Physical dependence or withdrawal is an expected effect of prolonged opioid therapy. Oxytrex (oxycodone + ultralow-dose naltrexone) is an investigational drug shown here to minimize physical dependence while providing strong analgesia with twice-daily dosing. In this 719-patient, double-blind, placebo- and active-controlled Phase III clinical trial in chronic low back pain, patients were randomized to receive placebo, oxycodone qid, or oxytrex qid or bid. Each oxytrex tablet contains 1 μg naltrexone; oxytrex bid and qid treatments provide 2 and 4 μg naltrexone/day, respectively. Following a washout, patients with pain ≥5 on a 0-10 scale were dose-escalated weekly from 10 up to 80 mg/day until reaching adequate pain relief (≤2) or a tolerable level of side effects. Following titration, the dose was fixed for 12 weeks. Active treatment groups attained comparable analgesia despite significantly lower drug use (P = .03) by oxytrex patients. Patients taking oxytrex bid reported 55% less physical dependence than patients on oxycodone (P = .01) by the Short Opiate Withdrawal Scale 24 h after treatment cessation. Oxytrex bid patients also reported decreased moderate-to-severe constipation (by 44%, P = .01), somnolence (by 33%, P = .03), and pruritus (by 51%, P < .001). This is the first large well controlled study to show strong analgesia with minimal withdrawal symptoms and better safety compared with oxycodone.

Previous clinical data have shown ultralow-dose naltrexone enhances and prolongs oxycodone analgesia, and preclinical data also show a suppression of opioid tolerance and dependence. A cellular mechanism of action has been demonstrated to be the prevention of aberrant G protein signaling by mu opioid receptors caused by chronic opioid administration.