In this prospective and controlled trial , 111 naive HP-positive patients were randomized to receive standard triple therapy omeprazole ( 20mg twice daily ) , amoxicillin ( 1g twice daily ) , and clarithromycin ( 500mg twice daily ) for 10 days ( OAC ) after antimicrobial susceptibility testing if there was no resistance to clarithromycin ( ClariS ) or empirical 10-day OAC for first-line therapy of HP ( ClariNA ) .