Baclofen overdose with cardiac conduction abnormalities: case report and review of the literature

FORWARDS-1: an adaptive, single-blind, placebo-controlled ascending dose study of acute baclofen on safety parameters in opioid dependence during methadone-maintenance treatment-a pharmacokinetic-pharmacodynamic study

Background

Treatment of opiate addiction with opiate substitution treatment (e.g. methadone) is beneficial. However, some individuals desire or would benefit from abstinence but there are limited options to attenuate problems with opiate withdrawal. Preclinical and preliminary clinical evidence suggests that the GABA-B agonist, baclofen, has the desired properties to facilitate opiate detoxification and prevent relapse. This study aims to understand whether there are any safety issues in administering baclofen to opioid-dependent individuals receiving methadone.

Methods

Opiate-dependent individuals (DSM-5 severe opioid use disorder) maintained on methadone will be recruited from addiction services in northwest London (NHS and third sector providers). Participants will be medically healthy with no severe chronic obstructive pulmonary disease or type 2 respiratory failure, no current dependence on other substances (excluding nicotine), no current severe DSM-5 psychiatric disorders, and no contraindications for baclofen or 4800 IU vitamin D (placebo). Eligible participants will be randomised in a 3:1 ratio to receive baclofen or placebo in an adaptive, single-blind, ascending dose design. A Bayesian dose-escalation model will inform the baclofen dose (10, 30, 60, or 90 mg) based on the incidence of ‘dose-limiting toxicity’ (DLT) events and participant-specific methadone dose. A range of respiratory, cardiovascular, and sedative measures including the National Early Warning Score (NEWS2) and Glasgow Coma Scale will determine DLT. On the experimental day, participants will consume their usual daily dose of methadone followed by an acute dose of baclofen or placebo (vitamin D3) ~ 1 h later. Measures including oxygen saturation, transcutaneous CO₂, respiratory rate, QTc interval, subjective effects (sedation, drug liking, craving), plasma levels (baclofen, methadone), and adverse events will be obtained using validated questionnaires and examinations periodically for 5 h after dosing.

Discussion

Study outcomes will determine what dose of baclofen is safe to prescribe to those receiving methadone, to inform a subsequent proof-of-concept trial of the efficacy baclofen to facilitate opiate detoxification. To proceed, the minimum acceptable dose is 30 mg of baclofen in patients receiving ≤ 60 mg/day methadone based on the clinical experience of baclofen’s use in alcoholism and guidelines for the management of opiate dependence.

Trial registration

Clinicaltrials.gov NCT05161351. Registered on 16 December 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06821-9.

Baclofen therapeutics, toxicity, and withdrawal: A narrative review

Baclofen is an effective therapeutic for the treatment of spasticity related to multiple sclerosis, spinal cord injuries, and other spinal cord pathologies. It has been increasingly used off-label for the management of several disorders, including musculoskeletal pain, gastroesophageal reflux disease, and alcohol use disorder. Baclofen therapy is associated with potential complications, including life-threatening toxicity and withdrawal syndrome. These disorders require prompt recognition and a high index of suspicion. While these complications can develop following administration of either oral or intrathecal baclofen, the risk is greater with the intrathecal route. The management of baclofen toxicity is largely supportive while baclofen withdrawal syndrome is most effectively treated with re-initiation or supplementation of baclofen dosing. Administration of other pharmacologic adjuncts may be required to effectively treat associated withdrawal symptoms. This narrative review provides an overview of the historical and emerging uses of baclofen, offers practical dosing recommendations for both oral and intrathecal routes of administration, and reviews the diagnosis and management of both baclofen toxicity and withdrawal.

Coma With Absent Brainstem Reflexes and a Burst Suppression on EEG Secondary to Baclofen Toxicity

Baclofen, a muscle relaxant prescribed for the alleviation of symptoms of spasticity acts primarily at the spinal level but with high doses, it penetrates the blood-brain barrier and can result in prominent central nervous depression. Baclofen toxicity has been associated with a variety of symptoms ranging from dizziness to deep coma. We report the clinical course, management, and outcome of a case of baclofen overdose who presented in deep coma with loss of brainstem reflexes and a burst suppression (BS) pattern on his electroencephalogram (EEG). In addition, we reviewed the presentation and outcomes of all reported cases of baclofen toxicity with a BS pattern on EEG to evaluate if those cases share a common clinical presentation and for the presence of signs and symptoms that would help the clinician to consider this diagnosis. There appears to be a common clinical picture associated with severe baclofen toxicity consisting of deep coma associated with loss of all brainstem reflexes including pupillary reactivity, frequent association with seizures/myoclonic jerks, and a BS pattern on EEG. The outcome is generally good, and serial EEGs are recommended to document a reversal of the abnormal electrographic features.

Toxicological considerations in the prescription of baclofen for the treatment of substance use disorders

Introduction: For many years, applications for baclofen have widened in the treatment of substance abuse disorder (SUD), mainly alcohol use disorder, with a growing rate of off-label prescriptions in Europe. Clinical effects seem to be both a decrease of craving and anxiety, leading to a decrease of drug or alcohol consumption. We described baclofen poisoning circumstances, therapeutic options and outcomes when used in substance use disorders.Areas covered: This review summarizes the toxicological considerations where baclofen was prescribed in humans for substance use or abuse disorder in randomized clinical trials, case series, case reports and observational studies between 1990 and 2020 according to the Preferred Reporting Items for Systemic reviews and Meta-Analysis.Expert opinion: The most frequent cause of severe intoxication is self-poisoning. A dose above 180 mg are expected to cause severe toxicity and death. The treatment is only symptomatic as no antidote is available. Off-label prescription remains unsafe because the optimal dose is not known and varies greatly between patients. As SUD are frequently associated with psychiatric disorders and such patients may have suicidal thoughts, the risk of self-poisoning is high. Potential co-ingestants should also be considered, especially CNS depressants, and they need to be closely monitored.

Baclofen overdose mimicking anoxic encephalopathy: a case report and review of the literature

A patient who has overdosed on baclofen can present with significant neurological symptoms suggestive of a serious brain insult, but with appropriate diagnosis and treatment they often fully recover within 72 h. If the patient had been maintained on chronic baclofen therapy prior to the overdose, one must be watchful for signs of baclofen withdrawal as recovery from the overdose occurs.

A nationwide register-based survey of baclofen toxicity

To study the use and misuse (poisonings) of baclofen in the time period of 2007-2012 and to evaluate the severity and clinical symptoms of poisonings including ingested baclofen. The National Patient Register (NPR) was searched for admissions due to baclofen poisonings from 2007 to 2012. The search was conducted with ICD-10 codes for poisoning, self-harm and suicide, and coupled with the baclofen ATC code. All enquiries about baclofen to the Danish Poison Information Centre (DPIC) in the same period were evaluated. Demographic and clinical data were extracted, and the poisonings were classified according to the Poison Severity Score. The number of baclofen poisonings did not increase from 2007 to 2012. Thirty-eight admissions with baclofen poisoning were registered at the NPR; however, only one-third of the reviewed DPIC cases were registered at the NPR with the correct coding. In the group of severely poisoned patients (PSS 3), three patients had only ingested baclofen (mean 2000 mg; SD 500 mg) and eight patients had ingested baclofen together with alcohol or psychotropic drugs (mean 900 mg; SD 641 mg). All patients presented with deep coma and respiratory depression. Additionally, seizures and cardiovascular events (mild hypo- or hypertension and bradycardia) occurred. There is a substantial degree of underreporting of baclofen poisonings in Denmark. Symptoms of baclofen poisoning progress very fast, and toxicity was observed even with doses as low as 150 mg. We therefore recommend that observation and treatment of these patients should be carried out in an intermediate- or intensive care unit. The most important treatment is the maintenance of a protected airway and respiration.

Baclofen toxicosis in dogs and cats: 145 cases (2004-2010)

OBJECTIVE

To identify dogs and cats with baclofen toxicosis and characterize the patient population, clinical signs, and outcome.

DESIGN

Retrospective case series.

ANIMALS

140 dogs and 5 cats with baclofen toxicosis.

PROCEDURES

An animal poison control center electronic database was reviewed from November 2004 through April 2010 to identify dogs and cats with baclofen toxicosis. Information on signalment, clinical signs, and amount of baclofen ingested was obtained. Clinical signs were categorized as CNS, gastrointestinal, general malaise, cardiovascular, respiratory, or urogenital. Follow-up communications were performed to determine overall outcome.

RESULTS

Dogs had a median age of 0.67 years (range, 0.1 to 15 years) and cats of 1 year (range, 0.7 to 16 years). Of 145 patients, 133 (92%) developed clinical signs of baclofen toxicosis. A total of 259 signs fell within defined categories: CNS (121/259 [46.7%]), gastrointestinal (69/259 [26.6%]), general malaise (27/259 [10.4%]), cardiovascular (23/259 [8.9%]), respiratory (14/259 [5.4%]), and urogenital (5/259 [1.9%]). For 68 dogs with known survival status, survival rate was 83.8% (57/68); of these dogs, the amount of baclofen ingested was known for 53 (46 survivors and 7 nonsurvivors). Amount of baclofen ingested was significantly lower in survivor dogs (median, 4.2 mg/kg [1.91 mg/lb]; range, 0.61 to 61 mg/kg [0.28 to 27.7 mg/lb]), compared with nonsurvivor dogs (median, 14 mg/kg [6.4 mg/lb]; range, 2.3 to 52.3 mg/kg [1.04 to 23.77 mg/lb]. Of 5 cats, 2 survived, 1 died, and 2 had unknown outcomes.

CONCLUSIONS AND CLINICAL RELEVANCE

Clinical signs of baclofen toxicosis occurred in most patients, with the CNS being the system most commonly affected.

Baclofen intoxication: a "fun drug" causing deep coma and nonconvulsive status epilepticus--a case report and review of the literature

The number of reports on baclofen intoxication has increased in recent years. We report a 15-year-old boy who was referred in a state of deep coma (Glasgow Coma Scale = 3). On clinical examination, he showed sinus bradycardia with normal blood pressure. On admission to the hospital, he presented intermittent short episodes of generalized tonic-clonic seizures. While results of imaging procedures and initial toxicological screening (including standard HPLC analysis and urine test) were negative, a nonconvulsive status epilepticus was diagnosed by electroencephalography (EEG). Identification of baclofen as causative agent was possible after the boy's father reported abusive baclofen intake. Subsequent toxicological target analysis of blood and urine samples confirmed the excessive intake of baclofen and showed a typical elimination pattern with a secondary release. Following 112 h of mechanical ventilation, the boy rapidly regained consciousness and recovered normal neurological behavior.

CONCLUSIONS

The present case demonstrates the importance of considering baclofen overdosage in cases of severe coma in combination with an abnormal EEG pattern and sinus bradycardia with normal blood pressure levels, in particular as the substance is popular in internet reports promoting baclofen as a rather harmless "fun drug." Furthermore, it underlines the difficulty to identify baclofen as a causative agent without anamnestic information. Nevertheless, by reviewing existing literature on oral baclofen overdosage, it is possible to picture a nearly specific pattern of clinical symptoms in baclofen intoxication.

Baclofen intoxication after accidental ingestion in a 3-year-old child

Baclofen is a skeletal muscle relaxant, used to control spasticity in both adults and children with neuromuscular disorders. Several cases of baclofen overdose have been reported, but only a small number have involved children. We report a 3-year-old girl with accidental ingestion of baclofen, who presented with coma, bradycardia and hypotension. She recovered within 24 hours with supportive treatment. The case emphasizes the importance of warning parents about the potential toxicity of baclofen when the drug is prescribed to a family member.

Electroencephalographic abnormalities in baclofen-induced encephalopathy

We report a patient in whom the characteristic electroencephalographic features of baclofen intoxication are highlighted and emphasize the role of electrographic abnormalities in the diagnosis of this condition.

Baclofen overdose: defining the spectrum of toxicity

OBJECTIVES

To describe the spectrum of toxicity of baclofen in overdose, and investigate dose-related clinical effects.

METHODS

Consecutive baclofen overdoses were identified from a prospective database of all poisoning admissions presenting to a regional toxicology service. Ingestion was corroborated on more than one occasion and from multiple sources. Demographic, clinical and outcome variables were extracted for each presentation for a retrospective review, and the data sets were divided into high dose (> or = 200 mg) and low dose (< 200 mg) groups for comparison of clinical effects.

RESULTS

There were 23 presentations, of which eight patients ingested baclofen alone. Seizures were reported in four cases, a decreased level of consciousness (GCS < 9) occurred in eight patients and delirium was recorded in eight patients. Five patients had miosis and seven patients had dilated pupils, 13 patients had absent or depressed reflexes. The only arrhythmias were sinus bradycardia in six patients and sinus tachycardia in five. Hypertension occurred in 13 patients and hypotension in one. The reported total ingested dose of baclofen was known in 19 patients (Mean 630 mg, SD 730 mg; 80-2500 mg). A higher ICU admission rate, rate of mechanical ventilation and prolonged length of stay occurred in those ingesting 200 mg or more. Coma, delirium and seizures occurred only with doses of 200 mg or more, and hypertension was more common with higher doses.

CONCLUSIONS

Baclofen overdose causes mainly neurological effects and excepting hypertension cardiovascular effects were uncommon. Doses greater than 200 mg were predictive of patients developing delirium, coma and seizures, requiring long hospital admissions and ICU admission.

Magnetic resonance spectroscopy and electroencephalography in baclofen coma

This report describes a 14-year-old female who presented with coma and seizures. Continuous electroencephalographic monitoring revealed suppression and semiperiodic sharp waves. Magnetic resonance spectroscopy performed 1 day after admission suggested a good outcome despite her clinical examination and electroencephalogram. She was subsequently found to have elevated serum baclofen levels after an intentional overdose. At the time of her discharge from the pediatric intensive care unit, she manifested no neurologic deficits, and on telephone follow-up 2 years after the ingestion the patient had no complaints of any cognitive problems or neurologic dysfunction.

A benefit-risk assessment of baclofen in severe spinal spasticity

Baclofen is used for treatment of the spasticity of spinal origin that is a common sequela of spinal cord injury and multiple sclerosis; spasticity occurs in about 50% of patients affected by these disorders. In open-label studies of oral baclofen, the drug improved spasticity in 70-87% of patients; additionally, improvement in spasms was reported in 75-96% of patients. In double-blind, crossover, placebo-controlled trials, baclofen was reported to be effective, producing statistically significant improvements in spasticity. Tizanidine is the antispasticity drug that has been most widely compared with oral baclofen; studies have generally found the two drugs to have equivalent efficacy. However, tizanidine has better tolerability, in particular weakness was reported to be occur less frequently with tizanidine than with baclofen. The main adverse effects of oral baclofen include: sedation or somnolence, excessive weakness, vertigo and psychological disturbances. The incidence of adverse effects is reported to range from 10% to 75%. The majority of adverse effects are not severe; most are dose related, transient and/or reversible. The main risks of oral baclofen administration are related to withdrawal: seizures, psychic symptoms and hyperthermia can occur. These symptoms improve after the reintroduction of baclofen, usually without sequelae. When not related to withdrawal; these symptoms mainly present in patients with brain damage and in the elderly. The limited data on baclofen toxicity in patients with renal disease suggest that administration of the drug in these persons may carry an unnecessarily high risk. Intrathecal baclofen is indicated for use in patients with spasticity of spinal origin unresponsive to treatment with maximum doses of oral baclofen, tizanidine and/or dantrolene. The benefits of continuous intrathecal baclofen infusion have been demonstrated: >80% and >65% of patients have improvement in tone and spasms, respectively. The main risks of intrathecal baclofen infusion are symptoms related to overdose or withdrawal; the latter is more important because of the associated severe effects on clinical status and the possibility of death, but it is responsive to rapid treatment. Overdose primarily arises from drug test doses or human error during refill and programming of the pump, and withdrawal most commonly occurs as a result of a problem with the delivery system. Since the adverse consequences do not exceed the benefits of oral and intrathecal baclofen for patients with spinal spasticity, the benefit/risk assessment is favourable.

Baclofen toxicity in an 8-year-old with an intrathecal baclofen pump

Baclofen delivered by intrathecal pumps (ITB) is increasingly being utilized in the pediatric population, however, resources and education to support problems with these devices are limited. Typical management strategies for systemic baclofen overdose include removal of baclofen from the device reservoir or removal of cerebrospinal fluid from the adjacent device catheter. Appropriate care of these patients requires awareness of the clinical patterns of toxicity and mechanics of the ITB pump delivery system. This report describes the clinical presentation, unfamiliar dilemmas, and the management of a pediatric patient with intrathecal baclofen toxicity, noting problems that may arise in the care of these patients.

Treatment of spontaneous and chemically induced EEG paroxysms in the Fischer-344 rat with traditional antiepileptic drugs or AED+CGP 35348 polytherapy

Twenty-four Fischer-344 rats implanted with cortical electroencephalograph (EEG) electrodes were evaluated for frequency, duration, and mean duration (duration/frequency) of both spontaneous and chemically induced spike-and-wave discharges (SWDs) during earlier and later adulthood. Fischer-344 rats, exhibiting a low level of spontaneous SWDs during earlier adulthood, progressed to exhibit a significantly larger number and duration of SWDs during later adulthood. The convulsant trimethylolpropane phosphate (TMPP), known to antagonize the GABAA inhibitory system through blockade of the chloride channel, induced or increased SWDs in every rat tested. Spontaneous or chemically induced SWDs in Fischer-344 rats were eliminated or reduced by several drugs used to control human absence seizures. The gamma-aminobutyric acid (GABA)B antagonist CGP 35348 reduced spontaneous EEG paroxysms; CGP 35348 as a polytherapy with several traditional antiabsence treatments improved control of TMPP-induced seizures. It would appear that the Fischer-344 rat provides an excellent research alternative to use of genetically selected rodent strains for investigation of progression of absencelike epilepsy with aging, induction of SWDs by toxicant exposures, and treatment of spontaneous and chemically induced paroxysms.

Anti-epileptic drugs-induced de novo absence seizures

The authors present three patients with de novo absence epilepsy after administration of carbamazepine and vigabatrin. Despite the underlying diseases, the prognosis for drug-induced de novo absence seizure is good because it subsides rapidly after discontinuing the use of the offending drugs. The gamma-aminobutyric acid-transmitted thalamocortical circuitry accounts for a major part of the underlying neurophysiology of the absence epilepsy. Because drug-induced de novo absence seizure is rare, pro-absence drugs can only be considered a promoting factor. The underlying epileptogenecity of the patients or the synergistic effects of the accompanying drugs is required to trigger the de novo absence seizure. The possibility of drug-induced aggravation should be considered whenever an unexpected increase in seizure frequency and/or new seizure types appear following a change in drug treatment. By understanding the underlying mechanism of absence epilepsy, we can avoid the inappropriate use of anticonvulsants in children with epilepsy and prevent drug-induced absence seizures.

Baclofen overdose in two siblings

Baclofen is a muscle relaxant used in both adults and children with neuromuscular disorders to control spasticity. In children, relatively few cases of overdose have been previously reported. We report two cases of baclofen overdose occurring in two siblings. One sibling with cerebral palsy was being treated with baclofen at the time of overdose. Both cases presented with severe respiratory depression requiring mechanical ventilation. Serum baclofen concentrations from both children were significantly elevated. We also review the published literature on baclofen overdose in children and adolescents. These cases emphasize the importance of warning parents about the potential toxicity of baclofen when prescribing the drug to a family member.

Baclofen and ethanol ingestion: a case report

The number of reported cases of skeletal muscle relaxant ingestion has been increasing in the United States, although fatalities are rare. A 30-year-old women ingested 300 mg of baclofen and ethanol. She was able to ambulate into the Emergency Department (ED) 50 min later, but within 30 min post-arrival had a Glasgow Coma Score of 3. She was treated with supportive care including mechanical ventilation for 36 h. Her neurologic status returned to her previous state. Coma may occur rapidly after baclofen overdose, and the respiratory depression may be exacerbated by the co-ingestion of ethanol. Primary importance in the treatment of such ingestions should be placed on maintenance of an airway and respiratory support.

Supraventricular tachyarrhythmia associated with baclofen overdose

Baclofen overdose occasionally results in cardiac effects, but serious tachyarrhythmias have not been reported. We present the case of a 21-year-old man with an acute baclofen overdose who developed increased cardiac conduction times and a rapid supraventricular tachyarrhythmia which required medical intervention. Acute baclofen toxicity can result in the development of tachyarrhythmias and cardiac monitoring is warranted in acute overdose states.