Antisecretory Activity
The antisecretory effect begins within one hour after oral administration of 20 mg rabeprazole sodium. The median inhibitory effect of rabeprazole sodium on 24 hour gastric acidity is 88% of maximal after the first dose. Rabeprazole sodium 20 mg 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 (1-2 hours) reflects the sustained inactivation of the H+, K+ATPase.
TABLE 3
GASTRIC ACID PARAMETERS RABEPRAZOLE SODIUM VERSUS PLACEBO AFTER 7 DAYS OF ONCE DAILY DOSING*(p<0.01 versus placebo)
|
Parameter
| Rabeprazole sodium (20 mg QD)
| Placebo
|
Basal Acid Output
| 0.4*
| 2.8
|
(mmol/hr)
| | |
Stimulated Acid Output
| 0.6*
| 13.3
|
(mmol/hr)
| | |
% Time Gastric pH>3
| 65*
| 10
|
Compared to placebo, rabeprazole sodium, 10 mg, 20 mg, and 40 mg, 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 (MMOLHR/L) RABEPRAZOLE SODIUM VERSUS PLACEBO ON DAY 7 OF ONCE DAILY DOSING (MEAN±SD)*(p<0.001 versus placebo)
|
| Treatment
|
AUC
| 10 mg
| 20 mg
| 40 mg
| Placebo
|
interval
| RBP
| RBP
| RBP
| (N=24)
|
(hrs)
| (N=24)
| (N=24)
| (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 0-24
| 155.5±90.6*
| 130.9±81*
| 85.8±64.3*
| 678.5±216
|
hours
| | | | |
After administration of 20 mg rabeprazole sodium tablets once daily for eight days, the mean percent of time that gastric pH>3 or gastric pH>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 rabeprazole sodium tablets administered once daily for eight days were compared to the same parameters for placebo, as illustrated below:
TABLE 5
GASTRIC ACID PARAMETERS RABEPRAZOLE SODIUM ONCE DAILY DOSING VERSUS PLACEBO ON DAY 1 AND DAY 8a No inferential statistics conducted for this parameter.
|
* (p<0.001 versus placebo)
|
b Gastric pH was measured every hour over a 24-hour period.
|
Parameter
| Rabeprazole sodium 20 mg QD
| 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>3b
| 54.6*
| 68.7*
| 19.1
| 21.7
|
% Time Gastric pH>4b
| 44.1*
| 60.3*
| 7.6
| 11.0
|
Effects on Esophageal Acid Exposure
In patients with gastroesophageal reflux disease (GERD) and moderate to severe esophageal acid exposure, rabeprazole sodium 20 mg and 40 mg tablets per day decreased 24-hour esophageal acid exposure. After seven days of treatment, the percentage of time that esophageal pH<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>4 for at least 35% of the 24-hour period; this level was achieved in 90% of subjects receiving rabeprazole sodium 20 mg and in 100% of subjects receiving rabeprazole sodium 40 mg. With rabeprazole sodium 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
In patients given daily doses of rabeprazole sodium for up to eight weeks to treat ulcerative or erosive esophagitis and in patients treated for up to 52 weeks to prevent recurrence of disease the median fasting gastrin level increased in a dose-related manner. The group median values stayed within the normal range.
In a group of subjects treated daily with rabeprazole sodium 20 mg tablets for 4 weeks a doubling of mean serum gastrin concentrations were observed. Approximately 35% of these treated subjects developed serum gastrin concentrations above the upper limit of normal. In a study of CYP2C19 genotyped subjects in Japan, poor metabolizers developed statistically significantly higher serum gastrin concentrations than extensive metabolizers.
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 rabeprazole sodium tablets (10 or 20 mg/day) 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 volunteers treated with rabeprazole sodium 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 rabeprazole sodium 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 rabeprazole sodium and ocular effects.
Microbiology
The following in vitro data are available but the clinical significance is unknown.
Rabeprazole sodium, amoxicillin and clarithromycin as a three drug regimen has been shown to be active against most strains of Helicobacter pylori in vitro and in clinical infections as described in the Clinical Studies (14) and Indications and Usage (1) sections.
Helicobacter pylori
Susceptibility testing of H. pylori isolates was performed for amoxicillin and clarithromycin using agar dilution methodology1, and minimum inhibitory concentrations (MICs) were determined.
Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures.
Incidence of Antibiotic-Resistant Organisms Among Clinical Isolates
Pretreatment Resistance: Clarithromycin pretreatment resistance rate (MIC ≥ 1 μg/mL) to H. pylori was 9% (51/560) at baseline in all treatment groups combined. A total of > 99% (558/560) of patients had H. pylori isolates which were considered to be susceptible (MIC ≤ 0.25 μg/mL) to amoxicillin at baseline. Two patients had baseline H. pylori isolates with an amoxicillin MIC of 0.5 μg/mL.
For susceptibility testing information about Helicobacter pylori, see Microbiology section in prescribing information for clarithromycin and amoxicillin.
TABLE 6
CLARITHROMYCIN SUSCEPTIBILITY TEST RESULTS AND CLINICAL/BACTERIOLOGIC OUTCOMESaFOR A THREE DRUG REGIMEN (RABEPRAZOLE 20 MG TWICE DAILY, AMOXICILLIN 1000 MG TWICE DAILY, AND CLARITHROMYCIN 500 MG TWICE DAILY FOR 7 OR 10 DAYS)aIncludes only patients with pretreatment and post-treatment clarithromycin susceptibility test results.
|
b Susceptible (S) MIC ≤ 0.25 μg/mL, Intermediate (I) MIC = 0.5 μg/mL, Resistant (R) MIC ≥ 1 μg/mL
|
Days of RAC Therapy
| Clarithromycin Pretreatment Results
| Total Number
| H. pylori Negative (Eradicated)
| H. pylori Positive (Persistent) Post-Treatment Susceptibility Results
|
| | | | S b
| I b
| R b
| No MIC
|
7
| Susceptible b
| 129
| 103
| 2
| 0
| 1
| 23
|
7
| Intermediate b
| 0
| 0
| 0
| 0
| 0
| 0
|
7
| Resistant b
| 16
| 5
| 2
| 1
| 4
| 4
|
10
| Susceptible b
| 133
| 111
| 3
| 1
| 2
| 16
|
10
| Intermediate b
| 0
| 0
| 0
| 0
| 0
| 0
|
10
| Resistant b
| 9
| 1
| 0
| 0
| 5
| 3
|
Patients with persistent H. pylori infection following rabeprazole, amoxicillin, and clarithromycin therapy will likely have clarithromycin resistant clinical isolates. Therefore, clarithromycin susceptibility testing should be done when possible. If resistance to clarithromycin is demonstrated or susceptibility testing is not possible, alternative antimicrobial therapy should be instituted.
Amoxicillin Susceptibility Test Results and Clinical/Bacteriological Outcomes: In the U.S. multicenter study, a total of >99% (558/560) of patients had H. pylori isolates which were considered to be susceptible (MIC ≤ 0.25 μg/mL) to amoxicillin at baseline. The other 2 patients had baseline H. pylori isolates with an amoxicillin MIC of 0.5 μg/mL, and both isolates were clarithromycin-resistant at baseline; in one case the H. pylori was eradicated. In the 7- and 10-day treatment groups 75% (107/145) and 79% (112/142), respectively, of the patients who had pretreatment amoxicillin susceptible MICs (≤ 0.25 μg/mL) were eradicated of H. pylori. No patients developed amoxicillin-resistant H. pylori during therapy.