Baclofen-Induced Neuro-Respiratory Toxicity in the Rat: Contribution of Tolerance and Characterization of Withdrawal Syndrome

Pneumomediastinum: A case report of baclofen toxicity

INTRODUCTION

Baclofen is a γ -aminobutyric acid (GABA) agonist used to treat spasticity; however, it may be toxic at dosages above 200 mg. The psychological, nervous, cardiovascular, gastrointestinal, musculoskeletal, and respiratory systems are all affected. This report represents a case with the rare respiratory complications brought on by baclofen toxicity: atelectasis and pneumomediastinum.

PRESENTATION OF CASE

A 19-year-old female was admitted to the emergency department after attempting suicide by taking 20 baclofen tablets (500 mg). Imaging revealed pneumomediastinum, atelectasis, and a leftward displacement of mediastinal structures. Her therapy included a chest tube to relieve the pneumomediastinum and sodium valproate, promethazine, biperiden, and quetiapine for neurological symptoms. Four days after being admitted, she was successfully extubated without any complications.

DISCUSSION

Baclofen activates GABA-A and GABA-B receptors. High doses of baclofen may induce central nervous system and respiratory depression, requiring intensive care. GABA receptors may cause hallucinations, delusions, and agitation in baclofen overdose. High dosages of baclofen may cause bronchial and bronchiolar muscular spasms, leading to breathing problems and atelectasis. Recent animal studies on baclofen toxicity showed that increased alveolar pressure, circulatory abnormalities, edema, alveolar hemorrhages, and infiltration cause rupture and pneumomediastinum. Pneumomediastinum may need bed rest, oxygen, antitussives, and analgesics, but severe cases may necessitate a chest tube.

CONCLUSION

A high index of suspicion is required for early diagnosis of acute baclofen poisoning, which could manifest as respiratory complications, including pneumomediastinum and atelectasis. Since most cases are benign, it is still crucial for clinicians to detect complications early for further management.

Simultaneous assessment of central nervous and respiratory systems using jacketed telemetry in socially-housed rats: Application of the "3Rs" principles in core battery safety pharmacology studies

Central nervous (CNS) and respiratory systems are routinely investigated in safety pharmacology core battery studies. For small molecules, the assessment of both vital organ systems is frequently done in rats in two distinct studies. With the advent of a miniaturized technology of jacketed external telemetry for rats (DECRO system), the simultaneous assessment of modified Irwin's or functional observational battery (FOB) test and respiratory (Resp) studies has become possible within a single study. Therefore, the objectives of this study were to perform the FOB and the Resp studies simultaneously in pair-housed rats fitted with jacketed telemetry, and to assess the feasibility and the outcome of this combination in control, baclofen, caffeine, and clonidine treated groups, i.e., with three agents having both respiratory and CNS effects. Our results provided evidence that performing both Resp and FOB assessment simultaneously in the same rat was feasible and the outcome was successful. The expected CNS and respiratory effects of the 3 reference compounds were accurately captured in each assay confirming the results' relevance. In addition, heart rate and activity level were recorded as additional parameters making this design as an enhanced approach for nonclinical safety assessment in rats. This work provides clear evidence that the "3Rs" principles can be effectively applied in core battery safety pharmacology studies while remaining in compliance with worldwide regulatory guidelines. Both reduction in animal use and refinements in procedures are demonstrated with this model.

Non invasive jacketed telemetry in socially-housed rats for a combined assessment of respiratory system, electrocardiogram and activity using the DECRO system

Respiratory and cardiovascular systems are among the vital organ systems that should be studied in safety pharmacology core battery test. Non-invasive jacketed external telemetry technology that enables concomitant monitoring of both systems has been available and used widely for non-rodent species. Recently, the DECRO system, a miniaturized technology system in line with the "3Rs" principles, has been developed to provide a similar approach in rats. However, data to evaluate this system in socially-housed rats is lacking. Therefore, the objectives of this study were to determine the tolerability and the material integrity of this novel solution in pair-housed rats in two conditions: i) in a single session of 22 h simulating a stand-alone safety pharmacology study design, and ii) in three repeated sessions of 22 h each, simulating the inclusion of safety pharmacology endpoints in a 1-month toxicology study. In both conditions, the GABA_B receptor agonist baclofen was used as a reference compound inducing cardiorespiratory changes. Our results provided evidence that this novel solution was well tolerated, the material was resistant to deterioration and that it allowed the accurate recording, in a non-invasive manner, of cardiorespiratory parameters and activity level in freely moving, pair-housed rats in the above two conditions. In addition, the expected respiratory depressant effects of baclofen were recorded. These results pave the way for considering this novel solution as an enhanced approach for nonclinical safety assessment in rats.

Baclofen (fun drug) and ethanol combined poisoning in humans: A histopathology and morphometry model

BACKGROUND

- This study intends to address the scarcity of data regarding the pathogenesis of Baclofen poisoning in humans, which has seen a recent increase, worldwide, especially amongst the young people. Another reason for the conduction of this study was lack of the substantial data about the histo-pathological findings of lungs, in synergistic toxicity of Baclofen with Ethanol, in-spite of it being very common in humans, and both being respiratory depressant with similar mechanism of action.

PURPOSE

- The authors aimed to understand the pathogenesis of fatal poisonings in humans due to Baclofen in combination with Ethanol via an animal research model. The enhancement of the overall scientific literature by extending research along the lines of the handful studies available in this regard was another adjunct goal of the study.

MATERIAL AND METHODS

Fifteen Wistar rats were divided into control and test group of five and ten subjects respectively. The test group was further divided into two sub-groups of five each, with Baclofen administered to one, and it in conjunction with Ethanol to the other, in lowest dosages adjusted for the humans. Rats in both the groups were euthanized by dislocation of the cervical vertebrae for the histopathology examination.

RESULTS

Capillary and venous plethora, hemorrhages in the inter-alveolar septi, hemorrhages into the alveoli and sludging was seen in the 1st sub-group. The plethora of venules, capillaries and arterioles, with sludging by the WBC (white blood corpuscle) infiltrates was seen in the 2nd sub-group. Desquamation of the ciliated epithelium and edematous thickening of the intra-alveolar septi, along with features suggestive of the peri-vascular edema was seen in the 2nd sub-group. The morphometric analysis of the micro vessels showed a significantly higher value of the arteriolar diameter in the 2nd sub-group, in comparison to 1st, but the venular diameter in the two sub-groups did not differ to any extent.

Antiemetic effects of baclofen in a shrew model of postoperative nausea and vomiting: Whole-transcriptome analysis in the nucleus of the solitary tract

Aims

The molecular genetic mechanisms underlying postoperative nausea and vomiting (PONV) in the brain have not been fully elucidated. This study aimed to determine the changes in whole transcriptome in the nucleus of the solitary tract (NTS) in an animal model of PONV, to screen a drug candidate and to elucidate the molecular genetic mechanisms of PONV development.

Methods

Twenty‐one female musk shrews were assigned into three groups: the Surgery group (shrew PONV model, n = 9), the Sham group (n = 6), and the Naïve group (n = 6). In behavioral studies, the main outcome was the number of emetic episodes. In genetic experiments, changes in the transcriptome in the NTS were measured. In a separate study, 12 shrews were used to verify the candidate mechanism underlying PONV.

Results

A median of six emetic episodes occurred in both the Sham and Surgery groups. Whole‐transcriptome analysis indicated the inhibition of the GABA_B receptor‐mediated signaling pathway in the PONV model. Baclofen (GABA_B receptor agonist) administration eliminated emetic behaviors in the shrew PONV model.

Conclusions

Our findings suggest that the GABA_B receptor‐mediated signaling pathway is involved in emesis and that baclofen may be a novel therapeutic or prophylactic agent for PONV.

Novel Agents for the Pharmacological Treatment of Alcohol Use Disorder

Alcohol use disorder (AUD) is a highly prevalent but severely under-treated disorder, with only three widely-approved pharmacotherapies. Given that AUD is a very heterogeneous disorder, it is unlikely that one single medication will be effective for all individuals with an AUD. As such, there is a need to develop new, more effective, and diverse pharmacological treatment options for AUD with the hopes of increasing utilization and improving care. In this qualitative literature review, we discuss the efficacy, mechanism of action, and tolerability of approved, repurposed, and novel pharmacotherapies for the treatment of AUD with a clinical perspective. Pharmacotherapies discussed include: disulfiram, acamprosate, naltrexone, nalmefene, topiramate, gabapentin, varenicline, baclofen, sodium oxybate, aripiprazole, ondansetron, mifepristone, ibudilast, suvorexant, prazosin, doxazosin, N-acetylcysteine, GET73, ASP8062, ABT-436, PF-5190457, and cannabidiol. Overall, many repurposed and novel agents discussed in this review demonstrate clinical effectiveness and promise for the future of AUD treatment. Importantly, these medications also offer potential improvements towards the advancement of precision medicine and personalized treatment for the heterogeneous AUD population. However, there remains a great need to improve access to treatment, increase the menu of approved pharmacological treatments, and de-stigmatize and increase treatment-seeking for AUD.

Baclofen-induced encephalopathy in overdose - Modeling of the electroencephalographic effect/concentration relationships and contribution of tolerance in the rat

Baclofen, a γ-amino-butyric acid type-B receptor agonist with exponentially increased use at high-dose to facilitate abstinence in chronic alcoholics, is responsible for increasing poisonings. Baclofen overdose may induce severe encephalopathy and electroencephalographic (EEG) abnormalities. Whether prior prolonged baclofen treatment may influence the severity of baclofen-induced encephalopathy in overdose has not been established. We designed a rat study to characterize baclofen-induced encephalopathy, correlate its severity with plasma concentrations and investigate the contribution of tolerance. Baclofen-induced encephalopathy was assessed using continuous EEG and scored based on a ten-grade scale. Following the administration by gavage of 116 mg/kg baclofen, EEG rapidly and steadily impaired resulting in the successive onset of deepening sleep followed by generalized periodic epileptiform discharges and burst-suppressions. Thereafter, encephalopathy progressively recovered following similar phases in reverse. Periodic triphasic sharp waves, non-convulsive status epilepticus and even isoelectric signals were observed at the most critical stages. Prior repeated baclofen administration resulted in reduced severity (peak: grade 7 versus 9; peak effect length: 382 ± 40 versus 123 ± 14 min, P = 0.008) and duration of encephalopathy (18 versus > 24 h, P = 0.0007), supporting the acquisition of tolerance. The relationship between encephalopathy severity and plasma baclofen concentrations fitted a sigmoidal E_max model with an anticlockwise hysteresis loop suggesting a hypothetical biophase site of action. The baclofen concentration producing a response equivalent to 50% of E_max was significantly reduced (8947 μg/L, ±11.3% versus 12,728 μg/L, ±24.0% [mean, coefficient of variation], P = 0.03) with prior prolonged baclofen administration. In conclusion, baclofen overdose induces early-onset and prolonged marked encephalopathy that is significantly attenuated by prior repeated baclofen treatment. Our findings suggest a possible role for the blood-brain barrier in the development of tolerance; however, its definitive involvement remains to be demonstrated.