[Peridural morphine analgesia: effects and pharmacokinetics. A double-blind study in vaginal hysterectomy patients]

In a controlled prospective double-blind-study we were able to show that the analgesic duration of epidurally applied morphine is more than four fold longer lasting than intravenous morphine. We found similar pharmacokinetics in both groups, suggesting a rapid absorption of epidurally applied morphine into the vascular system. The identical pharmacokinetics of intravenous and epidurally applied morphine suggest that only small amounts of morphine diffuse across the dura to the spinal cord, where it produces a long lasting analgesia at the opiate receptors. The comparison of serum morphine levels in patients who reported a very short lasting and very long lasting analgesia gave us no pharmacokinetic explanation for this difference.