METHODS	This double-blind , placebo-controlled , parallel-group study was conducted at 17 sites in the United States and enrolled adult subjects ( aged 18-80 years ) who were randomized to 4 groups ( IV acetaminophen 1000 mg [ 100 mL ] q6h ; IV acetaminophen 650 mg [ 65 mL ] q4h ; IV placebo 100 mL q6h ; or IV placebo 65 mL q4h ) , each given as a 15-minute infusion after surgery for 24 hours .\