Intrathecal opioid conversions: the importance of lipophilicity.

An intrathecal opioid infusion using an implanted programmable pump is frequently used for controlling refractory pain. Morphine, which is the only opioid presently approved by the FDA for use in such pumps, occasionally fails to work or is not tolerated by the patient; therefore other opioids are considered for infusions. When switching from one drug to another, it is important to consider not only equianalgesic dose conversions, but also lipophilicity. We report on three cases that demonstrate the need to use only a fraction of the equianalgesic dose when shifting from lipophilic to nonlipophilic opioids in such infusions.