Evaluation of the cardiotoxicity and resuscitation of rats of a newly developed mixture of a QX-314 analog and levobupivacaine

QX-OH/Levobupivacaine: A Structurally Novel, Potent Local Anesthetic Produces Fast-Onset and Long-Lasting Regional Anesthesia in Rats

Purpose

Local anesthetics (LAs) are an important alternative for postoperative analgesia; however, the short duration of LAs limits their use. Thus, we previously developed LL-1, a mixture of QX-OH and levobupivacaine (LB) that produces regional anesthesia for more than 10 h in rats. The aim of this study is to investigate the long-acting mechanism of LL-1 in vivo and in vitro.

Methods

Regional anesthetic effects and local toxicity of the LL-1, QX-OH and LB treatment groups were investigated in a sciatic nerve block rat model. Whole-cell patch-clamping recordings were used to measure the inhibition Na_v currents (I_Na) in ND7/23 cells.

Results

The onset of LL-1 (35mM QX-OH+10mM LB) and 10 mM LB was 10 min, which was much faster than 35 mM QX-OH (27 [18, 60] min, t[12] = −4.535, p = 0.001). The duration of LL-1 (35mM QX-OH+10 mM LB) was significantly longer than 35 mM QX-OH or 10 mM LB alone (F[3, 35] = 191.336, p < 0.0001). No differences in local tissue toxicity were found between LL-1 and LB. In patch-clamping recordings, 5 mM QX-OH produced ~20% inhibition of I_Na currents. LB at 40 μM inhibited I_Na by 65.51%±3.63%, while QX-OH 2 mM+LB 40 μM inhibited I_Na by 77.37%±3.36% (t[14] = 2.358, p = 0.025), and QX-OH 5 mM+LB 40 μM inhibited I_Na by 83.88%±1.57% (t[13] = 4.191, p = 0.0003). Furthermore, I_Na inhibition by QX-OH+LB was more persistent than that of LB alone during washout.

Conclusion

LL-1 can produce an additive and stable inhibition of Nag_v currents, which can contribute to the long-lasting regional anesthetic action.

The 14-day repeated-dose toxicity studies of a fixed-dose combination, QXOH/levobupivacaine, via subcutaneous injection in mice

QXOH-LB, a fixed-dose combination (35 mM QXOH and 10 mM levobupivacaine) has been shown to induce a long duration of local anesthesia in animal efficacy testing, which indicates potential for postoperative pain management. In this study, we evaluated the potential toxicity of QXOH-LB in NIH mice under the Guidance on the repeated-dose toxicity published by the China Food and Drug Administration. Mice (n = 30 per sex per group) were subcutaneously injected 5, 10, 20 mg/kg QXOH-LB, 5, 10, 20 mg/kg QXOH, and 5 mg/kg levobupivacaine (LB) once a day for 14 days with sacrifice of main study animals; remaining mice (n = 10 per sex per group) were monitored for an additional 4-week recovery period. Mice in the 10 and 20 mg/kg QXOH, and 20 mg/kg QXOH-LB died, which was considered due to excessive respiratory inhibition. The doses of 10 mg/kg QXOH-LB and 5 mg/kg QXOH were well tolerated without any clinical signs of toxicity. Therefore, the no-observed-adverse-effect level (NOAEL) of QXOH-LB and QXOH was considered to be 10 and 5 mg/kg/day, respectively. In the dose range from 5 to 20 mg/kg, the exposure of QXOH and LB in QXOH-LB was equal to each agent used alone at the same dose in NIH mice. There was no gender difference on exposure and no evidence of accumulation.

Quaternary Lidocaine Derivatives: Past, Present, and Future

Local anesthetics have the advantage of complete analgesia with fewer side effects compared to systemic analgesics. However, their clinical use is limited due to their short duration of action. Thus, local anesthetics with fast onset, long duration of action, selective nociceptive block, and low local and systemic toxicity are highly desirable. In the past electrophysiological studies, quaternary lidocaine derivatives (QLDs) showed these characteristics. Here, we review electrophysiological properties of QLDs and their pharmacodynamic characteristics to shed light on potential problems.

The 14-day repeated-dose toxicity study of a fixed-dose combination, QXOH/levobupivacaine, via subcutaneous injection in beagle dogs

QXOH-Levobupivacaine (LB) is a fixed-dose combination of 35-mM QXOH and 10-mM LB. It was developed for perioperative analgesia because of its long-acting analgesic effect. The purpose of this study was to evaluate the potential toxicity of QXOH-LB in beagle dogs in accordance with the Guidance on the repeated-dose toxicity published by the China Food and Drug Administration. Groups of five male and five female beagle dogs received normal saline, QXOH-LB (2, 4, and 8 mg/kg, calculated as QXOH), QXOH (2, 4, and 8 mg/kg), or LB (2 mg/kg, equals the concentration of LB in 8-mg/kg QXOH-LB group) at the volume of 1 mL/kg once per day for 14 days through subcutaneous injection. No mortality was observed. Dogs in the control group as well as animals treated with 2-mg/kg QXOH or QXOH-LB exhibited normal behaviors. Clinical signs of toxicity in dogs treated with 4 and 8 mg/kg of QXOH or QXOH-LB included decreased activity, unsteady gait, jerks, tremors, vocalization, emesis, ataxia, lateral/sternal recumbency, deep/rapid respiration, and gasping. Additionally, neurological function was found to be affected by QXOH and QXOH-LB at the doses of 4 and 8 mg/kg. All clinical signs were recovered within 24 h. The no-observed-adverse-effect level of QXOH and QXOH-LB was considered to be 2 mg/kg. Toxicokinetic data showed that exposure to QXOH and LB increased as QXOH-LB doses were increased from 4 to 8 mg/kg. There was no evidence of drug accumulation or any effect of gender.

A Fixed-Dose Combination, QXOH/Levobupivacaine, Produces Long-Acting Local Anesthesia in Rats Without Additional Toxicity

QXOH, a QX314 derivative with longer duration and lesser local toxicity, is a novel local anesthetic in preclinical drug development. Previous studies demonstrated that bupivacaine can prolong the effects of QX314. So, we attempted to combine QXOH with levobupivacaine to shorten the onset time and lengthen the duration. In this study, we investigated the efficacy, local and systemic toxicity in rats. In subcutaneous infiltration anesthesia, the inhibition of cutaneous trunci muscle reflex for QXOH-LB was greater than QXOH and levobupivacaine in the first 8 h (QXOH-LB vs. QXOH, P = 0.004; QXOH-LB vs. LB, P = 0.004). The completely recovery time for QXOH-LB (17.5 ± 2.5 h) was significantly longer than levobupivacaine (9.0 ± 1.3 h, P = 0.034) and QXOH (9.8 ± 0.9 h, P = 0.049). In sciatic nerve block, QXOH-LB produced a rapid onset time, which was obviously shorter than QXOH. For sensory, the time to recovery for QXOH-LB was 17.3 ± 2.6 h, which was statistically longer than 6.0 ± 1.8 h for QXOH (P = 0.027), and 4 h for levobupivacaine (P = 0.001). Meanwhile, the time to motor recovery for QXOH-LB was 7.9 ± 2.8 h, significantly longer than 4 h for levobupivacaine (P = 0.003) but similar to 6.0 ± 1.7 h for QXOH (P = 0.061). In local toxicity, there was no significant difference of histological score regarding muscle and sciatic nerve in QXOH-LB, QXOH, levobupivacaine and saline (P < 0.01). In the combination, the interaction index of LD₅₀ was 1.39, indicating antagonistic interaction between QXOH and levobupivacaine in terms of systemic toxicity. In this study, we demonstrated that QXOH-LB produced cutaneous anesthesia which was 2-fold greater than that produced by QXOH or LB alone, and elicited sciatic nerve block with a potency that was 5- and 3-fold that of LB and QXOH, respectively. Local tissue inflammation by QXOH-LB was mild, similar to that induced by LB. This fixed-dose combination led to an antagonistic interaction between QXOH and LB in terms of systemic toxicity. These results suggested that QXOH-LB induced a long-lasting local anesthesia, likely, avoiding clinically important local and systemic toxicities.