Peak plasma concentrations after oral morphine: A systematic review

We performed a systematic review of 69 studies with information on 2146 sub jects (454 patients and 1692 healthy volunteers) to examine the maximum pla sma concentration (C-max) and the time taken to reach maximum concentration (T-max) for different oral morphine formulations, and to clarify factors c ontributing to variability. Data from healthy volunteers reflected that see n for patients but was less variable. There was minimal difference between single and multiple doses, suggesting no accumulation of morphine. For imme diate-release morphine there was no difference in either dose-corrected C-m ax or T-max between solution and tablets, or between different salts. For c ontrolled-release formulations, little difference was observed between bran ds. Only for once-daily formulations was there any difference in absorption between fed and fasted, with a T-max for fed subjects considerably longer than for fasted. There was no evidence for any difference between values ob tained by radioimmunoassay (RIA) or high-performance liquid chromatography (HPLC). (C) U.S. Cancer Pain Relief Committee, 1998.