Berdine HJ and Nesbit SA. Equianalgesic dosing of opioids. J. Pain Palliat. Care Pharmacother.2006; 20: 79-84.
Souter KJ and Fitzgibbon D. Equianalgesic dose guidelines for long-term opioid use: Theoretical and practical considerations. Seminars in Anesthesia. Periop. Med. Pain 2004; 23: 271-280.