[Pharmacology of narcotics administered by the epidural or intrathecal route (author's transl)]

Owing to the presence of specific opiate receptors in the spinal cord, analgesia can be obtained with epidural or intrathecal injections of morphine derivatives. The duration of analgesia depends upon the degree of water solubility of the compound. Compounds with low coefficient of distribution in lipids (e.g. morphine) do not readily cross the blood-brain barrier and have a prolonged action, whereas the duration of analgesia induced by highly lipid-soluble compounds, such as dextromoramide and phenoperidine, is not very different from that obtained with more conventional routes of administration. The fact that large amounts of narcotics are taken up by the spinal cord explains that central effects are relatively rare. However, side-effects may be observed, and their frequency mainly depends upon the quantity of narcotic injected. These side-effects reduce the number of indications, which cannot yet be precisely determined. Epidural and intrathecal analgesia appears to be particularly useful during the post-operative period in patients liable to respiratory complications.