Adding Dopamine to Proxymetacaine or Oxybuprocaine Solutions Potentiates and Prolongs the Cutaneous Antinociception in Rats

Background: We evaluated the interaction of dopamine–proxymetacaine and dopamine– oxybuprocaine antinociception using isobolograms. Methods: This experiment uses subcutaneous drug (proxymetacaine, oxybuprocaine, and dopamine) injections under the skin of the rat's back, thus simulating infiltration blocks. The dose-related antinociceptive curves of proxymetacaine and oxybuprocaine alone and in combination with dopamine were constructed, and then the antinociceptive interactions between the local anesthetic and dopamine were analyzed using isobolograms. Results: Subcutaneous proxymetacaine, oxybuprocaine, and dopamine produced a sensory block to local skin pinpricks in a dose-dependent fashion. The rank order of potency was proxymetacaine (0.57 [0.52–0.63] μmol/kg) > oxybuprocaine (1.05 [0.96–1.15] μmol/kg) > dopamine (165 [154–177] μmol/kg; P oxybuprocaine > dopamine. Coadministration of proxymetacaine or oxybuprocaine with dopamine produced a synergistic antinociceptive effect. Dopamine prolonged the duration of skin antinociception caused by proxymetacaine or oxybuprocaine. This study tests subcutaneous injections under the hairy skin, thus simulating infiltration blocks that occur during surgery. Reprints will not be available from the authors. Address correspondence to Ching-Hsia Hung, PhD, Department of Physical Therapy, College of Medicine, National Cheng Kung University, No.1 Ta-Hsueh Rd, Tainan, Taiwan. Address e-mail to chhung@mail.ncku.edu.tw. © 2018 International Anesthesia Research Society

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