Additive effect of clarithromycin combined with 14-hydroxy clarithromycin, erythromycin, amoxycillin, metronidazole or omeprazole against Helicobacter pylori.

The in-vitro activities of clarithromycin, 14-OH clarithromycin, erythromycin, amoxycillin, metronidazole and omeprazole against Helicobacter pylori were determined at pH 7.2 and 5.5. At pH 5.5 the activities of clarithromycin and erythromycin decreased approximately 16 times while 14-OH clarithromycin was less influenced. Chequerboard titration indicated that the combined activity of clarithromycin and the other compounds was additive.