Quinidine overdose. Neurological and cardiovascular toxicity in a normal person

Rational Small Molecule Treatment for Genetic Epilepsies

Genetic testing has yielded major advances in our understanding of the causes of epilepsy. Seizures remain resistant to treatment in a significant proportion of cases, particularly in severe, childhood-onset epilepsy, the patient population in which an underlying causative genetic variant is most likely to be identified. A genetic diagnosis can be explanatory as to etiology, and, in some cases, might suggest a therapeutic approach; yet, a clear path from genetic diagnosis to treatment remains unclear in most cases. Here, we discuss theoretical considerations behind the attempted use of small molecules for the treatment of genetic epilepsies, which is but one among various approaches currently under development. We explore a few salient examples and consider the future of the small molecule approach for genetic epilepsies. We conclude that significant additional work is required to understand how genetic variation leads to dysfunction of epilepsy-associated protein targets, and how this impacts the function of diverse subtypes of neurons embedded within distributed brain circuits to yield epilepsy and epilepsy-associated comorbidities. A syndrome- or even variant-specific approach may be required to achieve progress. Advances in the field will require improved methods for large-scale target validation, compound identification and optimization, and the development of accurate model systems that reflect the core features of human epilepsy syndromes, as well as novel approaches towards clinical trials of such compounds in small rare disease cohorts.

Impact of P-Glycoprotein-Mediated Active Efflux on Drug Distribution into Lumbar Cerebrospinal Fluid in Nonhuman Primates

Estimation of unbound drug concentration in the brain (C_u,brain) is an essential part of central nervous system (CNS) drug development. As a surrogate for C_u,brain in humans and nonhuman primates, drug concentration in cerebrospinal fluid (C_CSF) collected by lumbar puncture is often used; however, the predictability of C_u,brain by lumbar C_CSF is unclear, particularly for substrates of the active efflux transporter P-glycoprotein (P-gp). Here, we measured lumbar C_CSF in cynomolgus monkey after single intravenous administration of 10 test compounds with varying P-gp transport activities. The in vivo lumbar cerebrospinal fluid (CSF)-to-plasma unbound drug concentration ratios (K_{p,uu,lumbar CSF}) of nonsubstrates or weak substrates of P-gp were in the range 0.885-1.34, whereas those of good substrates of P-gp were in the range 0.195-0.458 and were strongly negatively correlated with in vitro P-gp transport activity. Moreover, concomitant treatment with a P-gp inhibitor, zosuquidar, increased the K_{p,uu,lumbar CSF} values of the good P-gp substrates, indicating that P-gp-mediated active efflux contributed to the low K_{p,uu,lumbar CSF} values of these compounds. Compared with the drug concentrations in the cisternal CSF and interstitial fluid (ISF) that we previously determined in cynomolgus monkeys, the lumbar C_CSF were more than triple for two and all of the good P-gp substrates examined, respectively. Although lumbar C_CSF may overestimate cisternal CSF and ISF concentrations of good P-gp substrates, lumbar C_CSF allowed discrimination of good P-gp substrates from the weak and nonsubstrates and can be used to estimate the impact of P-gp-mediated active efflux on drug CNS penetration. SIGNIFICANCE STATEMENT: This is the first study to systematically evaluate the penetration of various P-glycoprotein (P-gp) substrates into lumbar cerebrospinal fluid (CSF) in nonhuman primates. Lumbar CSF may contain >3-fold higher concentrations of good P-gp substrates than interstitial fluid (ISF) and cisternal CSF but was able to discriminate the good substrates from the weak or nonsubstrates. Because lumbar CSF is more accessible than ISF and cisternal CSF in nonhuman primates, these findings will help increase our understanding of drug central nervous system penetration at the nonclinical stage.

Loperamide and P-glycoprotein inhibition: assessment of the clinical relevance

OBJECTIVES

Loperamide is a peripherally acting mu opioid receptor agonist and an avid substrate for P-glycoprotein. This may give rise to drug-drug interactions and increased risk for central adverse effects. The objective of this study was to re-evaluate the predictability of non-clinical data using loperamide as a probe P-glycoprotein substrate. We searched the literature for papers containing data on drug-drug interactions of loperamide-containing products in humans. We also reviewed the internal worldwide safety database of Johnson & Johnson for spontaneous case reports suggestive of a central opioid effect after coadministration of loperamide with a P-glycoprotein inhibitor or substrate.

KEY FINDINGS

Only one of the ten studies in our review supported the finding that inhibition of P-glycoprotein is associated with clinically relevant signs or symptoms of central nervous system (CNS) depression/opioid toxicity of loperamide. None of the 25 spontaneous case reports of interest were suggestive of signs or symptoms of CNS depression/opioid toxicity due to coadministration of loperamide and a P-glycoprotein inhibitor or substrate.

SUMMARY

Based on a review of the literature and a cumulative review of the spontaneous case reports, there is insufficient evidence that an interaction between loperamide and a P-glycoprotein inhibitor or substrate is associated with clinical symptoms of CNS depression/opioid toxicity when loperamide is taken at the recommended dose.

Hypokalemia after pediatric albuterol overdose: a case series

Sympathomimetic use results in a triad of hypokalemia, hyperglycemia, and elevated white blood cell count. Transient hypokalemia results from activation of the Na+/K+ pump and transport of potassium intracellularly. Increased serum glucose and insulin may also contribute to the intracellular shift of potassium after sympathomimetic use. Four cases of accidental pediatric albuterol ingestion with significant hypokalemia are reported. Four children between 1 and 6 years of age presented to the emergency department within 5 hours of ingesting 3.0, 1.1, 3.7, and 1.7 mg/kg albuterol, respectively. All four presented alert and oriented in no apparent distress. The most common findings were vomiting, sinus tachycardia, and hypokalemia (2.3, 2.5, 2.8, and 2.5 mmol/L, respectively). Each child received a single dose of activated charcoal and intravenous potassium replacement. All patients recovered uneventfully within 12 to 24 hours with supportive care only. These cases demonstrated that significant depressions in serum potassium can occur after pediatric albuterol overdose. Although transient, the dose-response relationship and duration of effect is unknown. Although significant hypokalemia can occur after ingestion of oral sympathomimetics, replacement should be managed on an individual basis until further studies are completed.

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical features, pathogenesis and management of drug-induced seizures

Many classes of pharmacological agents have been implicated in cases of drug-induced seizures. The list includes antidepressant drugs, lithium salts, neuroleptics, antihistamines (H1-receptor antagonists), anticonvulsants, central nervous system stimulants, general and local anaesthetics, antiarrhythmic drugs, narcotic and non-narcotic analgesics, non-steroidal anti-inflammatory drugs, antimicrobial agents, antifungal agents, antimalarial drugs, antineoplastic drugs, immunosuppressive drugs, radiological contrast agents and vaccines. For each of these classes of drugs, this article offers a revision of the literature and emphasises in particular the frequency of the adverse reaction, its clinical presentation, its presumed epileptogenic mechanism and the therapeutic strategy for the management of drug-induced seizures. An attempt is also made to distinguish seizures induced by standard dosages from those provoked by accidental or self-induced intoxication. For some classes of drugs such as antidepressants, neuroleptics, central nervous system stimulants (e.g. theophylline, cocaine, amphetamines) and beta-lactam antibiotics, seizures are a well recognised adverse reaction, and a large body of literature has been published discussing exhaustively the major aspects of the issue; sufficient data are available also for the other classes of pharmacological agents mentioned above. In contrast, several other drugs [e.g. allopurinol, digoxin, cimetidine, protirelin (thyrotrophin releasing hormone), bromocriptine, domperidone, insulin, fenformin, penicillamine, probenecid, verapamil, methyldopa] have not been studied thoroughly under this aspect, and the only source of information is the occasional case report. This review does not address the issue of seizures induced by drug withdrawal.

Quinine overdose: review of toxicity and treatment

Quinine sulfate is a commonly prescribed remedy for idiopathic nocturnal leg cramps and is now available "over the counter." A 24-year-old man ingested 8 g (a commonly dispensed quantity) of quinine sulfate in a suicide attempt. Despite hemoperfusion begun 10 h after ingestion, the patient died. This report reviews the toxic manifestations of quinine and the currently available modes of treatment.

Bicarbonate therapy for dysrhythmia and hypotension in tricyclic antidepressant overdose

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Entry of quinidine into cerebrospinal fluid

Some of the unwanted effects of quinidine commonly occurring in clinical practice involve the central nervous system. We therefore assessed the rate and extent of quinidine passage into cerebrospinal fluid (CSF) in humans and dogs. In eight human subjects receiving oral quinidine therapy, lumbar CSF quinidine concentrations averaged 16% of unbound serum concentrations (range: 4% to 37%). The findings were confirmed when simultaneous serum (total and unbound) and CSF quinidine concentrations were followed for up to 8 hours after a single intravenous dose of quinidine in anesthetized dogs. Quinidine appeared promptly in CSF of all animals, but CSF concentrations averaged only 37% to 46% of unbound serum levels. The in vitro octanol:water partition coefficient for quinidine at physiologic pH was greater than 100, indicating that unbound quinidine should readily traverse the blood-brain barrier. Thus, passage of quinidine into CSF appears not to be governed by passive diffusion alone. Quinidine may participate in an active transport system such as that which removes certain other basic substances from CSF.

The management of acute quinidine intoxication

A 16-year-old patient survived severe intoxication with quinidine. Hypotension, rapidly progressing to oliguria and shock, was resistant to the usual therapeutic interventions but responded favorably to the use of an intra-aortic balloon pump. Some hemodynamic implications are discussed. Pulmonary edema occurred and was treated with positive end-expiratory pressure. Electrocardiographic disturbances in conduction, transient bradycardia and recurrent ventricular arrhythmias characterized the initial 36-hour critical period. Unexplained electrolyte abnormalities occurred and further complicated management.

Cardiac pacing for cardiac arrest due to hyperkalemia plus digitalis and quinidine toxicity

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