Co-administration of APTIVUS and low dose ritonavir with single dose methadone was demonstrated to decrease methadone pharmacokinetic parameters (AUC0-24h ratio of 0.47 with 90% CI [0.44; 0.51] and Cmax ratio of 0.45 with 90% CI [0.41; 0.49]), in a study conducted in fasted healthy subjects.