The potency of substituted benzimidazoles such as E3810, omeprazole, Ro 18-5364 to inhibit gastric H+, K(+)-ATPase is correlatedwith the rate of acid-activation of the inhibitor

Mucosal Healing Effectiveness and Safety of Anaprazole, a Novel PPI, vs. Rabeprazole in Patients With Duodenal Ulcers: A Randomized Double-Blinded Multicenter Phase II Clinical Trial

Background: Proton pump inhibitors (PPIs) are validated gastric acid suppressors and have been widely used to treat patients with active duodenal ulcers. Although existing PPIs have shown great efficacy, many scientists are still devoted to developing more effective PPIs with better safety profile. Herein, we aimed to compare the safety and efficacy of anaprazole in duodenal mucosal healing, a novel PPI, to that of rabeprazole.

Methods: In this multicenter, randomized, positive-controlled, double-blinded, parallel-group phase II clinical trial, a total of 150 qualified patients with endoscopically confirmed active duodenal ulcers were randomized (1:1:1) to receive rabeprazole 10 mg, anaprazole 20 mg or anaprazole 40 mg for 4 weeks. The ulcer healing rates after 4 weeks of treatment were compared between groups by independent central review and investigator review. In addition, symptoms and safety were evaluated.

Results: Based on the independent central review, the ulcer healing rates of the 10 mg rabeprazole, 20 mg anaprazole and 40 mg anaprazole groups were 88.0, 85.1, and 87.5%, respectively, in the FAS population and 88.9, 86.0, and 90.9%, respectively, in the PPS population. The ulcer healing rate difference between anaprazole 20 mg and Rabeprazole 10 mg is −2.9% (95% CI, −16.5–10.7%), and −0.5% (95% CI, −13.5–12.5%) between anaprazole 40 mg and Rabeprazole 10 mg, in the FAS population. Based on the investigator review, the ulcer healing rates of the 10 mg rabeprazole, 20 mg anaprazole, and 40 mg anaprazole groups were 72.0, 70.2, and 77.1%, respectively, in the FAS population and 75.6, 72.1, and 79.5%, respectively, in the PPS population. The ulcer healing rate difference between anaprazole 20 mg and Rabeprazole 10 mg is −1.8% (95% CI, −19.8–16.3%), and 5.1% (95% CI, −12.2–22.3%) between anaprazole 40 mg and Rabeprazole 10 mg, in the FAS population. Most patients (>90%) eventually achieved complete symptom relief. The incidence rates of adverse events were of no significant differences among the treatment groups. Potential possible better liver tolerance was observed in two anaprazole dose groups than rabeprazole 10 mg group.

Conclusion: Both at a dosage of 20 and 40 mg daily, anaprazole, is effective with good safety profile in the treatment of active duodenal ulcers in this Phase 2 study, which allows anaprazole to be advanced to a phase III clinical trial.

Clinical Trial Registration:https://www.clinicaltrials.gov/ct2/results?cond=&term=NCT04503629&cntry=&state=&city=&dist=, Identifier: CTR20181464, NCT04503629.

Rabeprazole inhibits several functions of Entamoeba histolytica related with its virulence

Amoebiasis is a human parasitic disease caused by Entamoeba histolytica. The parasite can invade the large intestine and other organs such as liver; resistance to the host tissue oxygen is a condition for parasite invasion and survival. Thioredoxin reductase of E. histolytica (EhTrxR) is a critical enzyme mainly involved in maintaining reduced the redox system and detoxifying the intracellular oxygen; therefore, it is necessary for E. histolytica survival under both aerobic in vitro and in vivo conditions. In the present work, it is reported that rabeprazole (Rb), a drug widely used to treat heartburn, was able to inhibit the EhTrxR recombinant enzyme. Moreover, Rb affected amoebic proliferation and several functions required for parasite virulence such as cytotoxicity, oxygen reduction to hydrogen peroxide, erythrophagocytosis, proteolysis, and oxygen and complement resistances. In addition, amoebic pre-incubation with sublethal Rb concentration (600 μM) promoted amoebic death during early liver infection in hamsters. Despite the high Rb concentration used to inhibit amoebic virulence, the wide E. histolytica pathogenic-related functions affected by Rb strongly suggest that its molecular structure can be used as scaffold to design new antiamoebic compounds with lower IC₅₀ values.

Inhibition of gastric H+,K+-ATPase by 4-(2-butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB), an inhibitor of volume-regulated anion channel

4-(2-Butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB) has been used as an inhibitor of volume-regulated anion channel (VRAC), which is expressed in almost all cells (IC50 is around 4 µM). Here, we found that DCPIB significantly inhibited the activities of gastric proton pump (H+,K+-ATPase) in isolated gastric tubulovesicles and the membrane sample of the H+,K+-ATPase-expressing cells, and their IC50 values were around 9 µM. In the tubulovesicles, no significant expression of leucine rich repeat containing 8 family member A (LRRC8A), an essential component of VRAC, was observed. The inhibitory effect of DCPIB was also found in the membrane sample obtained from the cells in which LRRC8A had been knocked down. On the other hand, DCPIB had no significant effect on the activity of Na+,K+-ATPase or Ca2+-ATPase. In the H+,K+-ATPase-expressing cells, DCPIB inhibited the 86Rb+ transport activity of H+,K+-ATPase but not that of Na+,K+-ATPase. DCPIB had no effect on the activity of Cl- channels other than VRAC in the cells. These results suggest that DCPIB directly inhibits H+,K+-ATPase activity. DCPIB may be a beneficial tool for studying the H+,K+-ATPase function in vitro.

Benzimidazole derivative, BMT-1, induces apoptosis in multiple myeloma cells via a mitochondrial-mediated pathway involving H+/K+-ATPase inhibition

2-(1H-benzimidazol-2-yl)-4,5,6,7-tetrahydro-2H-indazol-3-ol (BMT-1), a bicyclic compound, belongs to the benzimidazole group and consists of the fusion of benzene and imidazole. The objective of the present study was to assess the effect of BMT-1 on the proliferation of multiple myeloma (MM) cells and identify whether BMT-1 induces apoptosis in MM cells. Our results showed a dose- and time-dependent decrease in the proliferation of MM cells treated with BMT-1. Further studies revealed that the antiproliferative effects of BMT-1 were caused by induction of apoptosis with activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase in MM cells. In addition, BMT-1 induced the loss of mitochondrial membrane potential resulting in the activation of caspase-8 and -9. Furthermore, the MM cells treated with BMT-1 showed a more acidic intracellular pH (pHi) as indicated by a lower FL1/FL2 ratio caused by inhibition of H+/K+-ATPase. Collectively, these findings demonstrated that a decrease in pHi, caused by H+/K+-ATPase inhibition induced by BMT-1, triggered the dysfunction of the mitochondria resulting in the apoptosis of MM cells. Therefore, BMT-1 may be used as a lead compound for the design and development of new agents with which to treat MM and other forms of cancer.

Effects of a proton pump inhibitor on the physiological accumulation of fluoro-2-deoxy-D-glucose (FDG) in FDG-positron emission tomography

PURPOSES

The physiological accumulation of fluoro-2-deoxy-D-glucose (FDG) is common in medical examinations of the digestive tract conducted using FDG-positron emission tomography (PET). The aim of this study was to determine the effects of a proton pump inhibitor (PPI) on the physiological FDG accumulation in the digestive tract.

METHODS

A total of 130 patients examined from July 2007 to October 2008 were included in the final analysis. A PPI was administered orally prior to FDG-PET in 65 patients. The remaining 65 patients underwent FDG-PET without administration of the PPI. The assessments used visual and quantitative evaluations.

RESULTS

Visual evaluation showed that physiological FDG accumulation in the stomach was significantly reduced (p = 0.037) in the PPI group compared with the control group. The quantitative evaluation also revealed a significant reduction in the maximum standardized uptake values (SUV(max)) in the stomach in the PPI group compared with the control group (p < 0.0001). Physiological FDG accumulation in the colon showed a decreasing trend on visual evaluation in the PPI group compared with the control group, and the quantitative evaluation found a significant reduction in the physiological FDG accumulation in the colon in the PPI group (p = 0.045).

CONCLUSIONS

The oral administration of a PPI was effective for reducing the physiological accumulation of the FDG in the alimentary tract. However, based on the error associated with SUV(max) measurement, a quantitative evaluation should therefore be combined with the visual evaluation.

A high-throughput scintillation proximity-based assay for human DNA ligase IV

Ionizing radiation (IR) and certain chemotherapeutic drugs are designed to generate cytotoxic DNA double-strand breaks (DSBs) in cancer cells. Inhibition of the major DSB repair pathway, nonhomologous end joining (NHEJ), will enhance the cytotoxicity of these agents. Screening for inhibitors of the DNA ligase IV (Lig4), which mediates the final ligation step in NHEJ, offers a novel target-based drug discovery opportunity. For this purpose, we have developed an enzymatic assay to identify chemicals that block the transfer of [α-(33)P]-AMP from the complex Lig4-[α-(33)P]-AMP onto the 5' end of a double-stranded DNA substrate and adapted it to a scintillation proximity assay (SPA). A screen was performed against a collection of 5,280 compounds. Assay statistics show an average Z' value of 0.73, indicative of a robust assay in this SPA format. Using a threshold of >20% inhibition, 10 compounds were initially scored as positive hits. A follow-up screen confirmed four compounds with IC(50) values ranging from 1 to 30 μM. Rabeprazole and U73122 were found to specifically block the adenylate transfer step and DNA rejoining; in whole live cell assays, these compounds were found to inhibit the repair of DSBs generated by IR. The ability to screen and identify Lig4 inhibitors suggests that they may have utility as chemo- and radio-sensitizers in combination therapy and provides a rationale for using this screening strategy to identify additional inhibitors.

Relationship between the Acid-Inhibitory Effects of Two Proton Pump Inhibitors and CYP2C19 Genotype in Japanese Subjects: A Randomized Two-Way Crossover Study

This two-way crossover study investigated possible differences between the proton pump inhibitors, omeprazole and rabeprazole, in their effect on gastric acid secretion in Japanese subjects with differing cytochrome P450, family 2, subfamily C, polypeptide 19 (CYP2C19) genotypes. A total of 23 Helicobacter pylori-negative healthy volunteers received omeprazole 20 mg/day and rabeprazole 10 mg/day. Each drug treatment was given for a continuous 7-day period allocated in random order, with an interval of at least 1 week between drug treatment periods to allow for wash-out. Intragastric pH was measured on days 1 and 7. Overall median intragastric pH levels at 7 and 8 h after the first administration were significantly higher with omeprazole. There was no significant difference in intragastric pH in homozygous extensive metabolizers, whereas intragastric pH was significantly higher with omeprazole in combined data from heterozygous extensive metabolizers and poor metabolizers at 6, 7 and 8 h after the first drug administration. There were no significant differences in intragastric pH between omeprazole and rabeprazole irrespective of genotype on day 7 of administration. In conclusion, on day 1 the time to onset of the antisecretory action of 20 mg/day omeprazole was more rapid than that of 10 mg/day rabeprazole in Japanese individuals who have a higher incidence of the CYP2C19 poor metabolizer genotype, however by day 7 no difference in antisecretory effect was found, regardless of genotype.

Spectrophotometric determination of certain benzimidazole proton pump inhibitors

Spectrophotometric method for the determination of certain proton pump inhibitors belonging to the benzimidazole class of compounds has been developed. The method is based on the reaction of omeprazole, lansoprazole, pantoprazole, rabeprazole and esomeprazole with iron (III) and subsequent reaction with ferricyanide under neutral condition which yields Prussian blue product with maximum absorption at 720–730 nm. The commonly encountered excipients and additives that often accompany pharmaceutical preparations did not interfere with the determination. The method was applied for the determination of omeprazole, lansoprazole, pantoprazole, rabeprazole and esomeprazole in pharmaceutical preparations and no difference was found statistically. Thus, the spectrophotometric method can be applied as inexpensive, rapid, easy, accurate and precise method for the routine analysis of the five proton pump inhibitors in pharmaceutical preparations.

Endoscopic analysis of gastric ulcer after one week's treatment with omeprazole and rabeprazole in relation to CYP2C19 genotype

In Japanese healthy CYP2C19 extensive metabolizers, rabeprazole 10 mg shows a faster onset of action and stronger inhibition of acid secretion than does omeprazole 20 mg on the first 3 days of administration. We evaluated gastric ulcer improvement after 1 week's treatment with rabeprazole or omeprazole in relation to CYP2C19 polymorphism. A 6-mm rubber disc was placed temporarily at the side of the ulcer for measurement of the ulcer area. The improvement ratios of ulcer area in homozygous extensive metabolizers (homoEMs), heterozygous extensive metabolizers (heteroEMs) and poor metabolizers (PMs) treated with rabeprazole 10 mg were 60.8, 65.0 and 55.3%, respectively, and these values are not significantly different. Corresponding values with omeprazole 20 mg were 46.3, 61.7 and 63.2%, respectively, and the value of homoEMs was significantly smaller than that of heteroEMs. The improvement ratios with rabeprazole in homoEMs and heteroEMs were significantly greater than that with omeprazole in homoEMs.

Omeprazole Induces Apoptosis in Normal Human Polymorphonuclear Leucocytes

We investigated in vitro apoptosis in human polymorphonuclear neutrophils (PMN) induced by omeprazole. This drug, both in the native (OM) and acidified (OM-HCl) form, is a potent inducer of PMN apoptosis. The effect is time- and dose-dependent. OM-HCl is more efficient than OM in inducing PMN apoptosis. In fact, after 24 h incubation in vitro at 1×10 −4M OM-HCl induces apoptosis in 70% of the cell population compared to 37% induced by OM. Apoptosis induced by both forms of the drug is caspase dependent being significantly reduced by pretreating cells with the caspase 3 inhibitor (DEVDH-CHO). However, some differences in the apoptosis mechanisms between the two forms of the drug seem to exist because PMN treatment with the specific caspase 8 inhibitor (Z-IETD-FMK) only blocks OM-HCl mediated apoptosis. We observed cleavage of caspase 8 only in the cells incubated with OM-HCl while the executioner caspase 3 was activated with both forms of the drug. Furthermore, pretreatment with GM-CSF, a known activator of intracellular survival pathways in PMN, partially protected cells from OM-HCl induced apoptosis but did not contrast the apoptotic effect of OM. Cysteine cathepsin proteases also seem involved in the apoptotic mechanism of both drug forms since the specific inhibitor E64d gave a significant protection. To verify if OM-HCl induced apoptosis was dependent on the sulfenamide bound with the cell sulfhydryl groups we used molecules with thiol groups such as β-mercaptoethanol (β-ME) and reduced glutathione (GSH). Reactions of OM-HCl with cellular sulfhydryl groups are strongly involved in both the triggering and evolving phase of the apoptotic mechanism since significant protection from apoptosis was obtained when PMN were pretreated for 1h with β-ME (lipid-permeable) or GSH (lipid-impermeable). These results show that OM and OM-HCl induce apoptosis in human PMN and suggest that the second binds the sulfhydryl groups, present on the cell membrane, to then penetrate the cell thus causing a further significant increase in apoptosis. OM-induced PMN apoptosis during the treatment of gastric inflammatory disease could be an advantage for the resolution of the phlogosis state. However, this aspect should be further elucidated to assess the optimal therapeutical regimen for gastric diseases which are related to infective agents.

Influence of rabeprazole and lansoprazole on the pharmacokinetics of tacrolimus in relation to CYP2C19, CYP3A5 and MDR1 polymorphisms in renal transplant recipients

The objective of this study was to evaluate whether genetic polymorphisms of CYP2C19, CYP3A5 and MDR1 significantly impact the interaction between tacrolimus and rabeprazole or lansoprazole. Seventy-three recipients were randomly assigned after renal transplantation to receive repeated doses of tacrolimus for 28 days with a regimen of either 20 mg of rabeprazole or 30 mg of lansoprazole. Blood concentrations of tacrolimus were measured by microparticle enzyme immunoassay. The mean daily dose and the dose-adjusted area under the plasma concentration-time curves from 0 to 12 h (AUC(0-12)) of tacrolimus coadministered with rabeprazole or lansoprazole were the lowest and highest, respectively, in CYP2C19 poor metabolizers (PMs) having the CYP3A5*3/*3 genotype (0.084 and 0.112 mg/kg/day and 1.269 and 1.033 ng.h/ml/mg/kg, respectively). On the other hand, the mean dose-adjusted AUC(0-12) of tacrolimus coadministered with rabeprazole or lansoprazole were the highest in CYP2C19 PMs having the MDR13435CC+CT genotype, but not significantly. The present study indicates that there are significant interactions between tacrolimus and rabeprazole or lansoprazole in CYP2C19 PM renal transplant recipients bearing the CYP3A5*3/*3 genotypes. For recipients having these genetic polymorphisms, lower dosages of tacrolimus are required to achieve the target therapeutic index.

Enantioselective disposition of rabeprazole in relation to CYP2C19 genotypes

AIM

Rabeprazole is metabolized to some extent by CYP2C19. The purpose of this study was to elucidate the pharmacokinetics of each rabeprazole enantiomer in three different CYP2C19 genotype groups.

METHODS

Twenty-four healthy subjects, of whom each each were homozygous extensive metabolizers (homEMs), heterozygous extensive metabolizers (hetEMs) and poor metabolizers (PMs) for CYP2C19, participated in our study. After a single oral dose of 20 mg of racemic rabeprazole, the plasma concentrations of the rabeprazole enantiomers were measured over the course of 24 h.

RESULTS

The area under the plasma concentration-time curves (AUC) of (R)-rabeprazole in homEMs, hetEMs and PMs were 1.8-, 2.2- and 2.4-fold, respectively, greater than those of (S)-rabeprazole; the relative AUC ratios of (R)- and (S)-rabeprazole in homEMs, hetEMs and PMs were 1:1.1:2.1 and 1:0.9:1.5, respectively. The mean maximum plasma concentrations (Cmax) of (R)-rabeprazole in homEMs, hetEMs and PMs were 1.7-, 1.9- and 1.8-fold higher, respectively, than those of the corresponding (S)-enantiomer (P<0.05). There was no difference between homEMs and PMs in the elimination half-life of (S)-rabeprazole, whereas the elimination half-life of (R)-rabeprazole was significantly longer in PMs than in homEMs [1.7 h (1.4, 2.0) (mean (95% confidence interval)]vs. 0.8 h (0.6, 1.0), respectively, P<0.0001).

CONCLUSIONS

(R)-Rabeprazole disposition was influenced to a greater degree by CYP2C19 genetic polymorphisms than was that of (S)-rabeprazole. The effect of CYP2C19 polymorphisms on the stereoselective disposition of rabeprazole was less than those of lansoprazole and omeprazole.

Comparison of the efficacy of rabeprazole 10 mg and omeprazole 20 mg for the healing rapidity of peptic ulcer diseases

AIM

Rabeprazole has been known to inhibit H(+)/K(+)-ATPase more rapidly than omeprazole, the prototype proton pump inhibitor (PPI). The aim of this study was to demonstrate equivalence between low-dose rabeprazole 10 mg and omeprazole 20 mg for the healing rapidity of active peptic ulcer and for improvement of symptoms. Also, the effect of CYP2C19 genotypes on ulcer healing rapidity was investigated.

METHODS

A total of 112 patients with active peptic ulcer were randomized to receive either rabeprazole 10 mg q.d. or omeprazole 20 mg q.d. for 6 weeks. The remaining ratios (%) and complete healing of the ulcer were determined by endoscopy at 1 week and 6 weeks of treatment. The severity of ulcer pain was also investigated during treatment. CYP2C19 genotype was determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

The remaining ratio of peptic ulcers after 1 week and the complete healing rate after 6 weeks in the rabeprazole versus omeprazole group were 45.5% versus 50.3% (P = 0.475) and 80.6% versus 87.0% (P = 0.423), respectively. CYP2C19 genotypes had no effect on the remaining ratio of peptic ulcers after 1 week and the healing rate of peptic ulcers after 6 weeks in both groups. The proportions of patients with symptom improvement or resolution were comparable between the two groups.

CONCLUSION

Low-dose rabeprazole 10 mg has a similar efficacy for the healing rapidity of active peptic ulcer disease and symptom improvement compared with standard-dose omeprazole 20 mg.

Enantioselective Disposition of Lansoprazole and Rabeprazole in Human Plasma

Lansoprazole is extensively metabolized by CYP2C19 and CYP3A4 in the liver, whereas rabeprazole is primarily converted non-enzymatically to rabeprazole-thioether, with only some being oxidized by CYP2C19 and CYP3A4. Lansoprazole and rabeprazole possess asymmetric sulfur in their chemical structure and have typically been used clinically as a racemic mixture. This article reviews the pharmacokinetic differences between enantiomers of lansoprazole and rabeprazole in relation to the CYP2C19 genotypes. In our studies in healthy Japanese subjects, the magnitude of contribution of each lansoprazole enantiomer for CYP2C19 was greater than that for CYP3A4. CYP2C19 influenced the disposition of (S)-lansoprazole to a greater extent than the (R)-enantiomer. The R/S ratios for the AUC of lansoprazole in CYP2C19 homEMs, hetEMs and PMs was 12.7, 8.5 and 5.8, respectively. On the other hand, (R)-rabeprazole disposition was influenced to a greater degree by CYP2C19 genetic polymorphisms than (S)-rabeprazole. However, the R/S ratios for the AUC of rabeprazole in CYP2C19 homEMs, hetEMs and PMs was only 1.8, 2.2 and 2.4, respectively, suggesting a lesser effect of CYP2C19 polymorphisms on the stereoselective disposition of rabeprazole compared to lansoprazole. Such a difference in the AUC between rabeprazole enantiomers is likely to be dependent on stereoselectivity in the CYP3A4-mediated metabolic conversion from rabeprazole-thioether to rabeprazole. Both enantiomers of these PPIs have been reported to possess equal potency. Therefore, particularly with lansoprazole, the use of (R)-lansoprazole alone would be highly desirable for use in clinical applications.

Determination of rabeprazole enantiomers and their metabolites by high-performance liquid chromatography with solid-phase extraction

Here, we describe the development of a rapid, simple and sensitive high-performance liquid chromatography (HPLC) method for the simultaneous quantitative determination of rabeprazole enantiomers (1a,b) and their metabolites, rabeprazole-thioether (2) and rabeprazole sulfone (3), in human plasma. Analytes and the internal standard (omeprazole-thioether) were separated using a mobile phase of 0.5 M NaClO4-acetonitrile (6:4, v/v) over a Chiral CD-Ph column. Analysis required only 100 microl of plasma and involved solid-phase extraction with an Oasis HLB cartridge, which gave high recovery (>91.8%) with good selectivity for all analytes. The lower limit of quantification was 5 ng/ml for analytes 1a, 1b and 3 and 10 ng/ml for 2. Linearity of this assay was determined to lie between 5 and 1000 ng/ml for 1a, 1b and 3 and 10 and 1000 ng/ml for 2 (r2>0.982 of the regression line). Inter- and intra-day coefficients of variation were less than 7.8% and accuracies were within 8.4% over the linear range for all analytes. Our results indicate that this method is applicable to the simultaneous monitoring of plasma levels of rabeprazole enantiomers and associated metabolites in human plasma.

Characterization of the inhibitory activity of tenatoprazole on the gastric H+,K+ -ATPase in vitro and in vivo

Tenatoprazole is a prodrug of the proton pump inhibitor (PPI) class, which is converted to the active sulfenamide or sulfenic acid by acid in the secretory canaliculus of the stimulated parietal cell of the stomach. This active species binds to luminally accessible cysteines of the gastric H+,K+ -ATPase resulting in disulfide formation and acid secretion inhibition. Tenatoprazole binds at the catalytic subunit of the gastric acid pump with a stoichiometry of 2.6 nmol mg(-1) of the enzyme in vitro. In vivo, maximum binding of tenatoprazole was 2.9 nmol mg(-1) of the enzyme at 2 h after IV administration. The binding sites of tenatoprazole were in the TM5/6 region at Cys813 and Cys822 as shown by tryptic and thermolysin digestion of the ATPase labeled by tenatoprazole. Decay of tenatoprazole binding on the gastric H+,K+ -ATPase consisted of two components. One was relatively fast, with a half-life 3.9 h due to reversal of binding at cysteine 813, and the other was a plateau phase corresponding to ATPase turnover reflecting binding at cysteine 822 that also results in sustained inhibition in the presence of reducing agents in vitro. The stability of inhibition and the long plasma half-life of tenatoprazole should result in prolonged inhibition of acid secretion as compared to omeprazole. Further, the bioavailability of tenatoprazole was two-fold greater in the (S)-tenatoprazole sodium salt hydrate form as compared to the free form in dogs which is due to differences in the crystal structure and hydrophobic nature of the two forms.

Liquid chromatographic/mass spectrometric assay of rabprazole in dog plasma for a pharmacokinetic study

In order to evaluate the pharmacokinetic (PK) profile of rabeprazole (RA) sterile powder for injection, a rapid, sensitive and specific assay for quantitative determination of RA in dog plasma was developed and validated. After a liquid-liquid extraction procedure, samples were analyzed by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) using omepazole as the internal standard (IS). The analyte and IS was chromatographed on a ZORBAX Extend-C(18) analytical column (50 x 2 mm i.d, 5 microm, Agilent Technologies, USA). The assay was linear in the range 1-2000 ng/mL. The lower limit of quantification of RA was 1 ng/mL. The recovery of RA was greater than 70%. The within- and between-batch accuracy was 102.7-107.4% and 103.5-105.7%, respectively. The plasma samples for the PK study were collected at defined time points during and after an intravenous injection (1 mg/kg) to beagle dogs and analyzed by LC-ESI-MS method. The PK parameters, such as half-life, volume of distribution, total clearance and elimination rate constant, were determined. The PK profile of RA gave insights into the application in the clinics.

Stereoselective metabolism of rabeprazole-thioether to rabeprazole by human liver microsomes

OBJECTIVE

Rabeprazole is metabolized mainly non-enzymatically to rabeprazole-thioether. This in vitro study was designed to clarify the stereoselective oxidation mechanism and to identify the enzyme(s) involved in the metabolic breakdown of rabeprazole-thioether to rabeprazole.

METHODS

Rabeprazole-thioether was incubated with human liver microsomes and several recombinant cytochrome P450 (CYP) enzymes (CYPs 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4). High-performance liquid chromatography was used for identification and quantification of each rabeprazole enantiomer.

RESULTS

The K(m ) and V(max ) values for the formation of (R)-rabeprazole from rabeprazole-thioether in human liver microsomes were 6.6 microM and 92 pmol/min/mg protein, respectively, whereas those for the formation of (S)-rabeprazole were 5.1 microM and 21 pmol/min/mg protein, respectively. CYP3A4 was found to be the major enzyme responsible for(R)- and (S)-rabeprazole formation from rabeprazole-thioether. The intrinsic clearance (V(max ) /K(m )) for the oxidation by CYP3A4 of (R)-rabeprazole was 3.5-fold higher than that for the (S)-enantiomer (81 nl/min/pmol of P450 vs. 23 nl/min/pmol of P450). On the other hand, CYP2C19 and CYP2D6 were the main enzymes catalyzing the formation of desmethylrabeprazole-thioether from rabeprazole-thioether. The mean K(m ) and V(max ) values of desmethylrabeprazole-thioether formation for CYP2C19 were 5.1 microM and 600 pmol/min/nmol of P450, respectively, whereas those for CYP2D6 were 15.1 microM and 736 pmol/min/nmol of P450, respectively.

DISCUSSION

Rabeprazole is reduced mainly non-enzymatically to rabeprazole-thioether, which is further stereoselectively re-oxidized by CYP3A4 mainly to (R)-rabeprazole. The difference in the enantioselective disposition of rabeprazole is determined by stereoselectivity in CYP3A4-mediated metabolic conversion from rabeprazole-thioether to rabeprazole.

Effects of rabeprazole on early symptom relief in gastro-oesophageal reflux disease: the Hellenic Rabeprazole Study Group surveillance study

BACKGROUND

In controlled clinical trials, rabeprazole effectively improves symptoms and heals oesophageal erosions in patients with gastro-oesophageal reflux disease (GORD).

AIM

To examine symptom relief during week 1 of rabeprazole therapy, in addition to GORD healing, in a clinical practice setting.

METHODS

In this 8-week, prospective, multicentre, postauthorisation surveillance study conducted in Greece, patients with GORD (intent-to-treat: efficacy, 272; safety, 273) were treated with rabeprazole 20 mg once daily. The primary efficacy end point was the change from baseline in GORD symptom severity on day 1, 2, 3 and 7 using a 5-point Likert scale (1 = no symptoms; 5 = severe symptoms). Oesophageal healing was also evaluated by comparing the results of endoscopic findings at baseline and after 4 and 8 weeks of treatment.

RESULTS

On day 1 of treatment, rabeprazole relieved GORD symptoms across all grades of oesophagitis, with statistically significant (p = 0.0001) improvement in heartburn, regurgitation, epigastric pain and dysphagia. Oesophageal healing was achieved in 77% of patients at week 4 and in 90% at week 8 and treatment was well tolerated.

CONCLUSIONS

In a clinical practice setting, rabeprazole provided rapid relief of GORD symptoms, confirming results seen in controlled clinical trials.

Review of rabeprazole in the treatment of gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GERD) is an increasing health problem in developed countries and is associated with enormous costs in terms of reduced quality of life, loss of productivity, health expenses and mortality. The gastrointestinal disease with the highest annual direct costs in the US (in the year 2000) was GERD (9.3 billion US dollars). GERD is primarily a motility disorder of the oesophagus, however, there are no available promotility drugs on the market. The main symptoms are heartburn and acid regurgitation arising from the reflux of gastric acid, which is the only factor at present suited for pharmacological intervention. The proton pump inhibitors (PPIs) give optimal benefit in the treatment of GERD. The sales of PPIs in the year 2002 amounted to 12 billion US dollars in North America and 4 billion US dollars in Europe and the sales have been increasing by > 10% annually. This paper reviews the use of PPIs in the treatment of GERD with particular focus on one of the newer agents, rabeprazole.

High-performance liquid chromatography method for the quantification of rabeprazole in human plasma using solid-phase extraction

A simple, sensitive and selective HPLC method with UV detection (284 nm) was developed and validated for quantitation of rabeprazole in human plasma, the newest addition to the group of proton-pump inhibitors. Following solid-phase extraction using Waters Oasistrade mark SPE cartridges, the analyte and internal standard (Pantoprazole) were separated using an isocratic mobile phase of 5 mM ammonium acetate buffer (pH adjusted to 7.4 with sodium hydroxide solution)/acetonitrile/methanol (45/20/35, v/v) on reverse phase Waters symmetry C(18) column. The lower limit of quantitation was 20 ng/mL, with a relative standard deviation of less than 8%. A linear range of 20-1000 ng/mL was established. This HPLC method was validated with between- and within-batch precision of 2.4-7.2% and 2.2-7.3%, respectively. The between- and within-batch bias was -1.7 to 2.6% and -2.6 to 2.1%, respectively. Frequently coadministered drugs did not interfere with the described methodology. Stability of rabeprazole in plasma was excellent, with no evidence of degradation during sample processing (autosampler) and 3 months storage in a freezer. This validated method is sensitive, simple and repeatable enough to be used in pharmacokinetic studies.

Voltammetric behaviour of rabeprazole at a glassy carbon electrode and its determination in tablet dosage form

The oxidative behaviour of rabeprazole was studied at a glassy carbon electrode in Britton-Robinson (BR) buffer solutions using cyclic, linear sweep and differential-pulse voltammetry. The oxidation process was shown to be irreversible over the pH range (6.0-11.0) and was diffusion-adsorption controlled. An analytical method was developed for the determination of rabeprazole in BR buffer solution at pH 8.0 as supporting electrolyte. The anodic peak current varied linearly with rabeprazole concentration in the range 1.0 x 10(-6) to 2.0 x 10(-5) M of rabeprazole with a limit of detection of 4.0 x 10(-7) M. Validation parameters, such as sensitivity, accuracy, precision and recovery, were evaluated. The proposed method was applied to the determination of rabeprazole in the tablet dosage form. The results were compared with those obtained by a published high-performance liquid chromatographic method. No difference was found statistically.

Inhibition of gastric H,K-ATPase activity and gastric epithelial cell IL-8 secretion by the pyrrolizine derivative ML 3000

Background

ML 3000 ([2,2-dimethyl-6-(4-chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizine-5-yl]-acetic acid) is an inhibitor of both cyclooxygenase and 5-lipoxygenase in vitro, and shows promise as a novel non-steroidal anti-inflammatory drug (NSAID). Unlike conventional NSAIDs which are associated with gastric ulcerogenic effects, ML 3000 causes little or no damage to the gastric mucosa, even though it significantly depresses gastric prostaglandin synthesis.

Methods

As part of an effort to clarify mechanisms underlying the gastric sparing properties of ML 3000, we studied the effects of ML 3000 on H,K-ATPase activity in vitro, on acid accumulation in isolated gastric parietal cells, and on IL-8 secretion by gastric epithelial cells in culture.

Results

SCH28080-sensitive H,K-ATPase activity in highly-purified pig gastric microsomes was dose-dependently inhibited by ML 3000 (IC₅₀ = 16.4 μM). Inhibition was reversible, and insensitive to ML 3000 acidification in the pH range 2.0–8.0. In rabbit gastric parietal cells,

ML 3000 dose-dependently inhibited histamine-stimulated acid accumulation (IC₅₀ = 40 μM) and forskolin-stimulated acid accumulation (IC₅₀ = 45 μM). Lastly, in human gastric adenocarcinoma (AGS) cells, ML 3000 dose-dependently inhibited both baseline and IL-1β-stimulated (20 ng/ml) IL-8 secretion with IC₅₀s of 0.46 μM and 1.1 μM respectively.

Conclusion

The data indicate that ML 3000 affects acid-secretory mechanisms downstream of cAMP mobilization induced by histamine H₂ receptor activation, that it directly inhibits H,K-ATPase specific activity, and that baseline gastric epithelial cell IL-8 secretory inhibition may be mediated by ML 3000 inhibition of 5-lipoxygenase activity. We conclude that these gastric function inhibitory data may underlie the gastric sparing properties of ML 3000.

Molecular and Cellular Regulation of the Gastric Proton Pump

The gastric H+, K+-ATPase is a proton pump that is responsible for gastric acid secretion and that actively transports protons and K+ ions in opposite directions to generate in excess of a million-fold gradient across the membrane under physiological conditions. This pump is also a target molecule of proton pump inhibitors which are used for the clinical treatment of hyperacidity. In this review, we wish to summarize the molecular regulation of this pump based on mutational studies, particularly those used for the identification of binding sites for cations and specific inhibitors. Recent reports by Toyoshima et al (2000, 2002) presented precise three-dimensional (3-D) structures of the sarcoplasmic reticulum (SR) Ca2+-ATPase, which belongs to the same family as the gastric H+, K+-ATPase. We have studied the structure-function relationships for the gastric H+, K+-ATPase using 3-D structures constructed by homology modeling of the related SR Ca2+-ATPase, which was used as a template molecule. We also discuss in this review, the regulation of cell surface expression and synthesis control of the gastric proton pump.

Effects of rabeprazole, lansoprazole and omeprazole on intragastric pH in CYP2C19 extensive metabolizers

AIM

To investigate the inhibitory effects on gastric acid secretion of three proton pump inhibitors, omeprazole, lansoprazole and rabeprazole, using a three-way crossover design in healthy Helicobacter pylori-negative,S-mephenytoin 4'-hydroxylase (CYP2C19) homo- and hetero-extensive metabolizers.

METHODS

Eight healthy Japanese male volunteers were enrolled. After the administration of rabeprazole (10 mg/day), lansoprazole (30 mg/day) or omeprazole (20 mg/day), intragastric pH monitoring was commenced from 24 h before the first proton pump inhibitor dose, and continued for days 1-3 after proton pump inhibitor administration. The pH electrode was used for 48 h and changed just before pH monitoring on day 2.

RESULTS

For the administration of 10 mg/day rabeprazole, the mean ratios of the 24-h pH > or = 3 holding time were 5.7 +/- 1.1%,13.6 +/- 2.2%, 35.3 +/- 2.7% and 62.8 +/- 3.1% for the pre-treatment day and days 1, 2 and 3, respectively. The same ratios for lansoprazole (30 mg/day) were 5.7 +/- 0.7%, 7.4 +/- 1.5%, 13.6 +/- 3.4% and 26.6 +/- 4.9%; the same ratios for 20 mg/day omeprazole were 5.9 +/- 0.9%, 6.1 +/- 1.2%, 11.4 +/- 2.8% and 16.4 +/- 4.6%. The mean ratio of the 24-h pH > or = 3 holding time of days 1-3 increased significantly compared to the pre-treatment day (P < 0.01) with the administration of rabeprazole and lansoprazole. The magnitude of inhibition of gastric acid secretion after rabeprazole administration was stronger than that after lansoprazole. A significant elevation of the mean ratio of the 24-h pH > or = 3 holding time was demonstrated on days 2 and 3 with omeprazole (P < 0.01).

CONCLUSIONS

In H. pylori-negative CYP2C19 extensive metabolizers, rabeprazole (10 mg/day) shows a faster onset of rising intragastric pH and a stronger inhibition of gastric acid secretion than do lansoprazole (30 mg/day) or omeprazole (20 mg/day).

Effects of CYP2C19 genotypic differences in the metabolism of omeprazole and rabeprazole on intragastric pH

BACKGROUND

Omeprazole is mainly metabolized in the liver by CYP2C19, a genetically determined enzyme, whereas rabeprazole is mainly reduced non-enzymatically and partially metabolized by CYP2C19. The therapeutic effects of rabeprazole are therefore assumed to be less affected by an individual's CYP2C19 status.

AIM

To investigate the acid inhibitory effects and plasma levels of omeprazole and rabeprazole with reference to different CYP2C19 genotypes.

METHODS

Fifteen healthy volunteers took a daily dose of 20 mg of omeprazole or rabeprazole for 8 days. On post-dose days 1 and 8, 24-h profiles of intragastric pH were recorded and plasma concentrations of omeprazole, rabeprazole and their metabolites were determined.

RESULTS

After single and repeated doses of omeprazole, the intragastric pH values and plasma concentrations of omeprazole and its metabolites were significantly dependent on the CYP2C19 genotype. Significant differences in the same kinetic and dynamic parameters were also observed after single doses of rabeprazole. Although the plasma levels of rabeprazole differed among the different CYP2C19 genotype groups after repeated doses, no significant differences in intragastric pH values were observed.

CONCLUSIONS

The acid inhibitory effects of omeprazole and rabeprazole are significantly dependent on the CYP2C19 genotype status, as well as on their intrinsic pharmacokinetic and pharmacodynamic characteristics and dosing schemes.

Cibenzoline, an ATP-sensitive K(+) channel blocker, binds to the K(+)-binding site from the cytoplasmic side of gastric H(+),K(+)-ATPase

1. Cibenzoline, (+/-)-2-(2,2-diphenylcyclopropyl-2-imidazoline succinate, has been clinically used as one of the Class I type antiarrhythmic agents and also reported to block ATP-sensitive K(+) channels in excised membranes from heart and pancreatic beta cells. In the present study, we investigated if this drug inhibited gastric H(+),K(+)-ATPase activity in vitro. 2. Cibenzoline inhibited H(+),K(+)-ATPase activity of permeabilized leaky hog gastric vesicles in a concentration-dependent manner (IC(50): 201 microM), whereas no effect was shown on Na(+),K(+)-ATPase activity of dog kidney (IC(50): >1000 microM). Similarly, cibenzoline inhibited H(+),K(+)-ATPase activity of HEK-293 cells (human embryonic kidney cell line) co-transfected with rabbit gastric H(+),K(+)-ATPase alpha- and beta-subunit cDNAs (IC(50): 183 microM). 3. In leaky gastric vesicles, inhibition of H(+),K(+)-ATPase activity by cibenzoline was attenuated by the addition of K(+) (0.5 - 5 mM) in a concentration-dependent manner. The Lineweaver-Burk plot of the H(+),K(+)-ATPase activity shows that cibenzoline increases K(m) value for K(+) without affecting V(max), indicating that this drug inhibits H(+),K(+)-ATPase activity competitively with respect to K(+). 4. The inhibitory effect of H(+),K(+)-ATPase activity by cibenzoline with normal tight gastric vesicles did not significantly differ from that with permeabilized leaky gastric vesicles, indicating that this drug reacted to the ATPase from the cytoplasmic side of the membrane. 5. These findings suggest that cibenzoline is an inhibitor of gastric H(+),K(+)-ATPase with a novel inhibition mechanism, which inhibits gastric H(+),K(+)-ATPase by binding its K(+)-recognition site from the cytoplasmic side.

Rabeprazole for the prevention of pathologic and symptomatic relapse of erosive or ulcerative gastroesophageal reflux disease. Rebeprazole Study Group

OBJECTIVE

We evaluated the effectiveness and safety profile of 10 and 20 mg of rabeprazole, a new proton pump inhibitor, once daily versus placebo in preventing endoscopic and symptomatic relapse for up to 1 yr among patients with healed erosive or ulcerative gastroesophageal reflux disease (GERD).

METHODS

The 52-wk trial used a multicenter, randomized, double-blind, parallel-group design in which 209 men and women were assigned to 10 or 20 mg of rabeprazole once daily in the morning or placebo.

RESULTS

Both rabeprazole doses were significantly superior to placebo in preventing endoscopic relapse (p < 0.001), and 20 mg was significantly more effective than 10 mg (p < 0.04). Both doses were also significantly superior to placebo in reducing the frequency and severity of heartburn relapse (p < 0.001). When adjusted for differences in exposure to study medication, no significant differences were found in the incidence of adverse events. No clinically significant changes were found regarding clinical laboratory parameters, vital signs, electrocardiograms, ophthalmological evaluations, body weight, serum gastrin, and enterochromaffin-like cell histology.

CONCLUSIONS

Once-daily therapy with 10 or 20 mg of rabeprazole effectively prevents pathological and symptomatic GERD relapse. The 20-mg dose is significantly more effective than the 10-mg dose in preventing endoscopic recurrence. Treatment was well tolerated, and no clinically significant safety findings emerged. Our findings support rabeprazole's efficacy in preventing GERD recurrence with excellent tolerability and a short-term favorable safety profile.

Proton pump inhibitors in the treatment of gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GERD) is the most common peptic acid disease in the western world and is the commonest indication for acid suppression therapy. Major advances have been made over the past 30 years in the understanding of lower oesophageal sphincter function and the mechanism of acid secretion. Developments in surgical and pharmacological therapy have paralleled these advances. Pharmacotherapy for GERD has evolved from antacids to H2-receptor antagonists (H2RAs) to prokinetics to proton pump inhibitors (PPIs). The H2RAs, while modestly effective in symptom relief and healing of GERD, are limited by pharmacological tolerance. The prokinetics (metoclopramide and cisapride) are limited by low efficacy, pharmacological tolerance and toxicity. The PPIs have emerged as the most effective therapy for symptom relief, healing and long-term maintenance. They have also proved to be remarkably safe and cost-effective in long-term therapy. This review evaluates the pharmacology, efficacy, tolerability, safety and cost-effectiveness of the four currently available PPIs, lansoprazole, omeprazole, pantoprazole and rabeprazole, in the treatment of GERD.

Inhibition of H+,K+ -ATPase by hinesol, a major component of So-jutsu, by interaction with enzyme in the E1 state

Hinesol, a major component of the crude drug "So-jutsu" (Atractylodis Lanceae Rhizoma), strongly inhibited H+,K+-ATPase activity with a IC50 value of 5.8x10(-5) M. It also inhibited Na+,K+-ATPase, Mg2+-ATPase, Ca2+-ATPase, and H+-ATPase activities, although the inhibition rate was lower. No effects on alkaline or acid phosphatase activities were observed. The mechanism by which hinesol inhibited H+,K+-ATPase activity was studied in detail. The inhibition was uncompetitive with respect to ATP, and it increased as the Mg2+ concentration was raised, whereas it was not affected by the K+ concentration. The activity of K+-dependent p-nitrophenyl phosphatase (K+-pNPPase), a partial reaction of H+,K+-ATPase, was inhibited by hinesol noncompetitively with respect to pNPP (IC50 value of 1.6x10(-4) M), and competitively with respect to K+, whereas it was not affected by the Mg2+ concentration. These results suggest that hinesol is a relatively specific inhibitor of H+,K+-ATPase. It appears that hinesol reacts with enzyme in the E1 state in the presence of ATP and Mg2+ and forms the complex hinesol-H+ E1-ATP or hinesol x E1-P, blocking the conformational change to the E2 state. Furthermore, hinesol enhanced the inhibitory effect of omeprazole on H+,K+-ATPase, and the inhibitory site of hinesol was different from that of omeprazole. The effect of So-jutsu as an anti-gastric ulcer agent may be ascribed to the inhibitory effect of hinesol on H+,K+-ATPase activity.

Pentagalloylglucose, an antisecretory component of Paeoniae radix, inhibits gastric H+, K(+)-ATPase

We purified a compound with strong inhibitory effect on H+, K(+)-ATPase from Paeoniae radix, which has been used in Japan for the treatment of gastritis and peptic ulcers. The compound was identified as 1,2,3,4,6,-penta-o-galloyl-beta-D-glucose by proton nuclear magnetic resonance, carbon-13 nuclear magnetic resonance, and fast atomic bombardment mass spectrometry. The IC50 of the compound for H+, K(+)-ATPase was 166 nmol/l. Kinetic analyses indicated that the inhibition of the enzyme by pentagalloylglucose was noncompetitive with respect to K+. Pentagalloylglucose had relatively weak inhibitory effects for Mg(+)-ATPase (IC50: > 10 mumol/l) and Na+, K(+)-ATPase (IC50: 2.7 mumol/l). Pentagalloylglucose also inhibited the accumulation of [14C]aminopyrine in parietal cells that had been isolated from guinea pig stomach and stimulated by 10 mumol/l histamine (IC50: 7.8 mumol/l) and 1 mmol/l dbc-AMP (IC50: 10 mumol/l). These results suggest that pentagalloylglucose is a potent inhibitor of H+, K(+)-ATPase and may be responsible for inhibition of acid secretion by Paeoniae radix.

Comparison of five antisecretory agents acting via gastric H+/K+-ATPase

Lansoprazole(L), pantoprazole (P), rabeprazole and RO-18-5364 (RO) are new benzimidazole derivatives which rival omeprazole (O) as proton pump inhibitors (PPIs) for treatment of ulcer disease. In this study, we compared the effects of these compounds on acid secretion and determined their relative potencies in relation to their effect on [14C]-aminopyrine (AP) accumulation in isolated gastric glands. Inhibition of AP (1.2 microCi x mL(-1)) accumulation was measured in rabbit isolated gastric glands. dbcAMP (1 mmol; stimulant of acid secretion) and Ro 20-1724 (0.1 mmol; a phosphodiasterase inhibitor) were added to the Eppendorf tubes containing the PPIs and AP and dose-response curves were done for each drug after incubating for 5, 10 and 20 min at 37 degrees C and AP accumulation was determined using a scintillation counter. All the PPIs significantly (P < 0.001) inhibited acid secretion as demonstrated by the inhibition of AP accumulation in the isolated gastric glands. Minimum inhibition occurred at a concentration of 0.001 micromol for lansoprazole and omeprazole, 0.01 micromol for rabeprazole and RO 18-5364 and 0.02 micromol for pantoprazole. No differences were observed between PPIs with regards to the maximum inhibition they produce. When expressed as a percentage inhibition of control at 10-min incubation and at concentrations of 1 micromol, L showed 85.6 +/- 0.5, O 87 +/- 0.5, P 83.2 +/- 1.1, R 86.4 +/- 1.1 and RO 87.8 +/- 1.9 inhibition respectively. When comparing the IC50 values, their relative potencies were different. Maximum potency was shown by L (0.007 micromol) > O (0.012 micromol) > R (0.018 micromol) > RO (0.034 micromol) > P (0.050 micromol). All the new PPIs showed different potencies as inhibitors of acid secretion as evident from their IC50s. Extensive ulcer healing trials demonstrated comparable efficacy with a number of studies indicating that symptoms relief are more rapid with P and L, while in this study L appeared to be the most potent in inhibiting AP accumulation in the isolated gastric glands.

Rabeprazole: a review of its use in acid-related gastrointestinal disorders

Rabeprazole is an inhibitor of the gastric proton pump. It causes dose-dependent inhibition of acid secretion and has a more rapid onset of action than omeprazole. Duodenal ulcers healed faster after treatment with rabeprazole 20 or 40 mg/day than placebo or ranitidine 150 mg 4 times daily and at a generally similar rate to omeprazole 20 mg/day in patients with duodenal ulcers; rabeprazole was similar or superior to these agents in relieving symptoms. Rabeprazole 20 and 40 mg/day healed gastric ulcers faster than placebo, and rabeprazole 20 mg/day healed ulcers at a similar healing rate, to omeprazole 20 mg/day in well controlled 6-week studies. Gastric ulcer symptom relief with rabeprazole was similar or superior to that provided by omeprazole or placebo. In 8-week studies in patients with gastro-oesophageal reflux disease (GERD), rabeprazole 10, 20 and 40 mg/day were more effective than placebo, rabeprazole 20 mg/day was more effective than ranitidine 150 mg twice daily, and rabeprazole 20 mg/day was similar in efficacy to omeprazole 20 mg/day. Symptom relief with rabeprazole in 8-week trials in patients with GERD was superior to that provided by placebo, and similar to ranitidine or omeprazole. Rabeprazole was similar to omeprazole and superior to placebo in both maintenance of healing and prevention of symptoms in patients with healed GERD in 1-year studies. One-week triple therapy with rabeprazole 20 mg twice daily plus 2 antibacterial agents achieved > or = 90% Helicobacter pylori eradication, but, as would be expected, a regimen of rabeprazole 20 mg twice daily plus 1 antibacterial agent was less successful. The drug was as effective as omeprazole and lansoprazole as part of triple therapy for H. pylori eradication. Rabeprazole successfully reduced acid output to target levels and prevented further pathological changes in 10 patients with Zollinger-Ellison syndrome. Usual dosages of rabeprazole are 20 mg/day for 4 weeks to treat duodenal ulcers, 6 weeks for gastric ulcers and 8 weeks for GERD, although some patients with duodenal ulcer may respond to a 10 mg/day dosage. For long term maintenance of GERD healing, 10 or 20 mg daily doses are adequate. Patients with hypersecretory states may need individualised dosages starting at 60 mg/day. The drug was well tolerated in clinical trials, with headache, rash, infection, diarrhoea and flu syndrome as the most common adverse events. In conclusion, rabeprazole appears to be a well tolerated proton pump inhibitor with a rapid onset of action and a low potential for drug interactions. The drug may be used to achieve healing and the relief of symptoms of duodenal ulcer, gastric ulcer and GERD, maintain GERD healing, and can form part of effective regimens to eradicate H. pylori.