Morphine Tolerance and Dependence

摘要

With the advent of blood morphine assay techniques, it is possible to be more objective about the status of a patient with respect to morphine tolerance. It is not the total/24 hours oral morphine dose that is important but the resultant blood morphine level that determines whether the patient's pain behaviour is morphine sensitive or morphine resistant. Our Pain Unit has built up a database of patients receiving either morphine or methadone [1] and has, based on the responses of chronic non cancer pain sufferers, somewhat empirically used a blood morphine level between 50 and 150 ng/ml as being the therapeutic level. The therapeutic blood level for methadone is the same as for morphine as, molecule for molecule, they have the same analgesic effect.. The term dependence is loosely used by both medical and non medical people but strictly refers to the onset of opioid withdrawal symptoms on the sudden cessation of the opioid drug. This has no relationship to addiction (the use of an opioid drug for non pain relieving reasons). Physical dependence refers to the need of chronic opioid users (whether it is by medical or recreational users) to have opioid substances occupying the opioid receptors - otherwise abstinence will occur. Psychological dependence refers to those recreational users of opioid drugs who use the opioids sporadically.