Rabeprazole Sodium (Page 7 of 11)

12.4 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 [see Indications and Usage (1) , Clinical Studies (14.5)].

Helicobacter pylori

Susceptibility testing of H. pylori isolates was performed for amoxicillin and clarithromycin using agar dilution methodology 1 , 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 mcg/mL) to H. pylori was 9% (51/560) at baseline in all treatment groups combined. Greater than 99% (558/560) of patients had H. pylori isolates which were considered to be susceptible (MIC ≤0.25 mcg/mL) to amoxicillin at baseline. Two patients had baseline H. pylori isolates with an amoxicillin MIC of 0.5 mcg/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 Outcomes a for a Three Drug Regimen (Rabeprazole Sodium Delayed-Release Tablets 20 mg Twice Daily, Amoxicillin 1000 mg Twice Daily, and Clarithromycin 500 mg Twice Daily for 7 or 10 Days)
a Includes only patients with pretreatment and post-treatment clarithromycin susceptibility test results. b Susceptible (S) MIC ≤0.25 mcg/mL, Intermediate (I) MIC = 0.5 mcg/mL, Resistant (R) MIC ≥1 mcg/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, greater than 99% (558/560) of patients had H. pylori isolates which were considered to be susceptible (MIC ≤0.25 mcg/mL) to amoxicillin at baseline. The other 2 patients had baseline H. pylori isolates with an amoxicillin MIC of 0.5 mcg/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 mcg/mL) were eradicated of H. pylori. No patients developed amoxicillin-resistant H. pylori during therapy.

12.5 Pharmacogenomics

In a clinical study in evaluating rabeprazole sodium delayed-release tablets in Japanese adult patients categorized by CYP2C19 genotype (n=6 per genotype category), gastric acid suppression was higher in poor metabolizers as compared to extensive metabolizers. This could be due to higher rabeprazole plasma levels in poor metabolizers. The clinical relevance of this is not known. Whether or not interactions of rabeprazole sodium with other drugs metabolized by CYP2C19 would be different between extensive metabolizers and poor metabolizers has not been studied.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

In an 88/104-week carcinogenicity study in CD-1 mice, rabeprazole at oral doses up to 100 mg/kg/day did not produce any increased tumor occurrence. The highest tested dose produced a systemic exposure to rabeprazole (AUC) of 1.40 mcg•hr/mL which is 1.6 times the human exposure (plasma AUC 0-∞ = 0.88 mcg•hr/mL) at the recommended dose for GERD (20 mg/day). In a 28-week carcinogenicity study in p53 +/- transgenic mice, rabeprazole at oral doses of 20, 60, and 200 mg/kg/day did not cause an increase in the incidence rates of tumors but produced gastric mucosal hyperplasia at all doses. The systemic exposure to rabeprazole at 200 mg/kg/day is about 17 to 24 times the human exposure at the recommended dose for GERD. In a 104-week carcinogenicity study in Sprague-Dawley rats, males were treated with oral doses of 5, 15, 30 and 60 mg/kg/day and females with 5, 15, 30, 60, and 120 mg/kg/day. Rabeprazole produced gastric enterochromaffin-like (ECL) cell hyperplasia in male and female rats and ECL cell carcinoid tumors in female rats at all doses including the lowest tested dose. The lowest dose (5 mg/kg/day) produced a systemic exposure to rabeprazole (AUC) of about 0.1 mcg•hr/mL which is about 0.1 times the human exposure at the recommended dose for GERD. In male rats, no treatment related tumors were observed at doses up to 60 mg/kg/day producing a rabeprazole plasma exposure (AUC) of about 0.2 mcg•hr/mL (0.2 times the human exposure at the recommended dose for GERD).
Rabeprazole was positive in the Ames test, the Chinese hamster ovary cell (CHO/HGPRT) forward gene mutation test, and the mouse lymphoma cell (L5178Y/TK+/–) forward gene mutation test. Its demethylated-metabolite was also positive in the Ames test. Rabeprazole was negative in the in vitro Chinese hamster lung cell chromosome aberration test, the in vivo mouse micronucleus test, and the in vivo and ex vivo rat hepatocyte unscheduled DNA synthesis (UDS) tests. Rabeprazole at intravenous doses up to 30 mg/kg/day (plasma AUC of 8.8 mcg•hr/mL, about 10 times the human exposure at the recommended dose for GERD) was found to have no effect on fertility and reproductive performance of male and female rats.

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