Regenerative capability of skeletal muscle in chicken muscular dystrophy

To examine the morphological sequence of regenerating fibers after myonecrosis in dystrophic muscles, 0.5 ml of 0.5% bupivacaine hydrochloride (BPVC) (Marcaine) solution, a local anesthetic with a cytotoxic effect on the muscle fibers, was injected directly into the dystrophic (line 413) and nondystrophic (line 412) posterior latissimus dorsi (PLD) muscles of young and adult chickens. Although the dystrophic muscles after BPVC injection showed a rapid recovery with a similar tempo to that of nondystrophic ones, they showed different morphological behavior in the early phase of regeneration, including marked variability in the size of fibers and in the intracytoplasmic enzyme activities of nicotinamide adenine dinucleotide, reduced-tetrazolium reductase (NADH-TR), acetylcholinesterase (AChE), and nonspecific esterase (NSE).

Comparative cardiotoxicity of bupivacaine and lidocaine in the isolated perfused mammalian heart

This study was designed to compare the direct actions of bupivacaine and lidocaine on the isolated perfused guinea pig Langendorff heart preparation. Sixty min after mounting, either bupivacaine HCl (0.3 or 3 micrograms/ml) or lidocaine HCl (10 or 30 micrograms/ml) was added to the perfusate, and the effect (if any) was compared to untreated control values 30, 60, and 90 min later. Although the highest concentrations of both drugs invariably produced statistically significant reductions in heart rate, df/dt, coronary blood flow, and myocardial oxygen consumption (MVO2), these reductions were consistently greater after bupivacaine. Moreover, arrhythmias occurred in 6 of 12 preparations in those hearts exposed to 3 micrograms/ml of bupivacaine. Most often these arrhythmias consisted of heart block and bi- or trigeminy. Additional studies indicated that the reduction in coronary blood flow and MVO2 produced by 3 micrograms/ml of bupivacaine was a consequence of its direct negative inotropic and chronotropic action. Although the myocardial depression produced by bupivacaine and lidocaine could be reversed readily by substituting fresh perfusate, increasing the extracellular calcium concentration in stepwise increments did not augment the negative inotropic or chronotropic effect produced by 3 micrograms/ml of bupivacaine or 10 micrograms/ml of lidocaine. We conclude that 3 micrograms/ml of unbound bupivacaine is more cardiotoxic than 30 micrograms/ml of unbound lidocaine in this model.

Bupivacaine-induced cardiac arrhythmias in sheep

Controversy persists about the cardiac toxicity of bupivacaine if accidentally administered intravenously during regional anesthesia. Using awake, unanesthetized sheep, we evaluated the cardiac effects of low and high equivalent doses of lidocaine and bupivacaine given intravenously over 10 s. All animals convulsed within 30 s of injections. Although both drugs significantly increased heart rate and systemic and pulmonary arterial blood pressure for up to 10 min, cardiac output was affected variably. The magnitude of hemodynamic changes that each drug produced did not differ significantly from each other at either dose level. However, of the sheep receiving intravenous lidocaine, none developed arrhythmias other than mild sinus tachycardia and minimal ST-T wave changes (which occurred in 25% of the animals). After intravenous bupivacaine injection, all sheep had transient changes on the EKG and/or arrhythmias (e.g., supraventricular tachycardia; atrioventricular condition blocks; ventricular tachycardia; multiform premature ventricular contractions; wide QRS complexes; ST-T wave changes; and in one animal, fatal ventricular fibrillation). Normal sinus rhythm usually returned within 8-10 min. Arterial blood gas and acid-base values stayed within the normal range during the studies, and serum potassium did not change significantly from control. In conclusion, in conscious adult sheep, equivalent doses of lidocaine or bupivacaine produced similar central nervous system (CNS) toxicity when rapidly injected intravenously. In the absence of marked hypoxia, respiratory or metabolic acidosis, hyperkalemia, or hypotension, serious cardiac arrhythmias occurred after bupivacaine but not lidocaine.

Effect of cycloheximide administration on bupivacaine-induced acute muscle degradation

We have examined the effect of cycloheximide on bupivacaine-induced, macrophage-mediated muscle degeneration in rats and obtained the following results. Direct intramuscular injection of bupivacaine into soleus muscle caused uniform muscle degeneration (Ishiura, S. et al. (1983) J. Biochem. 94, 311-314). The degeneration was most prominent 48 h after injection, with many infiltrating macrophages. Intraperitoneal administration of cycloheximide prevented the bupivacaine-induced macrophage invasion and decrease of structural proteins 48 h after injection. Cycloheximide inhibited the increase in lysosomal enzymes in bupivacaine-treated muscle. The peritoneal macrophages increased in number immediately after bupivacaine injection, while cycloheximide inhibited their accumulation. These results indicated that cycloheximide inhibited muscle degradation by preventing macrophage proliferation.

[Anti-arrhythmia properties of marcaine]

Comparative study of antiarrhythmic properties of marcaine and lidocaine was made on aconitine- and strophanthine-induced experimental arrhythmias and in rhythm disorders induced by electrical stimulation of the ventricles. Marcaine (5 mg/kg) prevented the development of rhythm disorders induced in rats by intravenous injection of aconitine (40 micrograms/kg) and also raised the arrhythmogenic dose of strophanthine (ouabain) in guinea-pigs. Administration of marcaine to anesthetized cats in a dose of 2 mg/kg reduced the assimilation of the rhythm imposed on the heart ventricles at the expense of an increase in the effective refractory period and increased the threshold of electrical fibrillation of the ventricles more noticeably and for a longer time as compared with lidocaine administered in a dose of 5 mg/kg. Marcaine compares very favourably with lidocaine as regards the potency and duration of the antiarrhythmic effect. However, it is inferior to lidocaine from the standpoint of the therapeutic action range. Toxic effects of marcaine do not make clear the prospects of its clinical use as an antiarrhythmic drug. Nevertheless the search of new effective antiarrhythmic drugs among marcaine analogs holds promise.

The myotoxicity of bupivacaine, a 31P n.m.r. investigation

Phosphorus nuclear magnetic resonance (n.m.r.) spectroscopy is a recently introduced method for the non-invasive study of muscle biochemistry. It was shown in the rat that an intramuscular injection of the drug resulted in degeneration that was reflected spectroscopically in a progressive decrease in the intracellular concentrations of phosphocreatine and adenosine triphosphate without a corresponding rise in that of inorganic phosphate. Furthermore, ATP was depleted in the presence of significant levels of phosphocreatine. As regeneration occurred spectra returned to normal and this was complete by day 10. No such spectroscopic effects were demonstrated in man following the use of bupivacaine in an intravenous regional anaesthetic. It is suggested that further studies in man are required before this drug can be administered intramuscularly with confidence.

Plasma bupivacaine concentrations in children during caudal epidural analgesia

Plasma bupivacaine concentrations were measured in 45 children, whose ages ranged from 4 months to 12 years, following administration of caudal epidural analgesia. Using 3 mg/kg of bupivacaine 0.25%, mean blood levels of 1.2-1.4 microgram/ml were reached, which are well within the limits of projected toxic levels. Simultaneous arterial and venous sampling showed a small but significant difference between these two sampling sites fo the first fifteen minutes.

A comparative in vivo study of local neurotoxicity of lidocaine, bupivacaine, 2-chloroprocaine, and a mixture of 2-chloroprocaine and bupivacaine

This study was undertaken because of several recent reports of adverse neurologic reactions following the use of 2-chloroprocaine. Carotid sheaths containing undisturbed vagus nerve were surgically exposed in rabbits and bathed in situ for up to 1 hour in one of the following-isotonic solutions: physiologic salt solution, lidocaine 2%, bupivacaine 0.75%, 2-chloroprocaine 3%, or a mixture of 2-chloroprocaine 1.5% and bupivacaine 0.375%. Each solution contained epinephrine, 5 micrograms/ml, (1:200,000). In other animals the carotid sheaths were bathed in physiologic salt solution, or 2-chloroprocaine 3% without epinephrine. The nerves were excised 10 to 12 days later. C-fiber impulse conduction was normal in nerves that had been exposed to physiologic salt solution with or without epinephrine, to lidocaine, or to bupivacaine. Conduction was absent or markedly impaired in several nerve specimens following exposure to 2-chloroprocaine. Histologic sections revealed the presence of epineurial cellular infiltration and fibrosis, perineurial fibrosis, and axonal degeneration in nerves that had been exposed to 2-chloroprocaine or the mixture of 2-chloroprocaine and bupivacaine. Histologic abnormalities were minor or absent following exposure to lidocaine, to bupivacaine, or to physiologic salt solution. These findings suggest that, under the conditions of the experiments, 2-chloroprocaine is more neurotoxic than lidocaine or bupivacaine.

Neurologic effects of subarachnoid administration of 2-chloroprocaine-CE, bupivacaine, and low pH normal saline in dogs

The purpose of this study was to evaluate the neurologic consequences of deliberate subarachnoid injection of large volumes of 2-chloroprocaine-CE in experimental animals. The possible role of low pH as well as total volume as potential factors in causing neurotoxicity was evaluated. The 65 dogs in the study received injections in the subarachnoid space as follows: 6 to 8 ml of bupivacaine (N = 15), 2-chloroprocaine-CE (N = 20), low pH normal saline (pH 3.0) (N = 20), or normal saline (N = 10). Of the 20 animals that received subarachnoid injection of 2-chloroprocaine-CE seven (35%) developed hind-limb paralysis. None of the animals that received bupivacaine, normal saline, or normal saline titrated to a pH 3.0 developed hind-limb paralysis. Of the 15 spinal cords of the animals that received 2-chloroprocaine-CE, 13 showed subpial necrosis; the nerve roots and subarachnoid vessels were normal. The spinal cords of the animals that received bupivacaine, low pH normal saline (pH 3.0), or normal saline did not show abnormal findings.

Mixtures of local anesthetics are no more toxic than the parent drugs

Mixtures of local anesthetics can combine the best features of both components. The authors assayed the systemic toxicity of local anesthetic mixtures given subcutaneously to mice. Convulsions regularly preceded death. The median convulsant dose (CD50) of bupivacaine was one-fourth that of lidocaine, and one-seventh that of chloroprocaine. The median lethal dose (LD50) of chloroprocaine was twice the CD50, whereas the LD50 of bupivacaine was but little greater than the CD50. Hence, the more potent the agent, the greater is the chance of death from a convulsant dose of local anesthetic. Conversion to lidocaine-equivalent doses permitted comparisons between mixtures. None of the mixtures were more convulsant or more lethal than their parent components; lidocaine-containing mixtures were significantly less lethal than the lidocaine norm. Mixing increased the distance between convulsant and lethal doses, with survival from convulsions induced by bupivacaine-containing mixtures enhanced in particular. It is concluded that local anesthetic toxicity is essentially additive.

Local anesthetics: injection route alters relative toxicity of bupivacaine

Site of injection affects the toxicity of local anesthetics, perhaps because differences in tissue binding, vascular uptake, and hepatic clearance affect drug disposition. Three local anesthetics with different physical and pharmacologic properties were given intraperitoneally or subcutaneously to mice assay median convulsant (CD50) and median lethal (LD50) doses. The toxicity of bupivacaine, a long-acting, tightly tissue-bound local anesthetic agent was increased only 30% to 40%, whereas the toxicities of lidocaine and chloroprocaine were increased 300% to 400%, by giving the drugs intraperitoneally rather than subcutaneously. Because of this, bupivacaine appeared to be 13 times more toxic than chloroprocaine when subcutaneously, but only 4.5 times more toxic relative to chloroprocaine when assayed intraperitoneally. We conclude that a drug's therapeutic index (ratio of potency to toxicity) relative to a standard drug is affected considerably by route of extravascular administration.

Deaths from local anesthetic-induced convulsions in mice

Median convulsant (CD50) and median lethal (LD50) doses of three representative local anesthetics were determined in adult mice to evaluate the threat to life of local anesthetic-induced convulsions. The CD50 and LD50, respectively, were 57.7 and 58.7 mg/kg for bupivacaine, 111.0 and 133.1 mg/kg for lidocaine, and 243.4 and 266.5 mg/kg for chloroprocaine. When given intraperitoneally, bupivacaine thus was only about twice as toxic as lidocaine and four times as toxic as chloroprocaine. Convulsions always preceded death, except after precipitous cardiopulmonary arrest from extreme doses. A CD50 dose of local anesthetic (causing convulsions in 50% of mice) was fatal in 90% of bupivacaine-induced seizures, in 57% of the chloroprocaine group, and in 6% of the lidocaine group. The narrow gap between convulsant and lethal doses of local anesthetics indicates that untreated convulsions present much more of a threat to life than heretofore appreciated.

Local anesthetics: importance of mode of application, concentration and adrenaline for the appearance of nerve lesions. An experimental study of axonal degeneration and barrier damage after intrafascicular injection or topical application of bupivacaine (Marcain)

Local anesthetics are designed for application in or close to nerve tissue. In spite of their wide clinical use, surprisingly few investigations deal with the neural toxicity of modern local anesthetics. In this experimental study, the effects were investigated of intrafascicular or topical application of the long-acting local anesthetic bupivacaine on the rabbit sciatic nerve. Axonal degeneration was histologically evaluated and a fluorescence-microscopic technique used to detect lesions in the blood-nerve barrier. Topical application of bupivacaine in clinically recommended concentrations around the nerve caused no detectable nerve injury, while intrafascicular injections caused considerable axonal degeneration and damaged the blood nerve barrier. Axonal degeneration was the same after injection of physiologic saline solution and bupivacaine 0.5%, but it increased with increasing bupivacaine concentration and especially with the addition of adrenaline. On the other hand, the acute effects of intrafascicular injection, as visualized in the barrier experiments, changed little with the addition of adrenaline, indicating that it is the injection trauma itself which is deleterious. It is concluded that intraneural injections should be avoided and that plain bupivacaine solutions should be routinely used.

Studies on the duration of local anaesthesia: structure/activity relationships in a series of homologous local anaesthetics

When the number of carbon atoms on the piperidine-nitrogen of the mepivacaine molecule was increased up to four or five carbons, the toxicity of the compounds and the duration of their local anaesthetic effects were increased. With longer N-alkyl-chains, the general toxicity and the local anaesthetic potency - but not the tissue toxicity - were reduced. In dental infiltration anaesthesia only the short-chain compounds offered an acceptable local anaesthesia. In these tests, the medium-chain compounds had a very unfavourable quotient between dental anaesthesia and soft tissue anaesthesia, while the long-chain compounds could not be tested at all in man because of their tissue irritating properties.

Bupivacaine (Marcaine): an evaluation of its tissue and systemic toxicity in humans

In countries other than the U.S.A., dosages of bupivacaine have been limited to 100 mg without epinephrine and 150 mg with epinephrine. A review of 7,688 regional block procedures employing bupivacaine in concentrations of 0.25, 0.5, and 0.75%, and in dosages as high as 600 mg, indicated that such stringent restrictions: (1) are unwarranted, (2) make comparisons with other local anesthetic agents difficult, and (3) are in need of revision.

Relation of etidocaine and bupivacaine toxicity to rate of infusion in rhesus monkeys

The relationship between infusion rate of etidocaine and bupivacaine and central nervous system toxicity was studied in three rhesus monkeys. Increasing the infusion rate from 0.5 to 2.0 mg/kg.min-1 decreased the seizure dosage of etidocaine but had no effect on that of bupivacaine. Arterial plasma concentrations of etidocaine and bupivacaine that induced electrical seizure activity increased as the infusion rate was increased from 0.5 to 1.0 mg/kg. min-1. A plasma decay study in a fourth animal demonstrated that etidocaine decayed more rapidly than did bupivacaine. These results suggest that the rate of administration of these agents is important in determining central nervous system toxicity.

Etidocaine, bupivacaine, and lidocaine seizure thresholds in monkeys

The central nervous system toxicities of etidocaine, bupivacaine, and lidocaine were studied during constant-rate intravenous infusions in rhesus monkeys. Comparison of drug effects was achieved by determining the drug dosages and arterial plasma concentrations that induced electrical seizure activity. The central nervous system toxicity of etidocaine was similar to that of bupivacaine. The toxicity of each was four times greater than that of lidocaine. Since the drug infusion rates were proportional to anesthetic potencies in clinical usage, the therapeutic-toxic ratios of these three drugs are similar.

Evaluation of clinical tolerance of local anaesthetic agents

The clinical tolerance to local anaesthetic drugs can be assessed from a knowledge of their pharmacokinetic behaviour, their absorption properties and the effects produced by controlled i.v. infusions. Pharmacokinetic behavior can be calculated from the plasma concentrations of the drugs injected i.v. in non-toxic doses. Absorption properties can likewise be determined from plasma concentrations following injection at various sites. Acute toxicity can be assessed by i.v. infusion of toxic doses into volunteers. The dosage required to produce symptoms can be compared with other drugs. Such dosage is considerably affected by the rate of injection. The venous plasma concentrations at the height of toxicity are unreliable guides to toxicity. Experiences using the new local anaesthetic etidocaine are reported.

Central nervous system effects of local anaesthetic agents

A review is given of an experimental study on cats where the influence of acid-base changes on central nervous system toxicity of local anaesthetic agents was studied. The conclusion of this study was that a respiratory acidosis increased the central nervous system toxicity of local anaesthetics and that the underlying metabolic conditions modified this increase. Thus a respiratory acidosis increased this toxicity more if it was based on a metabolic acidosis than on a metabolic alkalosis (Englesson, 1974; Englesson and Grevsten, 1974). An extended analysis is presented where automatic frequency analysis was performed on the e.e.g. recordings performed during the i.v. infusion of lignocaine, bupivacaine, L 134, HS 37 and its optical isomers. The preliminary results show that the electrical changes appearing in the e.e.g. from the start of the i.v. infusion until seizure activity were the same if this time interval was as short as 1 min or as long as 8 min. It also revealed remarkable individual differences between agents, for instance lignocaine displaying marked electrical changes already in the first third of this time period where bupivacaine showed no changes until shortly before seizures.

Evaluation of the toxicity of local anaesthetic agents in man

Etidocaine given by intravenous infusion has been compared, using a double-blind technique, with bupivacaine and lignocaine in respect of toxic symptoms and signs. The degree of toxicity is affected considerably by the rate of drug infusion. At 10 mg/min subjects could tolerate twice the dose of etidocaine as bupivacaine. Tolerance to etidocaine was less at 20 mg/min but still compared favourably with bupivacaine at 10 mg/min. Considering the difference in potency of the two agents it was considered that the therapeutic ratios would not be substantially different. Lignocaine at 20 mg/min was better tolerated than etidocaine. Venous plasma concentration during these experiments showed a more rapid decrease in the case of etidocaine compared with bupivacaine, but the concentrations were unhelpful in predicting the toxic effects. Similarly electroencephalography revealed no abnormalities in spite of marked subjective and objective signs of toxicity.