Pharmacologic correlation between local anesthetic-induced myotoxicity and disturbances of intracellular calcium distribution

Electroacupuncture alleviates multifidus muscle injury by modulating mitochondrial function and Ca2+ uptake

Multifidus muscles maintain the stability of the lumbar spine and play a crucial role in the pathogenesis of nonspecific lower back pain. Previous studies have shown that electroacupuncture (EA) can relieve the symptoms of low back pain and reduce injury to the lumbar multifidus muscles. In this study, a rat model of lumbar multifidus muscle injury was established by 0.05% bupivacaine injection and subsequently treated with EA at bilateral "Weizhong" (BL40) acupoints. Disruption of the function and structure of multifidus muscles, increased cytosolic Ca2+ in multifidus myocytes, and reduced mitochondrial fission and ATP production were observed in the model group. Additionally, increased expression of the mitochondrial calcium uniporter (MCU) promoted mitochondrial reuptake of Ca2+ , reversing the excessive increase in cytoplasmic Ca2+ . However, the excessive increase in MCU not only aggravated the increased cytoplasmic Ca2+ but also decreased the expression of the mitochondrial division proteins dynamin-related protein 1 (Drp1) and mitochondrial fission factor (MFF). EA inhibited the overexpression of MCU, promoted mitochondrial reuptake of Ca2+ , and reversed cytosolic Ca2+ overload. Furthermore, EA regulated the expression of the mitochondrial fission proteins Drp1 and MFF and promoted the production of ATP, helping the recovery of mitochondrial function after multifidus injury. Therefore, EA can protect against bupivacaine-induced mitochondrial dysfunction, possibly by attenuating MCU overexpression in the inner mitochondrial membrane and reducing Ca2+ overloading in muscle cells, thereby protecting mitochondrial function and maintaining the normal energy demand of muscle cells.

Effects of Remimazolam and Propofol on Ca2+ Regulation by Ryanodine Receptor 1 with Malignant Hyperthermia Mutation

BACKGROUND

We investigated the potential safety of remimazolam and propofol in malignant hyperthermia- (HM-) susceptible patients using ryanodine receptor 1- (RYR1-) expressing human embryonic kidney- (HEK-) 293 cells.

METHODS

We compared the enhanced responsiveness of HEK-293 cells expressing wild-type RYR1 with that of mutant RYR1 to caffeine following perfusion with remimazolam or propofol. Furthermore, we investigated whether RYR1 enhanced the responsiveness of cells to remimazolam or propofol and compared the median effective concentration (EC50; i.e., the concentration required to reach half-maximal activation) using an unpaired two-tailed t-test while a P < 0.05 was considered significant.

RESULTS

Remimazolam and propofol did not promote the caffeine-induced increase in intracellular Ca2+ levels in HEK-293 cells expressing mutant RYR1 even with exposure to approximately 100-fold the clinically used concentration. In wild-type RYR1, EC50 values of remimazolam following refusion vs. nonperfusion were 2.86 mM vs. 2.75 mM (P = 0.76) while for propofol perfusion vs. nonperfusion, they were 2.76 mM vs. 2.75 mM, respectively (P = 0.83). In mutant RYR1, EC50 values of remimazolam refusion vs. nonperfusion were 1.58 mM vs. 1.71 mM, respectively (P = 0.63) while for propofol perfusion vs. nonperfusion, they were 1.65 mM vs. 1.71 mM, respectively (P = 0.73). Remimazolam and propofol increased intracellular Ca2+ levels in a concentration-dependent manner, but the effect was not enhanced by RYR1. EC50 values of remimazolam with non-RYR1 vs. wild-type RYR1 were 1.00 mM vs. 0.92 mM, respectively (P = 0.91) while those of propofol were 1.09 mM vs. 1.05 mM, respectively (P = 0.84).

CONCLUSIONS

The increase in intracellular Ca2+ concentration caused by remimazolam or propofol was not considered an RYR1-mediated reaction. We conclude that remimazolam and propofol can be safely used as an anesthetic in MH-susceptible patients with RYR1-mutation without causing MH and may be safely substituted for an MH-triggering anesthetic when RYR1-mediated MH occurs.

Bupivacaine-induced myotoxicity during a continuous perineural femoral block: case report

Introduction: Regional anesthesia is widely used for postoperative analgesia in total knee arthroplasty (TKA). Although it is a safe and effective procedure, serious complications may still develop. In the event of an unusual or torpid evolution, the possibility of local anesthetic-induced myotoxicity should be suspected. Case presentation: A 54-year old patient, American Society of Anesthesiologists (ASA) II, underwent TKA due to primary gonarthrosis. The analgesic technique used was a femoral nerve block associated with continuous perineural infusion. 24hours later, the patient’s medical condition deteriorated presenting pain, edema, and functional limitation of the thigh of the operated extremity. The symptoms were suggestive of myotoxicity, confirmed with diagnostic images leading to the removal of the catheter. The patient experienced then a significant improvement and was discharged 5 days after surgery. Conclusion: The diagnosis of myotoxicity from local anesthetics is rare, since its manifestations may be masked by the usual symptoms of the postoperative period. Early identification of the condition is fundamental to reduce its negative impact on the patient’s recovery and satisfaction. Since the scope of the damage depends particularly on the concentration and duration of the exposure to the local anesthetic agent, there is a need to implement protocols that enable an effective block with the lowest concentration and volume of the medication.

Light-triggered release of conventional local anesthetics from a macromolecular prodrug for on-demand local anesthesia

An on-demand anesthetic that would only take effect when needed and where the intensity of anesthesia could be easily adjustable according to patients' needs would be highly desirable. Here, we design and synthesize a macromolecular prodrug (P407-CM-T) in which the local anesthetic tetracaine (T) is attached to the polymer poloxamer 407 (P407) via a photo-cleavable coumarin linkage (CM). P407-CM-T solution is an injectable liquid at room temperature and gels near body temperature. The macromolecular prodrug has no anesthetic effect itself unless irradiated with a low-power blue light emitting diode (LED), resulting in local anesthesia. By adjusting the intensity and duration of irradiation, the anesthetic effect can be modulated. Local anesthesia can be repeatedly triggered.

Effect of bupivacaine and adjuvant drugs on skeletal muscle tissue oximetry and blood flow: an experimental study

Background

Skeletal muscle microvascular blood flow plays a critical role in many myopathologies. The influence of bupivacaine and adjuvants on skeletal muscle microvascular perfusion and tissue oximetry is poorly understood but might be a relevant risk factor for myopathies after local anesthetic administration. The aim of this experimental study was to determine the effects of bupivacaine alone or in combination with epinephrine or clonidine on skeletal muscle perfusion and tissue oximetry.

Methods

Combined tissue spectrophotometry and Laser-Doppler flowmetry and tissue oximetry were used to assess local muscle blood flow in anesthetized pigs after topical administration of test solutions (bupivacaine, bupivacaine with epinephrine or clonidine, saline). Measurements were performed for up to 60 mins.

Results

The application of bupivacaine alone did not alter relative muscle blood flow significantly, whereas the addition of epinephrine or clonidine to bupivacaine resulted in a significant reduction of relative muscle blood flow at T30 and T60. However, bupivacaine resulted in a significant decrease of tissue oximetry values when compared to saline control group at T30 and T60. The application of bupivacaine combined with clonidine or epinephrine resulted in no significant reduction of tissue oximetry when compared to bupivacaine alone.

Conclusion

Bupivacaine alone results in a significant decrease of tissue oximetry in skeletal muscle which is not increased by the addition of epinephrine or clonidine despite further reductions of microcirculatory perfusion. Overall, bupivacaine alone or with adjuvants does produce local muscle ischemia for which pathological consequences need to be addressed in further studies.

Pharmacologic Properties of Novel Local Anesthetic Agents in Anesthesia Practice

Therapeutic duration of traditional local anesthetics when used in peripheral nerve blocks is normally limited. This article describes novel approaches to extend the duration of peripheral nerve blocks currently available or in development. Three newer approaches on extending the duration of peripheral nerve blocks include site-1 sodium channel blockers, novel local anesthetics delivery systems, and novel adjuvants of local anesthetics. Compared with plain amide-based and ester-based local anesthetics, alternative approaches show significant promise in decreasing postoperative pain, rescue opioid requirement, hospital length-of-stay, and overall health care cost, without compromising the established safety profile of traditional local anesthetics.

Low-level laser therapy (LLLT) accelerates the sternomastoid muscle regeneration process after myonecrosis due to bupivacaine

BACKGROUND

Because of its long-lasting analgesic action, bupivacaine is an anesthetic used for peripheral nerve block and relief of postoperative pain. Muscle degeneration and neurotoxicity are its main limitations. There is strong evidence that low-level laser therapy (LLLT) assists in muscle and nerve repair. The authors evaluated the effects of a Gallium Arsenide laser (GaAs), on the regeneration of muscle fibers of the sternomastoid muscle and accessory nerve after injection of bupivacaine.

METHODS

In total, 30 Wistar adult rats were divided into 2 groups: control group (C: n=15) and laser group (L: n=15). The groups were subdivided by antimere, with 0.5% bupivacaine injected on the right and 0.9% sodium chloride on the left. LLLT (GaAs 904nm, 0,05W, 2.8J per point) was administered for 5 consecutive days, starting 24h after injection of the solutions. Seven days after the trial period, blood samples were collected for determination of creatine kinase (CK). The sternomastoid nerve was removed for morphological and morphometric analyses; the surface portion of the sternomastoid muscle was used for histopathological and ultrastructural analyses. Muscle CK and TNFα protein levels were measured.

RESULTS

The anesthetic promoted myonecrosis and increased muscle CK without neurotoxic effects. The LLLT reduced myonecrosis, characterized by a decrease in muscle CK levels, inflammation, necrosis, and atrophy, as well as the number of central nuclei in the muscle fibers and the percentage of collagen. TNFα values remained constant.

CONCLUSIONS

LLLT, at the dose used, reduced fibrosis and myonecrosis in the sternomastoid muscle triggered by bupivacaine, accelerating the muscle regeneration process.

In vitro myotoxic effects of bupivacaine on rhabdomyosarcoma cells, immortalized and primary muscle cells

BACKGROUND

Rhabdomyosarcoma is a rare malignant skeletal muscle tumor. It mainly occurs in children and young adults and has an unsatisfactory prognosis. Prior studies showed a direct myotoxic effect of bupivacaine on differentiated muscle cells in vitro and in vivo. Exact mechanisms of this myotoxicity are still not fully understood, but a myotoxic effect on malignant muscle tumor cells has not been examined so far. Thus, the aim of this study was to examine if bupivacaine has cytotoxic effects on rhabdomyosarcoma cells, immortalized muscle cells and differentiated muscle cells.

METHODS

Cell lines of rhabdomyosarcoma cells, immortalized muscle cells and differentiated muscle cells were established. After microscopic identification, cells were exposed to various concentrations of bupivacaine (500, 1,000, 1,750, 2,500 and 5,000 ppm) for 1 and 2 h, respectively. 24 and 28 h after incubation the cultures were stained with propidium iodid and analyzed by flow cytometry. The fraction of dead cells was calculated for each experiment and the concentration with 50% cell survival (IC50) was computed. Cell groups as well as incubation and recovery time were compared (ANOVA/Bonferroni p < 0.01).

RESULTS

The total number of cultured cells was similar for the different local anesthetics and examined concentrations. Increasing concentrations of bupivacaine led to a decrease in survival of muscle cells. IC50 was highest for immortalized cells, followed by rhabdomyosarcoma cells and differentiated cells. Exposure time, but not recovery time, had an influence on survival.

CONCLUSION

Bupivacaine has clear but different cytotoxic effects on various muscle cell types in vitro. Differentiated primary cells seem to be more vulnerable than tumor cells possibly because of more differentiated intracellular structures.

In vivo study of an extended release bupivacaine formulation following site-directed nerve injection

Site-directed administration of local anesthetic agents incorporated into a slow controlled-release injectable implant prolongs the analgesic effect. However, there are potential neuro- and myotoxic consequences. We evaluated a local anesthetic agent (bupivacaine) loaded into a slow-release biodegradable polymer based on castor oil and poly(lactic acid). The formulation was applied directly to the sciatic nerve area in female imprinting control region mice along with appropriate controls. Local nerve and muscle and systemic toxicity were evaluated over a 3-month period following injection of 0.05, 0.1, and 0.125 mL of the 15% bupivacaine–polymer formulation. Histological samples were prepared and examined; no signs of severe inflammation were observed. Histological inflammation signs were more prominent in both nerves and muscles following application of the largest volumes of the polymer formulation (0.1 and 0.125 mL). Following application of 0.1 mL, 15% bupivacaine–polymer formulation, maximal changes were seen in nerve samples two days and two weeks after injection, with complete resolution one month following injection. Neither blank polymer nor plain bupivacaine 0.5% caused any histological changes. Local nerve and muscle toxicity were affected by duration the of exposure and dose of the local anesthetic agent. However, there were clear indications of time-related healing process 3 months after injection.

Rotator cuff healing after continuous subacromial bupivacaine infusion: an in vivo rabbit study

BACKGROUND

The objective of this study was to evaluate the effects of continuous subacromial bupivacaine infusion on supraspinatus muscle and rotator cuff tendon healing using gross, biomechanical, and histologic analyses.

MATERIALS AND METHODS

Thirty-three New Zealand White rabbits underwent unilateral supraspinatus transection and rotator cuff repair (RCR). Rabbits were assigned to 1 of 3 groups: (1) RCR only, (2) RCR with continuous saline infusion for 48 hours, or (3) RCR with continuous 0.25% bupivacaine with epinephrine (1:200,000) infusion for 48 hours. Rabbits were euthanized postoperatively at 2 weeks (for histologic assessment) or 8 weeks (for biomechanical and histologic assessment).

RESULTS

Tensile testing showed a significantly higher load to failure in intact tendons compared with repaired tendons (P < .01); however, no statistical differences were detected among RCR only, RCR saline, and RCR bupivacaine groups. Histologically, the enthesis of repaired tendons showed increased cellularity and disorganized collagen fibers compared with intact tendons, with no differences between treatment groups. Muscle histology demonstrated scattered degenerative muscle fibers at 2 weeks in RCR saline and RCR bupivacaine groups, but no degeneration was noted at 8 weeks.

CONCLUSIONS

The healing supraspinatus tendons exposed to bupivacaine infusion showed similar histologic and biomechanical characteristics compared with untreated and saline-infused RCR groups. Muscle histology showed fiber damage at 2 weeks for the saline and bupivacaine-treated groups, with no apparent disruption at 8 weeks, suggesting a recovery process. Therefore, subacromial bupivacaine infusion in this rabbit rotator cuff model does not appear to impair muscle or tendon after acute injury and repair.

Extended release formulations for local anaesthetic agents

Systemic toxicity through overdose of local anaesthetic agents is a real concern. By encapsulating local anaesthetics in biodegradable carriers to produce a system for prolonged release, their duration of action can be extended. This encapsulation should also improve the safety profile of the local anaesthetic as it is released at a slower rate. Work with naturally occurring local anaestheticss has also shown promise in the area of reducing systemic and neurotoxicity. Extended duration local anaesthetic formulations in current development or clinical use include liposomes, hydrophobic based polymer particles such as Poly(lactic-co-glycolic acid) microspheres, pasty injectable and solid polymers like Poly(sebacic-co-ricinoleic acid) P(SA:RA) and their combination with synthetic and natural local anaesthetic. Their duration of action, rationale and limitations are reviewed. Direct comparison of the different agents is limited by their chemical properties, the drug doses encapsulated and the details of in vivo models described.

Focal skeletal muscle uptake of 99mTechnetium-hydroxymethylene diphosphonate following peroneal nerve blocks in horses

We have observed focal skeletal muscle uptake of 99mTechnetium-hydroxymethylene diphosphonate (Tc-HDP), which could mimic a tibial lesion, in horses following peroneal nerve blocks. To characterize this observation further, 45 bone phase scintigrams were performed in 12 horses undergoing peroneal nerve blocks. Scans were performed before, and 1, 3, 7, and 14 days postblock. The superficial and deep branches of the peroneal nerve were blocked by injecting 10 ml of 2% mepivacaine in one limb and 20 ml in the other. Images were evaluated for uptake at the block site and uptake likely to mimic a tibial lesion. Regions of interest were placed over the block site and distal tibia. Count density ratios were used to estimate change in uptake intensity over time. The overall proportion affected was 0.52 (95% confidence interval [CI], 0.36-0.68; P < 0.001) 1 day postblock and 0.24 (95% CI, 0.13-0.40; P = 0.005) 3 days postblock. The overall proportion likely to mimic a tibial lesion was 0.19 (95% CI, 0.09-0.33; P < 0.001) 1 day postblock and 0.21 (95% CI, 0.09-0.40; P = 0.005) 3 days postblock. Focal skeletal muscle uptake was seen in only one horse 7 days postblock. Increased uptake intensity was associated with higher local anesthetic dose (P = 0.042). Peroneal nerve blocks cause focal skeletal muscle uptake of 99mTc-HDP on bone phase scintigraphy. This occurs in approximately 50% of blocked limbs and can mimic a tibial lesion on the lateral view in approximately 20% of blocked limbs.

Diplopia and strabismus following ocular surgeries

Postoperative diplopia and strabismus may result from a variety of ocular surgical procedures. Common underlying mechanisms include sensory disturbance, scarring, direct extraocular muscle injury, myotoxicity from injections of local anesthesia or antibiotics, and malpositioning of extraocular muscles by implant materials. The most common patterns are vertical and horizontal motility disturbance. Treatment options include prisms, botulinum, occlusion, or surgery.

Bupivacaine causes cytotoxicity in mouse C2C12 myoblast cells: involvement of ERK and Akt signaling pathways

AIM

The adverse effects of local anesthetics (LAs) on wound healing at surgical sites have been suggested, and may be related to their cytotoxicity. This study was aimed to compare the cellular toxicity of bupivacaine and lidocaine (two well-known LAs), and to explore the molecular mechanism(s).

METHODS

Toxicity of bupivacaine and lidocaine was assessed in cultured mouse C2C12 myoblasts by cell viability and apoptosis assays. Effects of LAs on extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) activation, which are essential for cell proliferation and survival, were evaluated by immunoblotting.

RESULTS

Both LAs, especially bupivacaine, prevented cell growth and caused cell death in a dose-dependent manner. The half maximal inhibitory concentrations (IC(50)) for bupivacaine and lidocaine were 0.49+/-0.04 and 3.37+/-0.53 mmol/L, respectively. When applied at the same dilutions of commercially available preparations, the apoptotic effect induced by bupivacaine was more severe than that of lidocaine in C2C12 cells. Furthermore, bupivacaine significantly diminished the ERK activation, which may underlie its anti-proliferative actions. Both LAs suppressed Akt activation, which correlated with their effects on apoptosis.

CONCLUSION

Our study demonstrated that, when used at the same dilutions from clinically relevant concentrations, bupivacaine is more cytotoxic than lidocaine in vitro. Anti-proliferation and cell death with concomitant apoptosis mediated by bupivacaine may offer an explanation for its adverse effects in vivo (eg slowing wound healing at the surgical sites). A less toxic, long-acting anesthetic may be needed.

Effect of chemical permeation enhancers on nerve blockade

Chemical permeation enhancers (CPEs) have the potential to improve access of local anesthetics to the nerve, thereby improving nerve block performance. We assessed the effects of six CPEs on nerve blockade from tetrodotoxin (TTX) and from bupivacaine. Each of the six surfactants, representing three CPE subgroups (anionic, cationic, and nonionic surfactants) was coinjected with TTX or bupivacaine at the sciatic nerve of Sprague-Dawley rats. Myotoxicity of CPEs, alone and with TTX, was assessed in vitro in C2C12 myotubes and in vivo via histological analysis. All enhancers produced marked concentration-dependent improvements in the frequency and duration of block with TTX but not bupivacaine. An in vitro toxicity assay showed a wide range of CPE myotoxicity, but in vivo histological assessment showed no signs of muscle or nerve damage at concentrations of CPEs that produced a half-maximal increase in the duration of block of TTX (except in the case of the cationic surfactant DDAB). This study demonstrates that CPEs can provide marked prolongation of nerve blockade from TTX but not bupivacaine, without apparent local tissue toxicity. These results may enhance the clinical applicability of TTX for prolonged-duration local anesthesia.

Polydeoxyribonucleotide (PDRN) restores blood flow in an experimental model of peripheral artery occlusive disease

OBJECTIVE

This study investigated whether polydeoxyribonucleotide (PDRN) may be efficacious in the treatment of peripheral artery occlusive diseases, which are a major cause of morbidity in Western countries and still lack standardized treatment.

METHODS

We investigated the effects of PDRN, a mixture of deoxyribonucleotides, in an experimental model of hind limb ischemia (HLI) in rats to stimulate vascular endothelial growth factor (VEGF)-A production and to avoid critical ischemia. The femoral artery was excised to induce HLI. Sham-operated on rats (sham HLI) were used as controls. Animals were treated daily with intraperitoneal PDRN (8 mg/kg) or its vehicle. Animals were euthanized at day 7, 14, and 21 after the evaluation of blood flow by laser Doppler. Dissected muscles were used to measure VEGF-A messenger RNA (mRNA) and protein expression, to evaluate edema, and to assess histologic damage.

RESULTS

Administration of PDRN dramatically increased VEGF mRNA throughout the study (day 14: HLI, 7 +/- 2.2 n-fold/beta-actin; HLI + PDRN, 13.3 +/- 3.8 n-fold/beta-actin; P < .0001) and protein expression (HLI, 11 +/- 3.4 integrated intensity; HLI + PDRN, 16 +/- 3.8 integrated intensity; P < .0001). The compound stimulated revascularization, as confirmed by blood flow restoration (P < .005 vs HLI + vehicle), and blunted the histologic damage and the degree of edema. PDRN did not modify VEGF-A expression and blood flow in sham HLI animals. Furthermore, the concomitant administration of 3,7-dimethyl-1-propargilxanthine (DMPX), a selective adenosine A(2A) receptor antagonist, abolished the positive effects of PDRN, confirming that PDRN acts through this receptor.

CONCLUSION

These results led us to hypothesize a role for PDRN in treating peripheral artery occlusive diseases.

Local myotoxicity from sustained release of bupivacaine from microparticles

BACKGROUND

Sustained release of local anesthetics is frequently associated with myotoxicity. The authors investigated the role of particulate delivery systems and of the pattern of drug release in causing myotoxicity.

METHODS

Rats were given sciatic nerve blocks with bupivacaine solutions, two types of bupivacaine-containing microparticles (polymeric microspheres and lipid-protein-sugar particles), or blank particles with or without bupivacaine in the carrier fluid. Myotoxicity was scored in histologic sections of the injection sites. Bupivacaine release kinetics from the particles were measured. Myotoxicity of a range of bupivacaine concentrations from exposures up to 3 weeks was assessed in C2C12 myotubes, with or without microparticles.

RESULTS

Both types of bupivacaine-loaded microparticles, but not blank particles, were associated with myotoxicity. Whereas 0.5% bupivacaine solution caused little myotoxicity, a concentration of bupivacaine that mimicked the amount of bupivacaine released initially from particles caused myotoxicity. Local anesthetics showed both concentration and time-dependent myotoxicity in C2C12s. Importantly, even very low concentrations that were nontoxic over brief exposures became highly toxic after days or weeks of exposure. The presence of particles did not increase bupivacaine myotoxicity in vitro but did in vivo. Findings applied to both particle types.

CONCLUSIONS

Whereas the release vehicles themselves were not myotoxic, both burst and extended release of bupivacaine were. A possible implication of the latter finding is that myotoxicity is an inevitable concomitant of sustained release of local anesthetics. Particles, and perhaps other vehicles, may enhance local toxicity through indirect mechanisms.

Tetrodotoxin for prolonged local anesthesia with minimal myotoxicity

Conventional local anesthetics such as bupivacaine cause considerable myotoxicity and neurotoxicity, whereas tetrodotoxin (TTX) does not. Tetrodotoxin combined with bupivacaine or vasoconstrictors produces long-duration nerve blockade. To assess whether these prolonged blocks can be produced without increased myotoxicity, Sprague-Dawley rats were injected with bupivacaine, TTX, and both, or TTX plus epinephrine. Median durations of thermal nociceptive blockade were, respectively, 188, 401, 882, and 972 min. On dissection 4 days later, all tissues appeared macroscopically pristine. Muscle injury was at most mild to moderate in all animals, and the muscle injury scores for the combination formulations were not higher than for bupivacaine alone. Similarly, in differentiated cells from a myoblast cell line (C2C12), TTX caused either no or minimal worsening of cell viability from bupivacaine at 2 or 7 days. Epinephrine did not worsen TTX's relatively minimal cytotoxicity. Tetrodotoxin may thus be useful in producing prolonged nerve block with minimal myotoxicity and perhaps neurotoxicity.

Myotoxizität von Lokalanästhetika

Intramuscular injections of local anaesthetic agents regularly result in reversible muscle damage, with a dose-dependent extent of the lesions. All local anaesthetic agents that have been examined are myotoxic, whereby procaine produces the least and bupivacaine the most severe muscle injury. The histological pattern and the time course of skeletal muscle injury appear relatively uniform: hypercontracted myofibrils become evident directly after injection, followed by lytic degeneration of striated muscle sarcoplasmic reticulum myocyte edema and necrosis. Intriguingly, in most cases myoblasts, basal laminae and connective tissue elements remain intact which subsequently ensures complete muscular regeneration. Subcellular pathomechanisms of local anaesthetic myotoxicity are still not understood in detail. Increased intracellular Ca(2+) levels are suggested to be the most important element in myocyte injury, since denervation, inhibition of sarcolemmal Na(+) channels and direct toxic effects on myofibrils have been excluded as sites of action. Although experimental myotoxic effects are impressively intense and reproducible, only few case reports of myotoxic complications in patients after local anaesthetic administration have been published. In particular, the occurrence of clinically relevant myopathy and myonecrosis has been described after continuous peripheral blockades, infiltration of wound margins, trigger point injections, peribulbar and retrobulbar blocks.

Ropivacaine myotoxicity after single intramuscular injection in rats

BACKGROUND AND OBJECTIVE

We conducted this study in order to evaluate the potential myotoxic effects of ropivacaine after single injection in rats and the time-course of the possible damage.

METHODS

One hundred and twenty-eight male Wistar rats were allocated to four different groups. The first three groups received intramuscular injections with ropivacaine 0.75%, ropivacaine 0.5% and normal saline, respectively, into the right tibialis anterior muscle. The fourth group received needle puncture without injection. Eight rats from each group were sacrificed 2, 4, 7 and 30 days after injection. Samples were blindly examined under light microscope for evidence of myotoxicity, scored as 0 = no damage to 3 = myonecrosis and statistically analysed. Samples obtained 7 days after injection were also examined under transmission electron microscope.

RESULTS

Ropivacaine 0.75% and ropivacaine 0.5% caused extensive destruction to muscles fibres, compared to saline or needle on days 2, 4 and 7. Statistically significant differences were found in muscle damage by drug injections among all groups except for saline vs. needle groups. Thirty days after injections all sample appearances had returned to normal.

CONCLUSIONS

Ropivacaine after single intramuscular injection caused reversible muscle damage in a dose-dependent manner.

Tissue injury from tricyclic antidepressants used as local anesthetics

Neurotoxicity has been reported with tricyclic antidepressants (TCAs) used as local anesthetics. We examined the hypothesis that TCAs cause tissue injury, particularly myotoxicity, as occurs with many local anesthetics. Animals were given sciatic nerve injections with 0-80 mM doxepin, amitriptyline, or bupivacaine (1.5 mL for histological studies, 0.3 mL for neurobehavioral studies). Four days after injection, the TCAs caused ischemic tissue injury. Subcutaneous tissue showed expansion and hardening, with hemorrhage and adhesion to overlying skin. Muscle was diffusely pale. Histopathology showed coagulative necrosis of muscle and surrounding soft tissues, with thrombus formation in vasculature near affected areas. These findings were much reduced with bupivacaine. TCA-injected and bupivacaine-injected animals also developed characteristic local anesthetic myotoxicity. Amitriptyline proved less potent than bupivacaine as a local anesthetic: the concentrations required to provide 100 min of nerve block were 20 mM and 3 mM, respectively. Some animals receiving large concentrations of amitriptyline developed spontaneous recrudescence of nerve blockade or had irreversible nerve blockade, both of which may reflect nerve injury. Neither finding occurred in animals injected with bupivacaine. TCAs do not appear to offer any advantages over conventional local anesthetics and do appear to risk substantially increased toxicity.

The Long Term Myotoxic Effects of Bupivacaine and Ropivacaine After Continuous Peripheral Nerve Blocks

Compared with bupivacaine, acute myotoxicity of ropivacaine is less severe. Thus, in this study we compared the long term myotoxic effects of both drugs in a clinically relevant setting. Femoral nerve catheters were inserted in anesthetized pigs, and either 20 mL of bupivacaine (5 mg/mL) or ropivacaine (7.5 mg/mL) was injected. Subsequently, bupivacaine (2.5 mg/mL) and ropivacaine (3.75 mg/mL) were continuously infused (8 mL/h) over 6 h. Control animals were treated with corresponding volumes of normal saline. After 7 and 28 days, respectively, muscle samples were dissected at the former injection sites, and histological patterns of muscle damage were blindly scored (0 = no damage to 3 = marked lesions/myonecrosis) and compared. No morphological tissue changes were detected in control animals. In the observed period, both local anesthetics induced morphologically identical patterns of calcific myonecrosis, formation of scar tissue, and a marked rate of fiber regeneration. However, bupivacaine's effects were constantly more pronounced than those of ropivacaine. These data show that both drugs induce irreversible skeletal muscle damage in a clinically relevant model, and confirm the exceeding rate of myotoxicity of bupivacaine. However, the clinical impact of these long term myotoxic effects still has to be assessed.

IMPLICATIONS

In a period of 4 wk after peripheral nerve block, both long-acting local anesthetics, bupivacaine and ropivacaine, produced calcific myonecrosis suggestive of irreversible skeletal muscle damage. In comparison with ropivacaine, however, the extent of bupivacaine-induced muscle lesions was significantly larger.

Site 1 sodium channel blockers prolong the duration of sciatic nerve blockade from tricyclic antidepressants

Many recent reports in the literature address the local anesthetics efficacy of tricyclic antidepressants (TCAs). Here we investigated whether nerve block from TCAs is prolonged by site 1 sodium channel blockers such as tetrodotoxin and saxitoxin, which are known to prolong block from conventional local anesthetics. Tetrodotoxin and saxitoxin greatly prolonged block from TCAs. For example, the median duration of thermal nociceptive blocks for 10 mM amitriptyline, nortriptyline and doxepin were 0, 0, and 124 min; co-injection with 20 microM TTX (median block duration=0), yielded blocks lasting 404, 325, and 697 min, respectively. Co-injection of 12 microM saxitoxin (median block duration=0) with 10 mM amitriptyline resulted in a thermal nociceptive block duration of 373 min. Co-injection of 7.7 mM bupivacaine and 7.7 mM amiptriptyline did not result in block prolongation. Systemic (subcutaneous) delivery of tetrodotoxin or amitriptyline did not result in prolongation of block from the other class of drug injected at the sciatic nerve. In TCA-containing formulations, motor blockade was consistently longer than thermal nociceptive block; motor blockade was also prolonged by tetrodotoxin and saxitoxin. In summary site 1 sodium channel blockers prolong the duration of TCAs via a locally mediated mechanism.

Benefit-Risk Assessment of Ropivacaine in the Management of Postoperative Pain

Ropivacaine is a long-acting amide-type local anaesthetic, released for clinical use in 1996. In comparison with bupivacaine, ropivacaine is equally effective for subcutaneous infiltration, epidural and peripheral nerve block for surgery, obstetric procedures and postoperative analgesia. Nevertheless, ropivacaine differs from bupivacaine in several aspects: firstly, it is marketed as a pure S(-)-enantiomer and not as a racemate, and secondly, its lipid solubility is markedly lower. These features have been suggested to significantly improve the safety profile of ropivacaine, and indeed, numerous studies have shown that ropivacaine has less cardiovascular and CNS toxicity than racemic bupivacaine in healthy volunteers. Extensive clinical data have demonstrated that epidural 0.2% ropivacaine is nearly identical to 0.2% bupivacaine with regard to onset, quality and duration of sensory blockade for initiation and maintenance of labour analgesia. Ropivacaine also provides effective pain relief after abdominal or orthopaedic surgery, especially when given in conjunction with opioids or other adjuvants. Nevertheless, epidurally administered ropivacaine causes significantly less motor blockade at low concentrations. Whether the greater degree of blockade of nerve fibres involved in pain transmission (Adelta- and C-fibres) than of those controlling motor function (Aalpha- and Abeta-fibres) is due to a lower relative potency compared with bupivacaine or whether other physicochemical properties or stereoselectivity are involved, is still a matter of intense debate. Recommended epidural doses for postoperative or labour pain are 20-40 mg as bolus with 20-30 mg as top-up dose, with an interval of >or=30 minutes. Alternatively, 0.2% ropivacaine can be given as continuous epidural infusion at a rate of 6-14 mL/h (lumbar route) or 4-10 mL/h (thoracic route). Preoperative or postoperative subcutaneous wound infiltration, during cholecystectomy or inguinal hernia repair, with ropivacaine 100-175 mg has been shown to be more effective than placebo and as effective as bupivacaine in reducing wound pain, whereby the vasoconstrictive potency of ropivacaine may be involved. Similar results were found in peripheral blockades on upper and lower limbs. Ropivacaine shows an identical efficacy and potency to that of bupivacaine, with similar analgesic duration over hours using single shot or continuous catheter techniques. In summary, ropivacaine, a newer long-acting local anaesthetic, has an efficacy generally similar to that of the same dose of bupivacaine with regard to postoperative pain relief, but causes less motor blockade and stronger vasoconstriction at low concentrations. Despite a significantly better safety profile of the pure S(-)-isomer of ropivacaine, the increased cost of ropivacaine may presently limit its clinical utility in postoperative pain therapy.

The acute myotoxic effects of bupivacaine and ropivacaine after continuous peripheral nerve blockades

Bupivacaine causes muscle damage. However, the myotoxic potency of ropivacaine is still unexplored. Therefore, we performed this study to compare the effects of bupivacaine and ropivacaine on skeletal muscle tissue in equipotent concentrations. Femoral nerve catheters were inserted into anesthetized minipigs, and 20 mL of either bupivacaine (5 mg/mL) or ropivacaine (7.5 mg/mL) was injected. Subsequently, bupivacaine (2.5 mg/mL) and ropivacaine (3.75 mg/mL) were continuously infused over 6 h. Control animals were treated with corresponding volumes of normal saline. Finally, muscle samples were dissected at injection sites. After processing and staining, histological patterns of muscle damage were blindly examined, scored (0 = no damage to 3 = myonecrosis), and statistically analyzed. After normal saline, only interstitial edema was found. Bupivacaine treatment caused severe tissue damage (score, 2.3 +/- 0.7), whereas ropivacaine induced fiber injury of a significantly smaller extent (score, 1.3 +/- 0.8). Furthermore, bupivacaine, but not ropivacaine, induced apoptosis in muscle fibers. In summary, both drugs induce muscle damage with similar histological patterns. Compared with bupivacaine, which induces both necrosis and apoptosis, the tissue damage caused by ropivacaine is significantly less severe. We conclude that ropivacaine's myotoxic potential is more moderate in comparison with that of bupivacaine.

IMPLICATIONS

After continuous peripheral nerve blockades, the long-acting local anesthetics bupivacaine and ropivacaine both induce fiber necrosis in porcine skeletal muscle tissue. In comparison with ropivacaine, bupivacaine causes tissue damage of a significantly larger extent and additionally induces apoptosis in skeletal muscle cells.

Superior oblique muscle paresis after sub-Tenon's anesthesia for cataract surgery

A 68-year-old man developed strabismus after having sub-Tenon's anesthesia for cataract extraction and intraocular lens implantation. An ipsilateral hypertropia with superior oblique muscle paresis developed in the operated eye. The hypertropia appeared 1 day after surgery and resolved 1 month later. Although sub-Tenon's anesthesia is considered safer than other methods of local anesthesia, strabismus may occur.

Local anaesthetic bupivacaine alters function of sarcoplasmic reticulum and sarcolemmal vesicles from rabbit masseter muscle

The effects of local anaesthetics, bupivacaine and lidocaine, on Ca2+ flux behaviour of sarcoplasmic reticulum and on sarcolemmal functions were studied in the rabbit masseter muscle. The experiments were performed on sarcoplasmic reticulum and sarcolemmal vesicles prepared at 1 to 10 days after injection of local anaesthetics or saline into masseter muscle as well as on sarcoplasmic reticulum vesicles prepared from non-treated rabbits (for assessment of the effect on in vitro incubation with local anaesthetics). Bupivacaine potently reduced the efficiency of active sarcoplasmic reticulum Ca2+ transport as evaluated by coupling ratio (Ca2+ transported/ATP hydrolyzed, in the presence of oxalate) at 3 days after the injection; there was only a slight degree of uncoupling of Ca2+ transport from ATP hydrolysis with lidocaine injection. Bupivacaine but not lidocaine, at 3 days after injection, decreased both the apparent permeability of sarcoplasmic reticulum vesicles to Ca2+, determined by measuring net efflux of Ca2+ after stopping pump-mediated fluxes, and the steady-state Ca2+ load in sarcoplasmic reticulum, but had no effect on overall turnover of the Ca2+ATPase. The effects of bupivacaine on apparent sarcoplasmic reticulum Ca2+ permeability and steady-state Ca2+ load were inhibited by a Ca2+ antagonist verapamil. The reduction of Ca2+ uptake of sarcoplasmic reticulum and the protective effect of verapamil were reproduced in unfractionated homogenates prepared at 3 days after bupivacaine injection. In vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine (0.5 to 50 mM) reduced steady-state Ca2+ load in a dose-dependent manner. The observed effect elicited by bupivacaine (25 mM) was partially protected by procaine, an inhibitor of Ca2(+)-induced Ca2+ release from sarcoplasmic reticulum, or by specific closure of the sarcoplasmic reticulum Ca2+ release channel by ryanodine, suggesting the possibility that in vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine may produce an increase in apparent permeability of sarcoplasmic reticulum to Ca2+. In sarcolemma, bupivacaine reduced Na+,K(+)-ATPase and Na(+)-Ca2+ exchange activities at 3 days after injection; the effects on sarcolemmal vesicles were prevented by verapamil. These results suggest that although the effects elicited by bupivacaine injection and the in vitro exposure to bupivacaine on steady-state Ca2+ load of sarcoplasmic reticulum vesicles were similar, the membrane properties of the vesicles from bupivacaine-treated masseter muscles and those from normal untreated muscles may not be the same, which indicates that pure bupivacaine effect is due partly by an effect on ryanodine- and procaine-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural changes in the masseter muscle of Macaca fascicularis resulting from intramuscular injections of botulinum toxin type A

Intramuscular injections of botulinum toxin type A (Oculinum) is used to treat strabismus and focal dystonias affecting orofacial muscles. However, the toxin-induced morphological changes that underlie the therapeutic alterations of tone in the muscles of mastication have not been described. In this study, paired intramuscular injections of botulinum toxin (10 units) were made in three adult monkeys (Macaca fascicularis) allowed to survive 14, 28 and 63 days. Another monkey received multiple injection-pairs over 84 days. Animals were killed by deep pentobarbital anaesthesia before transcardiac perfusion-fixation. Tissue sampled from comparable regions of the injected masseter, the uninjected masseter and an uninjected animal was processed for ultrastructural analysis. Few changes were found 14 days post-injection. However, muscle fibres showed myofibrillar dissolution, aberrations in the Z-line, and enlarged mitochondria in the region of the I-band by 28 days. In the 63-day and 84-day animals, the injected muscle was considerably smaller than the uninjected, contralateral muscle. Regions of the injected muscle contained fibres with markedly reduced cross-sectional area. Internalization of myonuclei, loss of myofibrillar organization, and helical complexes were common. Toxin-induced changes, though similar to those that follow denervation by axotomy, were not accompanied by degeneration of neuromuscular junctions. Instead, morphological evidence for axonal sprouting in the region of the neuromuscular junction, possibly contributing to functional recovery, was seen as early as 14 days in toxin-treated muscles.

An electron microscopic study of local anesthetic-induced skeletal muscle fiber degeneration and regeneration in the monkey

An electron microscopic study was done on abductor pollicis brevis muscles of 18 Rhesus monkeys after intramuscular injections of 0.75% bupivacaine, 2% mepivacaine, or 2% lidocaine + epinephrine. The muscles were examined for from 2 h to 28 days. Severe muscle fiber damage, consisting of breakdown of sarcolemma and myofibrils, was seen as early as 2 h. Phagocyte mediated fragmentation of the degenerating muscle fibers was at its peak during the third and fourth days. Myoblasts were abundant during the fourth day. Early myotubes appeared on the fifth and sixth days, and they matured during the second week. Satellite cells appeared alongside mature myotubes. Overall, the local anesthetic-induced breakdown and regeneration of skeletal muscle fibers in the monkey followed a course quite similar to that seen in the rat.

Mechanisms of creatine kinase release from isolated rat skeletal muscles damaged by propylene glycol and ethanol

The organic cosolvents propylene glycol and ethanol are found to cause skeletal muscle damage and creatine kinase release following intramuscular injection. The mechanisms of this organic cosolvent-induced enzyme release have not been elucidated. Cosolvent-induced creatine kinase release was enhanced by the addition of calcium to the incubation medium, and inhibited, albeit modestly, by dibucaine, a nonspecific phospholipase A2 inhibitor. The temporal pattern of creatine kinase release further suggested that cosolvent-induced enzyme release from skeletal muscles may be caused by an intracellular mechanism rather than by a direct solubilization of sarcolemma. This intracellular mechanism may involve the mobilization of calcium.

A test for muscle lesions and their regeneration following intramuscular drug application

A standard infiltration of the rat tibialis anterior muscle with 0.1 ml of local anesthetics was used as a model to help choose criteria for testing the intramuscular toxicity of drugs. Anesthetics used were 0.2% carbisocaine, 1% and 2% Lidocaine, 0.5% Marcaine, 1% and 2% Mesocaine, 1% and 2% Procaine. Increases in the serum levels of creatine kinase were monitored for 24 hours, and the weight, as well as macro- and microscopic changes in the muscle for a period of 1 month. Exposure of the muscle to local anesthetics resulted in 2 types of lesions. One was characterized by selective muscle fiber damage in the injected area. The other type of lesion was a generalized one that involved a number of cell types. To assess the intramuscular toxicity of drugs we defined the type of lesion, its size, and the rate of subsequent muscle regeneration. We recommend the following criteria for the assay of myotoxicity of new drugs being developed as pharmaceutical agents: 1) serum creatine kinase level 1 hour after intramuscular injection of the drug; 2) microscopic findings at 3, 7, and 21 days; 3) the cross-sectional area of the lesion at 3 days; and 4) the weight of the muscle at 7 and 21 days.

Exogenous ATP antagonizes the actions of phospholipase A2, local anesthetics, Ca2+ ionophore A23187, and lithium on glucose-1,6-bisphosphate levels and the activities of phosphofructokinase and phosphoglucomutase in rat muscle

ATP, added externally to the incubation medium of rat diaphragm muscles, abolished the decrease in the levels of glucose-1,6-bisphosphate (Glc-1,6-P2), the powerful regulator of carbohydrate metabolism, induced by phospholipase A2, local anesthetics, Ca2+ ionophore A23187, or lithium. Concomitantly to the changes in Glc-1,6-P2, the potent activator of phosphofructokinase (the rate-limiting enzyme in glycolysis) and phosphoglucomutase, the activities of these enzymes were reduced by the myotoxic agents and restored by exogenous ATP, when assayed under conditions in which these enzymes are sensitive to regulation by Glc-1,6-P2. These findings suggest that ATP may have broad therapeutic action, as it may stimulate the impaired glycolysis in muscle induced by various drugs and conditions which cause muscle weakness or damage.

Bupivacaine-induced muscle injury. The role of extracellular calcium

To investigate the role of extracellular calcium in bupivacaine-induced muscle injury, the effects of the drug on creatine kinase (CK) release and muscle ultrastructure were studied in the isolated rat soleus in the presence and absence of calcium and of the Ca-channel blockers verapamil and nifedipine. Control muscles maintained a constant CK release rate and normal morphology for at least 3 hours. CK release rates increased markedly after exposure to 1.5 mM and 5 mM bupivacaine and electron microscopy showed evidence of damage to mitochondria, sarcoplasmic reticulum and the plasmalemma of muscle fibres with disruption of the Z-lines, I-bands and M-lines of myofibrils. When calcium was omitted from the incubation medium, there was a 3-fold reduction in CK release rates; the morphological changes were less severe initially but by 120 min were comparable to those in muscles incubated with bupivacaine and calcium. Neither 10(-6) M verapamil nor 10(-6) M nifedipine reduced CK release or muscle fibre damage. Verapamil (10(-5) M) reduced CK release but not the severity of muscle damage. The findings indicate that extracellular calcium plays a part in mediating the muscle damage caused by bupivacaine but that other factors must also be involved, and that Ca-channel blockers do not prevent muscle damage.

Alterations in creatine kinase, ornithine decarboxylase, and transglutaminase during muscle regeneration

Creatine kinase (CK), transglutaminase (TGase) and ornithine decarboxylase (ODC), enzymes implicated in the regulation of growth processes, were studied during muscle regeneration subsequent to the injection of bupivacaine into rat tibialis anterior. Within 2 days, the percent BB isozyme of CK detected in the muscle was elevated 70-fold coincident with a marked decrease in total CK activity. The MB isozyme also increased and was 15-fold of control at 4-5 days postinjection. TGase activity was increased significantly to greater than 2-fold of control within 2 days of injection and significantly decreased at days 3 through 7 compared to controls. ODC activity was elevated significantly to 2- to 3-fold of control from 2-7 days after injection. These results suggest an early alteration in the expression of a coordinated battery of genes in this model of muscle degeneration-regeneration. The increased expression of MB and BB isozymes of CK in various human neuromuscular diseases may be a manifestation of an ongoing process of degeneration-regeneration.

Pathogenesis of skeletal muscle necrosis induced by tarantula venom

The pathogenesis of myonecrosis induced by venoms of the Arkansas tarantula (Dugesiella hentzi, Girard) and the Honduran tarantula (Aphonopelma spp.) was studied using light and electron microscopy, scanning electron microscopy and x-ray microprobe analysis, and histochemistry. White mice were injected intraperitoneally with a sublethal dose of tarantula venom. Gross examination 24 hr after injection revealed white areas of apparent calcification in the diaphragm muscle. Light microscopic examination at 15 min revealed hypercontracted muscle cells, and necrotic masses containing areas of condensed myofibrils and clumps of mitochondria. By 12 hr numerous phagocytic cells were present around degenerated muscle cells. Electron microscopic examination revealed a myonecrosis of rapid onset with plasma membrane rupture and contraction bands 15 min after injection. At 3 hr only small patches of plasma membrane remained and mitochondrial changes such as swelling, dense intracristal spaces, partitioning, and flocculent densities were prominent. By 12 and 24 hr very dark spicular densities were present in mitochondria and numerous phagocytic cells were located within the intact basal lamina of necrotic cells. X-ray analysis and histochemistry of 24 hr samples showed that necrotic cells contained very high levels of calcium and phosphate. These two tarantula venoms caused a rapid onset myonecrosis in which the primary injury was rupture of the plasma membrane followed by inability of mitochondria and sarcoplasmic reticulum to maintain normal levels of calcium in the cytoplasm leading to cell death.

Mechanism of epinephrine enhancement of lidocaine-induced skeletal muscle necrosis

Epinephrine significantly increases lidocaine-induced skeletal muscle necrosis, even in low concentrations that elicit no damage by themselves. Inasmuch as isoproterenol had no influence on lidocaine myotoxicity, a direct effect of epinephrine on muscle fibers is unlikely. Two vasoconstrictors with dissimilar mechanisms of action, phenylephrine and felypressin, duplicated the potentiating effect of epinephrine on fiber destruction in direct relation to their ability to retard lidocaine absorption from the tissue. It is concluded that the augmentation of muscle necrosis caused by epinephrine is largely due to its ability to increase exposure of skeletal muscle to the local anesthetic.