Plasma and CSF morphine concentrations after i.m. and epidural administration

Abstract Morphine concentrations in plasma and CSF after i.m. and epidural morphine administration were assayed in patients undergoing surgery of the low abdomen. Morphine concentration in CSF after i.m. administration of this drug is remarkably lower than morphine concentration in plasma. The highest value is attained in CSF after about 90' and is followed by a slow downsloping to lowest values, which were observed 4 hours after drug administration. Kinetics of morphine passage into plasma after epidural administration is similar to that found after i.m. administration. In the latter experimental condition (epidural administration), concentrations of morphine in CSF 30' after administration are markedly lower than those found in plasma. However, 60 min. after epidural administration plasma and CSF morphine concentrations are similar, in particular CSF concentrations are 4 to 8 times higher than those obtained after i.m. administration. Such high levels persists for a long time.