Background: Clarithromycin is a key antimicrobial in the combinations used to cure Helicobacter pylori infections, so there is a need to define the impact of in vitro resistance on in vivo results.
Methods: A prospective trial was designed to study the effectiveness of the 1-week combination of lansoprazole, clarithromycin and amoxycillin in 102 consecutive patients with active peptic ulcer. The pre-treatment and post-treatment sensitivity to amoxycillin, metronidazole and clarithromycin were studied by E-test, and H. pylori status was defined by histology, culture and urease test at diagnosis and one month after treatment, and by urea-breath test 2 months after treatment.
Results: The eradication rate (intention-to-treat analysis) was 77% (95% CI: 69-86). No clinical factor was found to be different between eradicated and non-eradicated patients. Clarithromycin-resistant strains were found in 10 (10%; CI: 5-17) patients. The eradication rate was 20% (CI: 3-56) in these patients vs. 83% (CI: 75-91) in patients harbouring clarithromycin-sensitive strains (P < 0.001). A logistic-regression analysis confirmed clarithromycin resistance as the only factor associated with treatment failure.
Conclusions: Clarithromycin resistance significatively impairs the effectiveness of the combination of lansoprazole, amoxycillin, and clarithromycin. The 80% efficacy goal will be difficult to reach in areas with high (>10%) primary clarithromyicin resistance, if currently recommended proton pump inhibitor-triple therapies are used.