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