Evaluation of the efficacy of intrathecal injection of amitriptyline and doxepin in spinal anesthesia in comparison with bupivacaine in rats

Background: Tricyclic antidepressants (TCAs) are commonly used orally for treating chronic pain states, such as neuropathic pain. TCAs produce analgesia by various mechanisms, including sodium channels, N-methyl-d-aspartate receptors, biogenic amines, opioids, inflammatory mediators, and substance P. Studies have shown that intrathecal tricyclic administration effectively attenuates pain and thermal hyperal- gesia in inflammatory and neuropathic pain in rats. Objectives: The aim of this study was to evaluate the effect of two tertiary TCAs in sen- sory and motor block. We also used bupivacaine as a strong local anesthetic for the control group. Materials and Methods: In a double-blind randomized controlled trial in an animal lab, intrathecal injection of drugs was performed in 30 Wistar male rats. We divided the subjects into 3 groups: group 1: 90 ىL Doxepine (50 mM), group 2: 90 ىl amitriptyline (60 mM). and group 3: 90 ىL bupivacaine (23 mM). Then sensory, motor, and proprio- ceptive changes were measured at 1, 2, 3, 4, 6, and 12 hours by one examiner. Results: In Groups 1 and 2, a total of 3 rats died. After adjusting the concentrations, amitriptyline had a similar potency but a longer duration of spinal blockade of motor, proprioception, and nociception than did bupivacaine (p < 0.05), whereas doxepin had a reasonable but lower efficacy and shorter duration of spinal blockade than did bupivacaine (p < 0.05). The full recovery time for Group 2 was significantly longer. Conclusions: It seems that tertiary amine drugs such as amitriptyline and doxepin had reasonable potencies of spinal blockade when compared to bupivacaine. However, amitriptyline had a more potent and long-acting spinal anesthetic effect. Amitripty- line may turn out to be a clinically valuable local anesthetic.