the protein expression of hepatic Cyp2e1. After the intravenous administration of CZX to 24 h KPLPS rats, the AUC(0-2 h) of OH-CZX and AUC(OH-CZX, 0-2 h)/AUC(CZX) were significantly smaller (by 40.5% and 71.2%, respectively) than those of controls due to the significant decrease (by 75.3%) in the protein expression of hepatic Cyp2e1. However, in 96 h KPLPS rats, the pharmacokinetic parameters of both CZX and OH-CZX were unchanged compared with controls due to the restoration of the protein expression of hepatic Cyp2e1 to control levels. These observations highlighted the existence of the time-dependent effects of KPLPS on the pharmacokinetics of CZX and OH-CZX in rats.

Time-dependent effects of Klebsiella pneumoniae endotoxin (KPLPS) on the pharmacokinetics of theophylline in rats: return of the parameters in 96-hour KPLPS rats to the control levels.

It has been reported that theophylline is primarily metabolized via hepatic CYP1A1/2, 2B1/2, and 3A1/2, and 1,3-dimethyluric acid (1,3-DMU) is primarily formed via CYP1A1/2 in rats. Compared with control rats, the expression of CYP1A subfamily, 2B1/2, and 3A subfamily significantly decreased 24 h (24-h KPLPS rats) after intravenous administration of lipopolysaccharide derived from Klebsiella pneumoniae (KPLPS) to rats but returned to that in control rats after 96 h (96-h KPLPS rats). After intravenous or oral administration of theophylline to 24-h KPLPS rats, the values for the total area under the plasma concentration-time curve from time zero to time infinity of theophylline and 1,3-DMU became significantly greater (46.5 and 34.0% increase after intravenous and oral administration, respectively) and smaller (36.3 and 21.6% decrease, respectively), respectively. Because theophylline is a low hepatic extraction ratio drug in rats, the above results could have been due to significantly slower CL(int) for the disappearance of theophylline and for the formation of 1,3-DMU (37.1 and 60.6% decrease, respectively). However, in 96-h KPLPS rats, the pharmacokinetic parameters of theophylline and 1,3-DMU returned fully or partially to those in control rats. These findings indicate the existence of time-dependent effects of KPLPS on the pharmacokinetics of theophylline and 1,3-DMU in rats.

Pharmacokinetic parameters of chlorzoxazone and its main metabolite, 6-hydroxychlorzoxazone, after intravenous and oral administration of chlorzoxazone to liver cirrhotic rats with diabetes mellitus.

Protein expression of the hepatic CYP2E1 has been reported to be increased in diabetic rats. This enzyme is the primary metabolizer of chlorzoxazone (CZX) to 6-hydroxychlorzoxazone (OH-CZX). Although patients with liver cirrhosis have a higher prevalence of diabetes mellitus, there have been no reported studies on the protein expression of CYP2E1 in rats induced to have liver cirrhosis and diabetes mellitus by injection of N-dimethylnitrosamine followed by streptozotocin [liver cirrhosis with diabetes mellitus (LCD) rats]. Thus, in the present study, the pharmacokinetics of CZX and OH-CZX were evaluated in LCD rats. Compared with control rats, LCD rats had significantly decreased (by 62%) total liver protein and significantly increased (by 124%) protein expression of CYP2E1, but the intrinsic clearance (Cl(int); formation of OH-CZX per milligram protein) was comparable in both groups of rats. As a result, the relative Cl(int) was also comparable for the two groups. Thus, OH-CZX formation in LCD and control rats was expected to be similar. As expected, after i.v. (20 mg/kg) and p.o. (50 mg/kg) administration of CZX, the area under the curve (AUC) of OH-CZX was comparable in control and LCD rats (i.v., 571 +/- 85.8 and 578 +/- 413 microg x min/ml, respectively; p.o., 1540 +/- 338 and 2170 +/- 1070 microg x min/ml, respectively). In LCD rats, the AUC(OH-CZX)/AUC(CZX) ratio was similar to the value in control rats after i.v. and p.o. administration. These results indicate that OH-CZX can be used as a chemical probe to assess the activity of CYP2E1 in LCD rats.

Effects of diabetes mellitus induced by alloxan on the pharmacokinetics of metformin in rats: restoration of pharmacokinetic parameters to the control state by insulin treatment.

PURPOSE: To test the effect of insulin treatment on the pharmacokinetics of metformin in rats with diabetes mellitus induced by alloxan (DMIA rats). The following results were reported from other studies. Metformin was metabolized via hepatic CYP2C11, 2D1, and 3A1/2 in rats. In DMIA rats, the protein expression and mRNA levels of hepatic CYP2C11 and 3A1/2 decreased and increased, respectively. In rat model of diabetes mellitus induced by streptozotocin, the protein expression of hepatic CYP2D1 was not changed. The increase in hepatic CYP1A2, 2B1, and 2E1, and decrease in hepatic CYP2C11 in DMIA rats was returned to the controls by insulin treatment. METHODS: Metformin (100 mg/kg) was administered intravenously and orally to the control rats, DMIA rats, and DMIA rats with insulin treatment for 3 weeks (DMIA rats with insulin). RESULTS: After intravenous administration of metformin to the DMIA rats, the CLR and CLNR of the drug were significantly slower than the controls. After oral administration of metformin to the DMIA rats, the AUC of the drug was also significantly greater than the controls. After intravenous administration of metformin to the DMIA rats with insulin, the significantly slower CLNR of the drug in the DMIA rats was returned to the controls. The altered pharmacokinetic indices observed following intravenous and oral administration of metformin to DMIA rats returned to the control values in the DMIA rats with insulin. CONCLUSIONS: The significantly slower CLNR of metformin in the DMIA rats could be due to the decrease in hepatic CYP2C11 than the controls. The comparable CLNR of metformin between the DMIA rats with insulin and the control rats could be due to restoration of hepatic CYP enzyme changes in DMIA rats to the controls.

Effects of cytochrome P450 (CYP) inducers and inhibitors on ondansetron pharmacokinetics in rats: involvement of hepatic CYP2D subfamily and 3A1/2 in ondansetron metabolism.

The types of hepatic microsomal cytochrome P450 (CYP) isozymes responsible for the in-vivo metabolism of ondansetron in rats have not been reported. In this study, ondansetron at a dose of 8 mg kg(-1) was administered intravenously to rats pretreated with various inducers of CYP isozymes, such as 3-methylcholanthrene, orphenadrine citrate, isoniazid and dexamethasone phosphate (the main inducers of CYP1A1/2, 2B1/2, 2E1 and 3A1/2 in rats, respectively), and inhibitors, such as SKF-525A (a non-specific inhibitor of CYP isozymes), sulfaphenazole, quinine hydrochloride and troleandomycin (the main inhibitors of CYP2C6, 2D subfamily and 3A1/2 in rats, respectively). In rats pretreated with quinine hydrochloride and troleandomycin, the time-averaged non-renal clearance of ondansetron was significantly slower (48.9 and 13.2% decrease, respectively) than that in control rats. In rats pretreated with dexamethasone phosphate, the time-averaged non-renal clearance was significantly faster (18.2% increase) than that in control rats. The results suggest that ondansetron is primarily metabolized via the CYP2D subfamily and 3A1/2 in rats.

Effects of cysteine on metformin pharmacokinetics in rats with protein-calorie malnutrition: partial restoration of some parameters to control levels.

Metformin is metabolized primarily via hepatic microsomal cytochrome P450 (CYP)2C11, CYP2D1 and CYP3A1/2 in rats. The expression and mRNA levels of hepatic CYP2C11 and CYP3A1/2 are decreased in rats with protein-calorie malnutrition (PCM), but these levels are fully or partially restored to control levels in PMC rats by oral cysteine supplementation (PCMC rats). Thus, it would be expected that the pharmacokinetic parameters of metformin in PCM rats would be returned to control levels in PCMC rats. Metformin was administered i.v. (100 mg kg(-1)) and orally (100 mg kg(-1)) to control, CC (control rats with oral cysteine supplementation), PCM and PCMC rats. The following pharmacokinetic parameters of metformin following i.v. administration were restored from levels in PCM rats to levels in control rats in PCMC rats: intrinsic clearance (0.0350, 0.0309, 0.0253 and 0.0316 mL min(-1) mg(-1) protein for control, CC, PCM, and PCMC rats, respectively), total area under the plasma concentration-time curve from time zero to time infinity (AUC; 4110, 4290, 5540 and 4430 microg min mL(-1), respectively), and time-averaged non-renal clearance (8.12, 7.95, 5.94 and 8.17 mL min(-1) kg(-1), respectively). AUC values following oral administration were comparable between control and PCMC rats (1520, 1480, 2290 and 1680 microg min mL(-1), respectively).

Effects of CYP inducers and inhibitors on the pharmacokinetics of intravenous theophylline in rats: involvement of CYP1A1/2 in the formation of 1,3-DMU.

The types of hepatic cytochrome P450 (CYP) isozymes responsible for the metabolism of theophylline and for the formation of 1,3-dimethyluric acid (1,3-DMU) in rats in-vivo does not seem to have been studied at the dose ranges of dose-independent metabolic disposition of theophylline in rats (up to 10 mg kg(-1)). Therefore, theophylline (5 mg kg(-1)) was administered i.v. to male Sprague-Dawley rats pretreated with various inducers and inhibitors of CYP isozymes. In rats pretreated with 3-methylcholanthrene (3-MC), orphenadrine or dexamethasone (main inducers of CYP1A1/2, CYP2B1/2 and CYP3A1/2, respectively, in rats), the time-averaged non-renal clearance (CLNR) of theophylline was significantly faster than in their respective controls (1260, 42.7 and 69.0% increases, respectively). However, in rats pretreated with troleandomycin (a major inhibitor of CYP3A1/2 in rats), CLNR was significantly slower than in the controls (50.7% decrease). The 24 h urinary excretion of 1,3-DMU was increased significantly only in rats pretreated with 3-MC. The ratio of area under the curve for 1,3-DMU and theophylline (AUC1,3-DMU/AUCtheophylline) was increased significantly in rats pretreated with 3-MC (160% increase) and decreased significantly in rats pretreated with troleandomycin (50.1% decrease); however, the ratio was not increased in rats pretreated with dexamethasone. These data suggest that theophylline is primarily metabolized via CYP1A1/2, CYP2B1/2, and CYP3A1/2, and that 1,3-DMU is primarily formed via CYP1A1/2, and possibly CYP3A1/2, in rats.

Faster clearance of omeprazole in rats with acute renal failure induced by uranyl nitrate: contribution of increased expression of hepatic cytochrome P450 (CYP) 3A1 and intestinal CYP1A and 3A subfamilies.

It has been reported that omeprazole is mainly metabolized via hepatic cytochrome P450 (CYP) 1A1/2, CYP2D1 and CYP3A1/2 in male Sprague-Dawley rats, and the expression of hepatic CYP3A1 is increased in male Sprague-Dawley rats with acute renal failure induced by uranyl nitrate (U-ARF rats). Thus, the metabolism of omeprazole would be expected to increase in U-ARF rats. After intravenous administration of omeprazole (20 mgkg(-1)) to U-ARF rats, the area under the plasma concentration-time curve from time zero to infinity (AUC) was significantly reduced (371 vs 494 microg min mL(-1)), possibly due to the significantly faster non-renal clearance (56.6 vs 41.2 mL min(-1) kg(-1)) compared with control rats. This could have been due to increased expression of hepatic CYP3A1 in U-ARF rats. After oral administration of omeprazole (40 mgkg(-1)) to U-ARF rats, the AUC was also significantly reduced (89.3 vs 235 microg min mL(-1)) compared with control rats. The AUC difference after oral administration (62.0% decrease) was greater than that after intravenous administration (24.9% decrease). This may have been primarily due to increased intestinal metabolism of omeprazole caused by increased expression of intestinal CYP1A and 3A subfamilies in U-ARF rats, in addition to increased hepatic metabolism.

Effects of cysteine on the pharmacokinetic parameters of omeprazole in rats with protein-calorie malnutrition: partial restoration of some parameters to control levels by oral cysteine supplementation.

BACKGROUND: It has been reported that omeprazole is mainly metabolized via the hepatic cytochrome (CYP) 1A1/2, 3A1/2, and 2D1, and the expressions and mRNA levels of CYP1A2, 2C11, and 3A1/2 decreased in protein-calorie malnutrition (PCM) rats compared with controls. Interestingly, the decreased CYP1A2, 2C11, and 3A1/2 in PCM rats returned fully or partially to control levels by oral cysteine supplementation (PCMC rats). Hence, it could be expected that some pharmacokinetic parameters of omeprazole might change in PCM rats and partially restore to control levels in PCMC rats. The purpose of this study is to investigate the pharmacokinetic changes of omeprazole in PCM rats and restoration of the parameters in PCMC rats to control levels. METHODS: Omeprazole was administered intravenously (20 mg/kg) and orally (40 mg/kg) to control, PCM, and PCMC rats. RESULTS: The following pharmacokinetic parameters were changed in PCM rats and partially returned to control levels in PCMC rats: the area under the plasma concentration-time curve (AUC; 387, 762, and 539 microg min/mL for control, PCM, and PCMC rats, respectively, after intravenous [IV] administration, and the corresponding values after oral administration: 115, 304, and 201 microg min/mL), total body clearance (51.7, 25.5, and 37.1 mL/min/kg, respectively), nonrenal clearance (51.5, 25.4, and 36.1 mL/min/kg, respectively), and in vitro intrinsic clearance (0.158, 0.118, and 0.138 mL/min/mg protein). CONCLUSIONS: PCM was associated with significant changes in some omeprazole pharmacokinetics and the pharmacokinetic parameters restored to control levels by oral cysteine.

Changes in omeprazole pharmacokinetics in rats with diabetes induced by alloxan or streptozotocin: faster clearance of omeprazole due to induction of hepatic CYP1A2 and 3A1.

PURPOSE: To investigate the effect of diabetes mellitus induced by alloxan (DMIA) or streptozotocin (DMIS) on the pharmacokinetics of omeprazole in rats. It has been reported that omeprazole is primarily metabolized via hepatic CYP1A2, 2D1, and 3A1 in rats. The expression and mRNA levels of hepatic CYP1A2 and 3A1 increases in DMIA and DMIS rats, but the expression of hepatic CYP2D1 does not change in DMIS rats. In addition, the metabolic activities of intestinal CYP3A1/2 decreases in DMIS rats. Thus, it could be expected that the pharmacokinetics of omeprazole would be affected by changes in both DMIA and DMIS. METHODS: Omeprazole was administered intravenously (20 mg/kg) and orally (40 mg/kg) to DMIA and DMIS rats and their respective controls. RESULTS: After intravenous administration of omeprazole, the CLNR of the drug was significantly faster in DMIA (52.6 versus 67.4 mL/min/kg) and DMIS (50.2 versus 73.0 mL/min/kg) rats than the respective controls. However, after oral administration of omeprazole, the AUC was comparable between each type of diabetic rat and the respective controls. CONCLUSIONS: The significantly faster CLNR of intravenous omeprazole could be due to increased expression and mRNA levels of hepatic CYP1A2 and 3A1 in both types of diabetic rat. The comparable AUC of oral omeprazole could be due to a decrease in the intestinal first-pass effect of omeprazole caused by decreased intestinal CYP3A1/2 in diabetic rats. Following both intravenous and oral administration in DMIA and DMIS rats, the pharmacokinetics of omeprazole were similarly altered.

Pharmacokinetic interaction between oltipraz and omeprazole in rats: Competitive inhibition of metabolism of oltipraz by omeprazole via CYP1A1 and 3A2, and of omeprazole by oltipraz via CYP1A1/2, 2D1/2, and 3A1/2.

In rats, oltipraz is metabolized via hepatic CYP1A1/2, 2B1/2, 2C11, 2D1/2, and 3A1/2, and omeprazole via hepatic CYP1A1/2, 2D1/2, and 3A1/2. Hence, pharmacokinetic interaction between oltipraz and omeprazole were evaluated after simultaneous single i.v. and p.o. administration of both drugs to rats. After i.v. administration of oltipraz (10 mg/kg) and omeprazole (20 mg/kg), the AUC of both drugs was significantly greater (32.3 and 28.1% increase for oltipraz and omeprazole, respectively) than those after each drug alone. This could have been due to a competitive inhibition of metabolism of oltipraz by omeprazole via CYP1A1 and 3A2, and of metabolism of omeprazole by oltipraz via CYP1A1/2, 2D1/2, and 3A1/2. This could be supported by the apparent inhibition constants (K(i)) and the concentrations of each drug in the liver. After oral administration of oltipraz (30 mg/kg) and omeprazole (40 mg/kg), the AUC of oltipraz was significantly greater (68.8% increase) than that after oltipraz alone. This could have been primarily due to an inhibition of intestinal metabolism of oltipraz by omeprazole. However, comparable AUC values of omeprazole between p.o. administration of omeprazole alone and both drugs could have been due to insufficient inhibitory effect of oltipraz on omeprazole metabolism in both the liver and intestine.

Dose-independent pharmacokinetics of clindamycin after intravenous and oral administration to rats: contribution of gastric first-pass effect to low bioavailability.

The pharmacokinetic parameters of clindamycin were evaluated after intravenous (at doses of 50, 100, and 200mg/kg) and oral (at doses of 75, 150, and 300mg/kg) administration of the drug to rats. The first-pass effect of clindamycin was also evaluated after intraportal, intragastric, and intraduodenal administration of the drug at a dose of 150mg/kg to rats. After both intravenous and oral administration of clindamycin, the pharmacokinetic parameters of the drug were dose-independent. Hence, the extent of absolute oral bioavailability (F) was also independent of oral doses. After oral administration of clindamycin (150mg/kg), 7.68% of oral dose was not absorbed up to 24h and F value was 28.2%. The gastric first-pass effect of clindamycin was 60.7% of oral dose. The first-pass effects of clindamycin in the lung, heart, intestine, and liver were almost negligible, if any, in rats. The low F of clindamycin in rats was mainly due to considerable gastric first-pass effect. Clindamycin was stable in rat gastric juice and various buffer solutions having pHs ranging from 1 to 13. The plasma-to-blood cells partition ratio of clindamycin was 7.59 in rat blood. The plasma protein binding of clindamycin in rats was 67.5%.

Pharmacokinetics of omeprazole after intravenous and oral administration to rats with liver cirrhosis induced by dimethylnitrosamine.

The aim of this study is to report the pharmacokinetics of omeprazole after intravenous (20 mg/kg) and oral (40 mg/kg) administration to rats with liver cirrhosis induced by dimethylnitrosamine (cirrhotic rats) with respect to CYP isozyme changes. The expressions of CYP1A2 and 3A1 decreased in cirrhotic rats and omeprazole is reported to be mainly metabolized via CYP1A1/2, 2D1, and 3A1/2 in male Sprague-Dawley rats. Hence, the pharmacokinetics of omeprazole could be changed in cirrhotic rats. After intravenous administration to cirrhotic rats, the AUC (1180 microg min/ml versus 474 microg min/ml) and CL(NR) (17.4 ml/min/kg versus 42.3 ml/min/kg) of omeprazole were significantly greater and slower, respectively, than the controls. This could be due to decrease in the expressions of CYP1A2 and 3A1 in cirrhotic rats. The significantly slower CL(NR) could be supported by significantly slower in vitro CL(int) for the disappearance of omeprazole from hepatic microsomal study (0.102 ml/min/mg protein versus 0.144 ml/min/mg protein) and slower hepatic blood flow rate in cirrhotic rats. After oral administration to cirrhotic rats, the AUC difference was considerably greater (451% versus 149%) than that after intravenous administration, possibly due to decrease in intestinal first-pass effect of omeprazole in addition to decrease in hepatic metabolism of omeprazole in cirrhotic rats.