In this phase 3 , double-blind , placebo-controlled study undertaken at 76 centres in Asia , Australia , Canada , Europe , and the USA , adults ( aged 18 years old ) with active psoriatic arthritis were randomly allocated in a 1:1:1:1 ratio with computer-generated blocks to receive subcutaneous placebo or secukinumab 300 mg , 150 mg , or 75 mg once a week from baseline and then every 4 weeks from week 4 .