Background The range of opioid dose in patients receiving palliative care is wide and not directly related to response. The levels of opioids in therapeutic and postmortem, population group studies and forensic studies have been studies in published data.

Aim To describe the results of studies of opioids levels in living patients receiving palliative care treated for pain, and in postmortem studies between 1970 and 2009.

Method Literature review of studies concerning five of the opioids; Diamorphine, Morphine, Oxycodone, Fentanyl and Methadone, by using: Hand Search, Cochrane library (systematic Review) and Medline OvidSP, in english language. The level of evidence on each clinical study or review is determined and the evaluation focuses on the relationship between doses and opioids levels, in overdose and therapeutic use.

Results The authors found few studies in palliative care describing fatal events and blood levels in opioid overdose with variation in level, due to differences in drug metabolism. Overall 300 papers were reviewed, 251 of studies were reviewed in therapeutic and postmortem. Number of papers 71 of Studies of ante-mortem/population Group studies/therapeutics (pharmacokinetics, overdose addiction (maintenance),postoperative,cancer pain, tolerance, respiratory depression,withdrawal and data collection(dose finding)). Number of papers 180 of studies of postmortem/cadaver group studies/plasma levels (Fatal suicides, trauma victim, and accident death, coincidental and other conditions). The remaining 49 of studies were concerned with (mechanisms, switching, drug monitoring and controversy over drugs use).

Conclusions Measurement of the relationship between fatal events and opioid blood levels is difficult, due to laboratory error, blood contaminants and variations between individual subjects. It does not appear to be wise to infer opioid levels in life from postmortem evidence in cases of therapeutic opioid use.