DOSE RATIO BETWEEN MORPHINE AND HYDROMORPHONE IN PATIENTS WITH CANCERPAIN - A RETROSPECTIVE STUDY

Morphine (M) and hydromorphone (HM) are commonly used opioid analgesic s fbr cancer pain. Opioid rotation is often necessary in the event of toxicity and/or inadequate analgesia. Equianalgesic reference tables b ased on single dose comparisons are possibly inadequate for patients o n chronic treatment and developing tolerance. This retrospective study of opioid rotation involving M and HM sought to determine the equiana lgesic dose ratio for 91 rotations in 74 consecutively evaluable cance r pain patients. Only rotations involving subcutaneous (sc-sc) and ora l (po-po) routes were evaluated. There were 44 rotations from M-HM (34 : sc-sc, 10: po-po) and 47 rotations from HM-M (35: sc-sc, 12: po-po). Expressing all ratios as M/HM, the median dose ratios (lower-upper qu artiles) for sc and po rotations were 4.92 (4.1-5.9) vs. 5.76 (4.9-5.8 ) for M-HM (P = 0.28, NS) and 4.0 (3.1-4.8) vs. 3.45 (2.8-4.2) for HM- M (P = 0.4, NS), respectively. Pain intensity, as measured on a visual analogue scale (VASP), showed no significant difference between mean values pre- and post-rotation. A unified overall median dose ratio of 4.29 (3.3-5.3, lower-upper quartiles) was calculated by expressing all of the HM-M dose ratios as M/HM and combining them with the dose rati os for all of the M-HM rotations. This suggests a potency ratio of app roximately 4.3:1 between M and HM. When expressed as M/HM for dose rat io comparison, the median dose ratio for all HM-M rotations was 3.7 (2 .9-4.5, lower-upper quartiles) vs. 5 (4.2-5.9) for M-HM rotations (P = 0.0001), suggesting that the opioid to which rotation is taking place is more potent than our proposed unified overall median dose ratio of 4.29:1 would predict. Our data suggests that HM is 5 times more poten t than M when given second (M-HM), but is only 3.7 times more potent w hen given first (HM-M). We therefore recommend a ratio of 5 for M/HM i n rotating from M to HM and ratio of 3.7 for M/HM when rotating from H M to M in patients exposed to chronic dosing of these opioids. There w as no correlation observed between M-HM and HM-M dose ratios and the l evel of previous opioid dose, in contrast to HM to methadone rotation where the dose ratio was higher in patients receiving higher doses of HM. (C) 1997 International Association for the Study of Pain. Publishe d by Elsevier Science B.V.