Omeprazole Stats & Data
Pharmacology
DrugBankDescription
Originally approved by the FDA in 1989, omeprazole is a _proton-pump inhibitor_, used to treat gastric acid-related disorders. These disorders may include gastroesophageal reflux disease (GERD), peptic ulcer disease, and other diseases characterized by the oversecretion of gastric acid. This drug was the first clinical useful drug in its class, and its approval was followed by the formulation of many other proton pump inhibitor drugs . Omeprazole is generally effective and well-tolerated, promoting its popular use in children and adults .
Mechanism of Action
Hydrochloric acid (HCl) secretion into the gastric lumen is a process regulated mainly by the H(+)/K(+)-ATPase of the proton pump , expressed in high quantities by the parietal cells of the stomach. ATPase is an enzyme on the parietal cell membrane that facilitates hydrogen and potassium exchange through the cell, which normally results in the extrusion of potassium and formation of HCl (gastric acid) . Omeprazole is a member of a class of antisecretory compounds, the substituted _benzimidazoles_, that stop gastric acid secretion by selective inhibition of the _H+/K+ ATPase_ enzyme system. Proton-pump inhibitors such as omeprazole bind covalently to cysteine residues via disulfide bridges on the alpha subunit of the _H+/K+ ATPase_ pump, inhibiting gastric acid secretion for up to 36 hours . This antisecretory effect is dose-related and leads to the inhibition of both basal and stimulated acid secretion, regardless of the stimulus . **Mechanism of H. pylori eradication** Peptic ulcer disease (PUD) is frequently associated with _Helicobacter pylori_ bacterial infection (NSAIDs) . The treatment of H. pylori infection may include the addition of omeprazole or other proton pump inhibitors as part of the treatment regimen , . _H. pylori_ replicates most effectively at a neutral pH . Acid inhibition in H.
Pharmacodynamics
**Effects on gastric acid secretion** This drug decreases gastric acid secretion . After oral administration, the onset of the antisecretory effect of omeprazole is usually achieved within one hour, with the maximum effect occurring by 2 hours after administration. The inhibitory effect of omeprazole on acid secretion increases with repeated once-daily dosing, reaching a plateau after four days . **Effects on serum gastrin** In studies of 200 or more patients, serum gastrin levels increased during the first 1-2 weeks of daily administration of therapeutic doses of omeprazole. This occurred in a parallel fashion with the inhibition of acid secretion. No further increase in serum gastrin occurred with continued omeprazole administration. Increased gastrin causes enterochromaffin-like cell hyperplasia and increased serum Chromogranin A (CgA) levels. The increased CgA levels may lead to false positive results in diagnostic studies for neuroendocrine tumors . **Enterochromaffin-like (ECL) cell effects** Human gastric biopsy samples have been obtained from more than 3000 pediatric and adult patients treated with omeprazole in long-term clinical studies. The incidence of enterochromaffin-like cell hyperplasia in these studies increased with time; however, no case of ECL cell carcinoids, dysplasia, or neoplasia have been identified in these patients.
Metabolism
Omeprazole is heavily metabolized in the liver by the cytochrome P450 (CYP) enzyme system. The main part of its metabolism depends on the polymorphically expressed CYP2C19, which is responsible for the formation of _hydroxyomeprazole_, the major metabolite found in plasma. The remaining part depends on CYP3A4, responsible for the formation of _omeprazole sulphone_ .
Absorption
Omeprazole delayed-release capsules contain an enteric-coated granule formulation of omeprazole (because omeprazole is acid-labile), so that absorption of omeprazole begins only after the granules exit the stomach . Absorption of omeprazole occurs rapidly, with peak plasma concentrations of omeprazole achieved within 0.5-3.5 hours . Absolute bioavailability (compared with intravenous administration) is approximately 30-40% at doses of 20-40 mg, largely due to pre-systemic metabolism. The bioavailability of omeprazole increases slightly upon repeated administration of omeprazole delayed-release capsules .
Toxicity
**Oral acute (LD50)**: 4000 mg/kg (mouse), 2210 mg/kg (rat) . **Overdose** Symptoms of overdose include confusion, drowsiness, blurred vision, tachycardia, nausea, diaphoresis, flushing, headache, and dry mouth. **Carcinogenesis and mutagenesis** In 24-month studies in rats, a dose-related significant increase in gastric carcinoid tumors and ECL cell hyperplasia was seen in male and female animals. Carcinoid tumors have also been found in rats treated with a fundectomy or long-term treatment with other proton pump inhibitors, or high doses of H2-receptor antagonists . Omeprazole showed positive clastogenic effects in an in vitro human lymphocyte chromosomal aberration study, in one of two in vivo mouse micronucleus tests, and in an in vivo bone marrow cell chromosomal aberration test. Omeprazole tested negative in the in vitro _Ames_ test, an in vitro mouse lymphoma cell forward mutation assay, and an in vivo rat liver DNA damage assay . **The use in breastfeeding** Limited data indicate that omeprazole may be present in human milk. There is currently no information on the effects of omeprazole on the breastfed infant or production of milk. The benefits of breastfeeding should be considered along with the level of need for omeprazole and any potential adverse effects on the breastfed infant from omeprazole .
Indication
Omeprazole, according to the FDA label is a proton pump inhibitor (PPI) used for the following purposes: • Treatment of active duodenal ulcer in adults • Eradication of Helicobacter pylori to reduce the risk of duodenal ulcer recurrence in adults • Treatment of active benign gastric ulcer in adults • Treatment of symptomatic gastroesophageal reflux disease (GERD) in patients 1 year of age and older • Treatment of erosive esophagitis (EE) due to acid-mediated GERD in patients 1 month of age and older • Maintenance of healing of EE due to acid-mediated GERD in patients 1 year of age and older • Pathologic hypersecretory conditions in adults
Half-life
0.5-1 hour (healthy subjects, delayed-release capsule) Approximately 3 hours (hepatic impairment)
Protein Binding
Approximately 95% bound to human plasma proteins .
Elimination
After a single dose oral dose of a buffered solution of omeprazole, negligible (if any) amounts of unchanged drug were excreted in urine. Most of the dose (about 77%) was eliminated in urine as at least six different metabolites. Two metabolites were identified as _hydroxyomeprazole_ and the corresponding _carboxylic acid_. The remainder of the dose was found in the feces. This suggests significant biliary excretion of omeprazole metabolites. Three metabolites have been identified in the plasma, the _sulfide_ and _sulfone_ derivatives of omeprazole, and _hydroxyomeprazole_. These metabolites possess minimal or no antisecretory activity .
Volume of Distribution
Approximately 0.3 L/kg, corresponding to the volume of extracellular water .
Clearance
Healthy subject (delayed release capsule), total body clearance 500 - 600 mL/min Geriatric plasma clearance: 250 mL/min Hepatic impairment plasma clearance: 70 mL/min
Effect Profile
CuratedStrong euphoria with moderate itching/nausea, mild sedation