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Updated: Mar 18, 2026

Electrophysiological Methods to Assess Peripheral Pain Block in an Anesthetized Rat
Published on: November 21, 2025
Intrathecal Nalbuphine and Naloxone Produce Nociceptive and Motor Block in Rats
An-Kuo Chou1,2, Chong-Chi Chiu3,4, Yu-Wen Chen5,6
1Department of Anesthesiology, China Medical University Hospital, Taichung, Taiwan.
Introduction:
Naloxone blocks Na+ channels and produces cutaneous analgesia, but it is unknown whether naloxone or its analog, nalbuphine, produces spinal anesthesia. The purpose of this study was to assess the effects of intrathecal nalbuphine and naloxone on motor and nociceptive blockade.
Methods:
Sprague-Dawley rats received intrathecal injections of nalbuphine, naloxone, and the local anesthetic lidocaine (n = 6 for each group). Following intrathecal injection, motor function (extensor strength) and nociceptive responses (pinch test) were assessed. A combination of intrathecal nalbuphine and lidocaine at four fixed ratios was employed for isobolographic analysis.
Results:
Intrathecal injection of nalbuphine (1.6 mg) and naloxone (1.6 mg) produced motor and nociceptive blockade. The ED50 (50% effective dose) values of intrathecal nalbuphine for motor (1.50 [1.39-1.62] mg) and nociceptive (1.39 [1.28-1.50] mg) blockade were greater than those of lidocaine for motor (0.36 [0.32-0.40] mg) and nociceptive (0.31 [0.28-0.35] mg) blockade, respectively. At equianesthetic doses (ED25, ED50, and ED75), the duration of motor and nociceptive blockade was longer with intrathecal nalbuphine than with lidocaine (p<0.01). After an isobolographic analysis of the interaction between intrathecal nalbuphine and lidocaine, the experimental ED50 values did not differ significantly from the calculated additive ED50 values.
Discussion:
Intrathecal nalbuphine produces a dose-dependent spinal block that is weaker but longer- lasting than lidocaine, and its combination with lidocaine results in an additive spinal block effect, similar to two local anesthetics.
Conclusions:
Intrathecal nalbuphine produces a dose-dependent spinal block. The spinal block induced by intrathecal nalbuphine is weaker than that of lidocaine but has a longer duration of action. The combined intrathecal injection of nalbuphine and lidocaine produces an additive spinal block effect, similar to the combination of two local anesthetics.
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