Obtundation and seizure following ondansetron overdose in an infant

Drug-specific risk of severe QT prolongation following acute drug overdose

Background: Severe QT prolongation (SQTP) has been identified as a strong predictor of adverse cardiovascular events in acute drug overdose, but drug-specific causes of SQTP in the setting of acute drug overdose remain unclear. We aimed to perform the most definitive study to date describing drug-specific risk of SQTP following acute drug overdose.Methods: This was a prospective multicenter cohort study at >50 hospital sites across the US using the ToxIC Registry between 2015 and 2018. Inclusion criteria were adults (≥18 years) receiving medical toxicology consultation for acute drug overdose. The primary outcome was SQTP, which was defined using the computer automated Bazett QT correction (QTc) on the ECG with the previously validated cut point of 500 milliseconds. Mean difference in QTc was also calculated for specific drugs. Drugs associated with SQTP were analyzed using multivariable logistic regression to control for known confounders of QT risk (age, sex, race, cardiac disease).Results: From 25,303 patients screened, 6473 met inclusion criteria with SQTP occurring in 825 (13%). Drugs associated with increased adjusted odds of SQTP included Class III antidysrhythmics (sotalol), sodium channel blockers (amitriptyline, diphenhydramine, doxepin, imipramine, nortriptyline), antidepressants (bupropion, citalopram, escitalopram, trazodone), antipsychotics (haloperidol, quetiapine), and the antiemetic serotonin antagonist ondansetron.Conclusions: This large US cohort describes drug-specific risk of SQTP following acute drug overdose. Healthcare providers caring for acute drug overdoses from any of these implicated drugs should pay close attention to cardiac monitoring for occurrence of SQTP.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT₃ receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT₃ receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT₃ receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

Fatal Cardiac Arrest in 2 Children: Possible Role of Ondansetron

INTRODUCTION

Ondansetron is commonly used to treat vomiting in gastroenteritis, but has a United States Food and Drug Administration black box warning for risk of Q wave to T wave time interval (QT) prolongation. We report 2 pediatric cases of fatal refractory cardiac arrest after administration of ondansetron.

CASES

A 10-year-old previously healthy boy presented to the emergency room with gastroenteritis symptoms. After intravenous fluids, morphine, antibiotics, and 2 doses of ondansetron, the patient became unresponsive with agonal respirations and a wide complex tachycardia consistent with ventricular tachycardia. In a second case, an 86-day-old infant with previously unidentified congenital cardiomyopathy presented to our emergency department with gastroenteritis symptoms. The patient received ondansetron and subsequently experienced repeated bouts of supraventricular tachycardia which progressed to ventricular fibrillation. Resuscitation efforts failed in each case, and both patients expired.

DISCUSSION

Ondansetron can cause dose-dependent QT prolongation effects, which are more clinically relevant when other proarrhythmic elements are present. There is very limited published experience on use of ondansetron in children younger than 2 years. Our 2 cases join 2 previous case reports of death after ondansetron administration for gastroenteritis. The pharmacology of ondansetron's cardiac effects and drug-induced QT prolongation is discussed.

CONCLUSIONS

Patients may have hidden risk factors that, together with ondansetron, could result in a proarrhythmic state that could lead to adverse effects, such as arrhythmias. Administration of ondansetron should be individualized and used cautiously in patients with risk factors for arrhythmia.

Behavioural screening of zebrafish using neuroactive traditional Chinese medicine prescriptions and biological targets

The mechanism of the therapeutic action of antidepressants remains uncertain in traditional Chinese medicine (TCM). In this study, we selected 7 classical TCM prescriptions and utilised an automatic video-tracking system to monitor the rest/wake behaviour of larval zebrafish at 4 days post-fertilisation (dpf) for 48 hours. We found that the curative effects of the prescriptions were dose-dependent. K-means clustering was performed according to the shared behavioural phenotypes of the zebrafish. The results revealed that the rest/wake behavioural profiles induced by the same class of prescriptions were similar. A correlation analysis was conducted between the TCM prescriptions and the known compounds. The results showed that the TCM prescriptions correlated well with some well-known compounds. Therefore, we predicted that they may share a similar mechanism of action. This paper describes the first study to combine TCM research with zebrafish rest/wake behaviour in vivo and presents a powerful approach for the discovery of the mechanism of action of TCM prescriptions.

Commonly used gastrointestinal drugs

This chapter reviews the spectrum and mechanisms of neurologic adverse effects of commonly used gastrointestinal drugs including antiemetics, promotility drugs, laxatives, antimotility drugs, and drugs for acid-related disorders. The commonly used gastrointestinal drugs as a group are considered safe and are widely used. A range of neurologic complications are reported following use of various gastrointestinal drugs. Acute neurotoxicities, including transient akathisias, oculogyric crisis, delirium, seizures, and strokes, can develop after use of certain gastrointestinal medications, while disabling and pervasive tardive syndromes are described following long-term and often unsupervised use of phenothiazines, metoclopramide, and other drugs. In rare instances, some of the antiemetics can precipitate life-threatening extrapyramidal reactions, neuroleptic malignant syndrome, or serotonin syndrome. In contrast, concerns about the cardiovascular toxicity of drugs such as cisapride and tegaserod have been grave enough to lead to their withdrawal from many world markets. Awareness and recognition of the neurotoxicity of gastrointestinal drugs is essential to help weigh the benefit of their use against possible adverse effects, even if uncommon. Furthermore, as far as possible, drugs such as metoclopramide and others that can lead to tardive dyskinesias should be used for as short time as possible, with close clinical monitoring and patient education.

The role of different serotonin receptor subtypes in seizure susceptibility

5-Hydroxytryptamine (5-HT) has the most diverse set of receptors in comparison with any other neurotransmitter or hormone in the body. To date, seven families of 5-HT receptors have been characterized. A great number of studies have been published regarding the role of 5-HT and its receptors in seizures. However, with a few exceptions, the net effect of activating or inhibiting each 5-HT receptor subtype on the development or severity of seizures remains controversial. Additionally, the results of studies, which have used knockout animals to investigate the role of 5-HT receptors in seizures, have sometimes been contradictory to those which have used pharmacological tools. The present study aims to review the available data regarding the influence of each receptor subtype on seizure development and, when possible, reconcile between the apparently different results obtained in these studies.

Characterization of electroencephalographic and biochemical responses at 5-HT promoting drug-induced onset of serotonin syndrome in rats

Many psychotropic substances used either for medications or illicit recreational purposes are able to produce an increase in extracellular serotonin (5HT) in the CNS. 5HT is well known to improve mood; however, only when the levels of its release are in an appropriate range. Excessive 5HT is harmful, and will generally result in serotonin syndrome. To date, clinical diagnosis of serotonin syndrome relies exclusively on observation of symptoms because of a lack of available laboratory tests. The goal of this study was to characterize the onset of the syndrome using laboratory settings to determine excessive 5HT-evoked neurological abnormalities. Experiments were carried out in rats with the syndrome being elicited by three groups of 5HT-promoting drugs: (i) (±)-3,4-methylenedioxymethamphetamine (MDMA); (ii) a combination of the monoamine oxidase inhibitor clorgyline with the 5HT precursor 5-hydroxytryptophan; (iii) clorgyline combined with the serotonin-selective reuptake inhibitor paroxetine. The onset of the syndrome was characterized by electroencephalography (EEG), tremor, and brain/plasma 5HT tests. We found that a mild syndrome was associated with reduced EEG amplitudes while a severe syndrome strongly with seizure-like EEG activity and increased tremor activity. The occurrence of the syndrome was confirmed with microdialysis, showing excessive 5HT efflux in brain dialysate and the increased concentration of unbound 5HT in the plasma. Our findings suggest that the syndrome onset can be revealed with EEG recording, measurements of tremor activity and changes of unbound 5HT concentration in the plasma.

Time-series analysis of ondansetron use in pediatric gastroenteritis

OBJECTIVE

Emergency department use of ondansetron in children with gastroenteritis is increasing; however, its effect on clinical outcomes is unknown. We aimed to determine whether increasing ondansetron usage is associated with improved outcomes in children with gastroenteritis.

METHODS

A retrospective cohort study was conducted at The Hospital for Sick Children, Toronto, Canada. Eligible children included those younger than 18 years old with gastroenteritis who presented to an emergency department between 2003 and 2008. There were 22,125 potentially eligible visits; 20% were selected at random for chart review. The primary outcome measure, the intravenous rehydration rate, was evaluated using an interrupted time-series analysis with segmented logistic regression. Secondary outcomes included emergency department revisits, hospitalization, and length of stay.

RESULTS

A total of 3508 patient visits were included in the final analysis. During the study period, there was a significant reduction in intravenous rehydration usage (27%-13%; P < 0.001) and an increase in ondansetron administration (1%-18%; P < 0.001). Time-series analysis demonstrated a level break (P = 0.03) following the introduction of ondansetron. The mean length of stay for children declined from 8.6 ± 3.4 to 5.9 ± 2.8 hours, P = 0.03. During the week following the index visit, there was a reduction in return visits (18%-13%; P = 0.008) and need for intravenous rehydration (7%-4%; P = 0.02).

CONCLUSIONS

Ondansetron use has increased significantly and is associated with reductions in the use of intravenous rehydration, emergency department revisits, and length of stay. The selective use of ondansetron is associated with improved clinical outcomes.

Risk of severe serotonin toxicity following co-administration of methylene blue and serotonin reuptake inhibitors: an update on a case report of post-operative delirium

In a previous case report, published in this journal, we described a postoperative delirium in a patient during recovery from parathyroidectomy. We noted that the delirium resembled serotonin toxicity and that the patient had been taking paroxetine until 2 days before surgery. We offered several tentative explanations for this event, including an adverse interaction between paroxetine and other agent(s) used in the course of the anaesthesia. Recent developments in characterisation of serotonin toxicity have prompted us to re-examine the clinical details surrounding this life-threatening event. It is now known to be important that the patient was given methylene blue, pre-operatively, to enable visualisation of the parathyroid glands. Methylene blue has been found to be a potent inhibitor of monoamine oxidase (MAO), and several cases of serotonin toxicity have been reported recently following its administration. All these cases are consistent with the well-known risk of serotonin toxicity when drugs that augment serotonergic transmission are given in combination with an MAO inhibitor. Methylene blue is used in a variety of surgical settings as well as for treatment of various types of hypotensive shock and methemoglobinaemia. It is also being studied for treatment of Alzheimer's disease and malaria. In this paper, we outline the pharmacology of methylene blue and the aetiology of serotonin toxicity to help prevent further unintentional co-administration of drugs that risk precipitating this life-threatening drug interaction.

Administration of ondansetron is associated with lethal outcome

We report here the case of a child with a known muscular abnormality and susceptibility to malignant hyperthermia who abruptly died after receiving a therapeutic dose of ondansetron. Also, we discuss the pharmacodynamic relationship of ondansetron to malignant hyperthermia in a susceptible host.

Ondansetron and seizures

Experimental studies suggest that 5-hydroxytryptamine (5-HT) receptors play a role in epileptogenesis and seizure propagation. Ondansetron, a 5-HT(3) receptor antagonist, has been reported to have proconvulsant and anticonvulsant effects in animals. We describe three patients who developed seizures after receiving ondansetron. There were two females and one male. Ages ranged from 38-56 years. None had a previous or family history of seizures. Four milligrams (mg) of ondansetron was given intravenously for severe nausea and vomiting in association with migraine, gastritis, and diabetic ketoacidosis. A generalized tonic-clonic seizure occurred in each patient--12, 15, and 22 min after injection. Brain magnetic resonance imaging (MRI) and electroencephalography (EEG) were normal in all patients. Although no antiepileptic drugs were given, none had seizure recurrence subsequently. The temporal relationship between ondansetron administration and seizures, lack of EEG or MRI abnormalities, and absence of seizure recurrence suggest that the seizures were causally related to ondansetron in our patients.