Benzonatate overdose associated with seizures and arrhythmias

Benzonatate Safety and Effectiveness: A Systematic Review of the Literature

OBJECTIVE

To review the available literature regarding the treatment effects and efficacy of benzonatate needed to better inform patients, providers, and regulators evaluating its role in modern medical therapies.

DATA SOURCES

Comprehensive literature searches were conducted in PubMed, Embase (Elsevier), Cochrane Library, and Scopus for original research articles evaluating the effectiveness, tolerability, and safety profile of benzonatate from January 1956 through August 2022.

STUDY SELECTION AND DATA EXTRACTION

The identified studies were screened for relevance and then assessed for inclusion through a full-text review, data extraction, and quality assessment by multiple reviewers using the online software Covidence.

DATA SYNTHESIS

The selection process resulted in 37 articles consisting of 21 cohort studies, 5 experimental studies, and 11 case studies and series. Initial clinical studies exploring potential therapeutic benefits collected data from very small populations and limited clinical settings. Safety is primarily assessed in terms of toxicity due to overdose or inappropriate use. Quality assessment raised concerns for high degrees of biases primarily related to the limited sample size, data collection, generalizability, and study design.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review reveals substantial limitations within existing evidence pertaining to the safety and clinical effectiveness of benzonatate and thus, a need for large observational studies or randomized trials to better characterize its role and value in modern medical practice.

CONCLUSIONS

Rising safety concerns should bring closer scrutiny upon the prescription of benzonatate whose approval is founded upon evidence that would not stand up to current regulatory review.

Benzonatate Exposure Trends and Adverse Events

BACKGROUND AND OBJECTIVES

Adverse events (AE), including death, occur in children with benzonatate use. This study aims to understand recent trends in benzonatate exposure and clinical consequences in pediatric patients.

METHODS

This retrospective analysis of data from IQVIA pharmacy drug dispensing, National Poison Data System, National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance Project, FDA Adverse Event Reporting System, and the medical literature evaluated exposure trends and medication-related AEs with benzonatate. Trends for comparator narcotic and nonnarcotic antitussive medications were analyzed where possible for context.

RESULTS

During the study period, pediatric benzonatate prescription utilization increased but remained low compared with pediatric utilization of dextromethorphan-containing prescription antitussive medications. Among the 4689 pediatric benzonatate exposure cases reported to US poison control centers from 2010 to 2018, 3727 cases (80%) were for single-substance exposures. Of these, 3590 cases (77%) were unintentional exposures and most involved children 0 to 5 years old (2718 cases, 83%). Cases involving intentional benzonatate exposure increased among children 10 to 16 years old with a more pronounced increase for multiple-substance exposures. Most benzonatate cases involving misuse or abuse were for children 10 to 16 years old (59 cases, 61%). The proportion of cases with serious adverse effects was low. There were few cases annually of serious AEs with benzonatate in children.

CONCLUSIONS

There were rising patterns of unintentional ingestion of benzonatate in children 0 to 5 years old and intentional benzonatate ingestion in children 10 to 16 years old. Rational prescribing and improved provider and caregiver awareness of benzonatate toxic effects may reduce risks associated with benzonatate exposure.

Benzonatate Overdose Presenting as Cardiac Arrest with Rapidly Narrowing QRS Interval

INTRODUCTION

Benzonatate is a local anesthetic-like sodium channel antagonist that is widely prescribed as an antitussive. While it may be reasonable to assume that patients would present with a prolonged QRS interval following benzonatate overdose, the published literature does not support this. We report a case of a patient presenting following a benzonatate overdose with a prolonged QRS on her initial electrocardiograph (ECG) rhythm strip with rapid normalization of QRS duration.

CASE REPORT

A 14-year-old girl presented in cardiac arrest following a benzonatate overdose. The patient was found in cardiac arrest within minutes of last being known well. Bystanders immediately provided cardiopulmonary resuscitation (CPR), and she was in asystole on emergency medical services (EMS) arrival. Return of spontaneous circulation (ROSC) was obtained following administration of intraosseous epinephrine and naloxone. EMS obtained an ECG rhythm strip following ROSC demonstrating a sinus rhythm with a QRS duration of 160 ms. Over the ensuing 30 minutes, there was progressive narrowing of the QRS. A 12-lead ECG obtained on arrival in the emergency department (ED) 44 minutes later demonstrated a QRS duration of 94 ms. Initially, EMS ECG rhythm strips were unavailable and an isolated benzonatate ingestion was considered less likely as ECG intervals were normal. Benzonatate exposure was later confirmed with a urine benzonatate concentration, which was 8.5 mcg/mL. The patient made a full recovery.

DISCUSSION

Cases of pediatric benzonatate overdose with rapid development of cardiac arrest and full recovery have been previously reported. In this case, evidence of cardiac sodium channel blockade was demonstrated with a prolonged QRS interval on initial ECG rhythm strip analysis. However, unlike previous cases, rapid resolution of QRS prolongation occurred in this case. While transient QRS prolongation may be observed, finding a normal QRS interval should not discount the possibility of benzonatate overdose.

A description of the clinical course of severe benzonatate poisonings reported in the literature and to NPDS: A systematic review supplemented with NPDS cases

BACKGROUND

Benzonatate is a commonly prescribed medication that can be lethal in acute overdose of a small number of capsules.

OBJECTIVE

This was a systematic review to describe the course of severe poisoning and deaths from benzonatate supplemented with the National Poison Data System (NPDS) fatalities module.

METHODS

The NPDS was queried from 2000 to 2018 for benzonatate fatalities. Pubmed, Cochrane, Embase, and Google Scholar were searched for combinations of benzonatate and "poisoning," "overdose," and "toxicity." References of relevant articles were searched for additional publications. Articles were included if they described the clinical course of at least one patient suffering from benzonatate poisoning and available in English. Dual independent review and extraction were performed.

RESULTS

Seventeen cases from NPDS and 19 published reports met the inclusion criteria resulting in 36 cases, mostly (28/36) self-harm ingestions. Most patients were young [17 (11-29), median (IQR)] and female (22). Onset of toxicity was rapid at <5 min (9). Most common symptoms included cardiac arrest (29), seizures (24), and dysrhythmias (24). Treatments included intubation (26), cardiopulmonary resuscitation (28), vasopressors (20) and others. Return of spontaneous circulation was achieved in 23/28 patients, but most had significant neurologic deficits or other end organ damage and 5 survived with a good neurologic outcome.

CONCLUSION AND RELEVANCE

Overdose ingestions of benzonatate can cause significant toxicity with a rapid onset. Interventions performed were generally supportive in nature. Duration of directly toxic effects is short, but dramatic with neurologic devastation and resuscitated patients often still have a poor outcome.

Arrhythmogenic Antitussive: A Case of Pediatric Benzonatate Overdose With Torsades de Pointes, Cardiac Arrest, and Complete Recovery Without Neurologic Deficits

Benzonatate is a commonly prescribed antitussive with rapid and deadly effects in overdose. We report a 14-year-old female who ingested 14 capsules containing 200 mg benzonatate. Her case represents the only reported benzonatate overdose with torsades de pointes, as well as the only reported pediatric benzonatate ingestion complicated by cardiac arrest with full recovery.

Benzonatate inhibition of voltage-gated sodium currents

Benzonatate was FDA-approved in 1958 as an antitussive. Its mechanism of action is thought to be anesthesia of vagal sensory nerve fibers that mediate cough. Vagal sensory neurons highly express the Nav1.7 subtype of voltage-gated sodium channels, and inhibition of this channel inhibits the cough reflex. Local anesthetics inhibit voltage-gated sodium channels, but there are no reports of whether benzonatate affects these channels. Our hypothesis is that benzonatate inhibits Nav1.7 voltage-gated sodium channels. We used whole cell voltage clamp recording to test the effects of benzonatate on voltage-gated sodium (Na(+)) currents in two murine cell lines, catecholamine A differentiated (CAD) cells, which express primarily Nav1.7, and N1E-115, which express primarily Nav1.3. We found that, like local anesthetics, benzonatate strongly and reversibly inhibits voltage-gated Na(+) channels. Benzonatate causes both tonic and phasic inhibition. It has greater effects on channel inactivation than on activation, and its potency is much greater at depolarized potentials, indicating inactivated-state-specific effects. Na(+) currents in CAD cells and N1E-115 cells are similarly affected, indicating that benzonatate is not Na(+) channel subtype-specific. Benzonatate is a mixture of polyethoxy esters of 4-(butylamino) benzoic acid having varying degrees of hydrophobicity. We found that Na(+) currents are inhibited most potently by a benzonatate fraction containing the 9-ethoxy component. Detectable effects of benzonatate occur at concentrations as low as 0.3 μM, which has been reported in humans. We conclude that benzonatate has local anesthetic-like effects on voltage-gated sodium channels, including Nav1.7, which is a possible mechanism for cough suppression by the drug.

Antitussives and substance abuse

Abuse of antitussive preparations is a continuing problem in the United States and throughout the world. Illicit, exploratory, or recreational use of dextromethorphan and codeine/promethazine cough syrups is widely described. This review describes the pharmacology, clinical effects, and management of toxicity from commonly abused antitussive formulations.

Benzonatate toxicity in a teenager resulting in coma, seizures, and severe metabolic acidosis

We report a benzonatate overdose in a teenager resulting in life-threatening toxicity to increase awareness of this overdose, and discuss recent pediatric warnings and labeling information provided by the US Food and Drug Administration (FDA). After an overdose of benzonatate, a 13-yr-old female presented to our emergency department with coma, seizures, hypotension, prolonged QT interval on electrocardiogram, and metabolic acidosis. Benzonatate is an antitussive medication with sodium channel-blocking properties and local anesthetic effects on the respiratory stretch receptors due to a tetracaine-like metabolite. Overdose is reported to cause coma, seizures, hypotension, tachycardia, ventricular dysrhythmias, and cardiac arrest. The FDA recently issued a Drug Safety Communication warning that accidental benzonatate ingestion in children younger than 10 years of age have increased risk of death and added the new information to the Warnings and Precautions section of benzonatate's label.

Benzonatate Ingestion Reported to the National Poison Center Database System (NPDS)

Little has been published on benzonatate ingestion, with the few case reports suggesting significant risk of seizures after poisoning. A 7-year retrospective review of all single substance ingestion of benzonatate reported to the National Poison Center Database System (NPDS) from 2000 to 2006. In this review, there were 2,172 patients, of which 1,280 (58%) were female. Mean age was 20 years, with 676 (30%) <6 years. Serious outcomes occurred in 116 (moderate, n = 81, 4%; major, n = 31, 1%; and death, n = 4, 0.2%). Mean age of those with serious outcome was 21 years, with 41 (35%) in children less than 6 years old. Forty-nine percent (1,084) patients were treated in a healthcare facility (HCF) of which 148 (7%) were admitted for medical care. Clinically significant effects that were documented included tachycardia (n = 31, 1%), agitation (n = 30, 1%), seizure (n = 23, 1%), coma (n = 14, 0.6%), ventricular dysrhythmia (n = 9, 0.4%), cardiac arrest (n = 8, 0.3%), hypotension (n = 7, 0.3%), and asystole (n = 6, 0.2%). Of patients with seizures reported, eight patients (0.4%) had multiple/discrete seizures and two had status epilepticus documented. Dysrhythmias but not seizures occurred in all fatalities in this review. Significant CNS and cardiac effects occurred in a small subset of this study (<1%), while half the patients received direct medical care in an HCF. No correlation between age and severity of medical outcome was detected by statistical analysis. A prospective study to better evaluate potential HCF triage criteria such as dosage, age, or preexisting conditions may be warranted. The fatalities from this study were due to dysrhythmias rather than seizures as previously reported in previous case reports. There were no clinical correlations between severity of outcomes and dose ingested. A median dose of 200 mg or greater suggests a potential for producing serious outcomes in a benzonatate exposure.

Acute cough: a diagnostic and therapeutic challenge

BACKGROUND

Acute cough is one of the most common complaints prompting patient visits to healthcare professionals. Despite the broad repercussions of acute cough on patient quality of life, school and work productivity, and public health resources, research on this condition is minimal, as are the available treatment options. Many patients use over-the-counter medicines, which are often ineffective for symptom relief. Some therapies may achieve antitussive activity, but at the expense of unpleasant or intolerable side effects.

UNMET NEEDS

When considering the treatments currently available for the management of acute cough, the multiple limitations of such treatments are quite apparent. Most of these treatments lack clinically proven efficacy and reliability to support their use. This reinforces the need for the generation of quality scientific data from well-performed clinical trials. Hopefully, the result will be the development of safer, more effective and more reliable therapeutic options in the management of acute cough.

COUGH ASSESSMENT AND MANAGEMENT

Acute cough can be due to a variety of causes, and it is worthwhile to consider these pathogenic factors in some detail. It is also important to be familiar with the effects that acute cough has on patients' quality of life, work productivity, and the healthcare system; proper awareness of these effects may contribute to better understanding of the social impact of cough. In reference to the available treatments for the management of acute cough, adequate knowledge of the type of over-the-counter and prescription products in the market, as well as their mode of action and advantages/disadvantages, may provide expanded pharmacotherapeutic opportunities and facilitate better clinical decisions. However, due to the drawbacks of current treatment options, ideas for future cough management and newer products need to be considered and tested.

CONCLUSION

In view of the socio-economic impact of acute cough and the limitations of available treatments, a renewed interest in the management of acute cough needs to be encouraged. The current strategies for acute cough management need to be reassessed, with a focus on developing new, reliable products and formulations with proven efficacy and safety.