title: Methylprednisolone shortens the effects of bupivacaine on sensory nerve fibers in vivo.
abstract: Perineural administration of corticosteroids is frequently applied in the treatment of a variety of chronic pain conditions. Methylprednisolone selectively inhibits the transmission of nerve impulses in C-fibers whereas A-fiber activity is unaffected. In the present study the effect of a mixture of 0.05 ml of methylprednisolone (40 mg/ml) and 0.05 ml of bupivacaine (5 mg/ml) was compared to that of 0.05 ml bupivacaine (5 mg/ml) using a plantar nerve block model in the rat. The conduction of impulses in electrically stimulated A-fibers of the plantar nerve was monitored by a bipolar volley recording from the sciatic nerve. Impulse conduction in electrically stimulated C-fibers was studied through a C-fiber evoked segmental flexion reflex. The function of both the A-fibers and the C-fibers exposed to the methylprednisolone-bupivacaine mixture showed a less profound block with signs of earlier recovery than those exposed to plain bupivacaine. The A-fibers recovered somewhat faster than the C-fibers. It is postulated that methylprednisolone adjuvant to bupivacaine affects the intra-axonal uptake of bupivacaine in C-fibers but not in A-fibers by some unknown mechanism. The effect seems to be longer lasting in C-fibers than in A-fibers.
authors.affiliation: Department of Anaesthesiology, Lund University, Malmö General Hospital, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Johansson
mesh_terms: D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology*; D008297:Male; D008775:Methylprednisolone / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000779:Anesthetics, Local; D005938:Glucocorticoids; D008775:Methylprednisolone; D002045:Bupivacaine