Mexiletine and its Interactions with Classical Antiepileptic Drugs: An Isobolographic Analysis

KM-408, a novel phenoxyalkyl derivative as a potential anticonvulsant and analgesic compound for the treatment of neuropathic pain

BACKGROUND

Epilepsy frequently coexists with neuropathic pain. Our approach is based on the search for active compounds with multitarget profiles beneficial in terms of potential side effects and on the implementation of screening for potential multidirectional central activity.

METHODS

Compounds were synthesized by means of chemical synthesis. After antiseizure and neurotoxicity screening in vivo, KM-408 and its enantiomers were chosen for analgesic activity evaluations. Further safety studies included acute toxicity in mice, the effect on normal electrocardiogram and on blood pressure in rats, whole body plethysmography in rats, and in vitro and biochemical assays. Pharmacokinetics has been studied in rats after iv and po administration. Metabolism has been studied in vivo in rat serum and urine. Radioligand binding studies were performed as part of the mechanism of action investigation.

RESULTS

Selected results for KM-408: K_i sigma = 7.2*10^-8; K_i 5-HT_1A = 8.0*10^-7; ED₅₀ MES (mice, ip) = 13.3 mg/kg; formalin test (I phase, mice, ip)-active at 30 mg/kg; SNL (rats, ip)-active at 6 mg/kg; STZ-induced pain (mice, ip)-active at 1 mg/kg (von Frey) and 10 mg/kg (hot plate); hot plate test (mice, ip)-active at 30 mg/kg; ED₅₀ capsaicin test (mice, ip) = 18.99 mg/kg; tail immersion test (mice)-active at 0.5%; corneal anesthesia (guinea pigs)-active at 0.125%; infiltration anesthesia (guinea pigs)-active at 0.125%.

CONCLUSIONS

Within the presented study a novel compound, R,S-2-((2-(2-chloro-6-methylphenoxy)ethyl)amino)butan-1-ol hydrochloride (KM-408) with dual antiseizure and analgesic activity has been developed for potential use in neuropathic pain treatment.

Effects of Antiarrhythmic Drugs on Antiepileptic Drug Action-A Critical Review of Experimental Findings

Severe cardiac arrhythmias developing in the course of seizures increase the risk of SUDEP (sudden unexpected death in epilepsy). Hence, epilepsy patients with pre-existing arrhythmias should receive appropriate pharmacotherapy. Concomitant treatment with antiarrhythmic and antiseizure medications creates, however, the possibility of drug–drug interactions. This is due, among other reasons, to a similar mechanism of action. Both groups of drugs inhibit the conduction of electrical impulses in excitable tissues. The aim of this review was the analysis of such interactions in animal seizure models, including the maximal electroshock (MES) test in mice, a widely accepted screening test for antiepileptic drugs.

Amiodarone Enhances Anticonvulsive Effect of Oxcarbazepine and Pregabalin in the Mouse Maximal Electroshock Model

Accumulating experimental studies show that antiarrhythmic and antiepileptic drugs share some molecular mechanisms of action and can interact with each other. In this study, the influence of amiodarone (a class III antiarrhythmic drug) on the antiseizure action of four second-generation antiepileptic drugs was evaluated in the maximal electroshock model in mice. Amiodarone, although ineffective in the electroconvulsive threshold test, significantly potentiated the antielectroshock activity of oxcarbazepine and pregabalin. Amiodarone, given alone or in combination with oxcarbazepine, lamotrigine, or topiramate, significantly disturbed long-term memory in the passive-avoidance task in mice. Brain concentrations of antiepileptic drugs were not affected by amiodarone. However, the brain concentration of amiodarone was significantly elevated by oxcarbazepine, topiramate, and pregabalin. Additionally, oxcarbazepine and pregabalin elevated the brain concentration of desethylamiodarone, the main metabolite of amiodarone. In conclusion, potentially beneficial action of amiodarone in epilepsy patients seems to be limited by neurotoxic effects of amiodarone. Although results of this study should still be confirmed in chronic protocols of treatment, special precautions are recommended in clinical conditions. Coadministration of amiodarone, even at low therapeutic doses, with antiepileptic drugs should be carefully monitored to exclude undesired effects related to accumulation of the antiarrhythmic drug and its main metabolite, desethylamiodarone.

Interactions of antiepileptic drugs with drugs approved for the treatment of indications other than epilepsy

Introduction: Comorbidities of epilepsy may significantly interfere with its treatment as diseases in the general population are also encountered in epilepsy patients and some of them even more frequently (for instance, depression, anxiety, or heart disease). Obviously, some drugs approved for other than epilepsy indications can modify the anticonvulsant activity of antiepileptics. Areas covered: This review highlights the drug-drug interactions between antiepileptics and aminophylline, some antidepressant, antiarrhythmic (class I-IV), selected antihypertensive drugs and non-barbiturate injectable anesthetics (ketamine, propofol, etomidate, and alphaxalone). The data were reviewed mainly from experimental models of seizures. Whenever possible, clinical data were provided. PUBMED data base was the main search source.Expert opinion: Aminophylline generally reduced the protective activity of antiepileptics, which, to a certain degree, was consistent with scarce clinical data on methylxanthine derivatives and worse seizure control. The only antiarrhythmic with this profile of action was mexiletine when co-administered with VPA. Among antidepressants and non-barbiturate injectable anesthetics, trazodone, mianserin and etomidate or alphaxalone, respectively, negatively affected the anticonvulsant action of some antiepileptic drugs. Clinical data indicate that only amoxapine, bupropion, clomipramine and maprotiline should be used with caution. Possibly, drugs reducing the anticonvulsant potential of antiepileptics should be avoided in epilepsy patients.

Anticonvulsant and analgesic in neuropathic pain activity in a group of new aminoalkanol derivatives

As part of the presented research, thirteen new aminoalkanol derivatives were designed and obtained by chemical synthesis. In vivo studies (mice, i.p.) showed anticonvulsant activity (MES) of nine compounds, and in the case of one compound (R,S-trans-2-((2-(2,3,5-trimethylphenoxy)ethyl)amino)cyclohexan-1-ol, 4) both anticonvulsant (ED₅₀ MES = 15.67 mg/kg, TD₅₀ rotarod = 78.30 mg.kg, PI = 5.00) and analgesic activity (OXA-induced neuropathic pain, active at 15 mg/kg). For selected active compounds additional in vitro studies have been performed, including receptor studies (5-HT_1A), evaluation of antioxidant activity (DPPH assay), metabolism studies as well as safety panel (mutagenicity, safety in relation to the gastrointestinal flora, cytotoxicity towards astrocytes as well as impact on their proliferation and cell cycle).

Dronedarone (a multichannel blocker) enhances the anticonvulsant potency of lamotrigine, but not that of lacosamide, pregabalin and topiramate in the tonic-clonic seizure model in mice

Accumulating experimental evidence indicates that some recently licensed antiarrhythmic drugs, including dronedarone (a multichannel blocker) play a crucial role in initiation of seizures in both, in vivo and in vitro studies. Some of these antiarrhythmic drugs elevate the threshold for maximal electroconvulsions and enhance the anticonvulsant potency of classical antiepileptic drugs in preclinical studies. This study was aimed at determining the influence of dronedarone (an antiarrhythmic drug) on the anticonvulsant potency of four novel antiepileptic drugs (lacosamide, lamotrigine, pregabalin and topiramate) in the maximal electroshock-induced seizure model in mice. To exclude any potential pharmacokinetic contribution of dronedarone to the observed interactions, total brain concentrations of antiepileptic drugs were measured. Dronedarone (50 mg/kg, i.p.) significantly enhanced the anticonvulsant potency of lamotrigine, by reducing its ED₅₀ value from 7.67 mg/kg to 4.19 mg/kg (P < 0.05), in the maximal electroshock-induced seizure test in mice. On the contrary, dronedarone (50 mg/kg, i.p.) did not affect the anticonvulsant properties of lacosamide, pregabalin or topiramate in the maximal electroshock-induced seizure test in mice. Measurement of total brain concentrations of lamotrigine revealed that dronedarone did not significantly alter total brain concentrations of lamotrigine in experimental animals. Additionally, the combination of dronedarone with pregabalin significantly impaired motor coordination in animals subjected to the chimney test. In contrast, the combinations of other studied antiepileptic drugs with dronedarone had no negative influence on motor coordination in mice. It is advisable to combine dronedarone with lamotrigine to enhance the anticonvulsant potency of the latter drug. The combinations of dronedarone with lacosamide, pregabalin and topiramate resulted in neutral interactions in the maximal electroshock-induced seizure test in mice. However, a special caution is advised to patients receiving both, pregabalin and dronedarone due to some possible adverse effects that might occur with respect to motor coordination.

Interactions of Mexiletine with Novel Antiepileptic Drugs in the Maximal Electroshock Test in Mice: An Isobolographic Analysis

The aim of the study was to evaluate precisely the type of interactions between mexiletine (an antiarrhythmic drug) and four new generation antiepileptic drugs: lamotrigine, oxcarbazepine, topiramate and pregabalin in the maximal electroshock test in mice (MES). The isobolographic analysis was used to assess the nature of interactions between the tested drugs. Total brain concentrations of antiepileptics were also measured to detect possible pharmacokinetic interactions. The results obtained indicated that the mixture of mexiletine and pregabalin at the fixed ratios of 1:1 and 3:1 led to supra-additive interaction in terms of seizure suppression, while the proportion of 1:3 occurred additive. Synergism was also demonstrated for the combination of mexiletine and topiramate in all three proportions. Combinations of mexiletine with lamotrigine and mexiletine with oxcarbazepine were found to be additive. Adverse-effect profiles of mexiletine, antiepileptics and drug combinations were evaluated in the chimney test (motor coordination) and step-through passive-avoidance task (long-term memory). Mexiletine and drug combinations did not impair long-term memory. Moreover, all combinations of mexiletine with lamotrigine, oxcarbazepine and topiramate had no significant effect on motor coordination. However, the results from the chimney test indicated that pregabalin, administered alone at its ED₅₀ dose from the MES-test, significantly impaired motor performance. Similar adverse effects were observed when mexiletine was co-administered with pregabalin at the fixed-dose ratio combinations of 1:1 and 1:3. However, reduction of pregabalin dose at the fixed ratio of 3:1 seems to prevent significant motor impairment. The results may indicate that mexiletine can be considered as an adjunctive drug in antiepileptic treatment, particularly in patients with concomitant cardiac arrhythmia.

Amiodarone, a multi-channel blocker, enhances anticonvulsive effect of carbamazepine in the mouse maximal electroshock model

Cardiac arrhythmia may occur in the course of epilepsy. Simultaneous therapy of the two diseases might be complicated by drug interactions since antiarrhythmic and antiepileptic agents share some molecular targets. The aim of this study was to evaluate the influence of amiodarone, an antiarrhythmic drug working as a multi-channel blocker, on the protective activity of four classical antiepileptic drugs in the maximal electroshock test in mice. Amiodarone at doses up to 75 mg/kg did not affect the electroconvulsive threshold in mice. Acute amiodarone at the dose of 75 mg/kg significantly potentiated the anticonvulsive effect of carbamazepine, but not that of valproate, phenytoin or phenobarbital in the maximal electroshock-induced seizures in mice. The antiarrhythmic agent and its combinations with antiepileptic drugs did not impair motor performance or long-term memory in mice, except for the combination of amiodarone and phenobarbital. Brain concentrations of antiepileptic drugs were not changed. Despite favourable impact of amiodarone on the anticonvulsive action of carbamazepine in the maximal electroshock, co-administration of the two drugs should be carefully monitored in clinical conditions. Further studies are necessary to evaluate effects of chronic treatment with amiodarone on seizure activity and the action of antiepileptic drugs.

Influence of propafenone on the anticonvulsant activity of various novel antiepileptic drugs in the mouse maximal electroshock model

BACKGROUND

The main mechanism of action of propafenone (antiarrhythmic drug) involves the inhibition of the fast inward sodium current during phase 0 of the action potential. Sodium channel-blocking activity is also characteristic for some antiepileptic drugs. Therefore, it could be assumed that propafenone may also affect seizures. In the present study, we evaluated the effect of propafenone on the protective effect of oxcarbazepine, lamotrigine, topiramate and pregabalin against the maximal electroshock-induced seizures in mice.

METHODS

Anticonvulsant activity of propafenone was assessed with the maximal electroshock seizure threshold (MEST) test. Influence of propafenone on the anticonvulsant activity of antiepileptic drugs was estimated in the mouse maximal electroshock model (MES). Drug-related adverse effects were determined in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Brain concentrations of antiepileptics were assessed by fluorescence polarization immunoassay.

RESULTS

Propafenone at doses 60-90mg/kg significantly increased the threshold of seizures, in turn at doses 5-50mg/kg did not affect this parameter. Administration of propafenone at the subthreshold dose of 50mg/kg increased antielectroshock activity of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine. As regards adverse effects, propafenone alone and in combination with antiepileptic drugs did not significantly impair motor coordination or long-term memory in mice. Propafenone (50mg/kg) significantly increased the brain level of pregabalin. Brain concentrations of topiramate and oxcarbazepine were not affected.

CONCLUSION

Our findings show that propafenone has own anticonvulsant action and enhances efficacy of oxcarbazepine, topiramate and pregabalin, but not that of lamotrigine, at least in experimental condition.