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. 2023 Feb 13;8(2):e1062. doi: 10.1097/PR9.0000000000001062

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Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of The International Association for the Study of Pain.

This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 3. — Effects of ketamine, lidocaine, combination of ketamine and lidocaine, and ascorbic acid in the prevention of fentanyl-induced hyperalgesia. Time 0 in all graphs indicates the measurements taken before the animals underwent surgery and fentanyl injection. Threshold values are presented as % of baseline and were normalized based on the threshold at time 0. All animals underwent fentanyl OIH induction and surgical procedure on the right hind paw. Graphs on the left side display paw withdrawal threshold values in seconds in the hot-plate test, and graphs on the right side displays right hind paw withdrawal threshold values in the test in grams obtained through the von Frey test. In all graphs, the black line represents the control group of animals and the colorful lines represent animals receiving ketamine (A and B), lidocaine (C and D), ascorbic acid (E and F), and the combination of lidocaine and ketamine (G and H) as a preventive treatment for OIH. *P < 0.05 compared with the PBS group. Two-way ANOVA, followed by the Dunnett multiple comparison test, N = 5–8 animals per group. ANOVA, analysis of variance; OIH, opioid-induced hyperalgesia.