Omeprazole drug interaction studies

Impact of fresh grape juice on the pharmacokinetics of omeprazole: results of a food-drug interaction study

Grapes have been widely used for dietary ailments due to their attributed pharmacological activities. Resveratrol, the chief constituent of grapes, is responsible for their pharmacological benefits. However, apart from their beneficial effects, grapes have also recently been considered in drug interaction studies. This study investigated the pharmacokinetic profile of omeprazole administered alone compared to omeprazole administered with grape juice, with a prior intake of grape juice, for 1 continuous week. The study was conducted on two groups of healthy male volunteers [n = 12]. One group was orally administered 40 mg of omeprazole alone, while the other group was administered omeprazole with grape juice. Blood samples were analyzed for omeprazole concentration by a reverse-phase HPLC method. Co-administration of 40 mg omeprazole with grape juice significantly decreased the AUC0-t and Cmax by 32% and 34%, respectively, suggesting a role being played by grapes in the activation of P-glycoprotein and omeprazole metabolizing enzymes, including CYP3A4 and CYP2C19. In conclusion, the addition of grapes as a dietary supplement in patients taking omeprazole for the management of peptic ulcer symptoms may lead to a higher required dose of omeprazole.

Cardiac Arrest Associated with Combination Cisapride and Itraconazole Therapy

We report a case of cardiac arrest associated with cisapride in combination with itraconazole and provide a brief review of pertinent literature. Cisapride (Propulsid; Janssen Pharmaceuticals, Titusville, NJ), a gastrointestinal prokinetic drug, has recently been reported to prolong the QT interval. Itraconazole, an oral antifungal agent, is an inhibitor of cytochrome P450 (CYP3A4) metabolism and may elevate serum drug levels of compounds metabolized by this pathway. A 31-year-old woman had a witnessed cardiac arrest while taking the combination of cisapride and itraconazole. Following resucitation, the prolonged QT interval returned to normal after withdrawal of both agents. Echocardiography and cardiac catheterization were within normal limits; electrophysiologic testing failed to induce ventricular tachycardia/ventricular fibrillation. She has had no documented arrhythmias since the arrest. This combination can now be added to a growing list of drugs that may cause torsades de pointes and sudden cardiac death.

Efficacy of Ketoprofen With or Without Omeprazole for Pain And Inflammation Control After Third Molar Removal

In view of the gastrointestinal problems generated by the ketoprofen use, the ketoprofen association with omeprazole is available on the market. However, this association efficacy in acute pain control has not been established. Bilateral extraction of lower third molars in similar positions is currently the most used model for the evaluation and investigation of the efficacy and pharmacological effects of new compounds for the treatment of acute postoperative pain. The randomized and crossover study consisted in evaluating the clinical efficacy of therapy performed by ketoprofen 100 mg (twice daily-b.i.d.) versus ketoprofen 200 mg + omeprazole 20 mg (once daily-q.d.) to pain, swelling and trismus control in the bilateral extraction model of lower third molars in similar positions in two different appointments, in 50 volunteers. Volunteers reported significantly less postoperative pain at various post-operative periods and consumed less rescue analgesic medication (acetaminophen 750 mg) throughout the study when they took the combination of ketoprofen 200 mg + omeprazole 20 mg (q.d.). Following administration of both study drugs, no gastrointestinal adverse reactions were reported by volunteers. Furthermore, the evaluations of the drugs in pain control by the volunteers were significantly favorable to ketoprofen 200 mg + omeprazole 20 mg (q.d.). For swelling and trismus control, the treatments presented similar results. In conclusion, when volunteers took ketoprofen 200 mg + omeprazole 20 mg (q.d.), they reported significantly less postoperative pain at various post-surgical periods and consumed less rescue analgesic medication throughout the study compared with ketoprofen 100 mg (b.i.d).

Drug Interactions with Antiulcer Agents: Considerations in the Treatment of Acid-Peptic Disease

All of the antiulcer agents have been implicated in drug interactions. These agents generally influence the absorption, metabolism, or elimination of other medications. However, these interactions can lead to alterations in pharmacodynamic response. The mechanisms by which antiulcer agents produce drug interactions differ among the agents. It is beyond the scope of this article to review all of the drug interactions that have been reported with antiulcer agents. However, it is the intent to provide the reader with a detailed understanding of the mechanisms by which antiulcer agents may interact with other medications and to provide insight into factors that may influence the potential magnitude or clinical consequences of these interactions. An understanding of antiulcer drug interactions will aid pharmacists in assisting clinicians with drug selection and/or monitoring of drug interactions. Specifically, pharmacists can assist with the identification of potential antiulcer drug interactions and develop strategies designed to minimize adverse consequences of these interactions.

Current Status of Gastric Proton Pump Inhibitors in the Treatment of Acid-Peptic Disease

Proton pump inhibitors represent an important advance in the treatment of acid-peptic disease. Omeprazole, the prototype of the drug class, produces a profound and sustained degree of gastric acid suppression. Recent studies confirm earlier reports that omeprazole 20 mg/d is generally more effective than standard histamine2 receptor antagonist (H2RA) dosage regimens in treating duodenal ulcer (DU), gastric ulcer (GU), and erosive esophagitis. Omeprazole tends to accelerate DU and GU healing, especially during the first 2 weeks of treatment, and also accelerates mucosal healing in patients with all grades of esophagitis. Omeprazole is the drug of choice for treating patients with large or refractory ulcers, severe or refractory erosive esophagitis, Barrett's esophagus, and Zollinger-Ellison syndrome. Maintenance therapy with omeprazole seems to reduce ulcer recurrence and esophagitis, but optimal treatment regimens must be established. Dual therapy with omeprazole and amoxicillin shows encouraging results in eradicating Helicobacter pylori, reducing duodenal ulcer recurrence rates, and altering the natural history of peptic ulcer disease. Further studies are required to determine the efficacy of omeprazole in preventing nonsteroidal anti-inflammatory drug-induced ulcers and stress-related mucosal bleeding, and in treating upper gastrointestinal bleeding. Omeprazole is well-tolerated in the majority of patients receiving either short-term or long-term treatment. The type and frequency of adverse effects are similar to those reported with the H2RAs. There is no evidence to support genotoxicity or hypergastrinemia-induced enterochromaffin-like cell carcinoid of the stomach in patients receiving omeprazole treatment for more than 5 years. Omeprazole interacts selectively with hepatic P-450 and may potentially interact with phenytoin, warfarin, or diazepam. Pharmacoeconomic studies suggest that treatment with omeprazole provides a significant cost-savings over the H2RAs in patients with moderate to severe erosive esophagitis and possibly in patients with DU. Lansoprazole, a newly developed proton pump inhibitor, seems to offer no clear advantage over omeprazole.

Omeprazole increases the efficacy of a soluble epoxide hydrolase inhibitor in a PGE₂ induced pain model

Epoxyeicosatrienoic acids (EETs) are potent endogenous analgesic metabolites produced from arachidonic acid by cytochrome P450s (P450s). Metabolism of EETs by soluble epoxide hydrolase (sEH) reduces their activity, while their stabilization by sEH inhibition decreases both inflammatory and neuropathic pain. Here, we tested the complementary hypothesis that increasing the level of EETs through induction of P450s by omeprazole (OME), can influence pain related signaling by itself, and potentiate the anti-hyperalgesic effect of sEH inhibitor. Rats were treated with OME (100mg/kg/day, p.o., 7 days), sEH inhibitor TPPU (3mg/kg/day, p.o.) and OME (100mg/kg/day, p.o., 7 days)+TPPU (3mg/kg/day, p.o., last 3 days of OME dose) dissolved in vehicle PEG400, and their effect on hyperalgesia (increased sensitivity to pain) induced by PGE2 was monitored. While OME treatment by itself exhibited variable effects on PGE2 induced hyperalgesia, it strongly potentiated the effect of TPPU in the same assay. The significant decrease in pain with OME+TPPU treatment correlated with the increased levels of EETs in plasma and increased activities of P450 1A1 and P450 1A2 in liver microsomes. The results show that reducing catabolism of EETs with a sEH inhibitor yielded a stronger analgesic effect than increasing generation of EETs by OME, and combination of both yielded the strongest pain reducing effect under the condition of this study.

Pharmacokinetic interaction between fluoxetine and omeprazole in healthy male volunteers: a prospective pilot study

BACKGROUND

Fluoxetine is an inhibitor of the main metabolizing enzymes (cytochrome P450 [CYP] 2C19 and CYP3A4) of omeprazole and thus might influence that drug's pharmacokinetics. The changes in omeprazole's pharmacokinetics may have clinical significance concerning efficacy and tolerability of the treatment.

OBJECTIVE

The aim of this study was to assess the pharmacokinetic interaction of fluoxetine with omeprazole in healthy volunteers.

METHODS

The study enrolled healthy adult men and consisted of 2 periods. In the first period, all subjects received a single 40-mg dose of omeprazole. This was followed by an 8-day period during which fluoxetine monotherapy (60 mg/d) was administered as a single oral daily dose. At the end of those 8 days, the subjects were administered a 40-mg dose of omeprazole with a 60-mg dose of fluoxetine. Plasma concentrations of omeprazole were determined at 0.5, 1, 1.33, 1.66, 2, 2.5, 3, 4, 5, 6, 7, 8, 10, and 12 hour(s) after study drug administration. Omeprazole plasma concentrations were determined by a validated HPLC method. Pharmacokinetic parameters of omep-razole were calculated using noncompartmental analysis. Adverse events were assessed throughout the study duration.

RESULTS

Eighteen healthy male volunteers (mean [SD] age, 22.11 [2.52] years [range, 18-26 years]; body mass index, 23.34 [2.31] kg/m(2) [range, 19.1-27.1 kg/m(2)]) were enrolled and completed the study. In the 2 periods of treatment, the mean Cmax of omeprazole was 730.8 ng/mL (omeprazole monotherapy) and 1725.5 ng/mL (combination treatment with fluoxetine). The observed AUC0-∞ was 1453.3 and 5072.5 ng/mL/h and AUC0-t was 1465.0 and 5185.3 ng/mL/h, respectively. The Tmax was 1.30 and 1.63 hours and the elimination rate constant was 0.753 and 0.482 hr(-1). The t½ was 0.96 and 1.47 hours, whereas the mean residence time was 2.33 and 3.35 hours, respectively. Statistically significant differences were observed for all parameters between periods 1 and 2 (all, P < 0.001).

CONCLUSION

The data found in this prospective pilot study suggest a pharmacokinetic interaction between fluoxetine and omeprazole in these healthy volunteers, but its relevance has to be confirmed.

Functional polymorphisms in the CYP2C19 gene contribute to digestive system cancer risk: evidence from 11,042 subjects

Background

CYP2C19 belongs to the cytochrome P450 superfamily of enzymes involved in activating and detoxifying many carcinogens and endogenous compounds, which has attracted considerable attention as a candidate gene for digestive system cancer. CYP2C19 has two main point mutation sites (CYP2C19*2, CYP2C19*3) leading to poor metabolizer (PM) phenotype. In the past decade, the relationship between CYP2C19 polymorphism and digestive system cancer has been reported in various ethnic groups; however, these studies have yielded contradictory results.

Methods

To clarify this inconsistency, we performed this meta-analysis. Databases including Pubmed, EMBASE, Web of Science and China National Knowledge Infrastructure (CNKI) were searched to find relevant studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of association.

Results

In total, 18 studies with 4,414 cases and 6,628 controls were included. Overall, significantly elevated digestive system cancer risk was associated CYP2C19 PM with OR of 1.66 (95%CI: 1.31–2.10, P<10⁻⁵) when all studies were pooled into the meta-analysis. There was strong evidence of heterogeneity (P = 0.006), which largely disappeared after stratification by cancer type. In the stratified analyses according to cancer type, ethnicity, control source and sample size, significantly increased risks were found.

Conclusions

In summary, our meta-analysis suggested that the PM phenotype caused by the variation on CYP2C19 gene is associated with increased risk of digestive system cancer, especially in East Asians.

Treatment for Eradication of Helicobacter pylori Infection among Chronic Hepatitis C Patients

BACKGROUND/AIMS

Helicobacter pylori infection causes gastritis, peptic ulcers and gastric malignancies, and its eradication has been advocated by many groups. We determined the H. pylori carrier status and eradication rates of patients with chronic hepatitis C virus (HCV) infection.

METHODS

In total, 76 chronically HCV-infected patients were enrolled for comparison with 228 HCV-noninfected, age- and sex-matched controls. H. pylori infection was confirmed by H. pylori antibody and urea breath testing.

RESULTS

The H. pylori infection rate was significantly higher for HCV-infected patients (67 of 76, 88.2%) than for HCV-noninfected controls (158 of 228, 69.3%). Endoscopic findings showed that the rates of gastric ulcers and gastritis were significantly higher for the 67 HCV-infected patients with H. pylori infection (34.3% and 77.6%) than for the 158 HCV-noninfected controls with H. pylori infection (15.2% and 57.6%). Treatment to eradicate H. pylori had a significantly higher success rate for HCV-infected patients (61 of 67, 91.0%) than for HCV-noninfected controls (115 of 158, 72.8%).

CONCLUSIONS

The markedly high H. pylori eradication rate observed in this study shows that eradication of H. pylori holds promise for the improvement of the long-term health condition of patients with chronic HCV infection.

The potential inhibitory effect of revaprazan, an acid pump antagonist, on anticoagulation with warfarin

Revaprazan is the first acid pump antagonist with a function similar to that of proton pump inhibitors (PPIs). It has a dual action, active suppression of gastric acid secretion and gastric mucosa protection. While PPIs are known to enhance the prolongation of prothrombin time by warfarin, no research has been done on the drug interaction between revaprazan and warfarin. This study was conducted in order to verify the potential drug interaction between revaprazan and warfarin. Omeprazole, a representative PPI, was used as the control for revaprazan. We searched for patients who were given either revaprazan or omeprazole along with warfarin using the medical record database of Seoul National University Hospital between July 2007 and June 2010. Among the 15 patients who took revaprazan and warfarin together, 73.3% (11/15) showed more than 30% reduction of anticoagulation effect by warfarin after revaprazan was added. The revaprazan group showed a significant shortening of prothrombin time during revaprazan administration compared to pre- and post-revaprazan medication (P < 0.05) while the omeprazole group did not show such difference. Revaprazan seems to have cumulative dose-dependent anti-warfarin or anti-coagulation effect, as judged from the fact that the longer medication with revaprazan showed correlation with the shortening of prothrombin time (R = -0.632, P < 0.05). This study shows a possible interaction between revaprazan and warfarin and suggests that revaprazan can cause shortening of prothrombin time. Therefore, when revaprazan is prescribed to patients on warfarin therapy, prothrombin time should be frequently monitored.

Omeprazole induces gastric permeability to digoxin

Previous animal and patient-based studies have shown that omeprazole induces a transepithelial paracellular gastric leak. This study reports on the potential for an omeprazole-induced leak of drugs with narrow therapeutic windows. Ussing chamber experiments investigated the effects of omeprazole on rat gastric corpus permeability to the drugs, digoxin and phenytoin. Digoxin (780 MW) permeated the gastric mucosa at an accelerated rate in the presence of omeprazole. This leak could contribute to dangerous elevations of blood digoxin levels in certain situations. Omeprazole was found to have no effect on the flux rate of phenytoin (252 MW). The tight-junctional leak generated by omeprazole thus exhibits specificity to the types of molecules it allows to permeate through the gastric mucosa. This leak may pose a clinical danger by increasing drug uptake into the bloodstream, a phenomenon which would act synergistically with the effect of omeprazole on inhibiting liver cytochrome P450s that remove drugs from the bloodstream, thereby elevating drug blood levels.

Acute vomiting in cats: rational treatment selection

PRACTICAL RELEVANCE

The control of nausea and vomiting in cats is important in order to prevent the development of food aversion, anorexia (with its associated complications of weight loss and dehydration), and hepatic lipidosis.

CLINICAL CHALLENGES

There are several antiemetic drugs that are clinically effective in cats. Making a rational choice from the available options requires knowledge of the likely cause of the vomiting, and the mechanisms of action and side effects of each drug. For example, a drug such as prochlorperazine, which can cause sedation, may be a useful first-line choice in a hospitalized cat that requires mild sedation to be handled, but would be undesirable in a critically ill cat.

AUDIENCE

For companion animal and feline practitioners, the vomiting cat is a common presentation.

EVIDENCE BASE

The guidance provided in this review draws on the findings of clinical trials in humans, experimental studies in cats, some clinical trials in cats, and clinical experience.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Estimation of CYP2C19 activity by the omeprazole hydroxylation index at a single point in time after intravenous and oral administration

OBJECTIVE

The purpose of this study was to identify the common time point to achieve hydroxylation index (HI: omeprazole plasma concentration/5-hydroxyomeprazole plasma concentration) reflecting AUCOPZ/AUC5OH-OPZ after intravenous (IV) and oral (PO) administration.

METHODS

Twenty young and 28 elderly healthy subjects, including different CYP2C19 genotypes, were enrolled in the study. The young subjects received either 40 mg PO or 20 mg IV omeprazole, whereas the elderly subjects received 10 mg IV. The relation between AUCOPZ/AUC5OH-OPZ and HI was determined by Spearman's rank correlation. Multiple stepwise linear regression analysis was performed to identify the common time point to calculate HI that reflects AUCOPZ/AUC5OH-OPZ after IV.

RESULTS

In the correlation between HI and AUCOPZ/AUC5OH-OPZ IV at observed time points, HI3h showed the highest correlation coefficients (r = 0.894, p < 0.001) in all 48 subjects. The correlation of HI between IV and PO at observed time points showed that HI3h was highest (r = 0.916, p < 0.001) in 20 young subjects. Additionally, there was no significant difference between HI(3h) of IV and that of PO (12.9 +/- 15.9 and 12.9 +/- 15.1, p = 0.997). The regression equation of HI3h was the best to estimate AUCOPZ/AUC5OH-OPZ (AUCOPZ/AUC5OH-OPZ = 1.37 * HI3h + 0.18 * Age - 7.83, r2 = 0.883, p < 0.001).

CONCLUSIONS

This study demonstrated that HI3h after omeprazole IV was able to estimate AUCOPZ/AUC5OH-OPZ, as well as HI3h after PO. Additionally, CYP2C19 activity can be estimated more definitely by using HI after omeprazole IV without intestinal absorption.

Omeprazole-associated digoxin toxicity

Omeprazole is a commonly prescribed inhibitor of the gastric proton pump and has numerous indications in the treatment of gastrointestinal diseases. It is primarily metabolized through the CYP2C19 enzyme, a member of the P450 mixed-function oxidase group, although a minor pathway of metabolism is through CYP3A4, another P450 enzyme. Digoxin is primarily metabolized outside the P450 system, but a minor pathway of metabolism is by CYP3A4. To our knowledge, this is the first known case of digoxin toxicity associated with omeprazole. The possible pathways for such an interaction are reviewed, including increased stomach absorption, p-glycoprotein activity and interactions in the P450 system.

Effect of omeprazole on the pharmacokinetics of paricalcitol in healthy subjects

Paricalcitol capsules are indicated for the prevention and treatment of secondary hyperparathyroidism in chronic kidney disease (CKD). Proton pump inhibitors are prescribed to CKD patients to treat gastroesophageal reflux. This was a single dose, crossover study evaluating the effect of omeprazole, change in gastric pH as a result thereof, on the pharmacokinetics (PK) of paricalcitol. Twenty-six healthy subjects were administered paricalcitol capsules (16 microg) alone (regimen A), and following a single dose of OMP (40 mg) (regimen B), with a washout of at least 7 days. Plasma samples for paricalcitol concentrations were collected for 48 h post-paricalcitol dose. The plasma paricalcitol concentrations were measured using an LC-MS/MS assay (LOQ=0.02 ng/ml) and paricalcitol pharmacokinetic parameters were estimated using non-compartmental methods. The point estimates and the corresponding 90% confidence intervals for Cmax and AUC0-infinity to evaluate paricalcitol-omeprazole interaction were 1.032 [0.920-1.158] and 1.041 [0.951-1.139], respectively. No significant differences in Tmax (regimen A: 2.9 h vs regimen B: 2.6 h) or t1/2 (6.83 h vs 6.6 h) between the regimens were observed. Hence, the co-administration of omeprazole does not affect the PK of paricalcitol. Both regimens were well tolerated and no apparent differences among the regimens with respect to safety were observed.

Gastrointestinal medications

Medications to address gastrointestinal disorders are among the most commonly dispensed somatic medications. The authors examine proton pump inhibitors, H(2) blockers, 5-HT(3) receptor-antagonists, and a few other drugs that are used to address this domain of medical concerns. The metabolic pathways, interactions with the P-glycoprotein transporter, and capabilities of inhibiting or inducing metabolic enzymes are elucidated for each drug. Specific drug-drug interactions with each agent are also detailed, including both psychotropic and non-psychotropic agents. Also, the article explores how different genotypic variants for specific cytochrome P450 enzymes have an impact on the effectiveness and likelihood of drug-drug interactions relating to specific gastro-intestinal medications.

Effect of omeprazole on bioavailability of an oral extended-release formulation of ciprofloxacin

PURPOSE

The effect of omeprazole on the oral bioavailability and urinary exposure of the Depomed formulation of extended-release (ER) ciprofloxacin was studied.

METHODS

A two-way crossover study was conducted in healthy subjects. Subjects received either a single dose of ER ciprofloxacin 1000 mg or a single dose of ER ciprofloxacin 1000 mg following three days of treatment with omeprazole 40 mg. Blood and urine samples were collected over 36 hours, and ciprofloxacin concentrations were determined using high-performance liquid chromatography.

RESULTS

Twenty-seven subjects (16 men, 11 women) received both treatments. The mean maximum concentration, mean area under the plasma-versus-concentration curve, and mean amount of ciprofloxacin excreted in urine were similar between the two treatments and met strict bioequivalence criteria.

CONCLUSION

Omeprazole did not affect the plasma or urinary pharmacokinetics of an oral ER formulation of ciprofloxacin.

In vivo metabolic activity of CYP2C19 and CYP3A in relation to CYP2C19 genetic polymorphism in chronic liver disease

To study whether chronic liver disease (CLD) and genetic polymorphism affect the hepatic activity of cytochrome P450 (CYP) isoforms, we compared in vivo CYP2C19 and CYP3A activities using 3-hour omeprazole hydroxylation index (plasma concentration ratio of omeprazole to its 5-hydroxylated metabolite; a higher index indicates lower CYP2C19 activity) and partial formation clearance of cortisol to 6beta-hydroxycortisol (CL(cortisol-->6beta-HC)) in 31 CLD patients (9 with chronic hepatitis; 22 with cirrhosis comprising 20 Child-Pugh type A, 1 type B, and 1 type C) and 30 healthy subjects with different CYP2C19 genotypes. The mean (+/-SEM) omeprazole hydroxylation index in CLD patients with homozygous extensive metabolizer (EM) genotype (*1/*1, n = 8), heterozyous EM (*1/*2, n = 11; *1/*3, n = 6) genotypes and poor metabolizer (PM) genotypes (*2/*2, n = 3; *3/*3, n = 3) were 17.15 +/- 2.12, 20.02 +/- 2.63, and 26.04 +/- 3.15, respectively, which were significantly higher compared with control subjects with the corresponding CYP2C19 genotypes (0.81 +/- 0.09, 1.55 +/- 0.20, and 15.5 +/- 1.52). CLD patients with PM genotype had significantly (P < .05) higher omeprazole hydroxylation indexes than did those with homozygous EM genotype, and those with heterozygous EM genotypes had intermediate values. The mean CL(cortisol-->6beta-HC) decreased significantly (P < .001) in CLD patients compared with control subjects (1.19 +/- 0.12 versus 2.26 +/- 0.24 mL/min). Multiple regression analysis showed that CLD, serum albumin level, and CYP2C19 genotype correlated significantly (P < .05) with the omeprazole hydroxylation index, whereas no significant correlation was observed between CL(cortisol-->6beta-HC) and other variables, except CLD. Because CLD and genetic polymorphism of CYP2C19 act additively to reduce CYP2C19 activity, genotyping these patients may be of value in averting adverse reactions of drugs that depend on CYP2C19 for elimination.

Poor metabolizer genotype status of CYP2C19 is a risk factor for developing gastric cancer in Japanese patients with Helicobacter pylori infection

BACKGROUND

Cytochrome P450 2C19 (CYP2C19) polymorphism has been associated with the development of lung, liver or oesophageal cancer by detoxification of carcinogen(s) or activation of procarcinogen(s).

AIM

To clarify the association between CYP2C19 polymorphisms and gastric cancer development in Japanese. Methods : We determined CYP2C19 genotypes (CYP2C19*1, *2 and *3) in 111 Helicobacter pylori-positive patients with gastric cancer and 315 H. pylori-positive controls without gastric cancer consisting of patients with gastritis only or peptic ulcer. Frequencies of CYP2C19 genotypes and serum pepsinogen I and II levels, a biomarker of gastric atrophy, in the gastric cancers and controls were compared.

RESULTS

Frequencies of homozygous extensive metabolizers, heterozygous extensive metabolizers and poor metabolizers were 31.5%, 42.3% and 26.2% in the gastric cancers and 38.1%, 47.0% and 14.9% in the controls, respectively (P = 0.046). Poor metabolizers were associated with an increased risk for developing gastric cancer with the age- and sex-adjusted odds ratio (OR) of 1.975 [95% confidence interval (CI): 1.068-3.649], especially for diffuse type (OR: 3.385, CI: 1.187-9.648). There is no significant association between CYP2C19 genotypes and serum pepsinogen I level or pepsinogen I/II ratios, although serum pepsinogen I level in gastric cancers were significantly decreased.

CONCLUSIONS

In H. pylori-positive Japanese, poor metabolizers of CYP2C19 appear to be at an increased risk for developing gastric cancer, especially diffuse type, and may require an intensive follow-up for scrutinizing possible gastric cancer development.

Influence of omeprazole on bioavailability of bismuth following administration of a triple capsule of bismuth biskalcitrate, metronidazole, and tetracycline

The objective of this study was to determine the impact of omeprazole on bismuth (Bi) bioavailability when given in a three-in-one capsule containing bismuth biskalcitrate, metronidazole, and tetracycline. Thirty-four healthy volunteers were randomly assigned to receive three capsules (each containing bismuth biskalcitrate 140 mg + metronidazole 125 mg + tetracycline 125 mg) qid alone x 6 days or the same treatment + omeprazole (OM) 20 mg bid. Blood was drawn at intervals for 24 hours after the last dose. After the last dose, mean (CV) C(min) for plasma bismuth was 2882 pg/mL (36%) and 1195 pg/mL (23%) (p< 0.001), with and without OM, respectively. Mean (CV) C(max) was 25493 pg/mL (69%) and 8061 pg/mL (28%) (p < 0.001) with and without OM, respectively. AUC(0-24) increased by 2.9 in presence of OM (p < 0.001). Adverse events in both groups were usually mild and of a gastrointestinal nature, and all had resolved by the end of the trial. This study confirms an interaction between Bi biskalcitrate and OM. Risk of Bi toxicity, seen after long-term use of Bi compounds, is minimal here because plasma levels of Bi remained well below the toxic levels of 50 microg/L, and the treatment period with this triple capsule + OM is only 10 days, a substantially lower number of days compared to that which might produce Bi toxicity.

Comparison of inhibitory effects of the proton pump-inhibiting drugs omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole on human cytochrome P450 activities

The human clearance of proton pump inhibitors (PPIs) of the substituted benzimidazole class is conducted primarily by the hepatic cytochrome P450 (P450) system. To compare the potency and specificity of the currently used PPIs (i.e., omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole) as inhibitors of four cytochrome P450 enzymes (CYP2C9, 2C19, 2D6, and 3A4), we performed in vitro studies using human liver microsomal preparations and recombinant CYP2C19. Sample analysis was done using selected reaction monitoring liquid chromatography/tandem mass spectometry. With several systems for CYP2C19 activity (two marker reactions, S-mephenytoin 4'-hydroxylation and R-omeprazole 5-hydroxylation, tested in either human liver microsomes or recombinant CYP2C19), the five PPIs showed competitive inhibition of CYP2C19 activity with K(i) of 0.4 to 1.5 microM for lansoprazole, 2 to 6 microM for omeprazole, approximately 8 microM for esomeprazole, 14 to 69 microM for pantoprazole, and 17 to 21 microM for rabeprazole. Pantoprazole was a competitive inhibitor of both CYP2C9-catalyzed diclofenac 4'-hydroxylation and CYP3A4-catalyzed midazolam 1'-hydroxylation (K(i) of 6 and 22 microM, respectively), which were at least 2 times more potent than the other PPIs. All PPIs were poor inhibitors of CYP2D6-mediated bufuralol 1'-hydroxylation with IC(50) > 200 microM. The inhibitory potency of a nonenzymatically formed product of rabeprazole, rabeprazole thioether, was also investigated and showed potent, competitive inhibition with K(i) values of 6 microM for CYP2C9, 2 to 8 microM for CYP2C19, 12 microM for CYP2D6, and 15 microM for CYP3A4. The inhibitory potency of R-omeprazole on the four studied P450 enzymes was also studied and showed higher inhibitory potency than its S-isomer on CYP2C9 and 2C19 activities. Our data suggest that, although the inhibitory profiles of the five studied PPIs were similar, lansoprazole and pantoprazole are the most potent in vitro inhibitors of CYP2C19 and CYP2C9, respectively. Esomeprazole showed less inhibitory potency compared with omeprazole and its R-enantiomer. The inhibitory potency of rabeprazole was relatively lower than the other PPIs, but its thioether analog showed potent inhibition on the P450 enzymes investigated, which may be clinically significant.

Induction of Testosterone Metabolism by Esomeprazole in aCYP2C19*2 Heterozygote

The authors describe a 42-year-old woman with previously normal sexual function who gradually developed loss of libido during treatment with esomeprazole. While taking esomeprazole, the patient's loss of libido improved with oral testosterone supplementation and deteriorated after testosterone withdrawal. There was steady improvement in both sexual function and serum free testosterone concentration after discontinuation of esomeprazole. Due to the temporal relationship between esomeprazole intake and sexual dysfunction, the authors postulate that esomeprazole causes induction of testosterone metabolism. The authors believe this to be the first case of female sexual dysfunction associated with esomeprazole described in the literature. They discuss a number of possible mechanisms for this effect.

Effect of omeprazole on the anticoagulant activity and the pharmacokinetics of warfarin enantiomers in rats

The effect of the proton pump inhibitor omeprazole on the anticoagulation and the pharmacokinetics of warfarin enantiomers was studied in rats. Omeprazole given intraperitoneally in a daily dose of 0.67 mg/kg over 8 days had no significant effect on the absorption, distribution and the total serum clearance values of the S- and R-enantiomers of warfarin. Omeprazole did not affect the pre-treatment baseline blood coagulation and the in vitro rat serum protein binding of warfarin enantiomers. In vitro study with rat liver microsomes showed that omeprazole had an inhibitory effect on the hydroxylation of warfarin enantiomers. Results obtained from in vivo urinary excretion study revealed that omeprazole inhibited the formation clearance of both S- and R-form oxidative metabolites, but increased that of the overall reductive metabolites, and the renal clearance of S- and R-enantiomers, of warfarin. As a consequence, the total serum clearance values for warfarin enantiomers remained unchanged and the hypoprothrombinaemic response produced by warfarin was not affected.

Impact of cotherapy with some proton pump inhibitors on medical claims among HMO patients already using other common drugs also cleared by cytochrome P450

Adverse drug event (ADE) rates resulting from coadministration of proton pump inhibitors (PPIs) and other drugs with potential for interaction with PPIs (DPIs) are unknown. This retrospective study assesses the occurrence of such ADEs and their potential impact on medical care costs by reviewing integrated medical and pharmacy claims. Managed care patients receiving one or more DPIs were identified. Within this sample, those who were also prescribed omeprazole or lansoprazole (DPI + PPI) were included. A second cohort (DPI alone) was created, matching for age, gender, and DPI use. Rates of ADEs were followed for 6 months after entry. Among PPI users, 58% used one or more DPIs, whereas 7% of DPI subjects used a PPI. Among claims arising from ADEs occurring in more than 1% of patients, 14 occurred in the DPI + PPI group and 2 occurred in the DPI-alone cohort, respectively, a highly significant difference. Crude odds ratios for the risks of specific ADEs were significantly increased for cotherapy with a PPI and warfarin, clarithromycin, corticosteroids, carbamazepine, nifedipine, or diclofenac. After adjustment, the first three associations remained significant. Coprescription of a PPI with potentially interacting drugs was common in practice and associated with significantly increased claims for medical care.

Pharmacologic features of proton pump inhibitors and their potential relevance to clinical practice

In conclusion, PPIs differ slightly in their PK and PD properties and in their propensity to interact with other medications. Inhibition of acid secretion is a function of proton pump inhibition, and PPIs work in a similar fashion to achieve this goal. PK/PD principles can be used to optimize PPI therapy when considering issues related to administration, such as timing of drug delivery relative to the number of active pumps and the drug's AUC.

Gastroesophageal reflux in children: pathogenesis, prevalence, diagnosis, and role of proton pump inhibitors in treatment

A substantial percentage of infants, children and adolescents experience gastroesophageal reflux disease (GERD) and its accompanying symptoms, as well as disease complications. The diagnosis of GERD in children is made based upon the child's history, and data derived primarily from pH monitoring tests and endoscopy. In those children with confirmed reflux disease, the options for management parallel those recommended in adult patients, with the first step consisting of lifestyle changes. Surgical procedures may also be performed; however, these are rarely recommended prior to an adequate course of pharmacologic therapy, and appropriate case selection is important. Among the current pharmacotherapeutic options available in the US, the prokinetic agents and the acid-inhibitory agents (histamine-2 receptor antagonists, proton pump inhibitors) are the most widely used. The clinical utility of the prokinetic agents has been limited by the recent withdrawal of cisapride from the US marketplace and the potential for irreversible central nervous system complications with metoclopramide. Numerous clinical studies performed in adults, and several studies involving children, have demonstrated that the proton pump inhibitors are more effective than the histamine-2 receptor antagonists in the relief of GERD symptoms and healing of erosive esophagitis. In children, omeprazole and lansoprazole may be administered as the intact oral capsule, or in those who are unable or unwilling to swallow, the granule contents of the capsule may be mixed with soft foods (e.g. apple sauce) or fruit drinks/liquid dietary supplements prior to oral administration with no detrimental effects on pharmacokinetics, bioavailability, or pharmacodynamics. Studies performed with omeprazole and lansoprazole in children have shown pharmacokinetic parameters that closely resemble those observed in adults. In over a decade of use in adults, the proton pump inhibitor class of agents has been found to have a good safety profile. Studies involving children have also shown these agents to be well tolerated. In numerous drug-drug interaction studies performed with these two proton pump inhibitors, relatively few clinically significant interactions have been observed.

Effect of omeprazole on oral and intravenous RS-methadone pharmacokinetics and pharmacodynamics in the rat

The effect of omeprazole on oral and intravenous (iv) RS-methadone pharmacokinetics and pharmacodynamics was studied in awake, freely moving rats, which were divided in four groups: oral RS-methadone (3 mg/kg) was given (a) to a control group (CO(oral)) (n = 65) and (b) to an omeprazole pretreated group (OP(oral)) (n = 77), and iv RS-methadone (0.35 mg/kg) was administered (c) to a control group (CO(iv)) (n = 86) and (d) to an omeprazole pretreated group (OP(iv)) (n = 86). Omeprazole (2 mg/kg) was given iv 2 h before RS-methadone. Plasma concentrations of RS-methadone (Cp) were determined by high-performance liquid chromatography and analgesic response by tail flick for 0-180 min (oral) and 0-120 min (iv). RS-Methadone rate of absorption (mean +/- SE) was faster in OP(oral) (k(01) = 0.31 +/- 0.04 min(-1)) than in CO(oral) (k(01) = 0.05 +/- 0.007 min(-1)), consequently plasma peak concentrations (C(max)) were greater (197.41 +/- 33.70 ng/mL versus 83.54 +/- 7.97 ng/mL) and the time to reach C(max) (t(max)) was shorter (11.23 +/- 1.32 min versus 39.18 +/- 1.74 min). Mean area under the Cp-time curve (AUC(0-infinity)) and hence bioavailability of oral RS-methadone were increased by omeprazole without significant changes in the elimination. Omeprazole did not affect the pharmacokinetics of iv RS-methadone. The changes of the analgesic effect of RS-methadone as a function of time were similar in all four groups. In the CO(oral) group, Cp and analgesic effect were defined by the E(max) model. The relationship between Cp and drug effect in the OP(oral) group showed a counterclockwise hysteresis (k(e0) of 0.018 +/- 0.006 min(-1)). For the iv groups (CO(iv) and OP(iv)), the Cp-analgesic effect relationship was described by an E(max) sigmoid model and omeprazole did not affect the pharmacodynamic parameters. It is concluded that omeprazole causes an increase in the bioavailability of oral RS-methadone without modifying the analgesic response but affecting the Cp-effect relationship.

Influence of fluconazole on the pharmacokinetics of omeprazole in healthy volunteers

Influence of fluconazole on the pharmacokinetics of omeprazole was evaluated by single oral administration of omeprazole capsule 20 mg (control group), or single oral administration of fluconazole capsule, 100 mg, and omeprazole, 20 mg, after 4 days of daily oral administration of fluconazole, 100 mg (treated group), to 18 healthy male volunteers. Omeprazole is extensively metabolized in the liver through 5-hydroxylation and sulfoxidation reactions catalyzed predominantly by CYP2C19 and CYP3A4, respectively. Fluconazole is a potent competitive inhibitor of CYP2C19 and a weak inhibitor of CYP3A4. In treated group, the area under the plasma concentration-time curve of omeprazole from time zero to time infinity (AUC) was significantly greater (3090 vs 491 ng h/ml), terminal half-life of omeprazole was significantly longer (2.59 vs 0.85 h), and peak plasma concentration of omeprazole (C(max)) was significantly higher (746 vs 311 ng/ml) than that in control group. The greater AUC and higher C(max) in treated group could be due to inhibition of omeprazole metabolism by fluconazole.

Pharmacogenetic diagnostics of cytochrome P450 polymorphisms in clinical drug development and in drug treatment

The current use and future perspectives of molecular genetic characterisation of cytochrome P450 enzymes (CYP) for drug development and drug treatment are summarised. CYP genes are highly polymorphic and the enzymes play a key role in the elimination of the majority of drugs from the human body. Frequent variants of some enzymes, CYP2A6, 2C9, 2C19 and 2D6, should be analysed in participants of clinical trials whenever these enzymes may play a role. It is suggested that a CYP genotype certificate is handed out to the volunteers or patients to avoid replicate analyses, and to allow that this information is available for future research and also for treatment with eventually needed drugs. Guidelines on what CYP alleles have to be analysed in drug development, as well as on analytical validation and CYP genotype data handling will be required. Treatment with several drugs may be improved by prior genotyping. The concepts and problems of CYP genotype-based clinical dose recommendations are presented and illustrated for selected drugs. The requirement for prospective trials on the medical and economic benefits of routine CYP genotyping is emphasised. Specific operationally defined recommendations dependent on genotype are a prerequisite for such studies and this review presents tentative CYP genotype-based dose recommendations systematically calculated from published data. Because of the multiplicity of factors involved, these doses will not be the optimal doses for each given individual, but should be more adequate than doses generally recommended for an average total population. Those CYP alleles and polymorphically metabolised drugs which are currently most interesting in drug development and drug treatment are reviewed, and more complete information is available from websites cited in this article.

Effect of omeprazole on the metabolism of cilostazol

OBJECTIVE

In vitro results suggest that cilostazol is metabolised by cytochrome P450 (CYP) isoforms 1A2, 2D6, 3A4 and 2C19. This study was designed to evaluate the effect of concomitant administration of omeprazole (a CYP2C19 inhibitor) on the pharmacokinetics of a single 100 mg oral dose of cilostazol.

DESIGN

This study was conducted as a single-centre, open-label, nonrandomised, 2-period, crossover pharmacokinetic trial. A single 100 mg dose of cilostazol was administered orally on days 0 and 14. Oral omeprazole (40 mg every day) was administered on days 7 to 18.

STUDY PARTICIPANTS

20 healthy nonsmoking male and female volunteers.

MAIN OUTCOME MEASURES

Serial blood samples were collected before and after cilostazol administration to characterise the pharmacokinetics of cilostazol and its metabolites.

RESULTS

Following omeprazole coadministration, the increases in cilostazol maximum plasma concentration (Cmax) and area under the plasma concentration-time curve at time t (AUCt) were 18% (p = 0.062) and 26% (p < 0.001), respectively. For the 2 major circulating metabolites, OPC-13015 and OPC-13213, the OPC-13015 Cmax and AUCt increased by 29 and 69%, respectively (p < 0.001). However, for OPC-13213, the Cmax and AUCt decreased by 22 and 31%, respectively (p < 0.001). The plasma protein binding of cilostazol was unaffected by coadministration of omeprazole.

CONCLUSIONS

Coadministration of cilostazol with omeprazole resulted in an increase in the systemic exposure of cilostazol and its active metabolite, OPC-13015, by 26 and 69%, respectively. For the other active metabolite, OPC-13213, systemic exposure decreased by 31% because of inhibition of cilostazol metabolism to this metabolite. These changes in systemic exposure were well tolerated. A dose of 50 mg cilostazol twice a day should be considered during coadministration of inhibitors of CYP2C19, such as omeprazole.

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.

Evaluation of omeprazole, lansoprazole, pantoprazole, and rabeprazole in the treatment of acid-related diseases

OBJECTIVE

To review the comparative efficacy and safety of the proton pump inhibitors (PPIs)--omeprazole, lansoprazole, pantoprazole, and rabeprazole--in the management of acid-related diseases.

DATA SOURCES

English-language journal articles retrieved from a MEDLINE search from 1990 to the present using these index terms: proton pump inhibitors, omeprazole, lansoprazole, pantoprazole, rebeprazole, and each of the acid-related diseases.

STUDY SELECTION

Clinical trials and pertinent review articles that discussed the pharmacology, pharmacokinetics, efficacy, and safety of PPIs in the management of acid-related disease.

DATA EXTRACTION

By the authors.

DATA SYNTHESIS

PPIs are substituted benzimidazoles that inhibit gastric acid secretion by covalently binding to the proton pump (H+/K+ ATPase). All undergo extensive hepatic metabolism and conjugation. The four agents differ in their metabolism by and effects on specific hepatic enzymes and thus in their ability to interact with other medications. PPIs are important agents used for eradicating Helicobacter pylori, in treating peptic ulcer disease, gastroesophageal reflux disease, Zollinger-Ellison syndrome, and upper gastrointestinal bleeding, and for preventing acid aspiration. Short-term side effects of the four agents are similar. The long-term safety of pantoprazole and rabeprazole appears similar to that of omeprazole and lansoprazole. Pantoprazole, which is in the final stages of approval for marketing in the United States, will be available in both an oral and injectable formulation.

CONCLUSION

Based on superior efficacy profiles, PPIs are the drugs of choice in managing patients with peptic ulcer disease, gastroesophageal reflux disease, and Zollinger-Ellison syndrome. The decision to select one PPI versus another is most likely to be based on the agents' acquisition costs, formulations, FDA-labeled indications, and overall safety profiles. Intravenous or parenteral pantoprazole may become the preferred antisecretory agent for patients unable to take oral medications (e.g., critically ill patients and those with Zollinger-Ellison syndrome).

Lack of pharmacokinetic interaction between lansoprazole and intravenously administered phenytoin

The objective of this randomized, double-blind, two-period crossover study was to investigate whether concomitant steady-state lansoprazole influences the pharmacokinetics of CYP2C9 substrates using single intravenously dosed phenytoin as a model substrate. In addition, the safety of concomitant administration of these two drugs was evaluated. Twelve healthy, nonsmoking, adult male subjects received 60 mg lansoprazole or placebo once daily for 9 days during each study period. On the morning of day 7, each subject received a single 250 mg intravenous phenytoin dose. There were no statistically significant differences between the two regimens for mean phenytoin Cmax or tmax. There was a minor (< 3%) but statistically significant difference between the two regimens for phenytoin AUC resulting from a very low intrasubject coefficient of variation (2.3%). The treatment and control mean plasma concentration phenytoin profiles were virtually super-imposable. In conclusion, concomitant multidose lansoprazole administration is unlikely to have any clinically significant effect on the pharmacokinetics of CYP2C9 substrates in general or intravenous phenytoin specifically.

Prevalence of potential proton-pump inhibitor drug interactions: a retrospective review of prescriptions in community pharmacies

Drug interactions are a major cause of drug-related problems. This study assessed the comparative frequency of potential drug-drug interactions in patients receiving either omeprazole or lansoprazole. We reviewed prescription data from 144 community pharmacies in 25 states for the period of October 12, 1996, through October 20, 1997, from which the rates at which patients received either proton-pump inhibitor concurrently with > or =1 potentially interacting drugs were determined. A total of 7306 patients received only omeprazole, and 2486 received only lansoprazole. In this sample, 722 patients (9.9%) who received omeprazole also received a potentially interacting medication at the same time, compared with 8 patients (0.3%) who received lansoprazole (P<0.001). These data suggest that clinicians should be conscientious when selecting or dispensing drugs for patients taking omeprazole, given the relatively high prevalence of potential drug interactions in clinical practice.

Lack of drug interaction between omeprazole, lansoprazole, pantoprazole and theophylline

AIMS

Theophylline is a model substrate of cytochrome P4501A2. The ability of the proton pump inhibitors (PPI) omeprazole, lansoprazole and pantoprazole to induce cytochrome P4501A2 has not yet been unequivocally resolved. The aim of this comprehensive study was to compare directly the effect of the three PPI on the absorption and disposition of theophylline.

METHODS

Twenty healthy, nonsmoking, male and female volunteers (extensive metabolisers of cytochrome P4502C19 and Helicobacter pylori negative) participated in a randomized, double-blind, four-period, placebo-controlled crossover study. In each of the four periods they received either omeprazole (40 mg), lansoprazole (60 mg), pantoprazole (80 mg) or placebo once daily for 10 days. Sustained release theophylline (350 mg twice daily) was coadministered from day 8-10. Pharmacokinetics of theophylline as well as of all three PPI were determined at steady-state (day 10).

RESULTS

In all periods, point estimates and 90% confidence intervals of the area under the concentration-time curves (AUC), maximum steady-state concentrations and peak-trough fluctuations of theophylline were not altered by PPI pretreatment and met the required limits for bioequivalence. Point estimates (90% confidence intervals) of the AUC ratios of theophylline plus PPI to theophylline alone were 0.92 (0.87-0.97), 0.90 (0.85-0.95) and 1.00 (0.95-1.06) for omeprazole, lansoprazole and pantoprazole, respectively.

CONCLUSIONS

Concomitant intake of omeprazole, lansoprazole or pantoprazole at high therapeutic doses does not affect the absorption and disposition of theophylline.

Reliability of the omeprazole hydroxylation index for CYP2C19 phenotyping: possible effect of age, liver disease and length of therapy

AIMS

To evaluate the reliability of the omeprazole hydroxylation index as a marker for polymorphic CYP2C19 activity in a Japanese population of healthy young subjects (n = 78) and patients with peptic ulcer (n = 72).

METHODS

Healthy subjects were administered a single dose of omeprazole (20 mg), whereas patients received 20 mg daily for at least 1 week. The ratio of the serum concentration of omeprazole to hydroxyomeprazole at 3 h postdose was determined and used as a measure of CYP2C19 activity. The CYP2C19 wild type (wt) gene and four mutant alleles associated with the poor metaboliser phenotype of (S)-mephenytoin, CYP2C19*2 in exon 5, CYP2C19*3 in exon 4, CYP2C19m4 in exon 9, and CYP2C19m3 in the initial codon were analysed.

RESULTS

In the healthy volunteer study there was complete concordance between genotype and phenotype. However, eight of the patients who had the EM genotype had a high value for their hydroxylation index, and were classified as phenotypic PMs. No CYP2C19m4 and CYP2C19m3 mutations were detected in the eight mismatched patients. They were all genotypic heterozygous EMs, elderly (> or = 65 years) and/or had hepatic disease. Therefore, impaired CYP2C19 activity combined with partial saturation of omeprazole metabolism during multiple dosing may have contributed to the discrepancy between CYP2C19 genotyping and phenotyping.

CONCLUSION

Although omeprazole has been used instead of mephenytoin as a probe for polymorphic CYP2C19, it does not appear to be reliable enough for clinical application in Japanese patients.

Clinically important pharmacokinetic drug-drug interactions: role of cytochrome P450 enzymes

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues and many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In the future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Genetic determinants of drug responsiveness and drug interactions

Six cytochrome P450 enzymes mediate the oxidative metabolism of most drugs in common use: CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. These enzymes have selective substrate specificity, and their activity is characterized by marked interindividual variation. Some of these systems (CYP2C19, CYP2D6) are polymorphically distributed; thus, a subset of the population may be genetically deficient in enzyme activity. Phenotyping procedures designed to identify subjects with impaired metabolism who may be at increased risk for drug toxicity have been developed and validated. This has been supplemented in recent years by the availability of genetic analysis and the identification of specific alleles that are associated with altered (i.e., reduced, deficient, or increased) enzyme activity. The potential of genotyping to predict pharmacodynamics holds great promise for the future because it does not involve the administration of exogenous compound and is not confounded by drug therapy. Drug interactions caused by the inhibition or induction of oxidative drug metabolism may be of great clinical importance because they may result in drug toxicity or therapeutic failure. Further understanding of cytochrome P450 complexity may allow, through a combined in vitro-in vivo approach, the reliable prediction and possible prevention of deleterious drug interactions.

A Comparison of Retrospective and Concurrent Drug Utilization Review of Omeprazole

Objective:

To compare the appropriateness of omeprazole prescriptions in a concurrent drug utilization review (DUR) with the assessed appropriateness of a retrospective DUR.

Methods:

A retrospective DUR of omeprazole was conducted on prescriptions written from August 23, 1993, to October 8, 1993, in a 340-bed university hospital. This DUR served as a baseline for a concurrent DUR that began on January 27, 1995, and ended on March 16, 1995. The concurrent DUR integrated three steps aimed at improving the quality of omeprazole use: Approval of the criteria by the pharmacology and therapeutics committee of the hospital, distribution of a drug bulletin to all physicians, and a pharmacist's verbal recommendations to physicians whose prescriptions did not meet explicit criteria.

Results:

Twenty-nine and 64 prescriptions were reviewed in the retrospective and concurrent DURs, respectively. During the concurrent DUR, the pharmacist made 34 verbal recommendations. Of these, 25 (74%) were agreed to by the prescribers. In comparison with the retrospective DUR, the percentage of prescriptions meeting the criteria of indication, combination therapy, and dosage went from 38% to 75% (p < 0.05), from 76% to 95% (p < 0.05), and from 83% to 100% (p > 0.05), respectively, during the concurrent DUR.

Conclusions:

The concurrent DUR appeared to successfully improve the quality of omeprazole utilization in the hospital.

Pharmacokinetic drug interactions with anti-ulcer drugs

The safety profile of any pharmacological agent is defined on the basis of its toxicity, tolerability and potential for pharmacokinetic and/or pharmacodynamic interactions with other compounds, which may belong to the same or to a different pharmacological class. Drug-drug interactions are important in clinical practice because short and long term therapeutic regimens frequently require coadministration of different drugs. The pharmacological treatment of gastric and duodenal ulcers (and of related syndromes) includes older and newer compounds, which have different mechanisms of action and exert different therapeutic effects. These compounds are widely prescribed in combination with other drugs being given for the treatment of concomitant diseases. This article reviews pharmacokinetic interactions with anti-ulcer drugs, paying particular attention to those which have clinically relevant adverse effects. Drugs mentioned in the literature as causing any pharmacokinetic interaction with anti-ulcer compounds are considered in this article.