Low rate of emergence of clarithromycin-resistant Helicobacter pylori with amoxycillin co-therapy

Background: Patients with persistent Helicobacter pylori infection following treatment with clarithromycin or omeprazole plus clarithromycin often develop clarithromycin resistance, Aim: To assess pre- and post-treatment antibiotic resistance in three double-blind trials of triple therapy with omeprazole, amoxycillin and clarithromycin. Methods: Patients with H. pylori and duodenal ulcer (studies 1 and 2) or history of duodenal ulcer (study 3) were randomly assigned to 10 day courses of omeprazole 20 mg b.d., amoxycillin 1 g b.d. and clarithromycin 500 mg b.d. (OAC) or placebo, amoxycillin 1 g b.d. and clarithromycin 500 mg b.d. (AC), Endoscopy was performed at baseline and 4 weeks after completion of therapy in studies 1 and 2, and at 4-6 weeks after therapy in study 3. At baseline, H. pylori was diagnosed by CLO test with confirmation by histology, or by culture. Eradication was defined as no positive biopsy test and greater than or equal to 2 negative tests. Susceptibility testing was performed using the Etest. Results: In the 91 patients with pre-treatment susceptible isolates who had persistent infection after AC, 10 developed resistance, eight had intermediate susceptibility and 73 continued to have clarithromycin-susceptible H. pylori isolates. In the 10 patients with pre-treatment susceptible isolates who had persistent infection after OAC, three developed clarithromycin resistance and seven still had susceptible isolates. Conclusions: Use of amoxycillin co-therapy results in a low rate of clarithromycin resistance developing in patients with persistent H. pylori infection following therapy with a clarithromycin-containing regimen.