AcipHex (Page 5 of 10)

11 DESCRIPTION

The active ingredient in ACIPHEX delayed-release tablets is rabeprazole sodium, which is a proton pump inhibitor. It is a substituted benzimidazole known chemically as 2-[[[4-(3-methoxypropoxy)-3-methyl-2-pyridinyl]-methyl]sulfinyl]-1H– benzimidazole sodium salt. It has an empirical formula of C18 H20 N3 NaO3 S and a molecular weight of 381.42. Rabeprazole sodium is a white to slightly yellowish-white solid. It is very soluble in water and methanol, freely soluble in ethanol, chloroform, and ethyl acetate and insoluble in ether and n-hexane. The stability of rabeprazole sodium is a function of pH; it is rapidly degraded in acid media, and is more stable under alkaline conditions. The structural figure is:

Figure 1

ACIPHEX is available for oral administration as delayed-release, enteric-coated tablets containing 20 mg of rabeprazole sodium.
(click image for full-size original)

ACIPHEX is available for oral administration as delayed-release, enteric-coated tablets containing 20 mg of rabeprazole sodium.

Inactive ingredients of the 20 mg tablet are carnauba wax, crospovidone, diacetylated monoglycerides, ethylcellulose, hydroxypropyl cellulose, hypromellose phthalate, magnesium stearate, mannitol, sodium hydroxide, sodium stearyl fumarate, talc, and titanium dioxide. Iron oxide yellow is the coloring agent for the tablet coating. Iron oxide red is the ink pigment.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

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.

12.2 Pharmacodynamics

Antisecretory Activity

The antisecretory effect begins within one hour after oral administration of 20 mg ACIPHEX delayed-release tablets. The median inhibitory effect of rabeprazole on 24 hour gastric acidity is 88% of maximal after the first dose. A 20 mg dose of ACIPHEX delayed-release tablets inhibits basal and peptone meal-stimulated acid secretion versus placebo by 86% and 95%, respectively, and increases the percent of a 24-hour period that the gastric pH>3 from 10% to 65% (see table below). This relatively prolonged pharmacodynamic action compared to the short pharmacokinetic half-life (1 to 2 hours) reflects the sustained inactivation of the H+ , K+ ATPase.

Table 3: Gastric Acid Parameters: ACIPHEX Delayed-Release Tablets versus Placebo After 7 Days of Once Daily Dosing
Parameter ACIPHEX delayed-release tablets(20 mg once daily) Placebo
Basal Acid Output (mmol/hr) 0.4* 2.8
Stimulated Acid Output (mmol/hr) 0.6* 13.3
% Time Gastric pH>3 65* 10

*(p<0.01 versus placebo)

Compared to placebo, 10 mg, 20 mg, and 40 mg of ACIPHEX delayed-release tablets, administered once daily for 7 days significantly decreased intragastric acidity with all doses for each of four meal-related intervals and the 24-hour time period overall. In this study, there were no statistically significant differences between doses; however, there was a significant dose-related decrease in intragastric acidity. The ability of rabeprazole to cause a dose-related decrease in mean intragastric acidity is illustrated below.

Table 4: AUC Acidity (Mmol•Hr/L): ACIPHEX Delayed-Release Tablets versus Placebo on Day 7 of Once Daily Dosing (Mean±SD)
ACIPHEX delayed-release tablets Placebo(N=24)
AUC interval(hrs) 10 mg (N=24) 20 mg(N=24) 40 mg(N=24)
08:00 – 13:00 19.6±21.5* 12.9±23* 7.6±14.7* 91.1±39.7
13:00 – 19:00 5.6±9.7* 8.3±29.8* 1.3±5.2* 95.5±48.7
19:00 – 22:00 0.1±0.1* 0.1±0.06* 0.0±0.02* 11.9±12.5
22:00 – 08:00 129.2±84* 109.6±67.2* 76.9±58.4* 479.9±165
AUC 0-24hours 155.5±90.6* 130.9±81* 85.8±64.3* 678.5±216

*(p<0.001 versus placebo)

After administration of 20 mg ACIPHEX delayed-release tablets once daily for eight days, the mean percent of time that gastric pH greater than 3 or gastric pH greater than 4 after a single dose (Day 1) and multiple doses (Day 8) was significantly greater than placebo (see table below). The decrease in gastric acidity and the increase in gastric pH observed with 20 mg ACIPHEX delayed-release tablets administered once daily for eight days were compared to the same parameters for placebo, as illustrated below:

Table 5: Gastric Acid Parameters ACIPHEX Delayed-Release Tablets Once Daily Dosing versus Placebo on Day 1 and Day 8
Parameter ACIPHEX delayed-release tablets 20 mg once daily Placebo
Day 1 Day 8 Day 1 Day 8
Mean AUC0-24 Acidity 340.8* 176.9* 925.5 862.4
Median trough pH (23-hr)a 3.77 3.51 1.27 1.38
% Time Gastric pH greater than 3b 54.6* 68.7* 19.1 21.7
% Time Gastric pH greater than 4b 44.1* 60.3* 7.6 11.0

a No inferential statistics conducted for this parameter.
b Gastric pH was measured every hour over a 24-hour period.* (p<0.001 versus placebo)

Effects on Esophageal Acid Exposure

In patients with GERD and moderate to severe esophageal acid exposure, a dose of 20 mg and 40 mg per day of ACIPHEX delayed-release tablets decreased 24-hour esophageal acid exposure. After seven days of treatment, the percentage of time that the esophageal pH was less than 4 decreased from baselines of 24.7% for 20 mg and 23.7% for 40 mg, to 5.1% and 2.0%, respectively. Normalization of 24-hour intraesophageal acid exposure was correlated to gastric pH greater than 4 for at least 35% of the 24-hour period; this level was achieved in 90% of subjects receiving ACIPHEX 20 mg and in 100% of subjects receiving ACIPHEX 40 mg. With ACIPHEX 20 mg and 40 mg per day, significant effects on gastric and esophageal pH were noted after one day of treatment, and more pronounced after seven days of treatment.

Effects on Serum Gastrin

The median fasting gastrin level increased in a dose-related manner in patients treated once daily with ACIPHEX delayed-release tablets for up to eight weeks for ulcerative or erosive esophagitis and in patients treated for up to 52 weeks to prevent recurrence of disease. The group median values stayed within the normal range.

In a group of subjects treated with 20 mg ACIPHEX delayed-release tablets for 4 weeks a doubling of mean serum gastrin concentrations was observed. Approximately 35% of these treated subjects developed serum gastrin concentrations above the upper limit of normal.

Effects on Enterochromaffin-like (ECL) Cells

Increased serum gastrin secondary to antisecretory agents stimulates proliferation of gastric ECL cells which, over time, may result in ECL cell hyperplasia in rats and mice and gastric carcinoids in rats, especially in females [ see Nonclinical Toxicology (13.1)].

In over 400 patients treated with ACIPHEX delayed-release tablets (10 or 20 mg) once daily for up to one year, the incidence of ECL cell hyperplasia increased with time and dose, which is consistent with the pharmacological action of the proton pump inhibitor. No patient developed the adenomatoid, dysplastic or neoplastic changes of ECL cells in the gastric mucosa. No patient developed the carcinoid tumors observed in rats.

Endocrine Effects

Studies in humans for up to one year have not revealed clinically significant effects on the endocrine system. In healthy male subjects treated with ACIPHEX delayed-release tablets for 13 days, no clinically relevant changes have been detected in the following endocrine parameters examined: 17 β-estradiol, thyroid stimulating hormone, tri-iodothyronine, thyroxine, thyroxine-binding protein, parathyroid hormone, insulin, glucagon, renin, aldosterone, follicle-stimulating hormone, luteotrophic hormone, prolactin, somatotrophic hormone, dehydroepiandrosterone, cortisol-binding globulin, and urinary 6β-hydroxycortisol, serum testosterone and circadian cortisol profile.

Other Effects

In humans treated with ACIPHEX delayed-release tablets for up to one year, no systemic effects have been observed on the central nervous, lymphoid, hematopoietic, renal, hepatic, cardiovascular, or respiratory systems. No data are available on long-term treatment with ACIPHEX delayed-release tablets and ocular effects.

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