In a multicentre phase 3 trial in Belgium , Germany , the Netherlands , Switzerland , France , Sweden , Austria , Italy , Spain , and the USA , patients ( age 10-18 years old ) with Duchenne muscular dystrophy were randomly assigned in a one-to-one ratio with a central interactive web response system with a permuted block design with four patients per block to receive idebenone ( 300 mg three times a day ) or matching placebo orally for 52 weeks .