Omeprazole 20 mg, Sodium Bicarbonate 1680 mg Oral suspension

Omeprazole belongs to a class of antisecretory compounds, the substituted benzimidazoles, that suppress gastric acid secretion by specific inhibition of the H+/K+ ATPase enzyme system at the secretory surface of the gastric parietal cell. Because this enzyme system is regarded as the acid (proton) pump within the gastric mucosa, omeprazole has been characterized as a gastric acid-pump inhibitor, in that it blocks the final step of acid production. This effect is dose related and leads to inhibition of both basal and stimulated acid secretion irrespective of the stimulus.

Absorption — Table 10 show the systemic exposures and the time reach peak concentration (Tmax) of omeprazole in healthy subjects following administration of Omeprazole and Sodium Bicarbonate for oral suspension, on an empty stomach one hour prior to a meal.

Following single or repeated once-daily dosing, peak plasma concentrations (Cmax) of omeprazole from Omeprazole and Sodium Bicarbonate were approximately proportional from 20 to 40 mg doses. A greater than dose proportional increase in mean steady-state AUC (more than three-fold increase on Day 7) was observed when doubling the dose to 40 mg. The bioavailability of omeprazole from Omeprazole and Sodium Bicarbonate increases upon repeated administration. The percent changes in Cmax and AUC between steady-state (Day 7) and single dose (Day 1) indicate omeprazole is a time-dependent autoinhibitor of CYP2C19.

When Omeprazole and Sodium Bicarbonate for oral suspension 40 mg was administered in a two-dose loading regimen, the omeprazole AUC(0-inf)(ng•hr/mL) was 1665 after Dose 1 and 3356 after Dose 2, while Tmax was approximately 30 minutes for both Dose 1 and Dose 2.

When Omeprazole and Sodium Bicarbonate for oral suspension 40 mg is administered one hour after a meal, the omeprazole AUC is reduced by approximately 27%, relative to administration one hour prior to a meal [see Dosage and Administration (2.3)].

Distribution — Omeprazole is bound to plasma proteins. Protein binding is approximately 95%.

Metabolism — Omeprazole is extensively metabolized by the cytochrome P450 (CYP) enzyme system. The major part of its metabolism is dependent on the polymorphically expressed CYP2C19 [see Clinical Pharmacology (12.5)], responsible for the formation of hydroxyomeprazole, the major metabolite in plasma. The remaining part is dependent on another specific isoform, CYP3A4, responsible for the formation of omeprazole sulphone.

The mean plasma omeprazole half-life following administration of Omeprazole and Sodium Bicarbonate for oral suspension in healthy subjects is approximately 1 hour (range 0.4 to 4.2 hours), and the total body clearance is 500 to 600 mL/min.

Excretion — Following single-dose oral administration of a buffered solution of omeprazole, the majority of the dose (about 77%) is eliminated in urine as at least six metabolites. Two metabolites have been identified as hydroxyomeprazole and the corresponding carboxylic acid. The remainder of the dose was recoverable in feces. This implies a significant biliary excretion of the metabolites of omeprazole. Three metabolites have been identified in plasma – the sulfide and sulfone derivatives of omeprazole, and hydroxyomeprazole. These metabolites have very little or no antisecretory activity.

Geriatric Patients — The elimination rate of omeprazole was somewhat decreased in the elderly, and bioavailability was increased. Omeprazole was 76% bioavailable when a single 40 mg oral dose of omeprazole (buffered solution) was administered to healthy elderly subjects versus 58% in young subjects given the same dose. Nearly 70% of the dose was recovered in urine as metabolites of omeprazole, and no unchanged drug was detected. The plasma clearance of omeprazole was 250 mL/min (about half that of young subjects), and its plasma half-life averaged one hour, similar to that of young healthy subjects.

Male and Female Patients — There are no known differences in the absorption or excretion of omeprazole between males and females.

Patients with Renal Impairment — In patients with chronic renal impairment (creatinine clearance between 10 and 62 mL/min/1.73 m2), the disposition of omeprazole was very similar to that in healthy subjects, although there was a slight increase in bioavailability. Because urinary excretion is a primary route of excretion of omeprazole metabolites, their elimination slowed in proportion to the decreased creatinine clearance. This increase in bioavailability is not considered to be clinically meaningful.