Amoxicillin is a penicillin antibiotic. Clarithromycin is a macrolide antibiotic. These antibiotics fight bacteria in the body. Lansoprazole decreases the amount of acid produced in the stomach. Amoxicillin, clarithromycin, and lansoprazole is a combination medicine used in people with Helicobacter pylori (H. pylori) infection and stomach ulcers.