Together , cohorts 2 and 3 included phe508del CFTR homozygous and heterozygous patients , randomly assigned to either 56 days of lumacaftor ( cohort 2 : 200 mg , 400 mg , or 600 mg once per day , cohort 3 : 400 mg every 12 h ) with ivacaftor 250 mg every 12 h added after 28 days , or 56 days of placebo .