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Originally approved by the Food and Drug Administration (FDA) in 1989, omeprazole is a proton pump inhibitor that decreases the amount of acid produced in the stomach. It is usually used to treat gastric acid-related disorders.
Originally approved by the Food and Drug Administration (FDA) in 1989, omeprazole is a proton pump inhibitor that decreases the amount of acid produced in the stomach. It is usually used to treat gastric acid-related disorders. [1,2]
Pharmacological Class: Proton pump inhibitor (PPIs)
Omeprazole works by selectively inhibiting the
parietal H+/K+ ATPase pump (the final step of acid production). This
reduces the secretion of stomach acid. [3] Omeprazole binds covalently to
cysteine residues via disulfide bridges on the alpha subunit of the H+/K+
ATPase pump, suppressing the
acid secretion. This anti-secretory effect is dose-related and leads to the
suppression of both basal and stimulated acid secretion. [2]
(a) Active duodenal ulcer
Adults: 20 mg P.O. (medication is taken by mouth twice a day) daily for 4 to 8 weeks.
(b) Gastric ulcer
Adults: 40 mg P.O. daily for 4 to 8 weeks.
(c) Severe erosive esophagitis; symptomatic, poorly responsive GERD
Adults: 20 mg P.O. daily for 4 to 12 weeks. Patients with GERD should have failed initial therapy with an H2 antagonist. May continue with a maintenance dosage of 20 mg daily for up to 1 year.
(d) Pathologic hypersecretory conditions (such as Zollinger-Ellison syndrome)
Adults: Initial dosage is 60 mg P.O. daily; adjust dosage based on patient response. Administer daily doses exceeding 80 mg in divided doses. Doses up to 120 mg t.i.d. (three times daily) have been administered. Continue therapy as long as clinically indicated.
(e) H.pylori eradication to lower duodenal ulcer recurrence risk
Dual therapy: Adults: 40 mg P.O. q morning plus 500 mg clarithromycin P.O. t.i.d. for 14 days followed by 14 days of omeprazole 20 mg daily.
Triple therapy: Adults: 20 mg P.O. b.i.d. (twice daily) plus 500 mg clarithromycin P.O. b.i.d. plus 1,000 mg amoxicillin P.O. b.i.d. for 10 days. For patients with an ulcer present at the time that therapy starts, an additional 18 days of omeprazole 20 mg once daily is suggested alone for symptom relief and ulcer healing.
(f) Dosage adjustment: Patients with liver disease may require dosage adjustments. Due to the increased bioavailability of omeprazole in Asian patients, they may need dosage adjustments.
Absorption:
Absorption of omeprazole occurs rapidly, with peak plasma concentrations of omeprazole achieved within 0.5-3.5 hours. [2] Bioavailability is about 40% because of instability in gastric acid as well as a significant first-pass effect. Bioavailability increases slightly with repeated dosing, possibly due to the drug’s effect on gastric acidity. [4]
Volume of distribution
Approximately 0.3 L/kg, corresponding to the volume of extracellular water
Protein binding
About 95% of omeprazole is bound to human plasma proteins
Metabolism:
Omeprazole is primarily metabolized in the liver by the cytochrome P450 (CYP) enzyme. CYP2C19 is responsible for the formation of hydroxyomeprazole (the major metabolite found in plasma). The remaining metabolism depends on CYP3A4 that is responsible for the formation of omeprazole sulphone.
Excretion:
Omeprazole is majorly excreted via the kidneys. The plasma half-life is 1/2 to 1 hour in healthy subjects and approximately 3 hours in patients with liver impairment. The clearance of omeprazole is as follows:
(a) Healthy subject (delayed-release capsule), total body clearance 500 -
600 mL/min
(b) Hepatic impairment plasma clearance: 70 mL/min
(c) Geriatric plasma clearance: 250 mL/min [2]
Contraindicated in patients having following the following
conditions:
Tacrolimus, Digoxin, Phenytoin, Warfarin, Diazepam, Citalopram, Methotrexate, Cilostazol, Saquinavir: Concomitant administration of omeprazole may increase the serum levels of these drugs in your body.
Ampicillin esters, Ketoconazole, Mycophenolate mofetil (MMF), Iron salts, Erlotinib: Concomitant administration of omeprazole may interfere with the absorption of these drugs and decrease their serum levels in your body.
Voriconazole: This drug may increase the levels of omeprazole in your body. This, in turn, raises the risk of side effects from omeprazole.
Rifampin: This drug may decrease the levels of omeprazole in your body and makes the drug less effective.
Clopidogrel: Omeprazole may reduce the effects of clopidogrel, causing your blood to clot.
Atazanavir, rilpivirine, and nelfinavir: Concomitant administration of omeprazole may reduce plasma levels and effects of these drugs, and could make them less effective over time.
More common side effects
Serious side effects
Aprotinin or remdesivir with omeprazole may help to treat COVID-19
In Germany, recent drug research demonstrated that omeprazole hampered the viral formation of SARS-CoV-2 beyond therapeutic plasma concentrations at 8 µM. However, at therapeutic concentrations, it elevated the anti-SARS-CoV-2 effects of aprotinin (an approved protease inhibitor) and remdesivir by 2.7-fold and tenfold, respectively. Therefore, aprotinin or remdesivir with omeprazole may represent as potent candidates for management of COVID-19 [9]
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