Domperidone 30 mg (SR), Rabeprazole 20 mg Hard-gelatin capsules

Rabeprazole belongs to a class of antisecretory compounds (substituted benzimidazole proton-pump inhibitors) that do not exhibit anticholinergic or histamine H2-receptor antagonist properties, but suppress gastric acid secretion by inhibiting the gastric H+, K+ATPase at the secretory surface of the gastric parietal cell. Because this enzyme is regarded as the acid (proton) pump within the parietal cell, rabeprazole has been characterized as a gastric proton-pump inhibitor. Rabeprazole blocks the final step of gastric acid secretion.

In gastric parietal cells, rabeprazole is protonated, accumulates, and is transformed to an active sulfenamide. When studied in vitro, rabeprazole is chemically activated at pH 1.2 with a half-life of 78 seconds. It inhibits acid transport in porcine gastric vesicles with a half-life of 90 seconds.

After oral administration of 20 mg rabeprazole sodium delayed-release tablets, peak plasma concentrations (Cmax) of rabeprazole occur over a range of 2 to 5 hours (Tmax). The rabeprazole Cmax and AUC are linear over an oral dose range of 10 mg to 40 mg. There is no appreciable accumulation when doses of 10 mg to 40 mg are administered every 24 hours; the pharmacokinetics of rabeprazole is not altered by multiple dosing.

Absorption — Absolute bioavailability for a 20 mg oral tablet of rabeprazole (compared to intravenous administration) is approximately 52%. When rabeprazole sodium delayed-release tablets are administered with a high fat meal, Tmax is variable; which concomitant food intake may delay the absorption up to 4 hours or longer. However, the Cmax and the extent of rabeprazole absorption (AUC) are not significantly altered. Thus rabeprazole sodium delayed-release tablets may be taken without regard to timing of meals.

Distribution — Rabeprazole is 96.3% bound to human plasma proteins.

Elimination — Metabolism: Rabeprazole is extensively metabolized. A significant portion of rabeprazole is metabolized via systemic nonenzymatic reduction to a thioether compound. Rabeprazole is also metabolized to sulphone and desmethyl compounds via cytochrome P450 in the liver. The thioether and sulphone are the primary metabolites measured in human plasma. These metabolites were not observed to have significant antisecretory activity. In vitro studies have demonstrated that rabeprazole is metabolized in the liver primarily by cytochromes P450 3A (CYP3A) to a sulphone metabolite and cytochrome P450 2C19 (CYP2C19) to desmethyl rabeprazole. CYP2C19 exhibits a known genetic polymorphism due to its deficiency in some sub-populations (e.g., 3 to 5% of Caucasians and 17 to 20% of Asians). Rabeprazole metabolism is slow in these sub-populations, therefore, they are referred to as poor metabolizers of the drug.

Excretion: Following a single 20 mg oral dose of 14C-labeled rabeprazole, approximately 90% of the drug was eliminated in the urine, primarily as thioether carboxylic acid; its glucuronide, and mercapturic acid metabolites. The remainder of the dose was recovered in the feces. Total recovery of radioactivity was 99.8%. No unchanged rabeprazole was recovered in the urine or feces.

Specific Populations — Geriatric Patients: In 20 healthy elderly subjects administered 20 mg rabeprazole sodium delayed-release tablets once daily for seven days, AUC values approximately doubled and the Cmax increased by 60% compared to values in a parallel younger control group. There was no evidence of drug accumulation after once daily administration [see Use in Specific Population (8.5)].

Pediatric Patients: The pharmacokinetics of rabeprazole was studied in 12 adolescent patients with GERD 12 to 16 years of age, in a multicenter study. Patients received 20 mg rabeprazole sodium delayed-release tablets once daily for five or seven days. An approximate 40% increase in rabeprazole exposure was noted following 5 to 7 days of dosing compared with the exposure after 1 day dosing. Pharmacokinetic parameters in adolescent patients with GERD 12 to 16 years of age were within the range observed in healthy adult subjects.

Male and Female Patients and Racial or Ethnic Groups: In analyses adjusted for body mass and height, rabeprazole pharmacokinetics showed no clinically significant differences between male and female subjects. In studies that used different formulations of rabeprazole, AUC0-∞ values for healthy Japanese men were approximately 50 to 60% greater than values derived from pooled data from healthy men in the United States.

Patients with Renal Impairment: In 10 patients with stable end-stage renal disease requiring maintenance hemodialysis (creatinine clearance ≤5 mL/min/1.73 m2), no clinically significant differences were observed in the pharmacokinetics of rabeprazole after a single 20 mg dose of rabeprazole sodium delayed-release tablets when compared to 10 healthy subjects.

Domperidone antagonizes dopamine receptors and has predominantly peripheral effects because it enters the brain poorly. The cited product information relates its antiemetic action to peripheral gastrointestinal effects and receptors in the chemoreceptor trigger zone.

The tablet reference reports oral bioavailability of approximately 15%, limited by gut-wall and hepatic first-pass metabolism. Protein binding is about 91–93%; metabolism includes CYP3A4 pathways. The single-dose plasma half-life is approximately 7–9 hours in healthy subjects and can be prolonged with severe renal impairment. These are immediate-release reference data.