• Ching-Hsia Hung, Chong-Chi Chiu, Kuo-Sheng Liu, Yu-Wen Chen, and Jhi-Joung Wang.
• Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan, Taiwan; Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
• Eur. J. Pharmacol. 2015 Oct 15; 765: 457-62.

AbstractThe purpose of the study was to estimate the ability of L-tyrosine to induce cutaneous analgesia and to investigate the interaction between L-tyrosine and the local anesthetic lidocaine. After subcutaneously injecting the rats with L-tyrosine and lidocaine in a dose-dependent manner, cutaneous analgesia (by blocking the cutaneous trunci muscle reflex-CTMR) was evaluated in response to the local pinprick. The drug-drug interaction was analyzed by using an isobolographic method. We showed that both L-tyrosine and lidocaine produced dose-dependent cutaneous analgesia. On the 50% effective dose (ED50) basis, the rank of drug potency was lidocaine (5.09 [4.88-5.38] μmol)>L-tyrosine (39.1 [36.5-41.8] μmol) (P<0.05). At the equipotent doses (ED25, ED50, and ED75), the duration of cutaneous analgesia caused by L-tyrosine lasted longer than that caused by lidocaine (P<0.01). Lidocaine co-administered with L-tyrosine exhibited an additive effect on infiltrative cutaneous analgesia. Our pre-clinical study demonstrated that L-tyrosine elicits the local/cutaneous analgesia, and the interaction between L-tyrosine and lidocaine is additive. L-tyrosine has a lower potency but much greater duration of cutaneous analgesia than lidocaine. Adding L-tyrosine to lidocaine preparations showed greater duration of cutaneous analgesia compared with lidocaine alone.Copyright © 2015 Elsevier B.V. All rights reserved.

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