Although infection with Helicobacter pylori has recently been studied quite actively, there have been virtually no studies on the relationship between prior antimicrobial therapy and antibiotic resistance of H. pylori .

In order to assess the effect of previous antimicrobial use on antibiotic resistance in H. pylori and to determine if resistance affects the results of treatment for Helicobacter pylori infection, experts from the Centers for Disease Control and Prevention (CDC) and the National Medical Center Alaska conducted a retrospective cohort study.

The study included 125 adult patients infected with H. pylori who were admitted to hospital in Encore, Alaska, USA.

During the study, patient medical records were analyzed and cases of prescription antimicrobial agents were noted for 10 years before detection of Helicobacter pylori infection. The sensitivity of the H. pylori strains obtained by biopsy with fibrogastroscopy to antibiotics was determined by dilution on agar. The healing criteria for the patients was a negative urease breath test, performed 2 months after antibiotic therapy.

The results of the study showed that out of 125 patients, 37 (30%) were infected with strains of H. pylori resistant to clarithromycin and 83 (66%) had strains of H. pylori resistant to metronidazole. Resistance to clarithromycin was associated with previous use of one of the macrolide antibiotics (p less than 0.001), resistance to metronidazole was associated with previous use of metronidazole (p less than 0.001). The number of strains of H. pylori resistant to clarithromycin increased according to the number of macrolide treatments (p less than 0.001).

Among the 53 patients who received eradication treatment, including clarithromycin, the treatment was ineffective in 77% of patients infected with H. pylori strains resistant to clarithromycin (10 out of 13 ) and in 13% of patients sensitive to clarithromycin strains (5 out of 40) (relative risk 6.2, 95% confidence interval 1.9-37.1; p less than 0.001).

By analyzing the results of the study, we can conclude that the prior use by patients of macrolide antibiotics and metronidazole leads to the appearance of strains H. pylori resistant to these drugs. Resistance to clarithromycin H. pylori increases the risk of treatment failure using clarithromycin regimens.