Effects of the enantiomers of lansoprazole (AG-1749) on (H+ + K+)-ATPase activity in canine gastric microsomes and acid formation in isolated canine parietal cells

Inhibition of gastric H+,K+-ATPase by new dihydropyrazole derivative KYY-008

The gastric proton pump (H⁺,K⁺-ATPase) responsible for the H⁺ secretion of gastric acid is an essential therapeutic target for acid-related diseases. H⁺,K⁺-ATPase belongs to a P₂-type ATPase family. Here, we examined the effects of a newly synthesized dihydropyrazole derivative KYY-008 on the H⁺,K⁺-ATPase. KYY-008 concentration-dependently inhibited the enzyme activity of the ATPase in the membrane fractions prepared from isolated hog gastric mucosa and from human kidney HEK293 cells in which gastric H⁺,K⁺-ATPase is exogenously expressed. The IC₅₀ values in these samples were 3.4 μM and 3.7 μM, respectively. In addition, KYY-008 significantly inhibited the H⁺,K⁺-ATPase-derived H⁺ uptake into the tightly sealed vesicles prepared from the hog gastric mucosa. In contrast, KYY-008 has no effect on the activities of other P₂-type ATPases such as Na⁺,K⁺-ATPase and Ca²⁺-ATPase. KYY-008 did not change the ionic currents of voltage-dependent Ca²⁺ channels, that were potential targets for some dihydropyrazole derivatives. Together, we discovered a new dihydropyrazole derivative which acts as a selective inhibitor of gastric H⁺,K⁺-ATPase.

Inhibition of Gastric H+,K+-ATPase Activity in Vitro by Dissolution Media of Original Brand-Name and Generic Tablets of Lansoprazole, a Proton Pump Inhibitor

To investigate the inhibitory effect of a commercial proton pump inhibitor (lansoprazole) on the gastric proton pump H⁺,K⁺-ATPase in vitro, we used orally disintegrating (OD) tablets including original brand-name and generic tablets. In the course of the development of generic products, dissolution and clinical tests are necessary to ensure their bioequivalence to the original brand-name products; by contrast, there is almost no opportunity to demonstrate their activity in vitro. This study initially compared the similarity of the dissolution of test generic tablets with that of the original brand-name tablets. The dissolution tests for 15 and 30-mg lansoprazole tablets found their dissolution properties were similar. Subsequently, the dissolution media were sampled and then their effects on the H⁺,K⁺-ATPase activity were measured using tubulovesicles prepared from the gastric mucosa of hogs. We confirmed that the inhibitory effects of the generic tablets on H⁺,K⁺-ATPase activity were consistent with those of the original brand-name tablets. Furthermore, lansoprazole contents in each tablet estimated from their inhibitory effects were in good agreement with their active pharmaceutical ingredient content. To our knowledge, this is the first technical report to compare the in vitro biochemical activity of lansoprazole OD tablets between the original brand-name and generic commercial products.

Potassium-competitive acid blockers: Advanced therapeutic option for acid-related diseases

Acid-related diseases (ARDs), such as peptic ulcers and gastroesophageal reflux disease, represent a major health-care concern. Some major milestones in our understanding of gastric acid secretion and ARD treatment reached during the last 50years include 1) discovery of histamine H₂-receptors and development of H₂-receptor antagonists, 2) identification of H⁺,K⁺-ATPase as the parietal cell proton pump and development of proton pump inhibitors (PPIs), and 3) identification of Helicobacter pylori (H. pylori) as the major cause of peptic ulcers and development of effective eradication regimens. Although PPI treatments have been effective and successful, there are limitations to their efficacy and usage, i.e. short half-life, insufficient acid suppression, slow onset of action, and large variation in efficacy among patients due to CYP2C19 metabolism. Potassium-competitive acid blockers (P-CABs) inhibit H⁺,K⁺-ATPase in a reversible and K⁺-competitive manner, and exhibit almost complete inhibition of gastric acid secretion from the first dose. Many pharmaceutical companies have tried to develop P-CABs, but most of their clinical development has been discontinued due to safety concerns or a similar efficacy to PPIs. Revaprazan was developed in Korea and was the first P-CAB approved for sale. Vonoprazan, approved in 2014 in Japan, has a completely different chemical structure and higher pKa value compared to other P-CABs, and exhibits rapid onset of action and prolonged control of intragastric acidity. Vonoprazan is an effective treatment for ARDs that is especially effective in healing reflux esophagitis and for H. pylori eradication. P-CABs, such as vonoprazan, promise to further improve the management of ARDs.

Cytoprotective effect of benzyl N'-(5-chloro-indol-3-yl-methylidene)-hydrazinecarbodithioate against ethanol-induced gastric mucosal injury in rats

Indolic compounds have attracted a lot of attention due to their interesting biological properties. The present study was performed to evaluate the subacute toxicity and anti-ulcer activity of BClHC against ethanol-induced gastric ulcers. Experimental animal groups were orally pre-treated with different doses of BClHC (50, 100, 200 and 400 mg/kg) in 10% Tween 20 solution (vehicle). Blank and ulcer control groups were pre-treated with vehicle. The positive group was orally pretreated with 20 mg/kg omeprazole. After one hour, all groups received absolute ethanol (5 mL/kg) to generate gastric mucosal injury except the blank control group which was administered the vehicle solution. After an additional hour, all rats were sacrificed, and the ulcer areas of the gastric walls determined. Grossly, the ulcer control group exhibited severe mucosal injury, whereas pre-treatment with either derivative or omeprazole resulted in significant protection of gastric mucosal injury. Flattening of gastric mucosal folds was also observed in rats pretreated with BClHC. Histological studies of the gastric wall of ulcer control group revealed severe damage of gastric mucosa, along with edema and leucocytes infiltration of the submucosal layer compared to rats pre-treated with either BClHC or omeprazole where there were marked gastric protection along with reduction or absence of edema and leucocytes infiltration of the submucosal layer. Subacute toxicity study with a higher dose of derivative (5 g/kg) did not manifest any toxicological signs in rats. In conclusions, the present finding suggests that benzyl N'-(5-chloroindol-3-ylmethylidene)hydrazinecarbodithioate promotes ulcer protection as ascertained by the comparative decreases in ulcer areas, reduction of edema and leucocytes infiltration of the submucosal layer.

Effect of MDR1 C3435T polymorphism on lansoprazole in healthy Japanese subjects

BACKGROUND AND AIMS

The effect of multidrug resistance transporter gene 1 (MDR1) on the bioavailability and kinetics of several substrates has not yet been fully elucidated. We evaluated the influence of MDR1 C3435T polymorphism on the pharmacokinetics and pharmacodynamics of lansoprazole in Japanese subjects.

METHODS

Fifteen healthy volunteers with the rapid extensive metabolizer genotype of CYP2C19 were classified into three MDR1 C3435T genotype groups: C/C (n = 5), C/T (n = 5), and T/T (n = 5). Lansoprazole 30 mg was administered orally for 15 days. The intragastric pH and plasma lansoprazole levels were determined on days 1 and 15.

RESULTS

On day 1, the mean C(max) of lansoprazole in the T/T group was significantly higher than that in the C/C or C/T groups (T/T 1,248, C/C 618, C/T 607 ng/ml; P = 0.038). On day 15, similar MDR1 genotype-dependent differences were observed in the C(max) of lansoprazole, although smaller than the differences observed on day 1. In contrast, the intragastric pH attained after lansoprazole administration did not differ among MDR1 genotype groups on either day 1 or day 15.

CONCLUSION

Although the sample size was small, our study demonstrated that the MDR1 C3435T polymorphism influenced the pharmacokinetics, but not the pharmacodynamics (i.e., intragastric pH), of lansoprazole in rapid metabolizers of CYP2C19.

The anti-secretory and anti-ulcer activities of esomeprazole in comparison with omeprazole in the stomach of rats and rabbits

Proton pump inhibitors (PPIs) are widely used to treat hyperacid secretion and stomach ulcers. The study investigated the anti-secretory and anti-ulcer effects of esomeprazole, the S-isomer of omeprazole on dimaprit, histamine and dibutyryl adenosine 3, 5 cyclic monophosphate (dbcAMP)-evoked gastric acid secretion, acidified ethanol (AE) and indomethacin (INDO)-induced haemorrhagic lesions and on prostaglandin E2 (PGE2) level in the rat in vivo and rabbit in vitro preparations. The effect of omeprazole was also investigated for comparison. Dimaprit-induced acid secretion was significantly (P < 0.05) inhibited by both PPIs in a dose-dependent manner. In the isolated rabbit gastric glands, both PPIs elicited marked reductions in histamine- and dbcAMP-evoked acid secretion with similar potency. The lesions induced by either AE or INDO were significantly (P < 0.05) reduced in the presence of either esomeprazole or omeprazole compared to control values. Increasing doses of esomeprazole before AE treatment resulted in a marked degree of cytoprotection and an elevation in the concentration of bound PGE2 in the stomach tissue homogenate. The results show that esomeprazole and omeprazole were equally effective against gastric haemorrhagic lesions induced by either AE or INDO and in inhibiting dimaprit-, dbcAMP- and histamine-induced gastric acid secretion in the rat and rabbit stomach both in vivo and in vitro. The gastro-protective effect of esomeprazole was found to be proportional to the bound PGE2 levels in the glandular area of the stomach.

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.

Enantioselective disposition of lansoprazole in relation to CYP2C19 genotypes in the presence of fluvoxamine

AIMS

Lansoprazole is affected by polymorphism of CYP2C19. The aim of this study was to examine the effects of fluvoxamine, a CYP2C19 inhibitor, on the pharmacokinetics of each lansoprazole enantiomer among three different CYP2C19 genotype groups.

METHODS

Eighteen healthy subjects, of whom six each were homozygous extensive metabolizers (homEMs), heterozygous extensive metabolizers (hetEMs), or poor metabolizers (PMs) for CYP2C19, participated in the study. Each subject received either placebo or fluvoxamine, 25 mg twice daily for 6 days, then a single oral dose of 60 mg of racemic lansoprazole. The plasma concentrations of lansoprazole enantiomers and lansoprazole sulphone were subsequently measured for 24 h post lansoprazole administration using liquid chromatography.

RESULTS

In the homEMs and hetEMs, fluvoxamine significantly increased the AUC(0, infinity) and C(max) and prolonged the elimination half-life of both (R)- and (S)-lansoprazole, whereas in the PMs, the only statistically significant effect of fluvoxamine was on the AUC(0, infinity) for (R)-lansoprazole. The mean fluvoxamine-mediated percent increase in the AUC(0, infinity) of (R)-lansoprazole in the homEMs compared with the PMs was significant (P = 0.0117); however, C(max) did not differ among the three CYP2C19 genotypes. On the other hand, fluvoxamine induced a significant percent increase in both the AUC(0, infinity) and C(max) for (S)-lansoprazole in the homEMs compared with the hetEMs (P = 0.0007 and P = 0.0125, respectively) as well as compared with the PMs (P < 0.0001 for each parameter). The mean R : S ratio for AUC(0, infinity) of lansoprazole in the homEMs was significantly different between the placebo and the fluvoxamine treatment groups (12.7 (9.1, 16.8) vs 6.4 (5.4, 7.4), respectively, P < 0.0001), though not in the PMs (5.5 (4.3, 6.7) vs 5.9 (5.3, 6.5), respectively).

CONCLUSIONS

The magnitude of the contribution of CYP2C19 to the metabolism of (S)-lansoprazole is much greater compared with that of the (R)-enantiomer. In extensive metabolizers, hepatic CYP2C19 plays an important role in the absorption and elimination of lansoprazole, particularly the (S)-enantiomer.

Pharmacokinetics of proton pump inhibitors in children

The use of proton pump inhibitors (PPIs) has become widespread in children and infants for the management of paediatric acid-related disease. Pharmacokinetic profiles of only omeprazole and lansoprazole have been well characterised in children over 2 years of age with acid-related diseases. Few data have been recently published regarding the pharmacokinetics of pantoprazole in children, and none are available for rabeprazole or esomeprazole. The metabolism of PPI enantiomers has never been studied in the paediatric population. A one-compartment model best describes the pharmacokinetic behaviour of omeprazole, lansoprazole and pantoprazole in children, with important interindividual variability for each pharmacokinetic parameter. Like adults, PPIs are rapidly absorbed in children following oral administration; the mean time to reach maximum plasma concentration varies from 1 to 3 hours. Since these agents are acid labile, their oral formulations consist of capsules containing enteric-coated granules. No liquid formulation is available for any of the PPIs. Thus, for those patients unable to swallow capsules, extemporaneous liquid preparations for omeprazole and lansoprazole have been reported; however, neither the absolute nor the relative bioavailabilities of these oral formulations have been studied in children. Intravenous formulations are available for omeprazole (in Europe), lansoprazole and pantoprazole. PPIs are rapidly metabolised in children, with short elimination half-lives of around 1 hour, similar to that reported for adults. All PPIs are extensively metabolised by the liver, primarily by cytochrome P450 (CYP) isoforms CYP2C19 and CYP3A4, to inactive metabolites, with little unchanged drug excreted in the urine. Similar to that seen in adults, the absolute bioavailability of omeprazole increases with repeated dosing in children; this phenomenon is thought to be due to a combination of decreased first-pass elimination and reduced systemic clearance. The apparent clearance (CL/F) of omeprazole, lansoprazole and pantoprazole appears to be faster for children than for adults. A higher metabolic capacity in children as well as differences in the extent of PPI bioavailability are most likely responsible for this finding. This may partly account for the need in children for variable and sometimes considerably greater doses of PPIs, on a per kilogram basis, than for adults to achieve similar plasma concentrations. Furthermore, no studies have been able to demonstrate a statistically significant correlation between age and pharmacokinetic parameters among children. Despite the small number of very young infants studied, there is some evidence for reduced PPI metabolism in newborns. The limited paediatric data regarding the impact of CYP2C19 genetic polymorphism on PPI metabolism are similar to those reported for adults, with poor metabolisers having 6- to 10-fold higher area under the concentration-time curve values compared with extensive metabolisers. Finally, because a pharmacokinetic/pharmacodynamic relationship exists for PPIs, the significant interindividual variability in their disposition may partly explain the wide range of therapeutic doses used in children. Further studies are needed to better define the pharmacokinetics of PPIs in children <2 years of age.

Effect of clarithromycin on the enantioselective disposition of lansoprazole in relation to CYP2C19 genotypes

The aim of this study was to examine the effect of clarithromycin, a CYP3A4 inhibitor, on the enantioselective disposition of lansoprazole among three different CYP2C19 genotype groups in healthy Japanese subjects. These subjects included 6 each of homozygous extensive metabolizers (homEMs), heterozygous extensive metabolizers (hetEMs), and poor metabolizers (PMs). In the EMs of CYP2C19, clarithromycin markedly increased Cmax and the AUC0-infinity of (S)-lansoprazole and (S)-hydroxylansoprazole compared with those of the corresponding (R)-enantiomers. Clarithromycin significantly increased Cmax and the AUC0-infinity of (S)-lansoprazole in the homEMs by 110% and 115%, respectively, and in the hetEMs by 105% and 103%, respectively, compared with placebo. Furthermore, clarithromycin slightly prolonged the elimination half-life of (R)-lansoprazole in the homEMs and hetEMs but did not alter that of (S)-lansoprazole. In the of PMs CYP2C19, clarithromycin significantly increased Cmax and the AUC0-infinity and significantly prolonged the elimination half-lives of (R)- and (S)-lansoprazole by 51% and 49%, respectively. The present study suggests that there are significant drug interactions between (R)- or (S)-lansoprazole and clarithromycin in EMs by inhibiting the CYP3A4-catalyzed sulfoxidation primarily during the first pass, whereas in PMs, the overall metabolism of lansoprazole is inhibited.

Pharmacokinetic differences between the enantiomers of lansoprazole and its metabolite, 5-hydroxylansoprazole, in relation to CYP2C19 genotypes

OBJECTIVE

The purpose of this study was to elucidate the pharmacokinetics of each enantiomer of lansoprazole and 5-hydroxylansoprazole in three different CYP2C19 genotype groups of Japanese subjects.

METHODS

Healthy subjects ( n=18), of whom 6 were homozygous extensive metabolizers (homEMs), 6 were heterozygous extensive metabolizers (hetEMs) and 6 were poor metabolizers (PMs), participated in the study. After a single oral dose of 60 mg of racemic lansoprazole, the plasma concentrations of the lansoprazole enantiomers, 5-hydroxylansoprazole enantiomers and lansoprazole sulfone were measured for 24 h post-dose.

RESULTS

The plasma concentrations of ( R)-lansoprazole were remarkably higher in all three CYP2C19 genotype groups than those of the corresponding ( S)-enantiomer. The mean maximum plasma concentration ( C(max)) of ( S)-lansoprazole differed significantly among the three groups, whereas there was no difference for the ( R)-enantiomer. The relative area under the plasma concentration (AUC) ratios of ( R)- and ( S)-lansoprazole in the homEMs, hetEMs, and PMs were 1:1.5:4.0 and 1:1.8:7.4, respectively. Yet, the relative AUC ratios of 5-hydroxylansoprazole to lansoprazole for the ( R)- and ( S)-enantiomers in the homEMs, hetEMs, and PMs were almost the same (1:0.73:0.12 and 1:0.77:0.13, respectively). However, the AUC ratios of the ( S)-enantiomer were 13-fold greater for the three CYP2C19 genotypes than those of the corresponding ( R)-enantiomer.

CONCLUSIONS

The magnitude of the contribution of CYP2C19 to the 5-hydroxylation of ( S)-lansoprazole was greater than that of the ( R)-enantiomer. The R/S ratios for the AUC of lansoprazole for the homEMs, hetEMs and PMs were 12.7, 8.5 and 5.8, respectively, suggesting a significant effect of CYP2C19 polymorphisms on the stereoselective disposition of lansoprazole.

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.

Stereoselective metabolism of lansoprazole by human liver cytochrome P450 enzymes

The stereoselective metabolism of lansoprazole enantiomers was evaluated by incubation of human liver microsomes and cDNA-expressed cytochrome p450 (p450) enzymes to understand and predict their stereoselective disposition in humans in vivo. The intrinsic clearances (Clint) of the formation of both hydroxy and sulfone metabolites from S-lansoprazole were 4.9- and 2.4-fold higher than those from the R-form, respectively. The sums of formation Clint of both metabolites were 13.5 and 57.3 microl/min/mg protein for R- and S-lansoprazole, respectively, suggesting that S-lansoprazole would be cleared more rapidly than the R-form. The p450 isoform selective inhibition study in liver microsomes, and the incubation study of cDNA-expressed enzymes, demonstrated that the stereoselective sulfoxidation is mediated by CYP3A4 and that the hydroxylation is mediated by CYP2C9 and CYP3A4 as well as by CYP2C19. Total Clint values of hydroxy and sulfone metabolite formation catalyzed by all these p450 enzymes were consistently higher for S-lansoprazole than for the R-form. The CYP3A4 produced the greatest difference of Clint between S- and R-enantiomers, mainly due to a difference of sulfoxidation metabolism (Clint 76.5 versus 10.8 microl/min/nmol of p450, respectively), whereas CYP2C19-catalyzed hydroxylation resulted in a minor difference of Clint between S- and R-enantiomers (179.6 versus 143.3 microl/min/nmol of p450, respectively). However, the affinity of CYP2C19 on hydroxylation was 5.7-fold higher for S-enantiomer than for the R-form (Km 2.3 versus 13.1 microM), suggesting that the role of CYP2C19 on stereoselective hydroxylation would be more prominent at concentrations around the usual therapeutic level. These findings suggest that both CYP2C19 and CYP3A4 are major enzymes contributing to the stereoselective disposition of lansoprazole, but stereoselective hydroxylation of lansoprazole enantiomers is mainly influenced by CYP2C19, especially at the usual therapeutic doses.

A comparative study on the activity of lansoprazole, omeprazole and PD-136450 on acidified ethanol- and indomethacin-induced gastric lesions in the rat

1. The proton pump inhibitors lansoprazole (LP) and omeprazole (OP) and the cholecystokinin (CCK)-receptor antagonist PD-136450 (PD) provide a broad spectrum of activities in their ability to inhibit gastric acid secretion and protect the stomach against ulcerogens. In the present study, we investigated the protective effects of these compounds against gastric ulcers induced by acidified ethanol (AE) and indomethacin. 2. Both AE (60% ethanol in 150 mmol/L HCl, 1 mL/rat) and indomethacin (30 mg/kg) produced gastric haemorrhagic lesions in the rat 1 and 6 h after oral administration, respectively. 3. The gastric mucosal protective effects of LP (1-20 mg/kg), OP (0.5-10 mg/kg) and PD (1-20 mg/kg), administered either orally or subcutaneously (s.c.) 30 min before the administration of AE or indomethacin, were dose dependent against both models of ulcer induction. 4. To determine whether the cytoprotective effect of LP, OP and PD (each 10 mg/kg) was mediated by endogenous prostaglandins (PG), indomethacin (10 mg/kg, s.c.) was administered 15 min before AE to inhibit prostanoids biosynthesis. Indomethacin reduced the cytoprotective effects of OP, but not LP, administered either orally or s.c. Indomethacin reduced the cytoprotective effect of PD administered orally, although the effect was much less significant than when PD was administered s.c. The results exclude the role of PG in mediating the protective effects of LP, whereas the possibility exists for PG to have a role in mediating the protective effects of OP and PD. 5. To investigate the possible involvement of endogenous nitric oxide (NO) in the cytoprotective action of LP, OP and PD, we treated rats with a selective inhibitor of NO synthesis, namely NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg, s.c.). Administration of L-NAME 15 min prior to LP, OP or PD (each 10 mg/kg) orally or s.c. and challenge with AE or indomethacin did not significantly increase the degree of the ulcer index and L-NAME was not able to antagonize the protective effects of LP, OP and PD, thus excluding the role of NO in mediating the protective effects of these drugs. However, the effects of PD in reducing the indomethacin-induced ulcer index were less significant in the presence than the absence of L-NAME (P < 0.05 vs P < 0.001, respectively), suggesting a role for NO. 6. In conclusion, the results of the present study suggest that LP and OP are equally effective against AE- as well as indomethacin-induced gastric ulcers and were more potent than PD in protecting the stomach against ulcer formation. Lansoprazole, OP and PD bring about their cytoprotective action through the reduction of acid secretion and some other unknown mechanisms. However, OP and PD may exert their cytoprotective action through PG and NO pathways.

Relative efficacies of gastric proton-pump inhibitors on a milligram basis: desired and undesired SH reactions. Impact of chirality

Gastric proton-pump inhibitors (PPIs) are prodrugs. Their acid activation at pH 1.0 inside the canaliculus of a parietal cell should be fast relative to their serum elimination rate. Actually, all PPIs display chemical activation half-lives at pH 1.0 of a few minutes at the most, while being eliminated from serum with a half-life of about 1 h. This is the main reason they show similar antisecretory efficacies on a milligram basis. It is in line with about 5% to 15% higher healing rates in GERD, DU and GU when 40 mg is compared to 20 mg of either omeprazole or pantoprazole. The comparably large biological variation between patient samples explains why some studies show statistically significant differences between the two doses, while others do not. However, it would matter to the individual patient if s/he was the one additionally healed by a 40 mg dose within a defined treatment period. Chemical activation of PPI prodrugs is unwanted in weakly acidic tissue compartments such as lysosomes or secretory granules. However, the ratio of the serum elimination half-life (availability at the target) to the chemical activation half-life at a critical pH 5.0 is reversed only with pantoprazole. when compared to pH 1.0 (i.e. the ratio is < 1 at pH 5.0 and > 1.0 at pH 1.0). This is the basis of the high pH selectivity of pantoprazole. In contrast, rabeprazole is activated at pH 5.0 almost as quickly as it is at pH 1.0 and much faster than it is eliminated from serum. This unwanted reactivity of rabeprazole at pH 5.0 does not contribute to the antisecretory action at pH 1.0 and results in poor pH selectivity. Omeprazole and lansoprazole lie in between, as they are activated, at pH 5.0, about as quickly as they are eliminated from serum. The above activation rates refer to room temperature. At 37 degrees C. the activation rates of all PPIs further increase, by about the same factor of between 3 and 4. This renders their differential pH selectivities even more critical for drug safety. Biological consequences have been reported in the literature. It has been claimed that a dose of 40 mg of the S-enantiomer of omeprazole (esomeprazole) results in 10%-15% higher healing rates in GERD patients, compared to 20 mg omeprazole racemate. The same difference is found when the two doses of omeprazole racemate are compared to each other. This is not surprising, as the chiral PPI prodrug is converted by acid into an achiral cyclic sulfenamide which only then reacts with the proton pump. There is therefore no pharmacodynamic argument in favour of any single enantiomer formulation of any PPI. Moreover, potential pharmacokinetic differences between the enantiomers seem to be of little if any importance in the patient.

Pharmacokinetic considerations in the eradication of Helicobacter pylori

As Helicobacter pylori plays an important role in the aetiopathogenesis of peptic ulcer, therapeutic strategies aimed at maintaining long term remission have shifted from the control of intragastric pH to targeting H. pylori. According to recent international guidelines the clinical goals--rapid ulcer healing and prevention of relapse--can be best accomplished by combination therapy consisting of an antisecretory drug (proton pump inhibitor or ranitidine) and 2 antimicrobial agents (preferable amoxicillin, clarithromycin or metronidazole). When applying such multidrug regimens, possible synergy between the agents suggests that pharmacokinetic considerations might help to improve H. pylori eradication rates, which should be above 85 to 90% on an intention-to-treat basis. The present review summarises the pharmacokinetic properties and interaction potential of all drugs presently used in the various H. pylori eradication regimens, with emphasis on particular patient populations such as the elderly and those with renal impairment. The drugs considered are omeprazole, lansoprazole, pantoprazole, rabeprazole, ranitidine and ranitidine bismutrex, bismuth salts, amoxicillin, clarithromycin, azithromycin, roxithromycin, metronidazole, tinidazole and tetracycline. When addressing the clinically important questions of the efficacy, safety and costs of the recommended regimens, the impact of drug disposition on H. pylori eradication should not be neglected.

Pharmacokinetic differences between lansoprazole enantiomers in rats

Because limited information is available about potential differences between the pharmacokinetics and pharmacodynamics of the enantiomers of lansoprazole, the enantioselective pharmacokinetics of the compound have been investigated in rats. There was a noticeable difference between the serum levels of the enantiomers of lansoprazole and of their metabolites, 5-hydroxylansoprazole enantiomers, after oral administration of the racemate (50 mg kg(-1)) to rats. Cmax (maximum serum concentration) and AUC (area under the serum concentration-time curve) for (+)-lansoprazole were 5-6 times greater than those for (-)-lansoprazole, whereas for (+)-5-hydroxylansoprazole both values were significantly smaller than those for the (-) enantiomer. CLtot/F values (where CLtot is total clearance and F is the fraction of the dose absorbed) for (+)-lansoprazole were significantly smaller than those for the (-) enantiomer. There was no significant difference between the absorption rate constants of the lansoprazole enantiomers in the in-situ absorption study. The in-vitro protein-binding study showed that binding of (+)-lansoprazole to rat serum proteins was significantly greater than for the (-) enantiomer. The in-vitro metabolic study showed that the mean metabolic ratio (45.9%) for (-)-lansoprazole was significantly greater than that (19.8%) for the (+) enantiomer in rat liver microsomes at 5.6 microM lansoprazole. These results show that the enantioselective disposition of lansoprazole could be a consequence of the enantioselectivity of plasma-protein binding and the hepatic metabolism of the enantiomers.

Pharmacokinetic properties of a novel gastric proton pump inhibitor, (+/-)-2-[(4-methoxy-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-9- yl)sulfinyl]-1H-benzimidazole sodium salt, in healthy subjects

The pharmacokinetics and safety of TY-11345 [(+/-)-2-[(4-methoxy-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-9- yl)sulfinyl]-1H-benzimidazole sodium salt], a novel gastric proton pump inhibitor, were studied in healthy male volunteers after single (20, 40, and 80 mg) and repeated oral doses (60 mg, once daily for 7 days) as enteric-coated tablet. At the single doses of 20 and 40 mg, intragastric pH was continuously monitored in each of two subjects. No abnormal findings definitely attributable to the test drug were observed throughout the study. In the single-dose study, the maximum plasma concentration (Cmax) and area under the plasma concentration-time curve of TY-11345 increased in a dose-proportional manner. The time to reach Cmax was about 3 h after dosing and plasma concentrations declined thereafter with a half-life of about 1 h irrespective of dose. The effect of food intake on the pharmacokinetic parameters of TY-11345, which was evaluated at the dose of 40 mg in a cross-over design, was not significant. TY-11345 was not detected in urine unchanged, while a main metabolite and its conjugate were identified in urine as 32-38% of the dose. An intragastric pH value over 4 was obtained about 3 h after the administration of 40 mg and maintained for more than 5 h, despite the fall of plasma concentration. This effect was less obvious at a dose of 20 mg. In the multiple-dose study, the pharmacokinetics exhibited no substantial difference between the first and last doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related differences in the pharmacokinetics and pharmacodynamics of lansoprazole

1. The pharmacokinetics and pharmacodynamics of lansoprazole, an antisecretory and antiulcer agent, were evaluated in 12 older (> 60 years) and 12 younger (< 60 years) healthy men. 2. Doses of lansoprazole (15 or 30 mg) or placebo were each given once daily for 7 consecutive days in this randomized, double-blind, three-way crossover study. Plasma concentrations and urinary excretion of lansoprazole and its metabolites, and gastric acid secretion were monitored after dosing on days 1 and 7 of each treatment period. 3. Within each age group, lansoprazole pharmacokinetics were linear. The mean clearance and elimination half-life of lansoprazole were about 40% lower and higher, respectively, in the older subjects (CL0: 12-14 vs 20-24 1 h(-1); t1/2,z: 1.90-2.19 vs 1.26-1.44 h). 4. At each dose level, acid secretion was more inhibited in the older group. However, the AUC associated with a 50% decrease in acid secretion was similar (849 vs 892 ng ml(-1) h) for both age groups. Multiple dosing decreased the maximum possible inhibition more in the older group than in the younger group. 5. Since the decrease in acid output associated with equivalent AUCs on day 1 was similar for the two age groups, the greater difference between day 1 and day 7 secretion in the older group indicates that recovery of secretory activity may decline with increasing age.

Lansoprazole. A review of its pharmacodynamic and pharmacokinetic properties and its therapeutic efficacy in acid-related disorders

Lansoprazole is an effective acid pump inhibitor acting at the final enzymatic step of the acid secretory pathway of the parietal cell, decreasing gastric acid secretion regardless of the primary stimulus. Results of short term (less than 8 weeks) clinical trials have shown lansoprazole to be significantly superior to placebo and ranitidine in the treatment of duodenal ulcer, both in the rate of healing and in overall healing at 4 weeks. Lansoprazole appears to heal duodenal ulcer more quickly than famotidine, and demonstrates slightly greater efficacy at 4 weeks, although both drugs appear to have equivalent efficacy overall. Gastric ulcers and reflux oesophagitis are also healed by lansoprazole 30 mg/day for 4 to 8 weeks, with healing rates after 8 weeks of approximately 85 to 95% for both indications. Lansoprazole appears to be superior to ranitidine and comparable to omeprazole in treating reflux oesophagitis. Furthermore, lansoprazole has relieved reflux symptoms more quickly than either ranitidine or omeprazole. Preliminary data also indicate that lansoprazole may be effective in the treatment of peptic ulcer disease and reflux oesophagitis refractory to H2-receptor antagonists, and in patients with Zollinger-Ellison syndrome. While direct comparisons with omeprazole are limited, results suggest that lansoprazole, used for short term treatment, is at least as effective as omeprazole in the treatment of peptic ulcer and reflux oesphagitis. Lansoprazole has been well tolerated in short term clinical trials, with an incidence of adverse effects comparable with that of other agents in its therapeutic class. Trials assessing long term tolerability data are ongoing and will be required as part of the assessment of the safety profile, if lansoprazole is to be used prophylactically to prevent ulcer recurrence. Thus, by virtue of its ability to heal ulcers and rapidly relieve associated symptomatology, lansoprazole represents a useful alternative for the treatment of acid related disorders.