Pharmacotherapeutic group: drugs for peptic ulcers and gastro-oesophageal reflux disease (GORD), Proton pump inhibitors.
ATCvet code: QA02BC01.
Pharmacodynamic properties
Omeprazole is a proton pump inhibitor belonging to the substituted benzimidazole class of compounds. It is an antacid, for treatment of peptic ulcers.
Omeprazole suppresses gastric acid secretion by specific inhibition of the H+/K+-ATPase enzyme system at the secretory surface of the parietal cell. The H+/K+-ATPase enzyme system is the acid (proton) pump within the gastric mucosa. Because H+/K+-ATPase is the final step involved in control of acid secretion, omeprazole blocks secretion irrespective of the stimulus. Omeprazole irreversibly binds to the gastric parietal cell H+/K+-ATPase enzyme that pumps hydrogen ions into the lumen of the stomach in exchange for potassium ions.
The full effect on the inhibition of acid secretion is reached by five days after the first administration.
Pharmacokinetic particulars
The absorption of omeprazole after oral administration as gastro resistant granules is rapid with time to maximum plasma concentrations (Tmax) of approximately one hour after dosing. Mean peak concentration (Cmax) is approximately 236.7 ng/ml after dosing with 2 mg/kg. There is a significant first-pass effect following oral administration. Omeprazole is rapidly metabolised principally into glucuronides of demethylated and hydroxylated omeprazole sulphide (urinary metabolites) and methyl sulphide omeprazole (biliary metabolite) as well as into reduced omeprazole (both). After oral administration at 2 mg/kg, omeprazole is detectable in plasma for 8 hours after treatment. Omeprazole is eliminated quickly, mainly by urinary route (43 to 61% of the dose), and to a smaller extent by faecal route, with a terminal half-life ranging from approximately 0.4 to 2.8 hours.
After repeated oral administration, there is no evidence of accumulation.