Omeprazole in the treatment of Zollinger-Ellison syndrome: a 4-year international study

Long-Term Proton Pump Inhibitor-Acid Suppressive Treatment Can Cause Vitamin B12 Deficiency in Zollinger-Ellison Syndrome (ZES) Patients

Whether the long-term treatment of patients with proton pump inhibitors (PPIs) with different diseases [GERD, Zollinger-Ellison syndrome (ZES), etc.] can result in vitamin B12 (VB12) deficiency is controversial. In this study, in 175 patients undergoing long-term ZES treatment with anti-acid therapies, drug-induced control acid secretory rates were correlated with the presence/absence of VB12 deficiency, determined by assessing serum VB12 levels, measurements of VB12 body stores (blood methylmalonic acid (MMA) and total homocysteine[tHYC]), and other features of ZES. After a mean of 10.2 yrs. of any acid treatment (5.6 yrs. with PPIs), 21% had VB12 deficiency with significantly lower serum and body VB12 levels (p < 0.0001). The presence of VB12 deficiency did not correlate with any feature of ZES but was associated with a 12-fold lower acid control rate, a 2-fold higher acid control pH (6.4 vs. 3.7), and acid control secretory rates below those required for the activation of pepsin (pH > 3.5). Over a 5-yr period, the patients with VB12 deficiency had a higher rate of achlorhydria (73% vs. 24%) and a lower rate of normal acid secretion (0% vs. 49%). In conclusion, in ZES patients, chronic long-term PPI treatment results in marked acid hyposecretion, resulting in decreased serum VB12 levels and decreased VB12-body stores, which can result in VB12 deficiency.

Insights into Effects/Risks of Chronic Hypergastrinemia and Lifelong PPI Treatment in Man Based on Studies of Patients with Zollinger-Ellison Syndrome

The use of proton pump inhibitors (PPIs) over the last 30 years has rapidly increased both in the United States and worldwide. PPIs are not only very widely used both for approved indications (peptic ulcer disease, gastroesophageal reflux disease (GERD), Helicobacter pylori eradication regimens, stress ulcer prevention), but are also one of the most frequently off-label used drugs (25–70% of total). An increasing number of patients with moderate to advanced gastroesophageal reflux disease are remaining on PPI indefinitely. Whereas numerous studies show PPIs remain effective and safe, most of these studies are <5 years of duration and little data exist for >10 years of treatment. Recently, based primarily on observational/epidemiological studies, there have been an increasing number of reports raising issues about safety and side-effects with very long-term chronic treatment. Some of these safety issues are related to the possible long-term effects of chronic hypergastrinemia, which occurs in all patients taking chronic PPIs, others are related to the hypo-/achlorhydria that frequently occurs with chronic PPI treatment, and in others the mechanisms are unclear. These issues have raised considerable controversy in large part because of lack of long-term PPI treatment data (>10–20 years). Zollinger–Ellison syndrome (ZES) is caused by ectopic secretion of gastrin from a neuroendocrine tumor resulting in severe acid hypersecretion requiring life-long antisecretory treatment with PPIs, which are the drugs of choice. Because in <30% of patients with ZES, a long-term cure is not possible, these patients have life-long hypergastrinemia and require life-long treatment with PPIs. Therefore, ZES patients have been proposed as a good model of the long-term effects of hypergastrinemia in man as well as the effects/side-effects of very long-term PPI treatment. In this article, the insights from studies on ZES into these controversial issues with pertinence to chronic PPI use in non-ZES patients is reviewed, primarily concentrating on data from the prospective long-term studies of ZES patients at NIH.

Role of acid suppressants in patients with Zollinger-Ellison syndrome

Virtually all symptoms in patients with Zollinger-Ellison syndrome are due to acid hypersecretion, thus the control of acid secretion is the first and most important step in the management of patients with this syndrome. Antisecretory medication is prescribed as soon as the diagnosis of Zollinger-Ellison syndrome is made, as patients may bleed or perforate with little warning. Acid output is reduced to less than 10 mmol/h to heal mucosal lesions, but in patients with a Billroth I or II gastrectomy and those with severe oesophagitis and stricture formation, acid output is reduced to less than 5 or less than 1 mmol/h. Acid output and not symptomatic response is a reliable guide of the adequacy of therapy. In sufficient doses, all H2-receptor antagonists are useful; however, side effects associated with cimetidine therapy limit its use. The ratio of potencies of cimetidine:ranitidine:famotidine is 1:4:32. Ranitidine given as a 50-mg intravenous bolus, followed by a continuous infusion of 0.5 mg.kg/h, controls acid hypersecretion acutely in patients with Zollinger-Ellison syndrome. Acid output is checked after 4 h, and the dose increased until acid output is less than 10 mmol/h. In 70% of patients with Zollinger-Ellison syndrome, 1 mg.kg/h reduces acid output to less than 10 mmol/h; however, doses up to 4 mg.kg/h have been used. When patients are switched to oral ranitidine, a useful dosage conversion is to administer 1.5 times the total daily intravenous dose in four equal doses every 6 h. Four doses of oral drug are given before the infusion is stopped. Six hours after the first/last oral dose, acid output is checked. In our patients, the mean dose of ranitidine was 2100 mg/day (range, 450-9200 mg/day). No serious toxicity was observed. Omeprazole, which has a long duration of action and is a potent inhibitor of gastric acid secretion, has simplified management. Once-daily dosing is sufficient in most patients, and a reasonable starting dose is 60 mg daily. The dose may be increased to 120 mg once daily; if this dosage fails to control acid secretion, 60 mg is administered every 12 h. In our studies, the median dose was 90 mg/day (range, 20-120 mg/day). Omeprazole was more effective than H2-receptor antagonists in providing symptom relief and mucosal healing and did not cause significant toxicity. In particular, no gastric carcinoid tumours developed during four years of use. Omeprazole is, therefore, the treatment of choice for control of acid secretion in patients with Zollinger-Ellison syndrome.(ABSTRACT TRUNCATED AT 400 WORDS)

Prospective study of the long-term efficacy and safety of lansoprazole in patients with the Zollinger-Ellison syndrome

The long-term safety and efficacy of lansoprazole were studied in 21 patients with Zollinger-Ellison syndrome. The initial maintenance dose was determined by acid inhibition studies. In all patients lansoprazole controlled gastric acid hypersecretion and peptic symptoms in both the short and long term. Patients were treated for a mean of 31 months (range 1-43 months) with all but 4 patients followed for > 18 months. The mean initial dose was 60 mg/day, with 2 patients requiring a twice daily dose and the others a single daily dose. During long-term treatment 6 patients required an increased dosage, 5 within the first year. Long-term maintenance doses were reduced in 5 of the 6 patients in whom this was attempted. No changes in serum gastrin concentration, haematological parameters, liver function studies or other biochemical parameters occurred due to lansoprazole. No patient developed a gastric carcinoid tumour while being treated with lansoprazole. These results demonstrate that long-term treatment with lansoprazole is both safe and effective in patients with Zollinger-Ellison syndrome, and suggest that this drug will be useful in such patients. Furthermore, maintenance doses of lansoprazole, determined by the currently recommended method of acute acid titration studies in patients with Zollinger-Ellison syndrome, are too high.

Serum gastrin in Zollinger-Ellison syndrome: II. Prospective study of gastrin provocative testing in 293 patients from the National Institutes of Health and comparison with 537 cases from the literature. evaluation of diagnostic criteria, proposal of new criteria, and correlations with clinical and tumoral features

In two-thirds of patients with Zollinger-Ellison syndrome (ZES), fasting serum gastrin (FSG) levels overlap with values seen in other conditions. In these patients, gastrin provocative tests are needed to establish the diagnosis of ZES. Whereas numerous gastrin provocative tests have been proposed, only the secretin, calcium, and meal tests are widely used today. Many studies have analyzed gastrin provocative test results in ZES, but they are limited by small patient numbers and methodologic differences. To address this issue, we report the results of a prospective National Institutes of Health (NIH) study of gastrin provocative tests in 293 patients with ZES and compare these data with those from 537 ZES and 462 non-ZES patients from the literature. In 97%-99% of gastrinoma patients, an increase in serum gastrin post secretin (Delta secretin) or post calcium (Delta calcium) occurred. In NIH ZES patients with <10-fold increase in FSG, the sensitivity/specificity of the widely used criteria were as follows: Delta secretin > or =200 pg/mL (83%/100%), Delta secretin >50% (86%/93%), Delta calcium > or =395 pg/mL (54%/100%), and Delta calcium >50% (78%/83%). A systematic analysis of the sensitivity and specificity of other possible criteria for a positive secretin or calcium test allowed us to identify a new criterion for secretin testing (Delta > or =120 pg/mL) with the highest sensitivity/specificity (94%/100%) and to confirm the commonly used criterion for calcium tests (Delta > or =395 pg/mL) (62%/100%). This analysis further showed that the secretin test was more sensitive than the calcium test (94% vs. 62%). Our results suggest that secretin stimulation should be used as the first-line provocative test because of its greater sensitivity and simplicity and lack of side effects. In ZES patients with a negative secretin test, 38%-50% have a positive calcium test. Therefore the calcium test should be considered in patients with a strong clinical suspicion of ZES but a negative secretin test. Furthermore, we found that some clinical (diarrhea, duration of medical treatment), laboratory (basal acid output), and tumoral (size, extent) characteristics correlate with the serum gastrin increase post secretin and post calcium. However, using the proposed criteria, the result of these provocative tests (that is, positive or negative) is minimally influenced by these factors, so secretin and calcium provocative tests are reliable in patients with different clinical, laboratory, and tumor characteristics. A systematic analysis of meal testing showed that 54%-77% of ZES patients have a <50% postprandial serum gastrin increase. However, 9%-20% of ZES patients had a >100% increase post meal, causing significant overlap with antral syndromes. Furthermore, we could not confirm the usefulness of meal tests for localization of duodenal gastrinomas. We conclude that the secretin test is a crucial element in the diagnosis of most ZES patients, the calcium test may be useful in selected patients, but the meal test is not helpful in the management of ZES. For secretin testing, the criterion with the highest sensitivity and specificity is an increase of > or =120 pg/mL, which should replace other criteria commonly used today.

Serum gastrin in Zollinger-Ellison syndrome: I. Prospective study of fasting serum gastrin in 309 patients from the National Institutes of Health and comparison with 2229 cases from the literature

The assessment of fasting serum gastrin (FSG) is essential for the diagnosis and management of patients with the Zollinger-Ellison syndrome (ZES). Although many studies have analyzed FSG levels in patients with gastrinoma, limited information has resulted from these studies because of their small size, different methodologies, and lack of correlations of FSG levels with clinical, laboratory, or tumor features in ZES patients. To address this issue, we report the results of a prospective National Institutes of Health (NIH) study of 309 patients with ZES and compare our results with those of 2229 ZES patients in 513 small series and case reports in the literature. In the NIH and literature ZES patients, normal FSG values were uncommon (0.3%-3%), as were very high FSG levels >100-fold normal (4.9%-9%). Two-thirds of gastrinoma patients had FSG values <10-fold normal that overlap with gastrin levels seen in more common conditions, like Helicobacter pylori infection or antral G-cell hyperplasia/hyperfunction. In these patients, FSG levels are not diagnostic of ZES, and gastrin provocative tests are needed to establish the diagnosis. Most clinical variables (multiple endocrine neoplasia type 1 status, presence or absence of the most common symptoms, prior medical treatment) are not correlated with FSG levels, while a good correlation of FSG values was found with other clinical features (prior gastric surgery, diarrhea, duration from onset to diagnosis). Increasing basal acid output, but not maximal acid output correlated closely with increasing FSG. Numerous tumoral features correlated with the magnitude of FSG in our study, including tumor location (pancreatic > duodenal), primary size (larger > smaller) and extent (liver metastases > local disease). In conclusion, this detailed analysis of FSG in a large number of patients with ZES allowed us to identify important clinical guidelines that should contribute to improved diagnosis and management of patients with ZES.

Three-year oral pantoprazole administration is effective for patients with Zollinger-Ellison syndrome and other hypersecretory conditions

BACKGROUND

Zollinger-Ellison syndrome and idiopathic hypersecretion are gastrointestinal hypersecretory conditions requiring long-term maintenance.

AIMS

The safety and efficacy data for short-term (6-month) treatment of Zollinger-Ellison syndrome and idiopathic hypersecretion with oral pantoprazole were previously published. This study extends the initial observations to 3 years.

METHODS

The primary efficacy end point for this report was the control of gastric acid secretion in the last hour before the next dose of oral pantoprazole (acid output of <10 mmol/h; <5 mmol/h in subjects with prior acid-reducing surgery). Dose titration was permitted to a maximum of 240 mg per 24 h.

RESULTS

Twenty-four subjects completed the study. The acid output of 28 of 34 subjects was controlled at initial enrolment. The mean acid output rates were <10 mmol/h throughout the 36 months of treatment for 90-100% of the patients. The majority of the patients were controlled with b.d. doses of 40 or 80 mg pantoprazole at 36 months (acid output was controlled in 24 of 24 subjects). Pantoprazole was generally well tolerated with minimal adverse events reported.

CONCLUSIONS

Maintenance oral pantoprazole therapy up to 3 years at dosages of 40-120 mg b.d. was effective and well tolerated in patients with Zollinger-Ellison syndrome and other hypersecretory conditions.

Treatment of Zollinger-Ellison Syndrome

In this article, we have reviewed the main therapeutic measures for the treatment of Zollinger-Ellison syndrome (ZES). Review of the literature was based on computer searches (Pub-Med, Index Medicus) and personal experiences. We have evaluated all the measures now available for treating patients with sporadic gastrinomas or gastrinomas associated with Multiple Endocrine Neoplasia Type 1, (MEN 1) including medical therapy such as antisecretory drugs and somatostatin analogs (SST), chemotherapy and chemoembolization, and surgical procedures. In ZES patients, the best therapeutic procedure is surgery which, if radical, can be curative. Medical treatment can be the best palliative therapy and should be used, when possible, in association with surgery, in a multimodal therapeutic approach.

Review article: Esomeprazole--enhanced bio-availability, specificity for the proton pump and inhibition of acid secretion

Esomeprazole, the S-isomer of omeprazole, is the first proton pump inhibitor available for clinical use as a single isomer. It demonstrates pharmacological and clinical benefits beyond those seen with the racemic omeprazole. Esomeprazole has higher and more consistent bio-availability than omeprazole, which results in a greater area under the plasma concentration-time curve. It is the area under the plasma concentration-time curve of omeprazole and esomeprazole that determines how much of each reaches the parietal cell, and thus the control of gastric acid secretion that is achieved. Esomeprazole, like other proton pump inhibitors, has a high specificity for the acidic environment of the parietal cell, where it is accumulated, activated and covalently inhibits the proton pump. Proton pumps elsewhere in the body do not achieve the level of acidity needed for accumulation and activation. Esomeprazole, 40 mg once daily, provides more effective control of gastric acid secretion than omeprazole, 20 or 40 mg once daily, and all other proton pump inhibitors given at their standard doses. This translates into greater clinical effect compared with omeprazole, 20 mg once daily, and lansoprazole, 30 mg once daily, in the management of reflux disease. Esomeprazole therapy is well tolerated, with a low adverse events profile, similar to that seen with omeprazole.

Maintenance oral pantoprazole therapy is effective for patients with Zollinger-Ellison syndrome and idiopathic hypersecretion

OBJECTIVE

Maintenance proton pump inhibitor (PPI) therapy is effective for gastric acid hypersecretory states, although data with pantoprazole are limited. The aim of this study was to evaluate the safety and efficacy of long term p.o. pantoprazole in individuals with hypersecretion.

METHODS

All subjects had Zollinger-Ellison syndrome or idiopathic hypersecretion. Baseline acid output was measured in the presence of prior maintenance antisecretory therapy before pantoprazole exposure. The starting dose was 40 mg b.i.d. in most cases, and the dose was adjusted to document control within the first 2 wk of therapy. The maximal allowable dose was 240 mg daily. Acid output was measured on day 28 and then quarterly from month 3. The primary efficacy endpoint was documented control of acid secretion at 6 months, i.e., acid output in the last 1 h before the next dose of therapy of <10 mEq/h (<5 mEq/h in subjects with prior acid-reducing surgery).

RESULTS

A total of 26 subjects had Zollinger-Ellison syndrome (six with multiple endocrine neoplasia syndrome type 1) and nine had idiopathic hypersecretion. Pre-enrollment therapy included omeprazole in 27 subjects and lansoprazole in eight, and 82.4% of subjects were controlled on their prior regimens. With upward dose titration, acid output was controlled in all subjects by day 10 and in all but two (6%) at the 6-month time point. Median acid secretion on therapy at 6 months was <2 mEq/h (mean 2.2 mEq/h; range 0-10.5 mEq/h) at a dose of 40 mg b.i.d. for 24 subjects, 80 mg b.i.d. for seven subjects, and 120 mg b.i.d. for two subjects. During the course of the study, five subjects required doses of 240 mg daily. Pantoprazole was generally well tolerated. No cases of anterior optic ischemic neuropathy occurred. Five subjects died during follow-up, all because of events unrelated to the study drug.

CONCLUSIONS

Maintenance p.o. pantoprazole therapy at a dose of 80-240 mg/day in divided doses was both effective and generally well tolerated for patients with Zollinger-Ellison syndrome and idiopathic hypersecretion.

Optimal Treatment of Zollinger-Ellison Syndrome and Related Conditions in Elderly Patients

Zollinger-Ellison syndrome is characterised by refractory peptic ulcer disease, severe diarrhoea and gastric acid hypersecretion associated with an islet-cell tumour of the pancreas (gastrinoma). The true incidence and prevalence of this rare disease is unknown; in the US, the frequency is one per one million people and the age at presentation varies from 7 to 90 years. Zollinger-Ellison syndrome is sporadic in 62-80% of cases and in 20-38% of cases is associated with multiple endocrine neoplasia type 1 (MEN 1). The diagnosis of Zollinger-Ellison syndrome is certain when the plasma gastrin is >1000 pg/mL and the basal acid output is >15 mEq/h in patients with an intact stomach, >5 mEq/h in gastrectomised patients, or when this hypergastrinemia is associated with a pH <2. The treatment is based on control of gastric acid hypersecretion and of the malignant tumour and its possible metastases. Proton pump inhibitors are the most effective antisecretory drugs and can be administered in the elderly at high dosages without drug-related adverse effects. As an initial therapy, daily dosages of omeprazole 80-100 mg or pantoprazole 40-160 mg are employed. In long-term treatment the doses can be greatly reduced once effective control of the gastric output has been established. Intravenous proton pump inhibitors may be administered when patients cannot take oral therapy, particularly in acute conditions. All sporadic localised gastrinomas should be excised if possible. When liver metastases are also present, their debulking may improve symptoms and survival, and facilitate medical treatment. There is some controversy as to the surgical approach for gastrinomas associated with MEN 1. Somatostatin analogues can be useful in reducing gastric acid hypersecretion, serum gastrin and gastric enterochromaffin-like (ECL) cells and can thus contribute to treating the disease more effectively. Their antiproliferative effect can be used in treating liver metastases. Chemotherapy is not the therapy of choice in patients with gastrinomas and is indicated only in those with malignant progressive disease; interferon alpha, embolisation and chemoembolisation are not advisable for the elderly. The treatment of elderly Zollinger-Ellison syndrome patients, similarly to all elderly oncological patients, should be based on the use of comprehensive geriatric assessment. This will enable the clinician to define the functional status of the elderly person, to decide whether the patient can tolerate surgery and/or the stress of antineoplastic therapy, and finally, to determine whether this patient can tolerate an aggressive treatment for Zollinger-Ellison syndrome or whether the only possible choice is palliative relief of symptoms.

Vitamin B12 levels during prolonged treatment with proton pump inhibitors

Reduced serum vitamin B12 (cobalamin) levels have been documented occasionally during long-term treatment with a proton pump inhibitor (PPI) in selected groups of patients. This has largely been confined to patients being treated for Zollinger-Ellison syndrome who have sustained drug-induced achlorhydria, which does not ordinarily occur during treatment with a PPI. An appreciation of normal cobalamin metabolism and the pharmacological action of the PPIs adequately explain the mechanism for this reduction. PPIs do not promote the development of pernicious anemia.

Review article: rabeprazole's tolerability profile in clinical trials

Rabeprazole is a new member of a class of substituted benzimidazole drugs known as proton pump inhibitors. Comparative trials have demonstrated that it is at least as effective as omeprazole for the treatment of gastrooesophageal reflux disease (GERD), duodenal ulcers, or gastric ulcers. It is significantly more effective than histamine2-receptor antagonists for acid suppression, GERD healing and pain relief, and duodenal ulcer healing and pain relief. Adverse events reported during clinical trials provide an important indication of a medication's tolerability. We demonstrate that rabeprazole has a favourable adverse events profile. It is well tolerated in placebo-controlled studies and comparative trials with omeprazole and H2-receptor antagonists. Moreover, no dose adjustments are required for special populations, such as the elderly or patients with renal or mild-to-moderate hepatic disease. Adverse events data from clinical trials support the use of rabeprazole as a treatment for acid-related diseases.

Effect of omeprazole, lansoprazole, and ranitidine on the DNA synthesis of mononuclear cells

OBJECTIVE

To examine and compare the effects of omeprazole, lansoprazole, and ranitidine on the DNA synthesis of peripheral blood mononuclear cells.

DESIGN

Ex vivo laboratory study.

SETTING

Clinical research laboratory of an academic medical center.

SUBJECTS

Healthy volunteers.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Venous blood was collected from normal subjects and peripheral blood mononuclear cells (PBMCs) were isolated using centrifugation techniques over a Ficoll-Hypaque density gradient. PBMCs were added to 12-well culture plates in four groups of media: a) control; b) control plus lansoprazole (25 microg/mL); c) control plus omeprazole (0.35 microg/mL); and d) control plus ranitidine (50 microg/mL). PBMCs were exposed to the drug for 96 hrs, with addition of phytohemagglutinin (2.5 microg/ mL) for the last 48 hrs, and 3H-thymidine (1 microCi) during the final 6 hrs. PBMCs were filtered onto glass-fiber filter paper and the radioactivity was determined by scintillation counting. Since radioactivity is measured only in those cells undergoing DNA synthesis or cell division, results are expressed as quantification of 3H-thymidine uptake. Median disintegrations per min (DPM)/number of PBMCs per well+/-SEM are reported: control 68.3+/-37.8; ranitidine 38.4 +/-94.2; lansoprazole 14.6+/-84.4; and omeprazole 15.1+/-48.9. There was a significant difference between lansoprazole vs. ranitidine (p< .01), and omeprazole vs. ranitidine (p< .05), and no significant difference between lansoprazole and omeprazole.

CONCLUSIONS

This is the first study to compare the potential immunomodulating effects of these commonly used agents. Ranitidine caused increased DNA synthesis in PBMCs when compared with lansoprazole and omeprazole. This phenomenon may be an important, often disregarded, effect of histamine-2-receptor antagonists when used in postsurgical or trauma patients who have T-lymphocyte-mediated immune suppression.

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.

Omeprazole-induced acute interstitial nephritis

Omeprazole is a proton pump inhibitor widely used for the treatment of peptic ulcer disease. We report a patient presenting nonoliguric acute renal failure following omeprazole treatment. Both eosinophilia and eosinophiluria were observed, and the patient was diagnosed as having drug-induced acute interstitial nephritis. Renal failure spontaneously resolved when omeprazole was discontinued.

A prospective study of the effectiveness of low dose omeprazole as initial therapy in Zollinger-Ellison syndrome

BACKGROUND

The proton pump inhibitors (omeprazole and lansoprazole) are the drugs of choice for the medical management of gastric acid hypersecretion in Zollinger-Ellison syndrome (ZES). These drugs are safe for long-term therapy but are acid-labile and high doses are expensive. The recommended starting dose of omeprazole is 60 mg/day. However, it has been shown in recent studies that the maintenance dose of omeprazole could be safely reduced to 20 mg once or twice a day in more than two-thirds of patients with ZES. The purpose of this study is to determine if an initial starting dose of omeprazole 20 mg/day is safe and effective in patients with ZES.

METHODS

Forty-nine consecutive patients with ZES being treated with ranitidine for at least 2 weeks were admitted to the NIH. Omeprazole 20 mg was started on day 1 of the admission and ranitidine discontinued 4 h after the first dose. Gastric acid output was measured for 1 h prior to the next omeprazole dose on day 2, then on day 3 if the value was > 10 mmol/h on the previous day. If acid-peptic symptoms developed or the gastric acid output remained > 10 mmol/h on day 3, the patient was considered to have failed omeprazole 20 mg/day initial therapy and the dose titrated daily to achieve adequate control of acid-peptic symptoms and gastric secretion.

RESULTS

In 33 of the 49 patients (68%) omeprazole 20 mg/day was successful as initial therapy. Sixteen patients (32%) failed this initial omeprazole dose (eight patients owing to persistent peptic symptoms and eight patients owing to inadequate acid control). The final daily omeprazole dose required in these patients was 40 mg in eight patients (16%), 60 mg in one patient (2%) and 80 mg in seven patients (14%). Basal acid output (BAO) was the only clinical or laboratory feature that was significantly different between the two groups in which low dose initial omeprazole therapy was or was not successful; all patients with basal acid output < 20 mmol/h had a successful outcome.

CONCLUSIONS

Because of the need to rapidly control gastric acid hypersecretion owing to the high risk of complications from peptic ulcer disease, patients with ZES should continue to be started on omeprazole 60 mg/day and the dose adjusted by acute titration methods as is currently recommended. After a maintenance dose is established, attempts should be undertaken to reduce the dose to 20 mg/ day once or twice a day. Only the minority of patients with ZES in whom basal acid output is known to be < 20 mmol/h (20% of patients) should be started on a low initial omeprazole dose.

A double-blind study of pantoprazole and ranitidine in treatment of acute duodenal ulcer. A multicenter trial. European Pantoprazole Study Group

Pantoprazole is a new substituted benzimidazole, which is a potent inhibitor of gastric acid secretion by its inhibition of H+,K(+)-ATPase. Pantoprazole, 40 mg, was compared with the H2-receptor antagonist ranitidine, 300 mg, in the healing of acute duodenal ulcer. Two hundred seventy-six patients with endoscopically diagnosed duodenal ulcer were studied in this multicenter double-blind study. Patients were reendoscopied after two weeks of treatment, and those patients whose ulcers remained unhealed were also endoscoped after an additional two weeks of treatment. The primary end point was the complete healing of the ulcer. Demographic characteristics were comparable in both treatment groups. After two weeks of treatment, 90/124 (73%) patients in the pantoprazole group had healed ulcers compared with 57/126 (45%) patients in the ranitidine group (P < 0.001, per-protocol analysis). After four weeks, the cumulative healing rates were 92% and 84% in the pantoprazole and ranitidine groups, respectively (P = 0.073). Symptoms were also improved at week 2, with 84% and 72% of patients in the pantoprazole and ranitidine groups, respectively, reporting no ulcer pain (P < 0.05, per-protocol analysis). Both treatments were well tolerated. This study has confirmed the superiority of pantoprazole compared with ranitidine in the healing of duodenal ulcers and pain relief after two weeks of treatment and has shown pantoprazole to be well tolerated in this indication.

Use of omeprazole in Zollinger-Ellison syndrome: a prospective nine-year study of efficacy and safety

H+, K(+)-ATPase inhibitors such as omeprazole are the antisecretory agents of choice for the management of gastric acid hypersecretory states, including the Zollinger-Ellison syndrome. However, long-term follow-up data on the overall efficacy and safety of these agents in large numbers of patients are lacking. In the current study we examined the long-term efficacy and safety of omeprazole in 116 patients with Zollinger-Ellison syndrome treated with oral omeprazole at a single centre for up to 114 months (mean +/- S.E.M. = 38 +/- 3 months). The initial omeprazole maintenance dose was established according to the acute upward dose titration method in 89/116 patients (77%). Gastric acid output was effectively controlled using 60 mg of omeprazole once daily in 41/89 patients (46%) and 22/89 patients (25%) required twice daily omeprazole therapy. The mean ranitidine equivalent dose for patients who required 60 mg omeprazole once daily (2.5 +/- 0.2 g/day) was significantly lower than the mean ranitidine equivalent dose for patients who required more than 60 mg omeprazole once daily (4.3 +/- 0.3 g/day). Long-term omeprazole maintenance therapy was discontinued in 36/116 patients (31%) but in no cases was discontinuation due either to drug-induced side-effects or uncontrolled gastric acid output. Fasting serum gastrin levels were significantly elevated above pre-treatment levels at only one time point during follow-up and were likely due to tumour growth rather than a drug effect. The final long-term omeprazole maintenance doses were lower than the initial doses but correlated closely with the pre-omeprazole basal acid output (r = 0.41, P < 0.001) and ranitidine equivalent dose requirements (r = 0.49, P < 0.001). We conclude that omeprazole effectively and safely controls gastric acid hypersecretion in all patients with Zollinger-Ellison syndrome for up to nine years without evidence by tachyphylaxis.

Review article: the management of Zollinger-Ellison syndrome

Awareness of the sometimes subtle features of Zollinger-Ellison syndrome is important in order not to miss the diagnosis. Immediately after initial diagnostic tests, the patient should be given antisecretory medication, while tests for the type of Zollinger-Ellison syndrome and tumour extent can be delayed. Acid output should be decreased to < 10 mmol/h to control symptoms and prevent complications. Histamine H2-antagonists remain the best available intravenous therapy but omeprazole is the most effective long-term oral therapy and has proved to be safe in nearly 10 years of continuous use. The management of the gastrinoma has changed in recent years since the discovery that the majority of gastrinomas arise outside the pancreas. Exploratory surgery with tumour resection is the treatment of choice in sporadic Zollinger-Ellison syndrome but there are few indications for surgery in patients with Zollinger-Ellison syndrome and multiple endocrine neoplasia type-1. None of the available therapies for metastatic gastrinoma is very effective.

Gastric endocrine cell evolution in patients with Zollinger-Ellison syndrome. Influence of gastrinoma growth and long-term omeprazole treatment

Evolution of gastrinoma tumoral mass, fasting serum gastrin concentrations, and gastric endocrine cells has been analyzed in 21 patients with the Zollinger-Ellison syndrome committed to long-term omeprazole treatment (up to 7.75 years, median 37 months). Gastrinoma growth was seen in eight patients. Significant increase in serum gastrin was only observed in the group of patients with gastrinoma growth. Fundic argyrophil cell densities were correlated with serum gastrin (r' = 0.68, P = 0.002). Argyrophil and antral gastrin cell densities significantly increased during the survey, but increases were greater in the group with gastrinoma growth (respectively, +136% and +131%) than in the other group (respectively, +34% and +43%). Progression in the degree of argyrophil cell hyperplasia, noted qualitatively, was observed in 11 patients. Fundic carcinoids developed in three of these 11 patients, all three having multiple endocrine neoplasia type 1 (MEN 1). Positive linear individual correlations (r > or = 0.85) between argyrophil cell densities and corresponding durations of omeprazole treatment were found in nine of the 10 patients studied at least three times and who had a clear-cut increase in those cell densities. Thus, increase in serum gastrin and fundic argyrophil cell densities appeared closely associated with gastrinoma growth; however, duration of drug-induced hypochlorhydria may also affect cell proliferation.

Control of gastric acid hypersecretion in the management of patients with Zollinger-Ellison syndrome

During the last 5 years important advances have occurred in the control of gastric acid hypersecretion in Zollinger-Ellison syndrome (ZES). The increased availability of potent gastric acid antisecretory agents such as histamine H2-receptor antagonists and more recently the H+K(+)-ATPase inhibitors such as omeprazole and lansoprazole have made it possible to medically control acid secretion in all patients. Increased understanding of the variation in antisecretory drug dosage between individual patients has led to identification of criteria to ensure effective antisecretory control and to the recognition of subgroups of patients who require special monitoring. Effective regimens for parenteral antisecretory control during surgery have been established. The importance of parathyroidectomy in patients with multiple endocrine neoplasia type I with ZES and the possible usefulness of highly selective vagotomy have been investigated. We review here the new data that led to increased understanding in each of these areas from our studies and studies by others.

Prospective study of the need for long-term antisecretory therapy in patients with Zollinger-Ellison syndrome following successful curative gastrinoma resection

A long-term cure is now possible in more than 30% of selected patients with Zollinger-Ellison syndrome who undergo gastrinoma resection. The need, however, for continued gastric acid antisecretory therapy in these patients remains controversial. The current study was designed to determine whether post-operative antisecretory therapy is needed in patients who have undergone successful gastrinoma resection and, if so, to attempt to define criteria with which to identify patients who require therapy. Twenty-eight consecutive patients who had previously undergone curative gastrinoma resection were prospectively studied. When antisecretory therapy was discontinued, 43% (12/28) of these patients developed gastro-oesophageal reflux, diarrhoea, acid-peptic symptoms or endoscopic evidence of acid-peptic disease within 2 weeks and were deemed to have failed a trial of antisecretory drug withdrawal. The remaining 57% (16/28) of patients who successfully discontinued antisecretory therapy were followed for a mean time of 31 months after withdrawal of therapy. Analysis of acid output studies pre-operatively, as well as at the time of drug withdrawal, demonstrated that patients who were unable to discontinue antisecretory therapy exhibited higher pre-operative maximal acid output values and higher basal acid output values at the time of attempted drug withdrawal than patients who were able to discontinue therapy. Despite these findings, there was significant overlap in acid output values between groups so that it was not possible to define specific acid output criteria for successful drug withdrawal. Pre-operative clinical characteristics, such as the presence or absence of gastro-esophageal reflux or acid-peptic disease, or post-operative laboratory values, such as the fasting serum gastrin level, did not correlate with the ability to discontinue antisecretory therapy. We conclude that following successful curative gastrinoma resection, 40% of patients still require antisecretory therapy and that both symptom evaluation as well as upper endoscopy should be used to guide attempted drug withdrawal. Although patients who are not able to discontinue therapy have significantly higher acid output measurements than those who are able to discontinue therapy, neither acid output criteria nor any other laboratory or clinical characteristics are able to predict the need for continued antisecretory therapy in these patients.

Long-term treatment with octreotide in patients with the Zollinger-Ellison syndrome

This study reports the effects of 4 and 5-year treatment with octreotide (200 micrograms sc bid) in the Zollinger-Ellison syndrome (ZES). No symptoms related to acid hypersecretion were observed in the four patients throughout the study, and upper GI endoscopy was normal. Basal acid output (BAO) measured 12 h after injection, was below 10 mmol h-1 in three to four patients and previous ranitidine treatment was discontinued. In the fourth case (pretreatment BAO value: 115 mmol h-1), BAO progressively decreased to 42 mmol h-1 after 5 years of octreotide treatment. At the end of the study, serum gastrin levels were 58.5% (30-68) of the pretreatment values and two patients had normal gastrin levels. Peak acid output (PAO) decreased markedly after 2, 4 and 5 years, by 68% (35-89) suggesting that octreotide had exerted an antitrophic effect on parietal cell mass. Diffuse hyperplasia of fundic argyrophil cells present in two patients before octreotide, decreased during the treatment. Mean argyrophil cell density for all patients was not significantly modified. Antral gastrin-cell density was in the normal range. No long-term side effect of octreotide treatment was observed. Although octreotide may not be considered as a substitute for benzimidazoles in the treatment of ZES, its specific properties may be of therapeutic benefit in some ZES patients.

Efficacy of long-term therapy with low doses of omeprazole in the control of gastric acid secretion in Zollinger-Ellison syndrome patients

Thirteen patients with Zollinger-Ellison syndrome were investigated: 8 without, and 5 with, previous gastric surgery. After 7-34 months of treatment with famotidine, 8 out of 13 patients were resistant to this drug. Omeprazole 60 mg/day was administered to these 8 patients; after one month, the dose was reduced to 40 mg/day, and after another month to 20 mg/day. Basal acid secretion was inhibited by every dose of omeprazole. The patients were then treated with a low dose (20 mg/day) of omeprazole for a longer period. Periodic clinical and endoscopic assessments, and measurement of basal acid secretion showed the efficacy of this low dose of omeprazole in our Zollinger-Ellison syndrome patients. The drug was discontinued after 12-32 months of omeprazole treatment, and gastric acid recovery was evaluated. Four patients recovered 50% of their 'initial basal acid secretion' after 5 days, while two patients who had been treated with omeprazole for a longer time (30-32 months) recovered only 38 and 40%, respectively, of their 'initial basal acid secretion' at the tenth day. Our results indicate that the omeprazole dosage to be used in the treatment of Zollinger-Ellison syndrome must be chosen principally on the basis of basal acid secretion determination. A low daily dose of omeprazole is able to control acid secretion in Zollinger-Ellison syndrome for a long period (10-30 months). The slow recovery of gastric secretory function demonstrates the prolonged inhibitory effects of omeprazole.

Prospective study of efficacy and safety of lansoprazole in Zollinger-Ellison syndrome

Lansoprazole, a new substituted benzimidazole H+,K(+)-ATPase inhibitor, profoundly inhibits gastric acid secretion and has potential use in the management of diseases such as Zollinger-Ellison syndrome (ZES). In the present study we evaluated the efficacy and safety of lansoprazole in controlling acid hypersecretion in 20 patients with ZES. The starting dose was 60 mg once daily. Control of acid hypersecretion was defined as the dose required to reduce acid secretion to < 10 meq/hr in the last hour before the next dose. Doses were adjusted upwards until effective control was achieved. Patients not controlled with 120 mg once daily were placed on twice daily lansoprazole. Most patients (90%) required lansoprazole once daily. During long-term follow-up (mean 18.5 months), 25% of patients required upward dose adjustments and 25% of patients required twice daily lansoprazole. Following cessation of therapy, the mean time for gastric acid output to reach half basal acid output was 39.1 hr. Lansoprazole was well-tolerated without side effects. Clinical chemistry and hematological studies were unchanged, and no gastric carcinoids developed. These results demonstrate that lansoprazole is a safe and effective inhibitor of gastric acid hypersecretion in patients with Zollinger-Ellison syndrome. Because it has a long duration of action, lansoprazole can be used to control gastric acid hypersecretion in most patients with Zollinger-Ellison syndrome using a once daily dosing schedule.

Currently used doses of omeprazole in Zollinger-Ellison syndrome are too high

The efficacy of omeprazole increases during the first few days of administration, suggesting that long-term maintenance dose requirements in patients with Zollinger-Ellison syndrome may be lower than those initially established by upward titration. Long-term maintenance doses of omeprazole were prospectively reduced in 37 patients who had been taking omeprazole for 22 +/- 4 months. Successful reduction was defined as reduction to 20 mg once or twice daily with an absence of symptoms, endoscopy without evidence of active acid-peptic disease, and a gastric acid output of < 10 mEq/h. Sixty-eight percent of patients (25/37) were successfully reduced to 20 mg of omeprazole once (18/24) or twice daily (7/13). Ninety-five percent of patients (20/21) without multiple endocrine neoplasia type I, severe gastroesophageal reflux disease, or previous partial gastrectomy had safe reductions of doses. It is concluded that the currently used omeprazole maintenance doses in patients with Zollinger-Ellison syndrome are too high and advocated that the initial dose still be established by acute daily upward titration followed by gradual reduction once control of acid output has been achieved.

Role of serum fasting gastrin in screening for hypergastrinemic syndromes in duodenal ulcer disease

Basal serum gastrin levels were measured in 237 patients with endoscopically confirmed duodenal ulcer and were higher than normal in 16 cases. Protein meal gastrin stimulation was performed on this group of 16 patients and on a control group of 48 patients with normal basal gastrin concentrations but high rates of either ulcer recurrence or of complications (e.g., bleeding or perforation); 21 patients from the two groups were also tested for serum gastrin inhibition with secretin. Four cases (25%) of antral G-cell hyperfunction were found in the first group, plus 1 case compatible with Zollinger-Ellison syndrome (6.2%). Only 1 case (2%) of antral G-cell hyperfunction was found among the 48 controls. These results suggest the clinical utility of routine basal gastrin measurement in screening for hypergastrinemic patients with duodenal ulcer disease.

Effects of curative gastrinoma resection on gastric secretory function and antisecretory drug requirement in the Zollinger-Ellison syndrome

The chronic hypergastrinemia in diseases such as the Zollinger-Ellison syndrome has trophic effects on the gastric mucosa, causing increased parietal cell mass reflected by increased maximal acid output (MAO) and basal acid output (BAO). The time course for the development of these gastric changes in humans is unknown, and controversy exists regarding whether reversal of the hypergastrinemia results in rapid normalization of gastric secretory function. To address these uncertainties, gastric secretory function was prospectively evaluated in 20 patients with the Zollinger-Ellison syndrome undergoing successful curative resection of gastrinoma. Each patient had gastric acid measurements, imaging studies, fasting serum gastrin and secretin provocative testing preoperatively, postoperatively at 3-6 months, and yearly thereafter. Preoperative mean BAO was 39 mEq/h, MAO 56 mEq/h, BAO-MAO ratio 0.73, and fasting gastrin output 1020 pg/mL. All patients were evaluated at 6 months, 17 at 1 year, 15 at 2 years, 13 at 3 years, and 9 at 4 years. By 3-6 months, MAO decreased by 50% in men (mean, 30 mEq/h) and by 35% in women (mean, 29 mEq/h) and then remained relatively unchanged for up to 4 years. Before surgery, 14 of 20 patients (70%) had an elevated MAO, whereas 4 years after resection, none of 9 patients had elevated levels. By 3-6 months, BAO decreased by 75% and remained unchanged for up to 4 years. At 3-6 months, 56% of patients were mild hypersecretors and 67% remained hypersecretors up to 4 years. Preoperatively, the BAO-MAO ratio was elevated in 16 of 20 patients (80%); postoperatively, only 5 of 18 patients (28%) at 3-6 months, 2 of 15 (13%) at 1 year, and 2 of 10 (20%) at 4 years continued to have elevated ratios. Preoperatively, the mean ranitidine dose was 1597 mg/day, whereas after surgery the mean dose was 535 mg/day at 3-6 months and approximately 300 mg/day at 1-4 years with 8 patients requiring no antisecretory drug. These results show that the trophic effects of chronic hypergastrinemia are, in general, rapidly reversible with a 50% decrease in MAO within 3-6 months of cure. Similarly, BAO decreased by 75% within 3-6 months. Despite these decreases, careful monitoring of acid secretion is required after reversal of the chronic hypergastrinemia in diseases such as the Zollinger-Ellison syndrome, because 55% of patients at 3-6 months and up to 67% at 4 years continue to remain mild hypersecretors and require low doses of antisecretory drugs.

Comparative tolerability profile of omeprazole in clinical trials

The tolerability of omeprazole was compared to control agents in 68 clinical studies that enrolled a total of 4846 patients, of whom 3096 received omeprazole. The incidence of adverse experiences was independent of omeprazole dose administered, the age of the patients, and the disease treated (duodenal ulcer or endoscopically verified gastroesophageal reflux disease). The most common clinical adverse experiences were headache, diarrhea, abdominal pain, and nausea. The most common laboratory adverse experiences were elevated aspartate aminotransferase and elevated alanine aminotransferase. Omeprazole was well tolerated, and the incidence of clinical and laboratory adverse experiences was similar in patients receiving omeprazole, placebo, cimetidine, or ranitidine.

Omeprazole

Omeprazole is a potent and effective antisecretory drug. Benefits in gastric and duodenal ulceration nevertheless seem marginal because standard treatments are very effective. More obvious advantages are discernible in oesophageal reflux disease where more profound acid inhibition may be needed to obtain symptom relief. Fears of important adverse effects either through inducing ECL cell hyperplasia or outright carcinogenesis, do not seem firmly founded, nor is there convincing evidence of significant interactions with other xenobiotics. Nevertheless, continued caution seems justified.

Pharmacokinetics of oral and intravenous omeprazole in patients with the Zollinger-Ellison syndrome

The pharmacokinetics and pharmacodynamics of oral and IV omeprazole after a single dose were studied in 9 patients with the Zollinger-Ellison syndrome to determine whether the increased dose required to control gastric acid hypersecretion could be explained on the basis of altered pharmacokinetics. Each patient was studied both after receiving a single IV bolus of omeprazole (40 mg) and after receiving a single oral dose of omeprazole (80 mg). Intravenous and oral omeprazole doses were administered 1 week apart. Gastric acid secretion and plasma concentrations of omeprazole after drug administration were determined in each patient. The area under the plasma concentration curve, clearance, and volume of distribution after IV omeprazole administration and the area under the plasma concentration curve, peak plasma concentration, and time required to reach the peak after oral omeprazole administration were not different from those reported previously for normal subjects and patients with peptic ulcer disease. Mean (+/- SEM) bioavailability of oral omeprazole for all patients was 68% +/- 16%, which was similar to the bioavailability reported previously for normal subjects. Three patients had a significantly lower bioavailability reported previously for normal subjects. Three patients had a significantly lower bioavailability (20% +/- 8%) than the others, and their basal acid outputs were significantly higher than those of the other 7 patients. For all patients there was an inverse correlation between bioavailability and basal acid output (r = 0.76; P less than 0.02). The mean (+/- SEM) elimination half-lives of IV and oral omeprazole were not different (2.3 +/- 0.4 vs. 2.4 +/- 0.5 hours) but were significantly longer than those reported previously for normal subjects (P less than 0.02). The duration of action correlated with the elimination half-life of the drug (r = 0.87; P less than 0.003) and area under the plasma concentration curve (r = 0.72; P less than 0.03). The mean durations of action of IV and oral omeprazole were not significantly different (34 +/- 7.2 vs. 35 +/- 6.2 hours). It was concluded that altered pharmacokinetics do not account for the increased drug requirement of omeprazole in patients with the Zollinger-Ellison syndrome. In contrast to a previous study, the oral and IV omeprazole had the same duration of action, suggesting that intermittent bolus administration of parenteral omeprazole will obviate the need for continuous infusion of histamine H2-receptor antagonists in patients requiring parenteral antisecretory drugs. Furthermore, an IV dose every 12 hours controlled acid secretion in all patients, suggesting this as the recommended dose interval in patients requiring parenteral drug therapy.

Zollinger-Ellison syndrome

As clinical experience with patients with ZES has grown, increasing recognition has been made of the broad spectrum of symptoms associated with gastrinomas. Diarrhea and acid-induced esophageal injury have taken their place alongside chronic peptic ulcer disease as indications for screening for gastrinoma. Diagnostic testing should begin with fasting serum gastrin levels and should include intravenous secretin infusion if fasting serum levels of gastrin are nondiagnostic and the patient is not found to be hypochlorhydric. Tumor localization is critical to aid in the identification of patients with potentially curable localized disease. Preoperative evaluation utilizing CT scanning with intravenous contrast should be done early and should be supplemented by other imaging modalities as necessary. Exploratory laparotomy, including a thorough examination of the duodenum and perhaps intraoperative ultrasound, should be performed in all patients with sporadic gastrinoma who lack evidence of extensive metastatic disease on preoperative evaluation. By utilizing this approach, it is likely that at least 20% of patients with ZES can be cured. With the availability of the highly effective H(+)-K(+)-ATPase inhibitor omeprazole, excellent control of symptoms related to gastric acid hypersecretion can be expected. Patients with unresectable gastrinoma may thus avoid potentially morbid antisecretory surgery and be managed with a fairly simple medical regimen. Further developments in the chemotherapeutic management of these patients with unresectable disease should be forthcoming in the future.

Omeprazole. An updated review of its pharmacology and therapeutic use in acid-related disorders

Omeprazole is the first of a new class of drugs, the acid pump inhibitors, which control gastric acid secretion at the final stage of the acid secretory pathway and thus reduce basal and stimulated acid secretion irrespective of the stimulus. In patients with duodenal or gastric ulcers, omeprazole as a single 20 mg daily dose provides more rapid and complete healing compared with ranitidine 150 mg twice daily or 300 mg at nighttime, or cimetidine 800 or 1000 mg/day. Patients poorly responsive to treatment with histamine H2-receptor antagonists respond well to omeprazole--most ulcers healed within 4 to 8 weeks of omeprazole 40 mg/day therapy. Omeprazole 20 or 40 mg/day has been administered as maintenance therapy for peptic ulcer disease for up to 5.5 years with very few ulcer recurrences. In patients with erosive or ulcerative oesophagitis, omeprazole 20 or 40 mg/day produces healing in about 80% of patients after 4 weeks, and is superior to ranitidine with respect to both healing and symptom relief. Healing rates of greater than 80% are achieved after 8 weeks in patients with severe reflux oesophagitis unresponsive to H2-receptor antagonists. Maintenance therapy with a daily 20 mg dose prevents relapse in about 80% of patients over a 12-month period. Omeprazole is considered to be the best pharmacological option for controlling gastric acid secretion in patients with Zollinger-Ellison syndrome. Daily dosages of 20 to 360 (median 60 to 70 mg successfully reduce basal acid output to target levels (less than 10 mmol/h or less than 5 mmol/h in patients with severe oesophagitis or partial gastrectomy) during treatment for up to 4 years. Omeprazole is well tolerated in short term studies (up to 12 weeks); the reported incidence of serious side effects (about 1%) being similar to that seen in patients treated with an histamine H2-receptor antagonist. The longer term tolerability of omeprazole has been investigated in patients treated for up to 5.5 years. Slight hyperplasia, but no evidence of enterochromaffin-like (ECL) cell dysplasia or neoplasia or ECL cell carcinoids has been reported. ECL cell carcinoids have been observed in rats after life-long treatment with high doses of omeprazole or ranitidine, or in rats with partial corpectomy; the weight of experimental evidence indicates that this is a result of prolonged hypergastrinaemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of omeprazole in patients with Zollinger-Ellison syndrome

Omeprazole, a substituted benzimidazole, has been shown to be a potent inhibitor of gastric acid secretion in patients with Zollinger-Ellison syndrome (ZES). We review our experience, as well as the published data on 210 patients with ZES who have required omeprazole for control of gastric acid hypersecretion over the past seven years. The dose of omeprazole required in individual patients ranged from 10 to 180 mg/24 hr with 20-60% requiring a split dosage regimen. Omeprazole was effective in approximately 99% of the patients over a period ranging from 0.5 to 54 months. Twenty-four percent of patients required an increase in omeprazole dose, while 26% required a decrease in dose. Adverse effects attributable to omeprazole were reported in 2% of patients, and in all cases, they were mild (ie, rash, constipation, headache). There was no effect of omeprazole on serum gastrin concentration or on gastric endocrine cells in three studies. Although one patient with multiple endocrine neoplasia, type-I syndrome (MEN-I) in this series developed a gastric carcinoid while taking omeprazole, evidence is presented that suggests the presence of MEN-I per se may be important in determining the development of gastric carcinoid in patients with ZES. It is concluded that omeprazole is safe and effective in patients with ZES, and in these patients, it is the drug of choice for the management of gastric acid hypersecretion. However, yearly assessment is indicated to clearly evaluate the long-term risk of gastric carcinoid as well as therapy directed at the gastrinoma itself.

Omeprazole. Overview and opinion

Omeprazole, a substituted benzimidazole, is a specific inhibitor of the enzyme H+/K(+)-ATPase, which is found on the secretory surface of the parietal cell. This enzyme, the "proton pump," catalyzes the final step in acid secretion. Omeprazole is a powerful inhibitor of gastric acid secretion. At the time of writing, omeprazole has been licensed in the United States for the treatment of severe grades of gastroesophageal reflux disease (GERD) as well as GERD unresponsive to treatment with currently available agents, and for the treatment of Zollinger-Ellison syndrome and other gastric hypersecretory states. Most recently, it has been recommended by the FDA advisory committee for approval as first-line therapy in duodenal ulcer disease.

Omeprazole. Gastrin and gastric endocrine cell data from clinical studies

Gastric enterochromaffin-like cell carcinoids have been detected in rats exposed lifelong to omeprazole. By inhibiting acid secretion, omeprazole causes hypergastrinemia which, with prolonged exposure, exerts a trophic effect on enterochromaffin-like cells with eventual enterochromaffin-like cell carcinoid formation in some animals. This mechanism seems to explain the appearance of enterochromaffin-like cell carcinoids in human hypergastrinemic states, whether associated with hyperchlorhydria, eg, Zollinger-Ellison syndrome, or with hypochlorhydria, eg, pernicious anemia (nonantral atrophic gastritis). Omeprazole produces modest serum gastrin elevations in humans when monitored over a 24-hr period. Gastrin levels are markedly lower and less sustained than in the above hypergastrinemic states. Extensive gastric biopsy data from patients enrolled in long-term studies indicate that omeprazole administration is not associated with clinically significant changes in the human oxyntic endocrine cell population. Man and rat differ markedly both in their gastrin response to a given level of acid inhibition and in their response to the trophic influence of gastrin on enterochromaffin-like cells. The rat model is a false indicator of risk in man.

Clinical pharmacology of omeprazole

Omeprazole is a specific inhibitor of H+,K(+)-ATPase or 'proton pump' in parietal cells. This enzyme is responsible for the final step in the process of acid secretion; omeprazole blocks acid secretion in response to all stimuli. Single doses produce dose-dependent inhibition with increasing effect over the first few days, reaching a maximum after about 5 days. Doses of omeprazole 20mg daily or greater are able to virtually abolish intragastric acidity in most individuals, although lower doses have a much more variable effect. Omeprazole causes a dose-dependent increase in gastrin levels. Omeprazole must be protected from intragastric acid when given orally, and is therefore administered as encapsulated enteric-coated granules. Absorption can be erratic but is generally rapid, and initially the drug is widely distributed. It is highly protein-bound and extensively metabolised. Its elimination half-life is about 1h but its pharmacological effect lasts much longer, since it is preferentially concentrated in parietal cells where it forms a covalent linkage with H+,K(+)-ATPase, which it irreversibly inhibits. Omeprazole binds to hepatic cytochrome P450 and inhibits oxidative metabolism of some drugs, the most important being phenytoin. Omeprazole has produced short term healing rates superior to the histamine H2-receptor antagonists in duodenal ulcer, gastric ulcer and reflux oesophagitis. It has also been shown to be highly effective in healing ulcers which have failed to respond to H2-receptor antagonists, and has been extremely valuable in treating patients with Zollinger-Ellison syndrome.