Diazepam in the prevention of seizures and death in cocaine-intoxicated rats

Investigation of the Mechanisms of Tramadol-Induced Seizures in Overdose in the Rat

Tramadol overdose is frequently associated with the onset of seizures, usually considered as serotonin syndrome manifestations. Recently, the serotoninergic mechanism of tramadol-attributed seizures has been questioned. This study’s aim was to identify the mechanisms involved in tramadol-induced seizures in overdose in rats. The investigations included (1) the effects of specific pretreatments on tramadol-induced seizure onset and brain monoamine concentrations, (2) the interaction between tramadol and γ-aminobutyric acid (GABA)A receptors in vivo in the brain using positron emission tomography (PET) imaging and 11C-flumazenil. Diazepam abolished tramadol-induced seizures, in contrast to naloxone, cyproheptadine and fexofenadine pretreatments. Despite seizure abolishment, diazepam significantly enhanced tramadol-induced increase in the brain serotonin (p < 0.01), histamine (p < 0.01), dopamine (p < 0.05) and norepinephrine (p < 0.05). No displacement of 11C-flumazenil brain kinetics was observed following tramadol administration in contrast to diazepam, suggesting that the observed interaction was not related to a competitive mechanism between tramadol and flumazenil at the benzodiazepine-binding site. Our findings do not support the involvement of serotoninergic, histaminergic, dopaminergic, norepinephrine or opioidergic pathways in tramadol-induced seizures in overdose, but they strongly suggest a tramadol-induced allosteric change of the benzodiazepine-binding site of GABAA receptors. Management of tramadol-poisoned patients should take into account that tramadol-induced seizures are mainly related to a GABAergic pathway.

Acute Cardiovascular Toxicity of Cocaine

Cocaine is one of the most commonly abused drugs and represents a major public health concern. Cocaine users frequently present to the emergency department, with chest pain being the most common presenting complaint. The incidence of acute myocardial infarction in patients with cocaine-associated chest pain is often quoted as 6%, but it is highly variable depending on the included population. Risk assessment can be challenging in these patients; serial assessment of electrocardiograms and troponins is often required. This review focuses on the assessment and management of patients presenting with cocaine-associated chest pain and cardiotoxicity. Specific treatments are discussed, including benzodiazepines, nitroglycerin, calcium channel blockers, and phentolamine, and how treatment priorities differ from patients with noncocaine presentations. The use of beta-blockers in this population remains controversial, and the literature around its use is reviewed. The most recent literature and recommendations for the use of percutaneous coronary intervention and fibrinolytics in cocaine-associated myocardial infarction is discussed as well. Cocaine-associated dysrhythmias are suggested to be the cause of sudden cardiac death in some users. The pathophysiology and evidence-based treatments for dysrhythmias are reviewed. This review provides evidence-based recommendations for the assessment and management of patients presenting with cocaine-associated cardiovascular toxicity.

Current strategies in the evaluation and management of cocaine-induced chest pain

With each successive year, the number of Emergency Department (ED) visits related to illicit drug abuse has progressively increased. Cocaine is the most common illegal drug to cause a visit to the ED. Cocaine use results in a variety of pathophysiological changes with regards to the cardiovascular system, such as constriction of coronary vessels, dysfunction of vascular endothelium, decreased aortic elasticity, hemodynamic disruptions, a hypercoagulable state, and direct toxicity to myocardial and vascular tissue. The clinical course of patients with cocaine-induced chest pain (CCP) is often challenging, and electrocardiographic findings can be potentially misleading in terms of diagnosing a myocardial infarction. In addition, there is no current satisfactory study regarding outcomes of use of various pharmacological drug therapies to manage CCP. At present, calcium-channel blockers and nitroglycerin are two pharmacological agents that are advocated as first-line drugs for CCP management, although the role of labetalol has been controversial and warrants further investigation. We performed an extensive search of available literature through a large number of scholarly articles previously published and listed on Index Medicus. In this review, we put forward a concise summary of the current approach to a patient presenting to the ED with CCP and management of the clinical scenario. The purpose of this review is to summarize the understanding of cocaine's cardiovascular pathophysiology and to examine the current approach for proper evaluation and management of CCP.

Assessment of propofol, midazolam and ziprasidone, or the combinations for the prevention of acute cocaine toxicity in a mouse model

STUDY OBJECTIVE

To evaluate the effects of pretreatment, midazolam (M), propofol (P), ziprasidone (Z), and two combinations of [(midazolam plus propofol (MP); midazolam plus ziprasidone (MZ)] in mice models in the prevention of seizures, and death due to acute cocaine toxicity.

METHODS

180 male CF-1 mice were randomized to 6 groups (30/group) in this experimental study. The animals were administered intraperitoneal injections of M (2mg/kg), P (25mg/kg), Z (4mg/kg), MP (2mg/kg and 25mg/kg) and MZ (2mg/kg and 4mg/kg) or saline (S) as a pretreatment. 10min later, the mice were administered intraperitoneal injections of 105mg/kg cocaine. The groups were observed for cocaine-induced seizure and lethality.

RESULTS

The MP and MZ combinations showed the highest protective effect in terms of seizure and lethality relative to P and S (p<0.001). M and Z were found effective compared to P and S (p<0.001). There were no significant differences among MP and MZ, however there were significant differences between MP and Z in terms of lethality (p=0.05). There were no significant differences among MP, MZ, M and Z groups in terms of seizure (p>0.05). No death was observed in the MP combination group. Seizure rate was observed o be least in the MZ group with respect to the other groups.

CONCLUSION

According to our particular mouse model, this study suggests that MP and MZ combinations may be more effective than M or Z only for the prevention of cocaine-induced seizure and lethality. However, P alone does not prevent cocaine-induced seizure and lethality.

Benzodiazepines and antipsychotic medications for treatment of acute cocaine toxicity in animal models – A systematic review and meta-analysis

There are no controlled human studies to determine the efficacy of benzodiazepines or antipsychotic medications for prevention or treatment of acute cocaine toxicity. The only available controlled data are from animal models and these studies have reported inconsistent benefits. The objective of this study was to quantify the reported efficacy of benzodiazepines and antipsychotic medication for the prevention of mortality due to cocaine poisoning. We conducted a systematic review to identify English language articles describing experiments that compared a benzodiazepine or antipsychotic medication to placebo for the prevention of acute cocaine toxicity in an animal model. We then used these articles in a meta-analysis with a random-effects model to quantify the absolute risk reduction observed in these experiments. We found 10 articles evaluating antipsychotic medications and 15 articles evaluating benzodiazepines. Antipsychotic medications reduced the risk of death by 27% (95% CI, 15.2%–38.7%) compared to placebo and benzodiazepines reduced the risk of death by 52% (42.8%–60.7%) compared to placebo. Both treatments showed evidence of a dose-response effect, and no experiment found a statistically significant increase in risk of death. We conclude that both benzodiazepines and antipsychotic medications are effective for the prevention of lethality from cocaine toxicity in animal models.

The effect of olanzapine pretreatment on acute cocaine toxicity in mice

BACKGROUND

Acute cocaine poisoning causes neuroexcitation and can be fatal. The toxic effects of cocaine can be attenuated by antagonists of serotonin, muscarinic cholinergic, and dopamine receptors. Olanzapine, an atypical antipsychotic medication, is an antagonist of these receptors. The objective of this study is to evaluate the efficacy of olanzapine pretreatment for attenuation of acute cocaine toxicity using a mouse model.

METHODS

Eighty male CF-1 mice were randomly assigned to olanzapine (1 mg/kg) or placebo pretreatment. Fifteen minutes later, all animals received 103 mg/kg intraperitoneal cocaine.

RESULTS

Overall mortality was 11% for olanzapine-treated animals and 45% for placebo. Olanzapine also appeared to alter the characteristics of seizures due to cocaine.

CONCLUSIONS

In this model of acute cocaine toxicity, olanzapine pretreatment attenuated acute cocaine toxicity. Olanzapine should be evaluated further as a potential treatment for acute cocaine poisoning.

Mechanisms of acute cocaine toxicity

Patients with acute cocaine poisoning present with life-threatening symptoms involving several organ systems. While the effects of cocaine are myriad, they are the result of a limited number of cocaine-protein interactions, including monoamine transporters, neurotransmitter receptors and voltage-gated ion channels. These primary interactions trigger a cascade of events that ultimately produce the clinical effects. The purpose of this article is to review the primary interactions of cocaine and the effects that these interactions trigger. We also describe the progression of symptoms observed in cocaine poisoning as they relate to serum cocaine concentrations.

Evaluation and Management of the Patient Who Has Cocaine-associated Chest Pain

Patients who have chest pain following the use of cocaine have become more common in emergency departments throughout the United States,with approximately 6% of these patients sustaining an acute MI. The authors have described the rationale for recommending aspirin, benzodiaze-pines, and nitroglycerin as first-line treatments and calcium-channel blockade or phentolamine as possible second-line therapies and have summarized the controversies surrounding the use of fibrinolytic agents. Admission for observation is one reasonable approach to the management of the low-risk cohort. Evaluation for underlying coronary artery disease is reasonable, particularly in patients who have acute MI. Patients who do not have infarction can undergo evaluation for possible coronary artery disease on an outpatient basis. Routine interventions for secondary prophylaxis as well as cocaine rehabilitation should be used in this patient population, because the long-term prognosis seems somewhat dependent upon the ability of the patient to discontinue cocaine use.

COCAINE USE AND ACUTE MYOCARDIAL INFARCTION

Cocaine use in the United States is widespread, affecting more than 30 million Americans. Although many of these persons do not seek healthcare, the overriding cause for hospitalization is cocaine-associated chest pain. Because only a minority of these patients suffer myocardial injury, it is important to exclude even rarer life-threatening causes for chest pain, such as aortic dissection or pneumothorax. Following that, a thorough knowledge of the pathophysiology and existing literature helps to provide cost-effective care, which focuses resources on those patients most likely to suffer complications. Regardless of the severity of complications, referral to cocaine detoxification programs, counseling, social support, and outpatient follow-up care for modification of cardiac risk factors is a fundamental component of long-term patient care.

Cocaine Addiction: Neurobiology and Related Current Research in Pharmacotherapy

In this article, recent research studies in the field of cocaine addiction are reviewed, with an eye toward emergent options for treatment innovation. Particular attention is paid to the neurobiology and specific neurotransmitter and receptor mechanisms involved in cocaine abuse, dependence, and other unique phenomena of addiction such as sensitization, craving, compulsive drug use, and withdrawal. The vicissitudes in the dopamine theory of brain reward mechanisms, dopaminergic effects of cocaine, and emerging roles of GABA, serotonin, glutamate, and nitric oxide in cocaine addiction and its sequelae are discussed. Neuroanatomic findings elicited with imaging studies using PET and functional MRI are summarized. These findings support the role of specific brain regions within the dopaminergic system such as the ventral tegmentum and nucleus accumbens in the induction of the cocaine "high" and craving, respectively. Research approaches to the problem of developing effective pharmacotherapeutic options to render cocaine ineffective and modalities under study, such as dopamine uptake inhibitors and immunotherapy, are also discussed in the context of a variety of practical problems faced by these experimental therapies. Pharmacotherapeutic strategies and new directions in this research, such as the adaptive changes of the opioid system in cocaine addiction, are reviewed. Potential areas for further study are brought forth for further debate and possible clinical evaluation.

Cocaine and lidocaine have additive inhibitory effects on the GABAA current of acutely dissociated hippocampal pyramidal neurons

Inhibition mediated by gamma-aminobutyric acid (GABA) is a major target for the central actions of cocaine and lidocaine, which can result in seizures, especially when these drugs are abused in combination. In the present study, we investigated how cocaine and lidocaine interact to depress GABA current (IGABA), recorded by the whole-cell technique in freshly isolated rat hippocampal neurons. Cocaine depressed IGABA in a concentration dependent manner, such that cocaine was more potent against lower than higher GABA concentrations: the cocaine IC50 was 0.13, 0.62 and 1.2 mM for GABA at 2, 10 and 100 microM, respectively. Cocaine depressed IGABA to the same extent in the absence and presence of 1 microM tetrodotoxin, indicating that cocaine inhibition of IGABA is distinct from its Na+ channel blocking action. Lidocaine reversibly depressed IGABA evoked by 10 microM GABA, with an IC50 of 9.8 mM. In the presence of 3 mM lidocaine, 0.3 mM cocaine depressed IGABA (10 microM GABA) to 30+/-7%. The significantly greater depression by the combined agents (p<0.05) indicates additive effects on the GABA receptor/channel complex, which are likely to contribute to the additive convulsant effects noted when these drugs are abused in combination.

Cocaine depresses GABAA current of hippocampal neurons

Although blockade of dopamine re-uptake and the resulting elevation of excitatory agonists is commonly thought the primary mechanism of cocaine-induced seizures, it is possible that other neurotransmitters such as gamma-aminobutyric acid (GABA) are involved. To examine this possibility, the effects of cocaine on the whole cell GABA current (IGABA) of freshly isolated rat hippocampal neurons were investigated with the patch-clamp technique. Preincubation or acute application of cocaine reversibly suppressed IGABA. The IC50 was 127 microM when cocaine was applied before the application of GABA. The concentration-response relations of cocaine in various GABA concentrations revealed that cocaine inhibited IGABA non-competitively. This effect of cocaine appeared to be independent of voltage. The present study suggests that the GABA receptor/channel complex is also a target for cocaine's action. The suppression of IGABA may contribute to cocaine-induced seizures.

Evaluation of patients with chest pain after cocaine use

Cocaine remains the most common cause of illicit drug-related visits to emergency departments, 40% of which result from chest pain. It is estimated that over half of the 64,000 patients evaluated annually for cocaine-associated chest pain will be admitted to hospitals for the evaluation of myocardial ischemia or infarction, at a health care cost of over eighty million dollars. Although the link between cocaine use and myocardial ischemia is well established, only about 6% of patients with cocaine-associated chest pain will demonstrate biochemical evidence of myocardial infarction. This article focuses on the evaluation of patients with chest pain following cocaine use, and concentrates on ways to improve diagnosis, management, and utilization of health care services.

The serotonin syndrome associated with paroxetine, an over-the-counter cold remedy, and vascular disease

There is a new, potentially fatal disorder that is infrequently reported. The apparent rareness may be because of a lack of recognition of the syndrome or its predisposing factors. Fluoxetine (Prozac, Dista Products Co, Division of Eli Lilly Co, Indianapolis, IN), sertraline (Zoloft, Roerig Division, Pfizer Inc, New York, NY), and paroxetine (Paxil, SmithKline Beecham Pharmaceuticals, Philadelphia, PA) belong to a new class of antidepressant medication: the serotonin reuptake-inhibitors (SRIs). The relative safety profile of the SRIs has led to their widespread use. However, a syndrome of excessive serotonergic activity, the "serotonin syndrome" (SS), has recently been recognized. It is characterized by changes in mental status, hypertension, restlessness, myoclonus, hyperreflexia, diaphoresis, shivering, and tremor. A high index of suspicion is required to make the diagnosis in these acutely ill patients. The most common agents implicated in SS are the monoamine oxidase inhibitors in combination with L-tryptophan or fluoxetine. A case of a patient with significant peripheral vascular disease who developed SS while taking paroxetine and an over-the-counter cold medicine is reported. There have been no prior reports of this interaction. Discontinuation of the offending agents, sedation, and supportive care are the mainstays of treatment. The interactions of serotonin with platelets and vascular endothelium are also discussed.

Flumazenil induces seizures and death in mixed cocaine-diazepam intoxications

STUDY HYPOTHESIS

Administration of the benzodiazepine antagonist flumazenil may unmask seizures in mixed cocaine-benzodiazepine intoxication.

DESIGN

Male Sprague-Dawley rats received 100 mg/kg cocaine IP alone, 5 mg/kg diazepam alone, or a combination of diazepam and cocaine. Three minutes later, groups were challenged with vehicle or flumazenil 5 or 10 mg/kg IP. Animal behavior, seizures (time to and incidence), death (time to and incidence), and cortical EEG tracings were recorded.

INTERVENTIONS

Administration of flumazenil to animals after they had received a combination dose of cocaine and diazepam.

RESULTS

In group 1, animals received cocaine followed by vehicle. This resulted in 100% developing seizures and death. Group 2 received diazepam alone followed by vehicle. Animals became somnolent and none died. Group 3 received diazepam followed by 5 mg/kg flumazenil. Animals became somnolent after diazepam and then active after flumazenil administration. In group 4, a combination of cocaine and diazepam was administered simultaneously. This resulted in no overt or EEG-detectable seizures and a 50% incidence of death. Group 5 received a similar combination of cocaine and diazepam, followed later by 5 mg/kg flumazenil. This resulted in an increased incidence of seizures, 90% (P < .01), and death, 100% (P < or = .01), compared with group 4. Group 6 received cocaine and diazepam followed by 10 mg/kg flumazenil. This also resulted in an increased incidence of seizures, 90% (P < or = .01), and death, 90% (P < or = .05), compared with group 4.

CONCLUSION

Flumazenil can unmask seizures and increase the incidence of death in a model of combined cocaine-diazepam intoxications.

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.

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.

The effect of cocaine on gastric mucosal PGE(2), LTC(4) and ulcerations

The association between cocaine use and acute gastroduodenal perforation is known. The effect of cocaine and stress on gastric mucosal ulceration and the levels of prostaglandin E₂ (PGE₂) and leukotriene C₄ (LTC₄) was studied in 40 Sprague–Dawley rats. Controls received intraperitoneal (i.p.) saline, ten received i.p. cocaine (35 mg/kg), ten were stressed by the cold restraint method, and ten had i.p. cocaine and stress. Cocaine alone did not induce ulceration, but decreased PGE₂ levels. Stress alone caused ulceration, but was not associated with a change in either PGE₂ or LTC₄ levels. When combined with stress, however, cocaine caused a three-fold increase in ulceration and a significant increase in PGE₂ and LTC₄ levels. Stress may predispose the cocaine addict to loss of gastroduodenal mucosal integrity, which is related to an imbalance of PGE₂ and LTC₄ synthesis.

Cocaine-induced ACTH secretion: dependence of plasma levels of the drug and mode of exposure

To determine whether changes in pituitary responsiveness might account for the lack of corticotropin (ACTH) stimulation following 6 consecutive days of continuous cocaine administration (5 or 25 mg/kg/day, via osmotic minipumps), the hormonal response of vehicle- or cocaine-pretreated male rats was compared. Intravenous injections of synthetic corticotropin-releasing factor (CRF) (0.2, 1, or 5 micrograms/kg) elicited dose-dependent increases in ACTH secretion irrespective of whether rats had been previously exposed to cocaine or not. Similarly, in both vehicle- and cocaine-pretreated rats ACTH response to acute injections of the drug was identical, indicating that pituitary corticotrophs remained responsive following continuous administration of cocaine. To determine and compare plasma concentrations of cocaine and its metabolites after continuous or acute administration of the drug, pharmacokinetics analysis of concentration vs. time was ascertained. Circulating concentrations of cocaine from rats continuously exposed to the drug were relatively low throughout the 6 days of exposure. In contrast, intravenous injections of cocaine produced peak concentrations of the drug that were significantly higher than those measured during continuous cocaine infusion. Such peak concentrations in cocaine correlated with marked increases in plasma ACTH levels. Plasma concentrations of the metabolites benzoylecgonine and methyl ester ecgonine followed a pharmacokinetic clearance similar to that of the parent compound, with low concentrations detected during continuous exposure whereas high concentrations were observed following intravenous injections of the drug. Our results suggest two nonmutually exclusive conclusions. First, there may be a critical threshold of cocaine plasma concentrations (as indicated by our results as being over 800 ng/ml) that are necessary for activation of the hypothalamic-pituitary-adrenal axis to occur.(ABSTRACT TRUNCATED AT 250 WORDS)

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

STUDY OBJECTIVE

To determine if respiratory depression is an important mechanism of cocaine-induced death in conscious rats.

DESIGN

Male Sprague-Dawley rats weighing between 200 and 300 g and fitted with cortical electrodes were pretreated intraperitoneally with either saline (vehicle), MK-801, or valproic acid for 30 minutes before challenge with 70 mg/kg IP cocaine followed by spontaneous breathing or mechanical ventilation after acute tracheostomy. Behavior, seizures, death, EEGs, and ECGs were observed and measured.

MEASUREMENTS AND MAIN RESULTS

In group 1, animals received saline followed by cocaine. The incidence rates of seizures and death were 92% and 83%, respectively. Group 2 received saline followed by cocaine and then were ventilated mechanically through an acute tracheostomy after respiratory arrest (late mechanical ventilation). This group experienced seizures in 100% and death in 67% of animals. Group 3 also received saline followed by cocaine but were ventilated mechanically immediately after the first seizures (early mechanical ventilation). They had experienced seizures in 100% and death in 30%, the latter being significantly (P less than .025) reduced compared with group 1. In group 4, an anticonvulsant (1 mg/kg MK-801) was given before cocaine challenge, resulting in seizures in 10% (P less than .002 compared with group 1) and death in 90%. Group 5 received MK-801 followed by cocaine and then were ventilated mechanically after respiratory arrest (late mechanical ventilation). They experienced seizures in 20% (P less than .002 compared with group 1), and no animals in this group died (P less than .002 compared with group 1 or 4). Group 6 received an anticonvulsant (400 mg/kg valproic acid), followed by cocaine. This resulted in seizures in 20% (P less than .002 compared with group 1) and death in 90%. Group 7 received valproic acid followed by cocaine and then were ventilated mechanically (late mechanical ventilation). They experienced seizures in 30% (P less than .002 compared with group 1), and all animals survived (P less than .002 compared with group 1 or 6).

CONCLUSION

Early mechanical ventilation reduces cocaine toxicity. Control of seizure activity with specific anticonvulsants allows delayed mechanical ventilation to protect against cocaine toxicity. This suggests that respiratory depression in conjunction with seizure activity plays a major role in the mechanisms of cocaine-induced death in this model.

Potentiation of cocaine and d-amphetamine toxicity with caffeine

The effect of caffeine when combined with cocaine or amphetamine was studied in rats. Animals were pretreated with intraperitoneal vehicle (normal saline [NS]) or caffeine 100 mg/kg, then challenged with intraperitoneal cocaine (0, 35, 50, 70, or 90 mg/kg) or intraperitoneal d-amphetamine (0, 15, 25, 35, or 42 mg/kg). Animal behavior, time to, and incidences of seizures and death were recorded. This dose of caffeine alone did not cause seizures or death. Caffeine pretreatment significantly increased the incidence of overt seizures induced by either cocaine or amphetamine. Caffeine increased the incidence of cocaine-induced death from 10% to 90% at the 70 mg/kg cocaine dose (P less than .01). Caffeine increased amphetamine-induced death from 0% to 80% at 15 mg/kg (P less than or equal to .01), 10% to 70% at 25 mg/kg (P less than or equal to .01), and 30% to 80% at 35 mg/kg (P less than or equal to .01). To investigate mechanisms, additional animals were pretreated with the adenosine agonist, 2-chloroadenosine (2.5 and 10 mg/kg), before being challenged with NS, 90 mg/kg cocaine, or 42 mg/kg amphetamine. Pretreatment with 2-chloroadenosine had no affect in reducing cocaine or amphetamine toxicity. Combination pretreatment with caffeine and 2-chloroadenosine potentiated cocaine toxicity. The phosphodiesterase inhibitor, pentoxifylline, did not potentiate cocaine toxicity. The authors conclude that caffeine potentiates the acute toxicity of both cocaine and amphetamine, and that the failure of 2-chloroadenosine to alter this suggests that the toxicity of the stimulants cocaine and amphetamine may be modulated by nonspecific rather than specific adenosine- or phosphodiesterase-induced mechanisms.

The effect of morphine and naloxone on cocaine toxicity

The effect of morphine and naloxone on acute cocaine toxicity was studied. Male Sprague-Dawley rats were pretreated intraperitoneally (ip) with saline, morphine sulfate 25 mg/kg, or naloxone 1.0 mg/kg 15 minutes prior to challenge by cocaine. After pretreatment, each group was challenged with one of three doses of cocaine (35, 50, or 75 mg/kg ip). Each of the nine drug combinations was tested on at least 10 animals. Animals were observed for behavior, seizures, and death. The animals pretreated with saline and challenged with cocaine (35, 50, or 75 mg/kg) had seizure incidences of 0%, 40%, and 100%, respectively, after increasing doses. Pretreatment with morphine resulted in cocaine-induced seizures of 20%, 80% and 100%, respectively (p less than or equal to 0.05 with cocaine 35 and 50 mg/kg). Time to seizures in these groups did not differ significantly compared to the saline groups. Pretreatment with naloxone resulted in cocaine-induced seizures of 0%, 50%, and 60% (p less than or equal to 0.05 at the 75 mg/kg dose). The incidence of death was significantly increased by pretreatment with morphine in animals that received cocaine 50 or 75 mg/kg. The time to death was not significantly different compared to saline controls. The death rate in naloxone pretreated animals was not significantly different from the saline groups. In additional studies, high-dose naloxone pretreatment (10 mg/kg) also failed to provide protection from acute cocaine toxicity. In conclusion, cocaine toxicity is potentiated by morphine and does not appear to be altered by naloxone.

Cocaine-induced respiratory depression in urethane-anesthetized rats: a possible mechanism of cocaine-induced death

Urethane-anesthetized rats were used to study the mechanism of cocaine-induced death. Continuous recording of the changes in five physiological parameters, including respiratory rate (RR), electroencephalogram (EEG), blood pressure (BP), electrocardiogram (ECG), and body temperature (BT), were conducted after intraperitoneal (IP) administration of a single dose of cocaine HCl (70 mg/kg). In the control group (normothermic with core body temperature 37.7 +/- 0.1 degree C and spontaneously breathing), the death rate was 88% (15/17), and the average time to respiratory arrest was 12.99 +/- 1.40 min (mean +/- SEM). The first set of experiments investigated the contribution of hypothermia to cocaine-induced death. The hypothermic group (core body temperature 33.9 +/- 0.3 degrees C and spontaneously breathing) had a death rate of 81.5% (22/27), and an average time to respiratory arrest of 16.70 +/- 1.24 min, which was significantly (p les than 0.05) prolonged. A substantial decrease in respiratory rate was seen in normothermic group, while all the other measured parameters remained relatively stable until respiratory arrest. Sequential arterial blood gas data in this group showed a decrease in PaO2 from 116.0 +/- 5.7 mmHg to 57.7 +/- 4.6 mmHg, an increase in PaCO2 from 27.7 +/- 2.2 mmHg to 42.7 +/- 3.0 mmHg, and a decrease in pH from 7.467 +/- 0.039 to 7.357 +/- 0.003. To confirm that respiratory depression was an important mechanism of cocaine-induced death in this model, ten normothermic rats underwent mechanical ventilation, and all survived cocaine exposure. This study points to the important role of respiratory depression as a cause of cocaine-induced death.

Continuous cocaine administration produces persisting changes in brain neurochemistry and behavior

Rats were administered either continuous cocaine, daily injections of cocaine, continuous amphetamine, or no drug for 5 days and then given a 30 day drug-free recovery period. When subsequently tested in open field, the daily cocaine injection animals were the most hyperactive whereas the cocaine pellet animals were the most fearful. In vitro autoradiography was then utilized to examine persisting changes in receptor binding for D2 ([3H]spiperone), D1 ([3H]SCH23390), benzodiazepine ([3H]flunitrazepam), 5-HT1 ([3H]5-HT), 5-HT2 ([3H]ketanserin), and muscarinic acetylcholine (ACh) receptors ([3H]QNB; quinuclidinyl benzilate). In the amphetamine pellet animals, there were large increases in [3H]spiperone binding in several dopamine (DA)-rich regions; these were accompanied by conversely decreased [3H]SCH23390 binding. Cocaine pellet animals showed a completely different pattern, with appreciable increases in [3H]flunitrazepam binding in DA-rich areas, cortex, and amygdala but decreased [3H]QNB binding in DA-rich areas, hippocampus, and amygdala. While cocaine injection animals showed elevated [3H]spiperone binding in caudate and substantia nigra, they had generally smaller changes in most brain regions than the other drug groups. These findings replicate and extend previous reports that continuous drug administration induces long-lasting alterations in brain chemistry, but indicate that continuous cocaine has enduring effects on different neurochemical systems from continuous amphetamine.

Experience with esmolol for the treatment of cocaine-associated cardiovascular complications

The authors report their experience using esmolol, an ultra-short acting beta-adrenergic antagonist, for the treatment of seven patients with cocaine-associated cardiovascular complications. No consistent hemodynamic benefit was found with the use of this drug. Although there was a decline in mean heart rate of 23% (range 0% to 35%), they were unable to show a consistent antihypertensive response. Adverse effects occurred in three patients. This included one patient with a marked exacerbation of hypertension and one who became hypotensive. Another patient developed emesis and lethargy during esmolol therapy and required endotracheal intubation. They do not recommend the routine use of esmolol for cocaine cardiotoxicity.

Genetic factors influence changes in sensitivity to the convulsant properties of cocaine following chronic treatment

Repeated administration of doses of cocaine below the threshold for seizure induction results in the development of an increased susceptibility to cocaine-induced seizures (cocaine-kindling). Genetic differences in susceptibility to cocaine-kindled seizures were evaluated in 4 inbred mouse strains and compared with susceptibility to seizures induced by acute administration of cocaine. The acute administration of cocaine produced convulsant activity in mice from all 4 genotypes, however, there were significant differences in the dose of cocaine required to induce seizures. C57 mice were highly susceptible and SJL mice highly resistant to convulsions induced by acute administration of cocaine, while BALB and DBA mice showed an intermediate degree of seizure susceptibility. The repeated administration of subconvulsant doses of cocaine resulted in rapid sensitization to cocaine-induced seizures. The 4 strains differed in the rate at which sensitization to cocaine-induced seizures developed, with the SJL strain being most sensitive and the C57 strain the least sensitive to the cocaine-kindling process. The susceptibility of the 4 strains to cocaine kindling was virtually opposite to their susceptibility to seizures induced by the acute administration of cocaine, suggesting that different mechanisms may be involved in the control of acute and kindled seizures did not persist upon further exposure to cocaine. Following a period of increased sensitivity to cocaine-induced seizures, tolerance to the convulsant properties of cocaine developed among C57, BALB and DBA mice. Only among the SJL mice did the development of a kindled state persist upon repeated exposure to cocaine. These differences emphasize the potential importance of inheritance in determining the effects of cocaine and suggest novel approaches to understanding the the mechanisms underlying the effects of cocaine.

Lidocaine potentiation of cocaine toxicity

STUDY HYPOTHESIS

The toxic effects of cocaine are enhanced in the presence of lidocaine.

STUDY POPULATION

Male Sprague-Dawley rats weighing 200 to 300 g.

METHODS

Animals received intraperitoneal injections of cocaine (10, 20, 35, or 50 mg/kg), lidocaine (30 or 40 mg/kg), or a combination of all doses of cocaine given simultaneously with 30 or 40 mg/kg lidocaine. The incidence and time to seizure and death were recorded in these groups and compared by chi 2 and analysis of variance analyses, respectively.

RESULTS

At doses of 30 or 40 mg/kg, lidocaine does not induce seizures or death. The effect of simultaneous injection of both cocaine and lidocaine was to dramatically increase the incidence of both seizures and death over that of cocaine alone. The incidence of seizures in animals receiving 35 mg/kg cocaine alone was 10%; this increased to 50% and 80% with the addition of 30 and 40 mg/kg lidocaine, respectively (P less than or equal to .05; P less than or equal to .01). Death did not occur in animals receiving 35 mg/kg cocaine alone; the addition of 30 and 40 mg/kg lidocaine resulted in death in 30% and 60% of animals, respectively (P less than or equal to .01 each group). Similarly, in rats receiving 50 mg/kg cocaine, the incidence of death increased from 0% to 60% and 80% with 30 and 40 mg/kg lidocaine, respectively (P less than or equal to .01).

CONCLUSION

In the rat, overall toxicity of cocaine is significantly increased with simultaneous exposure to lidocaine.

The cardiovascular effects of cocaine

Cocaine use and abuse continue to overwhelm urban economic, social, and health care systems. Patients frequently present to the emergency department with life-threatening manifestations of cocaine use, including trauma, acquired immune deficiency syndrome, psychomotor agitation, and cardiovascular collapse. Adequate treatment of the cocaine-intoxicated patient requires a critical understanding of the risk-to-benefit ratios for pharmacologic, toxicologic, and surgical or obstetric interventions. The pharmacologic and physiologic bases for the vascular manifestations of cocaine toxicity and experimental evidence for treatment strategies are reviewed.

Neurologic complications of cocaine abuse

The neurologic complications of cocaine toxicity are responsible for a major portion of the morbidity and mortality associated with cocaine. Most of the complications appear to be related to the hyperadrenergic state induced by cocaine and may be treated symptomatically. Diazepam is the most effective drug for cocaine-induced seizures.

Antagonism of cocaine, amphetamine, and methamphetamine toxicity

The effect of diazepam, haloperidol, MK-801, and propranolol in antagonizing behavioral symptoms induced by lethal doses of cocaine, amphetamine, and methamphetamine were studied in a rat model. Animals were first pretreated IP with potential antagonists, diazepam (2, 5, and 10 mg/kg), haloperidol (5, 10, and 20 mg/kg), propranolol (5, 10, and 20 mg/kg), MK-801 (0.5, 1.0, and 2.5 mg/kg), and then were challenged IP with cocaine (70 mg/kg) (LD85), d-amphetamine (75 mg/kg) (LD100), and methamphetamine (100 mg/kg) (LD90). Diazepam, at all doses, provided significant protection against cocaine- (p less than or equal to 0.01) and methamphetamine- (p less than or equal to 0.05) induced seizures and produced a dose-dependent effect against amphetamine-induced seizures. MK-801, at all doses, reduced seizures in all groups (p less than or equal to 0.01). Propranolol altered the incidence of methamphetamine-induced seizures. Significant protection against cocaine-induced death was afforded by diazepam (p less than or equal to 0.01) and propranolol (p less than or equal to 0.05). Significant protection against amphetamine-induced death was provided by haloperidol (all doses, p less than or equal to 0.1), MK-801 (all doses, p less than or equal to 0.1), and propranolol (10 and 20 mg/kg, p less than or equal to 0.1). No agent reduced the incidence of methamphetamine- (50 or 100 mg/kg) induced death. The failure of d-amphetamine antagonists to protect against methamphetamine-induced toxicity and death suggest that different mechanisms of toxicity may exist between these drugs.

Acute cocaine toxicity: antagonism by agents interacting with adrenoceptors

Agents which interact with alpha- or beta-adrenoceptors were evaluated for efficacy in preventing seizures and death from a lethal dose of cocaine. Rats were first pretreated with the test drug(s), then subjected to an intraperitoneal LD86 of cocaine (70 mg/kg). In this model, control vehicle-pretreated animals developed seizures within six minutes, followed by death within 10 minutes. Significant protection against death was afforded by pretreatment with clonidine (0.25 mg/kg), prazocin (5.0 to 20 mg/kg), propranolol (8.0 to 32 mg/kg), or labetalol (40 mg/kg). Surviving animals still experienced seizures as judged through behavior and EEG recordings. Phentolamine did not affect the incidence of seizures or death. Two nonadrenoceptor agents were also studied: hydralazine reduced the incidence of death and seizures at 5.0 and 10 mg/kg, but reserpine did not alter the incidence of death or seizures. A combination of prazocin and propranolol did not provide additional protection compared to single agents. We conclude that the pathogenesis of acute cocaine death is complex, and that this toxicity can be antagonized by agents having either central or peripheral effects.

Protection against d-amphetamine toxicity

The efficacy of diazepam, haloperidol, propranolol, and yohimbine in antagonizing the toxic manifestations of d-amphetamine were studied in rats. In the control group of animals given 75 mg/kg intraperitoneal (ip) d-amphetamine, 95% developed seizures, and 100% died in mean times of 12.6 +/- 1.0 and 50.1 +/- 5.9 minutes, respectively. Significant protection against d-amphetamine-induced death was afforded by pretreatment with haloperidol (1.0 to 20.0 mg/kg) or propranolol (20.0 to 30.0 mg/kg). Diazepam (5.0 to 10.0 mg/kg) significantly reduced the incidence of clinically overt seizures but offered no protection against death. Yohimbine (2.5 to 10.0 mg/kg) was ineffective in preventing either seizures or death. When haloperidol (1.0 mg/kg) was administered in combination with diazepam (2.0 mg/kg), the incidence of death was no different than if haloperidol were given alone. In combination, haloperidol (1.0 mg/kg) and propranolol (10.0 mg/kg) reduced death more than either agent alone. These data support a protective role of haloperidol or propranolol in the treatment of d-amphetamine intoxication and show no protection with diazepam or yohimbine.

Anticonvulsant modification of cocaine-induced toxicity in the rat

A number of anticonvulsant drugs were studied for their efficacy in preventing seizures and death from intoxication with cocaine. Rats were first pretreated with the test drug then subjected to large doses of intraperitoneally administered cocaine. In this model, control animals developed seizures in approximately 6 min, followed by death in approximately 10 min. Statistically significant protection against seizures and death was afforded by pretreatment with diazepam, phenobarbitol and the blocker of the uptake of gamma-aminobutyric acid (GABA), SKF 100330A. Only partial protection was afforded by the N-methyl-d-aspartate (NMDA) antagonist MK 801, the benzodiazepine antagonist, flumazenil and the novel aminobenzamide, LY 201116. Valproic acid and phenytoin demonstrated limited efficacy against cocaine-induced seizures, without consistently reducing death. Carbamazepine and ethosuximide did not significantly reduce seizures or death. In this model of acute cocaine toxicity, the anticonvulsants diazepam, phenobarbital and the blocker of the uptake of GABA, SKF 100330A were the most effective in protecting rats from cocaine-induced seizures and death. These data offer insight into future approaches for the treatment of patients with the acute toxic effects of cocaine.

The effect of SCH 23390 against toxic doses of cocaine, d-amphetamine and methamphetamine

The effect of SCH 23390, a dopamine-one (D1) antagonist, in preventing acute toxicity induced by lethal doses of cocaine, d-amphetamine, and methamphetamine was studied in the rat. Animals were first pretreated with SCH 23390 (0.0, 0.5, 1.0, and 2.5 mg/kg, i.p.) and then were challenged with cocaine (70 mg/kg, i.p., an LD85), d-amphetamine (75 mg/kg, i.p., an LD95), and methamphetamine (100 mg/kg, i.p., an LD90). SCH 23390 did not alter the incidence of stimulant-induced seizures compared to the vehicle controls. Significant protection against cocaine-induced death was afforded only by the lowest dose of SCH 23390 tested. Significant protection against d-amphetamine-induced death was provided by all doses, with a dose dependent effect noted so that the incidence decreased from 95% for vehicle to 30% (p less than or equal to 0.01) with 2.5 mg/kg SCH 23390 pretreatment. No statistically significant reduction in the incidence of methamphetamine-induced death was seen with SCH 23390 pretreatment. The ability of SCH 23390 to protect against d-amphetamine, but apparently not against methamphetamine-induced death, suggests that different mechanisms of toxicity may exist between these drugs at high doses.

The effect of haloperidol in cocaine and amphetamine intoxication

The effectiveness of haloperidol pretreatment in preventing the toxic effects of high doses of amphetamine and cocaine was studied in rats. In this model, toxic effects were induced by intraperitoneal (i.p.) injection of amphetamine 75 mg/kg (100% death rate) or cocaine 70 mg/kg (82% death rate). Haloperidol failed to prevent amphetamine-induced seizures, but did lower the mortality rate at most doses tested. Haloperidol decreased the incidence of cocaine-induced seizures at the two highest doses, but the lowering of the mortality rate did not reach statistical significance at any dose. These data suggest a protective role for the central dopamine blocker haloperidol against death from high-dose amphetamine exposure without reducing the incidence of seizures. In contrast, haloperidol demonstrated an ability to reduce cocaine-induced seizures without significantly reducing mortality.

Cocaine intoxication

Cocaine intoxication can be manifested by a multitude of chief presenting complaints. Although cardiovascular and central nervous system stimulation is common, patients may present with a broad array of symptoms. Thus, whenever the underlying cause of a set of symptoms is unexplained, the primary care physician needs to consider the possibility of cocaine abuse.