• Ching-Hsia Hung, Chong-Chi Chiu, Kuo-Sheng Liu, Yu-Wen Chen, and Jhi-Joung Wang.
• From the *Department of Physical Therapy and †Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University; and ‡Department of Electrical Engineering, Southern Taiwan University of Science and Technology, Tainan; §Department of General Surgery, Chi Mei Medical Center, Tainan and Liouying; ∥Department of Pharmacy, Chia Nan University of Pharmacy and Science, Tainan; ¶Department of Physical Therapy and Graduate Institute of Rehabilitation Science, College of Health Care, China Medical University, Taichung; and **Department of Medical Research, Chi Mei Medical Center, Tainan, Taiwan.
• Reg Anesth Pain Med. 2017 May 1; 42 (3): 351-356.

BackgroundThe purpose of this experiment was to investigate the interactions of the local anesthetic lidocaine combined with an agent (serotonin or dopamine) as infiltrative anesthetics.MethodsCutaneous analgesia was characterized by the blockade of the cutaneous trunci muscle reflex following 6 skin pinpricks on the rat back. Serotonin or dopamine at producing cutaneous analgesia in a dosage-dependent fashion was compared with lidocaine. Drug-drug interactions were calculated using the isobolographic analysis.ResultsWe revealed that serotonin, dopamine, and lidocaine provoked dose-related cutaneous analgesic effects. On the 50% effective dose basis, the rank of drugs' potency was found to be serotonin (1.70 [1.56-1.85] μmol) > lidocaine (5.18 [4.67-5.75] μmol) > dopamine (43.0 [40.9-45.2] μmol) (P < 0.01). At doses equivalent to their 25%, 50%, and 75% effective doses, serotonin or dopamine elicited a longer duration of action than lidocaine (P < 0.01) on producing cutaneous analgesia. Coadministration of serotonin or dopamine with lidocaine produced a synergistic effect.ConclusionsThe preclinical data showed that serotonin and dopamine produce dose-related cutaneous analgesic effects as an infiltrative anesthetic. Serotonin has a better potency with a much longer duration of action compared with lidocaine at provoking cutaneous analgesia. Serotonin or dopamine as an adjuvant increases the quality of lidocaine in cutaneous analgesia.

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