Omeprazole In Rats Research Articles

Oral Bioavailability and Pharmacokinetics of Sildenafil Orally Disintegrating Tablets under Various Gastric pH Levels Following Administration of Omeprazole in Rats.

Sildenafil citrate, an oral drug used to treat erectile dysfunction, has low water solubility and oral bioavailability. The solubility is greatly influenced by the pH, changing from 37.25 mg/mL to 0.22 mg/mL with a change in pH from 1.2 to 8.0. This indicates that the absorption may decrease in patients who use drugs, such as proton pump inhibitors (PPIs), for gastroesophageal reflux disease. To improve the absorption of sildenafil citrate at various gastric pH levels, a sildenafil citrate orally disintegrating tablet (ODT), which has a rapid disintegration feature, was produced by a 3D printing technique. Our study investigated the pharmacokinetic parameters of the sildenafil citrate ODT in rats after oral administration and compared the absorption of the sildenafil citrate ODT and sildenafil citrate commercial tablet (RLD), with and without PPI treatment. The LC/MS/MS analysis of the plasma sildenafil concentration revealed that the area under curve from time 0 to infinity (AUC0-∞) of sildenafil in the sildenafil citrate ODT group was significantly higher than in the sildenafil citrate RLD group whether it was in combination with the PPI or not (274.8% and 144%, respectively; p < 0.05). The relative systemic bioavailability of sildenafil citrate RLD significantly decreased with the PPI, but that of sildenafil citrate ODT was not affected by the PPI. These results indicate that the relative systemic bioavailability of sildenafil citrate ODT was increased when it was prepared using the 3D printing technique and the absorption of this formulation was not affected by the PPI.

Effects of Citri Reticulatae Pericarpium and grapefruit juice on the pharmacokinetics of omeprazole in rats.

The effects of Citri Reticulatae Pericarpium (CRP) and grapefruit juice (GFJ) on the pharmacokinetics of omeprazole were investigated in this study. Sprague-Dawley rats were pretreated with CRP decoction or GFJ for 28 consecutive days. After a single intragastric administration of 6.0mg/kg, the concentration of omeprazole in the plasma was determined by high-performance liquid chromatography (HPLC), and the pharmacokinetic parameters were calculated by Kinetica software 5.0. A high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (HPLC-Q-TOF-MS) method was established to identify the chemical components in CRP decoction and GFJ. The results showed that the AUCt-∞ was significantly increased when coadministrated with CRP. The AUC0-t and AUC0-∞ was remarkably increased; the Cl was decreased when coadministrated with GFJ. A total of 31 and 28 bioactive compounds were identified in the CRP decoction and GFJ, respectively. Flavonoids and furanocoumarins, including hesperidin, hesperetin, naringenin, sinensetin, tangeretin, nobiletin, and 6',7'-dihydroxybergamottin, were simultaneously identified in CRP decoction and GFJ. This study indicates that the increased bioavailability of omeprazole may be due to the inhibition of hepatic cytochrome P450 enzymes, and the systemic exposure should be monitored when concomitant administration with CRP and GFJ. PRACTICAL APPLICATIONS: Citri Reticulatae Pericarpium (CRP) has been widely consumed as a daily condiment, functional food, and a traditional Chinese medicine. Omeprazole, primary metabolized by CYP450 enzymes, was usually coadministered with CRP for the treatment of gastrointestinal disease. Studies have confirmed that much fruit juices, including grapefruit juice, may affect drug metabolism enzymes. CRP and grapefruit (Citrus paradisi Macf.) belong to the genus Citrus and family Rutaceae with different species. Therefore, the pharmacokinetic interaction of CRP decoction and grapefruit juice with omeprazole is worthy of attention. The results of this study can provide basic pharmacological data support for the safe and effective clinical use of omeprazole. It can also provide a theoretical basis for the development of new functional products and daily application of CRP.

УЛЬТРАСТРУКТУРНЕ ДОСЛІДЖЕННЯ КЛІТИН СЛИЗОВОЇ ОБОЛОНКИ ТОВСТОГО КИШЕЧНИКА ЩУРІВ ЗА ТРИВАЛОЇ ГІПЕРГАСТРИНЕМІЇ

Gastrin is considered one of the most important hormones regulating physiological processes. Trophic and proliferative effects of high gastrin levels on gastric mucosa are well known. Butinformation about gastrin effects on the colon is rather fragmentary and contradictory. In this study, ultrastructural changes in the proximal part of the colon induced in rats by chronic hypergastrinemia were analyzed by transmission electron microscopy. Experimental omeprazole-induced hypergastrinemia was reproduced using daily injections of proton pump inhibitor omeprazole in rats, resulted in hypersecrestion of gastrin by G-cells of stomach. Growth of gastrin level in the blood plasma was checked using radioimmunoassay method. Prolonged hypergastrinemia has been shown to be associated with increased cell proliferation and appearance of cellular atypia in the large intestine mucosa. The number of undifferentiated cells increased prominently. Intercellular contacts between such cells are altered, the space between them is unevenly expanded. Their organelles were observed significantly reduced, mitochondria contained destroyed crysts and signs of edema. Endocrinocytes did not contain their typical secretory granules. Cell nuclei were small, electron-dense, with invagination. In addition, numerous microorganisms were revealed in the intestinal lumen, as well as their invasion into the mucosa. Those ultrastructural changes were indicate increased hyperplastic processes and impaired cell differentiation in the epitheliocytes of large intestine. Therefore, long-term experimental hypergastrinaemia causes dysplastic changes in the large intestine mucosa of rats.

Pharmacokinetics of omeprazole in rats with dextran sulfate sodium–induced ulcerative colitis

Omeprazole is a commonly used drug in patients with ulcerative colitis (UC). This study investigated the pharmacokinetics of omeprazole in rats with UC induced by dextran sulfate sodium (DSS). The pharmacokinetics of intravenously administered omeprazole (20 mg/kg) was investigated in normal and UC rats using LC-MS/MS. The formation of 5-OH omeprazole, a main metabolite of omeprazole, in rat liver microsomes (RLMs) from normal and UC rats was compared. The protein levels of CYP1A2, CYP2D1, and CYP3A1 in the liver were measured by Western blot. Compared with normal rats, UC rats had increased plasma concentrations of omeprazole, resulting in an increased AUC0–240 min and decreased CL. DSS treatment decreased the formation rate of 5-OH omeprazole in RLMs but did not change the affinity of the enzymes. The Vmax and CLint of RLMs from UC rats were 62% and 48% those of RLMs from normal rats, respectively. The hepatic CYP1A2 and CYP3A1 protein levels in UC rats were 42.6 and 45.2% lower than those in normal rats, respectively; however, the protein levels of CYP2D1 in the two groups were similar. The activity and expression of some hepatic CYP450 isoforms were decreased by UC, leading to changes in the pharmacokinetics of omeprazole.

Protective effects of triple fermented barley extract (FBe) on indomethacin-induced gastric mucosal damage in rats

BackgroundHordeum vulgare L (barley) contains numerous phenolic substances with proven anticancer, antioxidant and gastroprotective activities. Saccharification increases the functionality and bioavailability of these compounds thus can aid in the development of a natural product based medicine. This study aimed to investigate the possible gastroprotective effects of saccharification on the indomethacin (IND)-induced gastric ulcers in rats using Weissella cibaria- and Saccharomyces cerevisiae-triple fermented H. vulgare extract (FBe).MethodsIn total, 60 healthy male 6-week old Sprague-Dawley SD (SPF/VAF Outbred CrljOri:CD1) rats were commercially purchased. The FBe extract (100, 200, and 300 mg kg− 1) was orally administered 30 min before an oral treatment of IND (25 mg kg− 1). Six hours after IND treatment, variations in the histopathology, myeloperoxidase (MPO) activity, gross lesion scores, lipid peroxidation, and antioxidant defense system component (superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH)) levels were measured.ResultsFBe treatment showed significant (p < 0.01 or p < 0.05) and dose-dependent decrease in gastric mucosal damage. In the present study hemorrhagic gross lesions, gastric MPO activity, and histopathological gastric ulcerative lesions were observed in IND-treated rats compared to the IND control rats. In particular, FBe, in a dose-dependent manner, strengthened the antioxidant defense systems, decreased lipid peroxidation and CAT activity by increasing the GSH levels and SOD activity, respectively. The 200 mg kg− 1 dose of FBe was similarly gastroprotective as the 10 mg kg− 1 dose of omeprazole in rats with IND-induced gastric mucosal damage.ConclusionsThe findings of the present study show that an oral administration of FBe had positive gastroprotective effects through strengthening the body antioxidant defense system and anti-inflammatory effects.

Effects of astragaloside IV on the pharmacokinetics of omeprazole in rats

Context: Omeprazole and astragaloside IV (AS-IV) are widely used for the treatment of gastric ulcers in China clinics.Objective: This study investigates the effects of AS-IV on the pharmacokinetics of omeprazole in rats.Materials and methods: The pharmacokinetics of orally administered omeprazole (2 mg/kg), with or without AS-IV (100 mg/kg/day for 7 days) pretreatment, were investigated in male Sprague-Dawley rats (two groups of six animals each) using LC–MS/MS. A Caco-2 cell transwell model and rat liver microsome incubation systems were also used to support the in vivo pharmacokinetic data and investigate its potential mechanism.Results: The results indicated that co-administration of AS-IV could decrease the systemic exposure of omeprazole significantly (p < 0.05), including AUC0–t (717.20 ± 177.63 vs. 1166.25 ± 186.65 ng h/mL) and Cmax (272.35 ± 25.81 vs. 366.34 ± 32.57 ng/mL). The t1/2 of omeprazole also decreased significantly (1.78 ± 0.15 vs. 2.23 ± 0.27 h, p < 0.05). The efflux ratio of omeprazole across the Caco-2 cell transwell model increased significantly from 1.73 to 2.67 (p < 0.05), and the metabolic stability of omeprazole was decreased from 42.6 ± 7.8 to 26.2 ± 5.1 min with the pretreatment of AS-IV (p < 0.05).Discussion and conclusions: AS-IV could decrease the systemic exposure of omeprazole in rats when AS-IV and omeprazole were co-administered, and it might exert these effects through decreasing the absorption of omeprazole by inducing P-gp, or through accelerating the metabolism of omeprazole in rat liver by inducing the activity of CYP3A4.

Effect of diammonium glycyrrhizinate on pharmacokinetics of omeprazole by regulating cytochrome P450 enzymes and plasma protein binding rate

1. In clinical practice, diammonium glycyrrhizinate is usually used with omeprazole in patients with viral hepatitis and cirrhosis accompanied by peptic ulcers. However, the drug interaction between diammonium glycyrrhizinate and omeprazole remains unclear.2. In this study, the effects of diammonium glycyrrhizinate on the pharmacokinetics of omeprazole was investigated by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method. Male Sprague–Dawley rats were randomly assigned to two groups: omeprazole and omeprazole + diammonium glycyrrhizinate, and the main pharmacokinetic parameters were estimated after oral administration. It was found that using the omeprazole along with the diammonium glycyrrhizinate increased the AUC, AUMC, Cmax for omeprazole.3. For this reason, we used the LC-MS/MS to detect the binding rate of plasma protein (BRPP) of omeprazole in rats, it was found that diammonium glycyrrhizinate could decrease the BRPP in rats. In addition, we found that diammonium glycyrrhizinate specifically inhibited the enzyme activity of the CYP2C19 and CYP3A4, which are involved in the metabolism of the omeprazole.4. These results mean that diammonium glycyrrhizinate could inhibit the metabolism and increase the plasma concentration of the omeprazole in rats. Overall, diammonium glycyrrhizinate can influence the pharmacokinetics of omeprazole by inhibiting CYP2C19 and CYP3A4 activities and decreasing BRPP of omeprazole.

Liver tumor promoting effect of omeprazole in rats and its possible mechanism of action

Omeprazole (OPZ), a proton pump inhibitor, is a cytochrome P450 (CYP) 1A1/2 inducer. Some CYP1A inducers are known to have liver tumor promoting effects in rats and the ability to enhance oxidative stress. In this study, we performed a two-stage liver carcinogenesis bioassay in rats to examine the tumor promoting effect of OPZ (Experiment 1) and to clarify a possible mechanism of action (Experiment 2). In Experiment 1, male F344 rats were subjected to a two-third partial hepatectomy, and treated with 0, 138 or 276 mg/kg OPZ by oral gavage once a day for six weeks after an intraperitoneal injection of N-diethylnitrosamine (DEN). Liver weights significantly increased in the DEN+OPZ groups, and the number and area of glutathione S-transferase placental form (GST-P) positive foci significantly increased in the DEN+276 mg/kg OPZ group. In Experiment 2, the same experiment as Experiment 1 was performed, but the dosage of OPZ was 0 or 276 mg/kg. The number and area of GST-P positive foci as well as liver weights significantly increased in the DEN+276 mg/kg OPZ group. The number of proliferative cell nuclear antigen (PCNA)-positive cells also significantly increased in the same group. Real-time RT-PCR showed that the expression of AhR battery genes including Cyp1a1, Cyp1a2, Ugt1a6 and Nqo1, and Nrf2 battery genes including Gpx2, Yc2, Akr7a3, Aldh1a1 Me1 and Ggt1 were significantly upregulated in this group. However, the production of microsomal reactive oxygen species (ROS) and formation of thiobarbituric acid-reactive substances (TBARS) decreased, and 8-hydroxydeoxyguanosine (8-OHdG) content remained unchanged in this group. These results indicate that OPZ, CYP1A inducer, is a liver tumor promoter in rats, but oxidative stress is not involved in the liver tumor promoting effect of OPZ.

The Role of Alpha-2 Adrenergic Receptors in the Anti-ulcerative Activity of Famotidine and Omeprazole in Rats and its Relationship with Oxidant-antioxidant Parameters

The Role of Alpha-2 Adrenergic Receptors in the Anti-ulcerative Activity of Famotidine and Omeprazole in Rats and its Relationship with Oxidant-antioxidant Parameters

Effect of soybean administration on the pharmacokinetics of carbamazepine and omeprazole in rats

Influence of soybean administration on the bioavailability of carbamazepine and omeprazole was studied after single dose administration of soybean (10 g/kg p.o.) or after chronic administration of soybean (50% w/w mixed with normal feed) for 15 days in rats. Carbamazepine was administered orally at a dose of 10 mg/kg and omeprazole at a dose of 20 mg/kg. Soybean decreased the bioavailability of carbamazepine after both single dose and chronic administration. It produced a significant decrease in C(max), T(max), AUC(0-t) of carbamazepine after single dose administration and increased the plasma clearance and V(d) along with decrease in C(max), T(max), AUC(0-t) and AUC(0-infinity) after chronic administration. On the contrary, soybean administration increased the bioavailability of omeprazole by producing an increase in C(max), AUC(0-t) and AUC(0-infinity) and a decrease in V(d) after single dose administration and a decrease in plasma clearance along with increase in C(max), AUC(0-t) and AUC(0-infinity) after chronic administration. The half-life of omeprazole was also increased after both acute and chronic administration of soybean. It was concluded that soybean decreases the bioavailability of carbamazepine and increases the bioavailability of omeprazole after both single dose and chronic administration.

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.

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

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. Omeprazole was administered intravenously (20 mg/kg) and orally (40 mg/kg) to DMIA and DMIS rats and their respective controls. 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. 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.

Development of Pancreatic Acinar Cell Metaplasia After Successful Administration of Omeprazole for 6 Months in Rats

Long-term use of proton pump inhibitors (PPIs) has been reported to worsen corpus atrophic gastritis in patients with Helicobacter pylori infection. On the other hand, PPIs have been associated with fundic gland-type gastric polyps and various histological changes. In the present study, we attempted to establish a protocol for omeprazole (OPZ) administration to rats over a longer period and examined the morphological changes in the gastric mucosa after administration of OPZ for 6 months. A total of 34 Wistar rats (8 weeks old) were used. In a preliminary experiment to determine the appropriate dose of OPZ, the rats had ad libitum access to food containing different doses of OPZ for 1 month. We found an approximate dose of 100 mg/kg body weight/day of OPZ to be most suitable from the point of view of intragastric pH, body weight, and serum gastrin level. In the experiment proper, rats were divided into two groups, either control or OPZ diets, and morphological changes in the gastric mucosa in each group were then examined by hematoxylin and eosin and immunohistochemical staining with alpha-amylase, trypsin, and chromogranin A. Multiple vacuolar degeneration of parietal cells and numerous small mucous cells were evident at 1 month after treatment with OPZ. At 6 months after treatment with OPZ, cystic degeneration and acinar-cell-like cells containing red granules positive for alpha-amylase and trypsin and negative for chromogranin A were detected in the OPZ rats. The serum gastrin level in the OPZ group was significantly higher than that in the control group. We have established a protocol for long-term administration of OPZ in rats that is a useful model for analyzing morphological changes after long-term PPI therapy. Long-term OPZ treatment causes hypergastrinemia and pancreatic acinar cell metaplasia in this animal model.

Rebamipide Contributes to Reducing Adverse Effects of Long-Term Administration of Omeprazole in Rats

Proton pump inhibitors (PPIs) have become of great importance for the treatment of peptic ulcer disease and gastroesophageal reflux disease. However, these drugs have several adverse effects, including worsening of corpus atrophic gastritis in patients with H. pylori infection, various histological changes including fundic gland-type polyps, inhibition of glycoprotein production, and hypergastrinemia. On the other hand, it has been reported that rebamipide, a gastroprotective drug, has the potential to increase mucous secretion and basically regulate physiological defensive functions aimed to maintain tissue integrity. In this study, we attempted to clarify whether rebamipide improves morphological changes and hypergastrinemia after administration of omeprazole (OPZ) for 1 year in rats. Eight-week-old male Wistar rats were used. Rats were divided into four groups according to diet as follows: 100 mg/kg body weight OPZ group, 100 mg/kg body weight OPZ and 30 mg/kg body weight rebamipide (OPZ + trebanipide group), 30 mg/kg body weight rebamipide, and normal diet (CRF-1). Morphological changes in gastric mucosa in all groups were studied using hematoxylin and eosin staining, periodic acid-Schiff staining, and immunohistochemical staining for alpha-amylase. Serum gastrin level and basal acid secretion were also examined. In the OPZ group, cystic degenerations with amorphous eosinophilic contents, decreased mucous secretion, decreased chief cells, and development of pancreatic acinar cell metaplasia were detected. However, in the OPZ+rebamipide group, these morphological changes were significantly milder than in the OPZ group. Serum gastrin level and basal acid secretion in the OPZ group increased significantly compared to those in the control group. But these factors in the OPZ+rebamipide group were almost normalized (similar to those of control animals). In conclusion, long-term OPZ treatment causes various morphological changes, hypergastrinemia, and basal acid hypersecretion. The present results suggest that rebamipide contributes to reducing these adverse effects caused by long-term OPZ treatment in rats.

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

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. Omeprazole was administered intravenously (20 mg/kg) and orally (40 mg/kg) to control, PCM, and PCMC rats. 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). PCM was associated with significant changes in some omeprazole pharmacokinetics and the pharmacokinetic parameters restored to control levels by oral cysteine.

Determination of omeprazole in rat plasma by high-performance liquid chromatography without solvent extraction

A HPLC method without solvent extraction and using ultraviolet detection at 302 nm for the determination of omeprazole in rat plasma has been validated. Plasma samples after pretreatment with acetonitrile to effect deproteinization were dried under N(2) at 40 degrees C and reconstituted with mobile phase. The standard calibration curve for omeprazole was linear (r(2)=0.9999) over the concentration range of 0.02-3 microgml(-1). The intra- and inter-day assay variability range was 4.8-9.2% and 5.2-10.3% individually. This method has been successfully applied to a pharmacokinetic study of omeprazole in rats.

Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous omeprazole in rats

A series of experiments using various inducers and inhibitors of the hepatic microsomal cytochrome P450 (CYP) isozymes were conducted to find CYP isozymes responsible for the metabolism of omeprazole in male Sprague-Dawley rats. Omeprazole, 20 mg/kg, was administered intravenously. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats), the time-averaged nonrenal clearance (Cl(nr)) was significantly slower (77.1% decrease) than that in untreated rats. This indicated that omeprazole is metabolized via CYP isozymes in rats. Hence, rats were pretreated with various enzyme inducers and inhibitors. In rats pretreated with 3-methylcholanthrene and dexamethasone (main inducers of CYP1A1/2 and 3A1/2 in rats, respectively), the Cl(nr) values were significantly faster (43.8% and 26.3% increase, respectively). In rats pretreated with troleandomycin and quinine (main inhibitors of CYP3A1/2 and 2D1 in rats, respectively), the Cl(nr) values were significantly slower (20.9% and 12.9% decrease, respectively). However, the Cl(nr) values were not significantly different in rats pretreated with orphenadrine, isoniazid and sulfaphenazole (main inducers of CYP2B1/2 and 2E1, and a main inhibitor of 2C11, respectively, in rats) compared with those of respective control rats. The above data suggested that omeprazole could be mainly metabolized via CYP1A1/2, 3A1/2 and 2D1 in male rats.

Pharmacokinetics of omeprazole in rats with water deprivation for 72 hours

Dehydration can occur by excessive sweating, polyuria, severe diarrhea and hyperthermia. Previous studies reported that the expressions of CYP1A1/2 and 3A1(23)/2 were not changed in male Sprague-Dawley rats with 72 h water deprivation (dehydrated rats), and that the metabolism of omeprazole is mainly catalysed via CYP1A1/2, 2D1 and 3A23/2 in rats. Hence, it could be expected that the hepatic metabolism of omeprazole would not be changed considerably in dehydrated rats, if the contribution of CYP2D1 to the metabolism of omeprazole in dehydrated rats is not considerable. Therefore, the pharmacokinetics of omeprazole were compared after intravenous (20 mg/kg) and oral (40 mg/kg) administration in control rats and in dehydrated rats. After intravenous administration, the time-averaged nonrenal clearance (Cl(nr)) values of omeprazole were comparable between the two groups of rats. This could be supported by comparable in vitro intrinsic clearance (Cl(int)) values for the disappearance of omeprazole in rat hepatic microsomes and the comparable free (unbound to plasma proteins) fractions of omeprazole in plasma in the two groups of rats. After oral administration, the AUC values of omeprazole were also comparable in the two groups of rats. The above data suggest that the dehydration state did not affect considerably the pharmacokinetics of omeprazole in rats.

Liver regeneration is enhanced by omeprazole in rats following partial hepatectomy.

The effect of omeprazole on liver regeneration was studied in rats following partial (65 per cent) hepatectomy. Omeprazole 0.2 mg/kg increased the relative liver weight (weight of liver as a proportion of body-weight) and mitotic index (P < 0.05). There was no difference in food and water intake. The serum gastrin concentration was significantly higher in animals receiving omeprazole 0.2 mg/kg than in controls (P < 0.05). Omeprazole administration induced an increase in the level of serum alkaline phosphatase (P < 0.05) but had no effect on serum albumin, glutamic-pyruvic transaminase and total bilirubin levels. Omeprazole stimulates liver regeneration after partial hepatectomy and this regeneration may be mediated by gastrin.