Structure-activity relation of N-alkyl tetracaine derivatives as neurolytic agents for sciatic nerve lesions

Real-time ultrasound-guided infraorbital nerve block to treat trigeminal neuralgia using a high concentration of tetracaine dissolved in bupivacaine

Background Trigeminal neuralgia is a neuropathic disorder characterized by episodes of intense pain in the face. Drug therapy is the first choice of treatment. However, in cases where drug therapy are contraindicated due to side effects, patients can get pain relief from lengthy neurosurgical procedures. Alternatively, a peripheral trigeminal nerve block can be easily performed in an outpatient setting. Therefore it is a useful treatment option for the acute paroxysmal period of TN in patients who cannot use drug therapy. We performed real-time ultrasound guidance for infraorbital nerve blocks in TN patients using a high concentration of tetracaine dissolved in bupivacaine. In this report, we examine the efficacy of our methods. Patients As approved by the Institutional Review Board, the medical records in our hospital were queried retrospectively. Six patients with TN at the V2 area matched the study criteria. All patients could not continue drug therapy with carbamazepine due to side effects and they received an ultrasound-guided infraorbital nerve block with a high concentration of tetracaine dissolved in bupivacaine. Methods The patient was placed in the supine position and the patient's face was sterilized and draped. An ultrasound system with a 6-13 MHz linear probe was used with a sterile cover. The probe was inserted into the horizontal plane of the cheek just beside the nose and was slid in the cranial direction to find the dimple of the infraorbital foramen. The 25G 25 mm needle was inserted from the caudal side just across from the probe using an out-of-plane approach. To lead the needle tip to the foramen, needle direction was corrected with real-time ultrasound guidance. After the test block with lidocaine (2%, 0.5 ml), a solution of tetracaine (20 mg) dissolved in bupivacaine (0.5%, 0.5 ml) was injected. During each injection, the spread of the agent around the nerve was confirmed using ultrasound images. Results Ten blocks were performed for six patients. Immediately after the procedure, all 10 blocks produced analgesia and relieved the pain. In the three blocks, pain was experienced in a new trigger point outside of the infraorbital nerve region (around the back teeth) within a week after the block and pain were relieved using other treatment. Two patients developed small hematomas in the cheek but they disappeared in a week. All patients did not complain about other side effects including paraesthesia, hyperpathia, dysaesthesia, or double vision. Hypoaesthesia to touch and pain in the infraorbital region were observed in all blocks after 2 weeks. Conclusions We performed real-time ultrasound-guided infraorbital nerve block for TN with a high concentration of tetracaine dissolved in bupivacaine. Our method achieved a high success rate and there were only minor and transient side effects. Implications Real-time ultrasound-guided infraorbital nerve block is one of the useful options to treat the acute paroxysmal period of TN at the infraorbital nerve area. Ultrasound-guided injections may become the standard practice for injecting peripheral trigeminal nerves. Using this high concentration of tetracaine as a neurolytic agent is effective and appears to have only minor side effects.

Cyclic nucleotide-gated channel block by hydrolysis-resistant tetracaine derivatives

To meet a pressing need for better cyclic nucleotide-gated (CNG) channel antagonists, we have increased the biological stability of tetracaine-based blockers by synthesizing amide and thioamide linkage substitutions of tetracaine (1) and a higher affinity octyl tail derivative (5). We report the apparent K(D) values, the mechanism of block, and the in vitro hydrolysis rates for these compounds. The ester linkage substitutions did not adversely affect CNG channel block; unexpectedly, thioamide substitution in 1 (compound 8) improved block significantly. Furthermore, the ester linkage substitutions did not appear to affect the mechanism of block in terms of the strong state preference for closed channels. All ester substituted compounds, especially the thioamide substitutions, were more resistant to hydrolysis by serum cholinesterase than their ester counterparts. These findings have implications for dissecting the physiological roles of CNG channels, treating certain forms of retinal degeneration, and possibly the current clinical uses of compound 1.