[The estimation of the i.m. morphine-equivalent in cancer pain treatment with different opioids or different routes of administrations. Practical meaning and limitations.].

During the long-term treatment with opioids it is sometimes important to switch the opioid or change the route of administration. The estimation of morphine-equivalents can be helpful in this range because it clarifies the dose in milligramm required for different clinical situations. The basis of this estimation is the equianalgesic potency of opioids. One i.m. morphine-equivalent is the analgesic dose of an opioid (i.m. injected) equal to the analgesic effect of 1 mg morphine (i.m.). The relationships between equianalgesic doses and intramuscular and oral routes of applications are listed in tables. The cross-tolerance between different opioids during long-term treatment is not complete. To avoid an overdose, we suggest a reduction in the calculated opioid dose of 50%. Additional "rescue doses" can be used during the period immediately the change to provied satisfactory pain control. A new opioid dosage should be calculated every 24 hours based on the basaline dose plus the total quantity of "rescue" medication required by the patient. Useful starting point for calculation an effective dose when changing from one opioid or route of administration to another can result in improved pain control that is more responsive to patient need. The limitations are 1. individual differences in the response to opioids, especially during long-term treatment and in the development of analgesic tolerance, 2. individual differences in the response to alternatives routes of administration, and 3. the unknown degree of cross tolerance among opioid drugs. The scientific meaning of the estimation of i.m. morphine-equivalent is discussed.