In this 9 month, randomized, placebo-controlled, parallel-group, multicenter intervention trial, 500 patients will be randomly assigned (1:1 ratio) to receive either azithromycin or placebo on top of standard therapy in the acute treatment of COPD exacerbations requiring hospitalization. The study drug (azithromycin or placebo) will be initiated and uploaded within 48 hours after hospital admission (500mg once a day for 3 days) and subsequently administered for a prolonged period of 3 months at a lower maintenance dose (250mg every 2 days). An additional follow-up period of 6 months without study drug will be foreseen to study relapse after study drug withdrawal.