title: Sodium channel blockade may contribute to the analgesic efficacy of antidepressants.
abstract: Sodium channel blockers such as lidocaine, lamotrigine, and carbamazepine can be effective in the treatment of neuropathic pain. Though not approved for neuropathic pain indications, tricyclic antidepressants are often considered first-line treatment for conditions such as post-herpetic neuralgia and diabetic neuropathy. Several tricyclic antidepressants have been shown to block peripheral nerve sodium channels, which may contribute to their antihyperalgesic efficacy. In this study, we compared the sodium channel-blocking potency of a number of antidepressants, including tricyclic antidepressants and selective serotonin reuptake inhibitors. All compounds tested inhibited Na(V)1.7 in a state- and use-dependent manner, with affinities for the inactivated state ranging from 0.24 micromol/L for amitriptyline to 11.6 micromol/L for zimelidine. The tricyclic antidepressants were more potent blockers of Na(V)1.7. Moreover, IC(50)s for block of the inactivated state for amitriptyline, nortriptyline, imipramine, desipramine, and maprotiline were in the range of therapeutic plasma concentrations for both the treatment of depression as well as neuropathic pain. By contrast, fluoxetine, paroxetine, mianserine, and zimelidine had IC(50)s for Na(V)1.7 outside their therapeutic concentration ranges and generally were not efficacious against post-herpetic neuralgia or diabetic neuropathy. These results suggest that block of peripheral nerve sodium channels may contribute to the antihyperalgesic efficacy of certain antidepressants.
  
  
  CONCLUSIONS
  Tricyclic antidepressants are often considered first-line treatment for neuropathic pain. Some tricyclic antidepressants block sodium channels, which may contribute to their antihyperalgesic efficacy. In the current study, we compared the potency of peripheral sodium channel blockade for several tricyclic antidepressants and selective serotonin reuptake inhibitors with their therapeutic efficacy.
authors.affiliation: Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey 07065-0900, USA.
authors.forename: Ivy E
authors.initials: IE
authors.lastname: Dick
authors.forename: Richard M
authors.initials: RM
authors.lastname: Brochu
authors.forename: Yamini
authors.initials: Y
authors.lastname: Purohit
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Kaczorowski
authors.forename: William J
authors.initials: WJ
authors.lastname: Martin
authors.forename: Birgit T
authors.initials: BT
authors.lastname: Priest
mesh_terms: D000700:Analgesics; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D062556:NAV1.7 Voltage-Gated Sodium Channel; D009475:Neurons, Afferent / Q000187:drug effects; D017374:Paroxetine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000700:Analgesics; D000779:Anesthetics, Local; D000928:Antidepressive Agents; D018687:Antidepressive Agents, Second-Generation; D000929:Antidepressive Agents, Tricyclic; D062556:NAV1.7 Voltage-Gated Sodium Channel; C486866:SCN9A protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D017374:Paroxetine; D013779:Tetrodotoxin