Cocaine-induced respiratory depression and seizures are synergistic mechanisms of cocaine-induced death in rats

Stimulants and the lung : review of literature

Illicit stimulants, such as cocaine, amphetamine, and their derivatives (e.g., "ecstasy"), continue to exact heavy toll on health care in both developed and developing countries. The US Department of Health and Human Service reported over one million illicit drug-related emergency department visits in 2010, which was higher than any of the six previous years. Both inhaled and intravenous forms of these substances of abuse can result in a variety of acute and chronic injuries to practically every part of the respiratory tract, leading potentially to permanent morbidities as well as fatal consequences--including but not limited to nasal septum perforation, pulmonary hypertension, pneumothorax, pneumomediastinum, interstitial lung disease, alveolar hemorrhage, reactive airway disease, pulmonary edema, pulmonary granulomatosis, infections, foreign body aspiration, infections, bronchoconstriction, and thermal injuries. Stimulants are all rapidly absorbed substances that can also significantly alter the patient's systemic acid-base balance and central nervous system, thereby leading to further respiratory compromise. Mounting evidence in the past decade has demonstrated that adulterants coinhaled with these substances (e.g., levamisole) and the metabolites of these substances (e.g., cocaethylene) are associated with specific forms of systemic and respiratory complications as well. Recent studies have also demonstrated the effects of stimulants on autoimmune-mediated injuries of the respiratory tract, such as cocaine-induced midline destructive lesions. A persistent challenge to studies involving stimulant-associated respiratory toxidromes is the high prevalence of concomitant usage of various substances by drug abusers, including tobacco smoking. Now more than ever, health care providers must be familiar with the multitude of respiratory toxidromes as well as the diverse pathophysiology related to commonly abused stimulants to provide timely diagnosis and effective treatment.

Possible Strategies for the Diagnosis of Fatal Excited Delirium Syndrome

Excited Delirium Syndrome (ExDS) is a term traditionally used in forensic literature to describe the symptoms and signs seen in a subgroup of patients with delirium who die in an agitated state. Components of this syndrome are altered mental status, combativeness and/or aggressiveness, increased tolerance to significant pain, tachypnea, profuse sweating, severe agitation, elevated temperature, delirium, and noncompliance with law enforcement and medical personnel. The individual may display “superhuman” strength and wear clothing inappropriate for the environment. Patients with this presentation are almost guaranteed to cause difficulties for law enforcement officers and medical staff. This review is written in hopes of minimizing some of these difficulties by 1) increasing general awareness and specific knowledge about this condition, 2) explaining the neurochemical and neuroanatomical alterations that have been shown to cause those symptoms, and 3) by suggesting new lines of research that might identify easily measured biomarkers for the disease. If the disease mechanism can be deciphered, then it should be possible to devise effective strategies for treatment. It would also be of enormous value to the legal system. When defending a diagnosis before the court, physical evidence always trumps knowledge and experience. It would be far better to be able to present physical proof than to opine that the decedent's behavior was typical for the disease. In this aspect, ExDS is analogous to myocardial infarction: if a man dies suddenly, it is much easier to prove the cardiac origin of the event if an occlusive thrombus is found in a major coronary artery.

Clair C, Nichols J, Narasimhan D, Ko MC, Sunahara RK, Woods JH. Effects of a long-acting mutant bacterial cocaine esterase on acute cocaine toxicity in rats

BACKGROUND

A longer acting, double mutant bacterial cocaine esterase (CocE T172R/G173Q; DM CocE) has been shown to protect mice from cocaine-induced lethality, inhibit the reinforcing effects of cocaine in rats, and reverse cocaine's cardiovascular effects in rhesus monkeys. The current studies evaluated the effectiveness of DM CocE to protect against, and reverse cocaine's cardiovascular, convulsant, and lethal effects in male and female rats.

METHODS

Pretreatment studies were used to determine the effectiveness and in vivo duration of action for DM CocE to protect rats against the occurrence of cardiovascular changes, convulsion and lethality associated with acute cocaine toxicity. Posttreatment studies were used to evaluate the capacity of DM CocE to rescue rats from the cardiovascular and lethal effects of large doses of cocaine. In addition, male and female rats were studied to determine if there were any potential effects of sex on the capacity of DM CocE to protect against, or reverse acute cocaine toxicity in rats.

RESULTS

Pretreatment with DM CocE dose-dependently protected rats against cocaine-induced cardiovascular changes, convulsion and lethality, with higher doses active for up to 4h, and shifting cocaine-induced lethality at least 10-fold to the right. In addition to dose-dependently recovering rats from an otherwise lethal dose of cocaine, post-treatment with DM CocE also reversed the cardiovascular effects of cocaine. There were no sex-related differences in the effectiveness of DM CocE to protect against, or reverse acute cocaine toxicity.

CONCLUSIONS

Together, these results support the development of DM CocE for the treatment of acute cocaine toxicity.

Prevention and reversal by cocaine esterase of cocaine-induced cardiovascular effects in rats

The present study is the first to utilize bacterial cocaine esterase (CocE) to increase elimination of a lethal dose of cocaine and evaluate its cardioprotective effects. Rats received one of 5 treatments: CocE 1 min after saline; CocE 1 min after a lethal i.p. dose of cocaine; saline 1 min after a lethal i.p. dose of cocaine; CocE immediately after observing a cocaine-induced convulsion; and CocE 1 min after observing a cocaine-induced convulsion. Measures were taken of ECG, blood pressure, and cardiac troponin I (cTnI). The specificity of CocE against cocaine was determined by evaluating its actions against the cocaine analogue, WIN-35,065-2, which lacks an ester attack point for CocE. In addition, CocE's effects were compared with those of midazolam, a benzodiazepine often used to manage cocaine overdose. Whereas CocE alone had negligible cardiovascular effects, it blocked or reversed cocaine-induced QRS complex widening, increased QTc interval, ST elevation, bradycardia, and hypertension. When administered 1 min after cocaine, CocE inhibited myocardial damage; however, administered 1 min after a cocaine-induced convulsion (approximately 40s before cocaine-induced death), CocE did not block cTnI release, but did restore cardiac function. Midazolam blocked convulsions, but exhibited inadequate protection against cocaine-induced cardiotoxicity. The majority of rats given cocaine plus midazolam died. CocE did not prevent the lethal cardiovascular effects of WIN-35,065-2. In all likelihood, CocE rapidly and specifically reduced the body burden of cocaine and inhibited or reversed the cardiovascular consequences of high-dose cocaine. These results support CocE as a potential therapeutic avenue in cocaine overdose.

Cocaine-induced status epilepticus and death generate oxidative stress in prefrontal cortex and striatum of mice

Oxidative stress (OS) has been related to cocaine's actions and also to numerous nervous system pathologies, including seizures. The purpose of this work was to determine the alterations in glutathione (GSH) content, nitrite/nitrate and MDA levels after cocaine-induced toxicity. Male Swiss mice were injected (i.p.) with cocaine 90 mg/kg and observed during 1h. After this cocaine overdose some animals presented status epilepticus (SE) while some died after seizures. These animals were divided in two groups, SE and death. A group with an association of the antioxidant Vitamin E (Vit E, 400mg/kg, i.p.) plus Coc 90 (Vit E plus Coc 90) was undertaken to assess the neuroprotective effect of Vit E. Neurochemical analyses were carried out in prefrontal cortex (PFC) and striatum (ST). GSH levels increased only after cocaine-induced death in both areas studied. Cocaine-induced SE has increased nitrite/nitrate content in PFC and ST, while after death the increase was only in PFC. MDA (the lipid peroxidation marker) was elevated after SE and death in ST and only after death in PFC. Antioxidant treatment significantly reduced the GSH, nitrite/nitrate in ST and MDA levels. Only nitrite/nitrate content in PFC has not been decreased by Vit E pretreatment. The results relate that oxidative stress occurs after cocaine-induced toxicity mainly after death indicating that probably the increase of OS in the animal's brain leads to seizures and death, also showing a protective effect of Vit E in this process. Together with previous results this study contributes to the knowledge of cocaine-induced toxicity and possible in the near future to the use of antioxidants in the prevention of cocaine-induced CNS toxicity.

A bacterial cocaine esterase protects against cocaine-induced epileptogenic activity and lethality

STUDY OBJECTIVE

Cocaine toxicity results in cardiovascular complications, seizures, and death and accounts for approximately 20% of drug-related emergency department visits every year. Presently, there are no treatments to eliminate the toxic effects of cocaine. The present study hypothesizes that a bacterial cocaine esterase with high catalytic efficiency would provide rapid and robust protection from cocaine-induced convulsions, epileptogenic activity, and lethality.

METHODS

Cocaine-induced paroxysmal activity and convulsions were evaluated in rats surgically implanted with radiotelemetry devices (N=6 per treatment group). Cocaine esterase was administered 1 minute after a lethal dose of cocaine or after cocaine-induced convulsions to determine the ability of the enzyme to prevent or reverse, respectively, the effects of cocaine.

RESULTS

The cocaine esterase prevented all cocaine-induced electroencephalographic changes and lethality. This effect was specific for cocaine because the esterase did not prevent convulsions and death induced by a cocaine analog, (-)-2beta-carbomethoxy-3beta-phenyltropane. The esterase prevented lethality even after cocaine-induced convulsions occurred. In contrast, the short-acting benzodiazepine, midazolam, prevented cocaine-induced convulsions but not the lethal effects of cocaine.

CONCLUSION

The data showed that cocaine esterase successfully degraded circulating cocaine to prevent lethality and that cocaine-induced convulsions alone are not responsible for the lethal effects of cocaine in this model. Therefore, further investigation into the use of cocaine esterase for treating cocaine overdose and its toxic effects is warranted.

Alterations in monoamine levels after cocaine-induced status epilepticus and death in striatum and prefrontal cortex of mice

Seizures and death are the more important toxic consequences related to cocaine overdose. Some reports have shown that pharmacological manipulations in dopaminergic, serotonergic and noradrenergic systems alter the occurrence of cocaine-induced convulsions and death. Based on this fact, this work was performed to determine the changes in monoamine levels (DA, 5-HT and NE) and their metabolites (DOPAC, HVA and 5-HIAA) after cocaine-induced status epilepticus (SE) and death in striatum and prefrontal cortex (PFC). The monoamines and their metabolites were assayed by reverse-phase high-performance liquid chromatography with electrochemical detection. Animal SE in striatum presented a decrease in DA and NE levels and an increase in HVA although in PFC there was an increase in DA, 5-HT and NE. Animals that died from cocaine-induced seizures in striatum showed an increase only in NE levels, but on the other hand in PFC a decrease occurred in DA and NE levels. Taken together these results indicated that cocaine-induced SE and death altered monoamine levels in different ways depending on the brain area studied, suggesting that different mechanisms are involved.

Naltrindole, a selective delta-opioid receptor antagonist, potentiates the lethal effects of cocaine by a central mechanism of action

The potentiation of the toxic and lethal effects of cocaine by the selective delta-opioid receptor antagonist naltrindole was explored in unrestrained, unanesthetized rats that received a continuous intravenous infusion of cocaine until death. The lethal dose of cocaine was lowered dose dependently in animals administered naltrindole intracisternally (3.0-30 microg), but not intravenously (30-300 microg). There was also a decrease in the lethal dose of cocaine following an injection of the nonselective opioid antagonist naltrexone, but not naloxone. However, the seizure-producing dose of cocaine was decreased dose dependently in rats that received naltrindole, regardless of the route of administration, naloxone, or naltrexone. In contrast, the effect of cocaine on heart rate was altered only by centrally administered naltrindole or intravenous naltrexone, with a dose of 30 microg naltrindole and 10 mg/kg naltrexone abolishing the bradycardic effect of cocaine. Despite this, neither naltrindole nor naltrexone changed the hypertensive effect of cocaine. Higher doses of naltrindole (100 microg i.c.) produced significant increases in heart rate and mean arterial pressure and were not tested in combination with cocaine. Because the lethal dose of cocaine was reduced only when naltrindole was administered intracisternally, the potentiation of the lethal effects of cocaine by naltrindole is through a central mechanism of action that may involve changes in cardiovascular function.

Methcathinone intoxication in the rat: abrogation by dextrorphan

STUDY OBJECTIVE

Methcathinone, a designer drug, has high abuse liability. In this study we characterized acute methcathinone toxicity in rats, attempting to determine whether the excitatory amino acid receptor antagonist dextrorphan can antagonize methcathinone intoxication.

METHODS

Intoxication was produced with IV methcathinone infusion (5 mg/kg/minute; 100 mg/mL) in conscious rats. We studied pretreatment, in which dextrorphan or vehicle was injected 30 minutes before methcathinone infusion. In a second protocol, dextrorphan or saline solution was given immediately after the onset of convulsions.

RESULTS

Methcathinone caused tachycardia (maximal increase, 131 +/- 10 beats/minute), hyperthermia (+2.3 degrees C), convulsions, and cardiorespiratory collapse in vehicle-pretreated rats (n = 9). Death occurred after 32.0 +/- 1.1 minutes of infusion. Dextrorphan pretreatment (25 mg/kg; n = 7) significantly reduced hyperthermia (+.1 degree +/- .3 degree C) and tachycardia and increased the convulsive (dextrorphan, 134 +/- 9 mg/kg; vehicle, 67 +/- 4 mg/kg) and lethal doses (dextrorphan, 204 +/- 9 mg/kg; vehicle, 160 +/- 5 mg/kg). Dextrorphan, given immediately after the initial methcathinone convulsion, reduced hyperthermic and tachycardic responses but not the lethality of methcathinone.

CONCLUSION

Blockade of excitatory amino acid receptors by dextrorphan minimizes acute methcathinone intoxication.

Premorbid behaviors produced by cocaine, ethanol and cocaethylene in the mouse

1. The premorbid behaviors produced by the administration of cocaine, ethanol, their combination, as well as a metabolite produced by their co-administration, viz. cocaethylene, were defined, determined and quantified in the HS strain of mice. 2. The LD50 for ethanol was 9.71 g/kg in males and 9.45 g/kg in females, whereas the LD50 values in male and female mice for cocaine were 101.55 and 90.00 mg/kg, respectively. 3. The data indicate that clonic-tonic seizures continued into status epilepticus after cocaine administration and prior to cocaine-induced lethality. In contrast, administration of the cocaine-ethanol metabolite cocaethylene produced status epilepticus without producing clonic-tonic seizures yet still resulted in lethality. 4. Thus, both cocaine and cocaethylene may produce their lethal effects in mice through neuro-regulatory mechanisms mediating protracted seizure induction.

The effect of cocaine and amphetamines on vital signs in trauma patients

The object of this study was to determine if the presence of sympathomimetics (cocaine, benzoylecgonine, or amphetamine), detected by routine urine toxicology screen, affect the initial presenting pulse, blood pressure, respiratory rate, or level of consciousness in trauma patients. A retrospective chart review was performed on 1,679 patients enrolled in an urban level 1 trauma registry between October 1987, and July 1992, for whom complete toxicology data were available. There were no clinically significant differences in the vital signs of patients with positive toxicology screens and those with negative screens. There was a statistically significant increase in prehospital respiratory rate among patients with benzoylecgonine or amphetamines on admission toxicology screens when potential confounding factors were controlled. However, these effects disappeared upon arrival at the hospital. The detection of sympathomimetics by toxicology screening had no effect on pulse and systolic blood pressure when age, sex, mechanism, type, and severity of injury, prehospital IV fluid volume, and alcohol intoxication were controlled.

The effects of lidocaine pretreatment on cocaine neurotoxicity and lethality in mice

OBJECTIVE

To evaluate the effects of an antiarrhythmic dose of lidocaine on cocaine-induced ataxia, seizures, and death in mice.

METHODS

A randomized, controlled, blinded investigation was conducted using 220 female Swiss albino mice. Groups of 20 animals received intraperitoneal (IP) administration of either 31.6 mg/kg of lidocaine hydrochloride in 0.9% NaCl (ten animals) or an equal volume of 0.9% NaCl solution (ten animals). After 5 minutes, all the animals received IP cocaine in incremental doses ranging from 40 to 110 mg/kg. The animals were observed for ataxia, seizures, and death. The animals pretreated with lidocaine were compared with the control animals for the number of adverse effects from cocaine at each dose tested.

RESULTS

Lidocaine significantly increased the overall incidences of cocaine-induced ataxia (p = 0.02) and seizures (p < 0.001). However, pretreatment with lidocaine offered protection against cocaine lethality (p < 0.0001).

CONCLUSION

In this preexposure model, lidocaine protects mice against cocaine-induced lethality. These effects seem to be independent of convulsive activity. Further study is required to determine the safety and efficacy of lidocaine for the management of cocaine-induced arrhythmias.

Hyperthermia in psychostimulant overdose

Psychostimulant drugs such as amphetamines, amphetamine derivatives, and cocaine produce a variety of potentially lethal effects, and an understanding of these toxic effects is important for emergency physicians. While some effects of psychostimulant poisonings such as cardiovascular compromise and seizures have been discussed extensively, other metabolic derangements such as hyperthermia are less well characterized. In fact, hyperthermia is a common feature of severe-to-lethal poisonings and may be the primary mode of demise in some patients. Animal studies confirm that drug-induced hyperthermia alone can be lethal in some species, although other toxic effects may predominate at different drug doses or rates of administration. In non-lethal poisonings, hyperthermia can produce rhabdomyolysis, leading to further morbidity. Clinical reports and animal studies indicate that hyperthermia is a primary effect of psychostimulant drugs and can occur independently of seizures or increased motor activity. Furthermore, activation of particular dopamine receptors in the central nervous system appears to mediate psychostimulant-induced hyperthermia. The literature suggests cooling and tranquilization of psychostimulant-poisoned patients after cardiovascular stabilization. Paralysis and mechanical ventilation may be required. The involvement of dopamine receptor activation in psychostimulant toxicity suggests that dopamine-blocking neuroleptic drugs may be a useful adjunct to current treatment regimens. However, further studies are required to assess this approach. In summary, hyperthermia is a potentially lethal but treatable manifestation of severe psychostimulant poisoning.

Cocaine toxicity and the calcium channel blockers nifedipine and nimodipine in rats

Two dihydropyridine type calcium channel blockers (CCBs) were studied for any protective or therapeutic effect upon cocaine-induced toxicity and death in rats. To test for the protective effects, rats were pretreated with vehicle (control), nifedipine or nimodipine, intraperitoneally (IP) 30 minutes prior to an LD85 of cocaine, or intravenously (IV) 10 minutes prior to cocaine administration. Animals receiving IP control vehicle developed seizures in 5.6 +/- 1.0 minutes and respiratory arrest in 9.8 +/- 1.4 minutes. Animals pretreated IP with nifedipine or nimodipine developed seizures and respiratory arrest significantly sooner than the controls, although the overall incidences of seizures and respiratory arrest were not significantly different. Pretreatment with IV CCBs resulted in similar findings. To test the therapeutic effect of CCBs given following cocaine overdose, rats were administered cocaine IP and then treated with IV nifedipine or nimodipine once seizures occurred. In these animals, there was no significant difference in the incidence or time to respiratory arrest compared to vehicle controls. This study demonstrates that neither pretreatment nor posttreatment with the CCBs nifedipine or nimodipine reduces cocaine toxicity in this rodent model.

Urethane anesthesia reverses the protective effect of noncompetitive NMDA receptor antagonists against cocaine intoxication

The present experiments examined whether pretreatment with the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists, MK-801 and dextrorphan, could antagonize cocaine-induced convulsions and lethality in conscious Sprague-Dawley (SD) rats and whether urethane anesthesia alters the observed interactions. Conscious, restrained male SD rats received continuous i.v. infusions of cocaine hydrochloride (1.25 mg/kg.min) until convulsions and death occurred. Cocaine doses of 21.2 +/- 1.8 and 29.5 +/- 2.5 mg/kg caused convulsions and death, respectively, in saline treated rats (n = 8). Convulsions were absent in MK-801 (1 mg/kg, i.v.; n = 8) pretreated rats; the lethal cocaine dose was 44.0 +/- 2.7 mg/kg (p < 0.05). In contrast, urethane anesthesia (1.2 g/kg, i.p.) decreased the dose of cocaine required to cause toxicity, compared to that in saline controls (24.8 +/- 0.8 mg/kg, n = 13), in MK-801 (2.0 +/- 0.3, n = 7; p < 0.01) and in dextrorphan mg/kg, n = 13), in MK-801 (2.0 +/- 0.3, n = 7; p < 0.01) and in dextrorphan (25 mg/kg, i.v.; 13.1 +/- 1.4, n = 6; p < 0.01) pretreated rats. Pressor responses with little change in heart rate were evident during cocaine infusion in vehicle pretreated rats. Bradycardiac responses were noted to cocaine in groups following NMDA receptor blockade. Reversal of the pressor response to cocaine was noted in MK-801 pretreated animals, while dextrorphan pretreatment moderated cocaine-induced increases in blood pressure. Ventilatory support protected against cocaine lethality in urethane anesthetized rats, indicating that respiratory failure is the proximate cause of death with cocaine infusion. However, artificially ventilated rats, pretreated with MK-801, were more sensitive (lethal cocaine dose, 76.6 +/- 8.0 mg/kg, n = 5) than vehicle pretreated rats (129.4 +/- 15.8 mg/kg, n = 6), indicating that MK-801 may increase both the respiratory and the cardiac toxicity of cocaine in urethane anesthetized rats. Interactions between NMDA receptors and cocaine are modified by urethane anesthesia.

Tetracaine protects against cocaine lethality in mice

STUDY HYPOTHESIS

Tetracaine will enhance cocaine toxicity.

STUDY POPULATION

Two hundred forty female Swiss albino mice weighing 27 to 45 g.

METHODS

Intraperitoneal injections of tetracaine and cocaine were given to groups of ten mice each in a controlled, blinded fashion. Either tetracaine or an equal volume of normal saline was given five minutes before one of six incremental doses of cocaine, ranging from 60 to 110 mg/kg. The experiment was repeated twice using two different doses of tetracaine: either an LD10 (40 mg/kg determined from preliminary studies), or one-twentieth of the dose of cocaine (which approximates the ratio used in tetracaine, epinephrine, and cocaine). Lethality was recorded at 24 hours. Lethality between groups was compared with a Wilcoxon sign-rank test.

RESULTS

Tetracaine reduced cocaine lethality at all doses. This reduction in lethality was statistically significant at both tetracaine doses (P < .05).

CONCLUSION

In the mouse, pretreatment with tetracaine significantly decreases cocaine lethality.

Acute cocaine toxicity: the effect of agents in non-seizure-induced death

Death from cocaine intoxication results from one or more of the multiple mechanisms including seizures, cardiovascular collapse, or apnea. In the free-moving rat model, continuous seizures are a major cause of death. To study other mechanisms of death unrelated to seizures in this model, we suppressed lethal seizures with diazepam (DZP) and investigated the effect of several pharmacological agents. Rats were pretreated with vehicle alone, diazepam 5 mg/kg alone, or a combination of DZP plus either nifedipine (NIFD) 2 mg/kg, propranolol (PROP) 10 mg/kg, or prazosin (PRAZ) 5 mg/kg. Five minutes after pretreatment, all animals received cocaine 100 mg/kg. Each test group consisted of 15 animals and all agents were given IP. Two animals in each group had cortical electrodes implanted. Animals that received vehicle followed by cocaine had 100% incidence of seizures and death. Those rats that received DZP alone followed by cocaine had no seizures and 53% death. Rats that received DZP plus NIFD or DZP plus PROP had suppression of seizures but no significant change in the incidence of death. The group that received DZP and PRAZ followed by cocaine had no seizures and 13% incidence of death (p < 0.001). Electroencephalogram recordings showed cortical electrical spike activity or spike-and-wave afterdischarges in all animals clinically observed to have seizures. In the absence of clinical seizure activity, no significant cortical spike activity was noted. It is concluded that animals protected from seizures with diazepam can still have nonseizure deaths after high-dose cocaine. The incidence of death in these animals is not reduced with nifedipine or propranolol pretreatment but is reduced with prazosin pretreatment.