title: Potentiation of local anesthetic activity of neosaxitoxin with bupivacaine or epinephrine: development of a long-acting pain blocker.
abstract: Local anesthetics effectively block and relieve pain, but with a relatively short duration of action, limiting its analgesic effectiveness. Therefore, a long-acting local anesthetic would improve the management of pain, but no such agent is yet available for clinical use. The aim of this study is to evaluate the potentiation of the anesthetic effect of neosaxitoxin, with bupivacaine or epinephrine in a randomized double-blind clinical trial. Ten healthy males were subcutaneously injected into the left and right forearms with a randomized pair of the following treatments: (i) bupivacaine (5 mg); (ii) neosaxitoxin (10 microg); (iii) neosaxitoxin (10 microg) plus bupivacaine (5 mg), and (iv) neosaxitoxin (10 microg) plus epinephrine (1:100.000), but all participant received all four formulations (in 2 ml; s.c.), with 1 month elapsing between the two round of experiments. A validated sensory and pain paradigm was used for evaluating the effect of the treatment 0-72 h after the injections, measuring sensory, pain, and mechanical touch perception threshold. The duration of the effect produced by combined treatments was longer than that by the single drugs. In conclusion, bupivacaine and epinephrine potentiate the local anesthetic effect of neosaxitoxin in humans when co-injected subcutaneously. The present results support the idea that neosaxitoxin is a new long-acting local pain blocker, with highly potential clinical use.
authors.affiliation: Membrane Biochemistry Laboratory, Programme of Physiology and Biophysics, ICBM, Faculty of Medicine, University of Chile, P.O. Box 70005, Santiago 7, Chile.
authors.forename: Alberto J
authors.initials: AJ
authors.lastname: Rodriguez-Navarro
authors.forename: Marcelo
authors.initials: M
authors.lastname: Lagos
authors.forename: Cristian
authors.initials: C
authors.lastname: Figueroa
authors.forename: Carlos
authors.initials: C
authors.lastname: Garcia
authors.forename: Pedro
authors.initials: P
authors.lastname: Recabal
authors.forename: Pamela
authors.initials: P
authors.lastname: Silva
authors.forename: Veronica
authors.initials: V
authors.lastname: Iglesias
authors.forename: Nestor
authors.initials: N
authors.lastname: Lagos
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology / Q000627:therapeutic use*; D002045:Bupivacaine / Q000494:pharmacology / Q000627:therapeutic use*; D004311:Double-Blind Method; D004338:Drug Combinations; D004357:Drug Synergism; D004837:Epinephrine / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D006930:Hyperalgesia / Q000188:drug therapy*; D008297:Male; D017288:Pain Threshold / Q000187:drug effects; D010812:Physical Stimulation / Q000009:adverse effects; D012530:Saxitoxin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D012684:Sensory Thresholds / Q000187:drug effects; D013997:Time Factors; D055815:Young Adult
chemical_list: D000779:Anesthetics, Local; D004338:Drug Combinations; D012530:Saxitoxin; C034902:neosaxitoxin; D002045:Bupivacaine; D004837:Epinephrine