Local anesthetic drugs: penetration from the spinal extradural space into the neuraxis.

Local anesthetics, injected into the spinal extradural space, can be recovered from the spinal cord and brain. Transport from the extradural space into the neuraxis is independent of an active circulation. Distribution is greatest in the periphery of the cord and is most intense near the site of injection. The drugs probably diffuse into the subperineural spaces of the mixed nerves and then pass centripetally along the spinal roots into the cerebrospinal fluid and the cord.