Abstract
Topical drugs avoid many of the problematic side effects of systemic agents. Immersion of the tail of a mouse into a solution of dimethyl sulfoxide (DMSO)-containing morphine produces a dose-dependent, naloxone-sensitive, analgesia (ED50 6.1 mM; CL 4.3, 8.4) limited to the portion of the tail exposed to the drug. DMSO alone in this paradigm had no analgesic activity. Like morphine, the opioids levorphanol (ED50 5.0 mM; CL 3.8, 7.8) and buprenorphine (ED50 1.1 mM; CL 0.7, 1.5) were effective topical analgesics. Lidocaine also was active in the tail-flick assay (ED50 2.5 mM; CL 2.0, 3.4), with a potency greater than morphine. As expected, the free base of lidocaine was more potent than its salt. Combinations of a low dose of lidocaine with a low dose of an opioid yielded significantly greater than additive effects for all opioids tested. Isobolographic analysis confirmed the presence of synergy between lidocaine and morphine, levorphanol and buprenorphine. These studies demonstrate a potent interaction peripherally between opioids and a local anesthetic and offer potential advantages in the clinical management of pain.
Footnotes
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Send reprint requests to: Gavril W. Pasternak, M.D., Ph.D., Department of Neurology, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY 10021. E-mail:pasterng{at}mskmail.mskcc.org
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↵1 This work was supported, in part, by a research grant (DA07241) and a Senior Scientist Award (DA00220) (to G.W.P.) and a Mentored Scientist Award (DA00405) (to Y.A.K.) from the National Institute on Drug Abuse, as well as a core grant (CA08748) from the National Cancer Institute and a grant from EpiCept Corporation.
- Abbreviations:
- DMSO
- dimethyl sulfoxide
- NMDA
- N-methyl-d-aspartate
- CL
- confidence limits
- Received April 17, 2000.
- Accepted June 28, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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