Reversal by naloxone of the antihypertensive action of clonidine: involvement of the sympathetic nervous system

Pharmacologic Treatment of Opioid Use Disorder: a Review of Pharmacotherapy, Adjuncts, and Toxicity

Opioid use disorder continues to be a significant source of morbidity and mortality in the USA and the world. Pharmacologic treatment with methadone and buprenorphine has been shown to be effective at retaining people in treatment programs, decreasing illicit opioid use, decreasing rates of hepatitis B, and reducing all cause and overdose mortality. Unfortunately, barriers exist in accessing these lifesaving medications: users wishing to start buprenorphine therapy require a waivered provider to prescribe the medication, while some states have no methadone clinics. As such, users looking to wean themselves from opioids or treat their opioid dependence will turn to alternative agents. These agents include using prescription medications, like clonidine or gabapentin, off-label, or over the counter drugs, like loperamide, in supratherapeutic doses. This review provides information on the pharmacology and the toxic effects of pharmacologic agents that are used to treat opioid use disorder. The xenobiotics reviewed in depth include buprenorphine, clonidine, kratom, loperamide, and methadone, with additional information provided on lofexidine, akuamma seeds, kava, and gabapentin.

Toxic bradycardias in the critically ill poisoned patient

Cardiovascular drugs are a common cause of poisoning, and toxic bradycardias can be refractory to standard ACLS protocols. It is important to consider appropriate antidotes and adjunctive therapies in the care of the poisoned patient in order to maximize outcomes. While rigorous studies are lacking in regards to treatment of toxic bradycardias, there are small studies and case reports to help guide clinicians' choices in caring for the poisoned patient. Antidotes, pressor support, and extracorporeal therapy are some of the treatment options for the care of these patients. It is important to make informed therapeutic decisions with an understanding of the available evidence, and consultation with a toxicologist and/or regional Poison Control Center should be considered early in the course of treatment.

β-Endorphin involvement in the regulatory response to body sodium overload

The present study was performed to examine the role of the endogenous beta-endorphinergic system on blood pressure regulation, sympathetic and brain activity during body sodium overload. Beta-endorphin knockout (beta end-/-), heterozygous (beta end+/-) and wild-type (beta end+/+) mice were submitted for two weeks to either a normal- or a high-sodium diet (NSD and HSD, respectively), and systolic blood pressure (SBP), urinary catecholamines (as an index of sympathetic nervous system activity), and the brain pattern of Fos-like immunoreactivity (as a marker of neuronal activation) were evaluated in each group. HSD caused a significant increase in SBP in beta end-/- mutant mice compared with beta end+/+ mice kept in the same experimental conditions (P < 0.01), but no statistical differences were observed between beta end+/- and beta end+/+ on a HSD. Moreover, when animals from the three genetic lines were fed with a NSD no changes in SBP were evidenced. With regard to brain activity, beta end-/- mice maintained on a HSD showed a significant increase in Fos-like immunoreactive neurons in the median preoptic nucleus (P < 0.01) compared with beta end+/- and beta end+/+ animals. Additionally, beta end-/- mice had higher levels of urinary epinephrine excretion (P < 0.05) on a HSD in comparison to beta end+/+ and beta end+/- animals in the same experimental conditions. No differences, however, were registered in norepinephrine and dopamine urinary excretion in animals from the three genetic lines after two weeks on either a HSD or a NSD. In summary, our results indicate that the beta-endorphinergic system may play a part in the compensatory response to sodium overload, since the absence of beta-endorphin causes an increase in systolic blood pressure, and increases median preoptic nucleus neural activity and urinary epinephrine excretion.

Ophthalmic drops causing coma in an infant

A 1-month-old infant with Peters anomaly had recurrent episodes of unresponsiveness, hypotension, hypotonia, hypothermia, and bradycardia. An extensive medical evaluation determined these episodes to be caused by brimonidine, an anti-glaucoma agent. There is the potential for serious toxic effects from the systemic absorption of topically applied ophthalmic agents in children.

Alpha-lactorphin lowers blood pressure measured by radiotelemetry in normotensive and spontaneously hypertensive rats

Cardiovascular effects of subcutaneous administration of synthetic alpha-lactorphin, a tetrapeptide (Tyr-Gly-Leu-Phe) originally derived from milk alpha-lactalbumin, were studied in conscious spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY) with continuous radiotelemetric monitoring. Alpha-lactorphin dose-dependently lowered blood pressure (BP) without affecting heart rate in SHR and WKY. The lowest dose which reduced BP was 10 microg/kg, and the maximal reductions in systolic and diastolic BP (by 23+/-4 and 17+/-4 mm Hg, respectively) were observed at 100 microg/kg dose in SHR. No further reductions were obtained at a higher dose of 1 mg/kg. There were no significant differences in the BP responses to alpha-lactorphin between SHR and WKY. Naloxone (1 and 3 mg/kg s.c.), a specific opioid receptor antagonist, abolished the alpha-lactorphin-induced reduction in BP and reversed it into a pressor response, which provides evidence for an involvement of opioid receptors in the depressor action of the tetrapeptide.

Imidazoline receptors: from discovery to antihypertensive therapy (facts and doubts)

The hypothesis and indirect evidence of imidazoline receptors has been promoted since some 15 years ago and it gave a substantial impetus for research in this field, resulting in a better understanding of neuronal and cardiovascular regulatory processes. The nomenclature of the imidazoline receptors has been accepted by international forums but no direct proof for the existence of these receptors has been published. Authors summarise the most important available data, including facts and doubts as far as the discovery, characterisation, and function of imidazoline receptors and their subtypes, the differences between imidazoline receptors and alpha-2 adrenoceptors, and also on their participation in regulatory processes.

Vasospasm in smooth coronary arteries as a cause of asystole and syncope

In a patient with proven myocardial infarction, coronary artery disease was excluded angiographically. Four weeks later the patient experienced recurrent syncope of unknown cause. By means of Holter monitoring, ST-segment elevation with subsequent first-degree AV block progressing to asystole and resulting in loss of consciousness were documented. Treatment with gallopamil and a VVI-pacemaker led to complete relief of all symptoms. Hence, Prinzmetal's angina may be a rare cause of syncope even in smooth coronary arteries.

Visine overdose: case report of an adult with hemodynamic compromise

Imidazole decongestants are present in a variety of over-the-counter medications, including eye drops and nasal sprays. Their primary mechanism of action is vasoconstriction, accomplished by direct stimulation of alpha receptors on blood vessels. Accidental and intentional poisonings involving these substances are increasing, and can cause mental status and respiratory depression, as well as other effects related to alpha receptor stimulation. We present a case of tetrahydrozoline ingestion in an adult who presented with chest pain, bradycardia, mental status depression, miosis, and other signs and symptoms of imidazole compound poisoning. It is important for physicians to be familiar with the adverse effects of these ingestions and to be aware of the potential therapies for management.

A comprehensive review of naloxone for the emergency physician

Naloxone has enjoyed long-standing success as a safe and effective opioid antagonist and has been invaluable in defining the role of endogenous opioid pathways in the response to pathological states such as sepsis and hypovolemia. We look forward to exciting research to further elucidate these pathways and to improve outcome by modulating the patient's physiological response to these stresses.

Stress and endogenous opioids: behavioral and circulatory interactions

Endogenous opioid peptides are the basis of a diverse system of complex neuroregulatory and endocrine mechanisms. While relatively quiescent in the resting state, these peptides are released during intense stimulation and modify, in a number of ways, circulatory homeostatic mechanisms. The endogenous opioids, primarily via endorphins and enkephalins, are capable of influencing circulatory responses to stress at the behavioral, the endocrinological, and the neural level. Recent research in humans and animals has described several roles for opioids in regulation of the circulatory stress response, and has also provided clues about the significance of opioid dysregulation in the pathophysiology of stress. Increased understanding of the basic mechanisms of stress and endogenous opioids will clarify the potential roles of opioids in important pharmacologic and behaviorally based therapeutics.

Update in medical toxicology

This article examines some current issues in toxicologic care. First there is a review of the scope of pediatric poisonings and some aspects of initial management. Then there is a discussion of the decision-making process required to properly use gastric decontamination in the management of poisonings. Each of the common methods available--emesis, gastric lavage, activated charcoal, catharsis, and whole bowel irrigation--is discussed. Finally, several new and old antidotes are reviewed, namely naloxone, glucagon, bicarbonate, dimercaptosuccinic acid, digoxin-specific fab fragments, and flumazenil.

Alpha2-adrenergic agonists in cardiovascular anesthesia

At this time, the unique attributes of alpha 2-agonists in anesthesia lie in their ability to blunt the adrenergic response to the stresses of major surgery, in patients in whom this response is especially undesirable, without incurring the penalty of respiratory depression that attends the use of opioids. It has become more and more apparent that sympathetic/adrenergic activation often has adverse consequences for patient morbidity and mortality, and modification of such activation by drugs may be a valuable option for the anesthesiologist. However, at present, the evidence supporting this statement is "soft," such as improved hemodynamic and metabolic stability. What must be done is to generate solid support in the form of well-designed outcome studies. The potential value of alpha 2-agonists is greatest in major surgery in brittle patients involving the risk of significant adverse outcome. There are plenty of adequate anesthesia regimens to cover lesser surgical interventions. In these cases, it is not the choice of a specific anesthetic agent or technique, but rather the competence and diligence of the anesthesiologist that is most important for outcome. In contrast, in major cardiovascular surgery in high-risk patients, the optimal anesthetic approach attains more importance, and is still undecided. The final consensus as to whether or not this optimal approach will include the use of alpha 2-adrenergic agonists will depend on the results of more extensive clinical investigations.

Relapse to opiate use provokes biphasic changes of blood pressure in heroin-withdrawn addicts treated with clonidine

The effect of relapse to opiate use on blood pressure and heart rate has been studied in heroin-withdrawn addicts treated with clonidine in an outpatient detoxification procedure. The daily dose of clonidine was established according to body weight and amount of heroin usually consumed at the onset of treatment. Patients who returned to heroin use were detected by increased urinary levels of opiates. Clonidine elicited significant reductions of blood pressure and heart rate reaching a plateau in the second day of treatment. Heroin consumption was found to provoke a further decrease of both systolic and diastolic pressure when the time interval between the relapse and the cardiovascular determinations was about 3 h as estimated by the patients. At longer intervals (16 h) this effect was reversed and both the hypotensive and the bradycardiac actions of clonidine seemed to be impaired. The possible impact of endogenous opioids and alpha-2 receptor sensitivity on these biphasic alterations is discussed.

Effect of clonidine on beta-endorphin, ACTH and cortisol secretion in essential hypertension and obesity

The role of alpha 2-adrenoceptor stimulation by clonidine on the secretion of beta-endorphin, ACTH, and cortisol in essential hypertension and obesity was studied in 45 subjects: 15 non-obese hypertensives, 10 obese hypertensives, 11 obese normotensives, and 9 healthy subjects. The circadian rhythm of plasma beta-endorphin, ACTH, and cortisol was determined after placebo and after three days on clonidine 0.45 mg daily. Clonidine lowered the blood pressure and blood ACTH and cortisol levels in all the subjects. A significant decrease in beta-endorphin after clonidine occurred in the healthy subjects. In obese normotensives basal beta-endorphin concentrations were significantly higher than in healthy subjects and did not change after clonidine. In about 50% of non-obese and obese hypertensives a significant increase in beta-endorphin secretion after clonidine was noted (responders). In the subgroup of non-obese hypertensive responders no circadian rhythm of beta-endorphin was observed. The results suggest that adrenergic regulation of beta-endorphin secretion is altered in obesity and in certain patients with essential hypertension.

Reversal of clonidine toxicity by naloxone

Clonidine is a centrally acting antihypertensive agent used in the management of essential hypertension. Oral clonidine loading is now used frequently in the management of hypertensive urgencies (ie, increases in arterial pressure not associated with acute, life-threatening end-organ injury). We report the case of a patient with an acute inferior myocardial infarction associated with blunt chest trauma who developed an abrupt and unexplained increase in arterial pressure 24 hours after admission and who was treated with oral clonidine (0.5 mg in divided doses over two hours). Drug therapy was followed by prolonged (four hours) systemic arterial hypotension (mean arterial pressure less than 70 mm Hg). Four milligrams of naloxone in two divided doses was given. Each naloxone bolus was followed by a 15-mm-Hg increase in mean arterial pressure and a return to values that were normal for this patient. Naloxone may be of value in reversing clonidine toxicity when clonidine is given to treat an acute rise in arterial pressure.

Clonidine normalizes low plasma beta-endorphin concentration and blood pressure in young men with mild essential hypertension

In young men with mild essential hypertension and age-matched normotensive volunteers, plasma concentrations of the endogenous opioid beta-endorphin were determined hourly from 9:00 p.m. to 2:00 a.m. The hypertensive patients' mean plasma beta-endorphin concentration was significantly lower in comparison with normotensive controls. After 14 days of treatment with clonidine, systolic and diastolic blood pressure was significantly reduced in both groups. Plasma beta-endorphin concentration increased in the hypertensive patients, but remained unchanged in the normotensive volunteers. The present findings point to a possible involvement of reduced beta-endorphinergic activity in blood pressure regulation of young men with essential hypertension.

Narcotic withdrawal in the emergency department

Patients in narcotic withdrawal can be very disruptive in an emergency department. An understanding of the dynamics of narcotic addiction and withdrawal is useful for the emergency physician. Narcotics are used for the euphoria they provide; however, chronic use results in physiological and psychological changes. Research into the endorphin system has provided a model of narcotic addiction and withdrawal. Effective therapies now exist for use in the emergency department.

Beta-endorphin contributes to the antihypertensive effect of clonidine in a subset of patients with essential hypertension

Naloxone [0.4 mg iv.] increased blood pressure and heart rate of 13 clonidine-treated [0.3 mg per os for 3 days] patients with essential hypertension [reacting group] while it has no such effect in 11 clonidine-treated patients [non-reacting gr.] Clonidine increased plasma beta-endorphin concentration of the reacting patients by 17.53 +/- 1.68 pM/1 and in the non-reacting ones by 5.91 +/- 0.88 pM/1. Significant linear correlation was found between the clonidine-induced increase in plasma beta-endorphin level and the naloxone-induced change in mean blood pressure [r = 0.9572, n:24, p less than 0.001]. In another group of 8 patients clonidine [0.15 mg iv.] decreased mean blood pressure but naloxone, 30 min after the clonidine injection, did not reverse the clonidine hypotension. We suggest that beta-endorphin, released by chr. clonidine therapy, contributes to the anti-hypertensive effect only in the reacting group.