Flupirtine, an Effective Analgesic, but Hepatotoxicity Should Limit Its Use

Signals from randomized clinical trials predicting hepatotoxicity of flupirtine: systematic review

BACKGROUND

The aim of this study was to systematically review clinical trials evaluating the flupirtine to identify any biochemical or clinical indicators that could signal serious hepatotoxicity.

METHODS

This systematic review included randomized controlled trials (RCTs) evaluating flupirtine-containing medicines for any clinical condition. Trials involving any population, comparator, or outcome were considered eligible for inclusion. A comprehensive search was conducted in Embase, MEDLINE, and CENTRAL from their inception until August 14, 2023. The risk of bias (RoB) in the included trials was assessed using Cochrane's 2011 RoB tool. Due to the heterogeneity of the included trials, a meta-analysis could not be performed.

RESULTS

A total of 35 trials published between 1983 and 2022 were included in this systematic review, with 1408 participants receiving flupirtine. Only five trials reported any data related to liver function tests. Among these, four trials documented transient, asymptomatic liver abnormalities that returned to normal after the trial period, while one trial was prematurely terminated. One trial reported normal liver test results in all participants. Of the three trials published after 2018, only one acknowledged the withdrawal of flupirtine from the European market. The majority of risk of bias (RoB) domains were classified as having an unclear risk of bias.

CONCLUSION

Published RCTs did not report any evidence of serious hepatotoxicity associated with flupirtine based on the available biochemical or clinical data. However, liver function test results were reported in only 5 out of 35 included trials. Published RCTs are not reliable information about flupirtine-related hepatotoxicity.

REGISTRATION

Protocol was published in PROSPERO (CRD42018085123).

Neuroprotection by 4R-cembranoid against Gulf War Illness-related Chemicals is mediated by ERK, PI3K, and CaMKII pathways

Gulf War Illness (GWI) has been consistently linked to exposure to pyridostigmine (PB), N,N-Diethyl-meta-toluamide (DEET), permethrin (PER), and traces of sarin. In this study, diisopropylfluorophosphate (DFP, sarin surrogate) and the GWI-related chemicals were found to reduce the number of functionally active neurons in rat hippocampal slices. These findings confirm a link between GWI neurotoxicants and N-Methyl-D-Aspartate (NMDA)-mediated excitotoxicity, which was successfully reversed by Edelfosine (a phospholipase Cβ (PLCβ3) inhibitor) and Flupirtine (a Kv7 channel agonist). To test whether 4R-cembranoid (4R), a nicotinic α7 acetylcholinesterase receptor (α7AChR) modulator known for its neuroprotective properties, can restore hippocampal neurons from glutamate-induced neurotoxicity, we exposed rat hippocampal slices with DFP for 10 min followed by 60 min treatment with 4R. We investigated the 4R mechanisms of neuroprotection after preincubation with LY294002, PD98059, and KN-62. The inhibition of the phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MEK1/2), and calcium/calmodulin-dependent protein kinase (CaMKII) abrogated the protective effect of 4R against DFP-induced neurotoxicity. In separate experiments, after incubation with DFP, followed by 4R for 1 h, cellular extracts were prepared for Western blotting of phospho-Akt, phospho-GSK3β, phosphorylated extracellular signal-regulated kinase (ERK)1/2, CaMKII and cAMP response element-binding protein (CREB). Our results show that DFP induces neuronal dysfunction by dephosphorylation, while 4R restores the phosphorylation of Akt, GSK3, ERK1/2, CREB, and CaMKII. Moreover, our proteomics analysis supported the notion that 4R activates additional signaling pathways related to enhancing neuronal signaling, synaptic plasticity, and apoptotic inhibition to promote cell survival against DFP, offering biomarkers for developing treatment against GWI.

Pharmacological Activation of Neuronal Voltage-Gated Kv7/KCNQ/M-Channels for Potential Therapy of Epilepsy and Pain

Native M-current is a low-threshold, slowly activating potassium current that exerts an inhibitory control over neuronal excitability. The M-channel is primarily co-assembled by heterotetrameric Kv7.2/KCNQ2 and Kv7.3/KCNQ3 subunits that are specifically expressed in the brain and peripheral nociceptive and visceral sensory neurons in the spinal cord. Reduction of M-channel function leads to neuronal hyperexcitability that defines the fundamental mechanism of neurological disorders such as epilepsy and pain, indicating that pharmacological activation of Kv7/KCNQ/M-channels may serve the basis for the therapy. The well-known KCNQ opener retigabine (ezogabine or Potiga) was approved by FDA in 2011 as an anticonvulsant used for an adjunctive treatment of partial epilepsies. Unfortunately, retigabine was discontinued in 2017 due to its side effects of blue-colored appearance of the skin and eyes after prolonged intake. In addition, flupirtine, a structural derivative of retigabine and a centrally acting non-opioid analgesic, was also withdrawn in 2018 for liver toxicity. Fortunately, these side effects are compound-structures related and can be avoided. Thus, further identification and development of novel potent and selective Kv7 channel openers may lead to an effective therapy with improved safety window for anti-epilepsy and anti-nociception.

Hulk-Like Urine: A Case of Green Urine Caused by Flupirtine Intoxication

Acute intoxications are common causes of admission to the Emergency Department (ED). Flupirtine is a non-opioid analgesic, originally used for acute and chronic pain. Because of several reports of severe liver toxicity, its use was limited to acute pain in 2013 by the European Medicines Agency. Although withdrawn from the European market in March 2018, there are still flupirtine tablets in many households, and most people are unaware of the hazards they might be facing. A 58-year-old man was admitted to the ED after a suicide attempt with 1 g of flupirtine. He was lethargic and confused but presented no focal neurological deficits or other symptoms, and the rest of his clinical examination was unremarkable. His cerebral CAT and blood chemistry showed no alterations. The only remarkable feature was that he had green urine. After a careful literature search, a similar case was found caused by flupirtine intoxication. After 24 hours of vigilance in the ED, he improved his neurological status and his urine lost part of its greenish color. He was then transferred to the Psychiatric Department, where he presented a complete remission of the clinical alterations. A follow-up check-up showed no permanent deficits.

Liver Transplant Due to Flupirtine-Induced Acute Liver Failure

OBJECTIVES

Acute drug-induced liver failure is a rare indication for liver transplant. There is only one case of flupirtine-induced liver failure requiring transplant in the literature. In February 2018, the European Medicines Agency issued a withdrawal of approval for flupirtine medication in European countries as a result of the risk of acute liver failure.

MATERIALS AND METHODS

The aim of this study was a German-wide collection of data regarding patients with liver transplant as a result of flupirtine-associated liver failure.

RESULTS

A total of 9 patients received transplants. All patients were women with a mean age of 43 years. Indication for flupirtine medication was musculoskeletal symptoms and migraine headache. The medication was taken over a period of approximately 3 months. All patients developed progressive acute liver failure, and no patient had previous chronic liver disease or cirrhosis. The mean laboratory Model for End Stage Liver Disease score for the patients was 31 ± 7 at time of transplant. Eight of the 9 patients were listed as "high urgency" for transplant. After transplant, they had an uneventful course with a prolonged mean intensive care unit stay of 13 ± 8.7 days. The whole hospitalization time was 43 ± 21 days.

CONCLUSIONS

This is the largest published series of patients who received liver transplant after a drug-induced acute liver failure from flupirtine medication.