Mutual interaction between remacemide hydrochloride and carbamazepine: two drugs with active metabolites

Isobolographic analysis of interactions between remacemide and conventional antiepileptic drugs in the mouse model of maximal electroshock

Using the mouse maximal electroshock-induced seizure model, indicative of tonic-clonic seizures in humans, the present study was aimed at characterizing the interaction between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. Isobolographic analysis indicated additive interactions between remacemide and valproate, carbamazepine, and phenytoin (for all fixed ratios of tested drugs: 1:3, 1:1, and 3:1). Additivity was also observed between remacemide and phenobarbital applied in proportions of 1:1 and 3:1. In contrast, the combination of remacemide and phenobarbital at the fixed-ratio of 1:3 resulted in antagonism. Neither motor performance nor long-term memory was impaired by remacemide or by carbamazepine, phenobarbital, phenytoin, and valproate whether or not these drugs were administered singly or in combination. In combination with remacemide, brain concentrations of carbamazepine, phenobarbital, and phenytoin were increased by 71, 21, and 16%, respectively. Although brain valproate concentrations were unaffected by remacemide co-administration, brain concentrations of remacemide and its active metabolite, desglycinyl-remacemide, were increased by 68 and 162%, respectively. In contrast, phenobarbital co-administration was associated with decreases in brain remacemide (27%) and desglycinyl-remacemide (9%) concentrations, whereas only remacemide concentrations (increased by 131%) were affected by carbamazepine co-administration. In conclusion, significant and desirable pharmacodynamic interactions were observed between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. However, the concurrent pharmacokinetic interactions associated with remacemide complicate these observations and do not make remacemide a good candidate for adjunctive treatment of epilepsy.

Influence of cytochrome P450 induction on the pharmacokinetics and pharmacodynamics of remacemide hydrochloride

Remacemide hydrochloride (RMD) is a putative anticonvulsant agent with an active metabolite, desglycinyl-remacemide (DGR) and a broad spectrum of activity in experimental seizure models. In clinical trials, however, the efficacy of RMD is questionable. In the case of add-on studies, the inconclusive findings may be related to pharmacokinetic interactions between RMD and established antiepileptic drugs. We have investigated the influence of cytochrome P450 (CYP(450)) induction following repeated treatment with phenobarbital (PB) on the pharmacokinetics and pharmacodynamics of RMD in mice. Pre-treatment with PB (80 mg/kg; once daily for 4 days) significantly increased CYP(450) content and activity in mouse liver. This was associated with a consistent reduction in the brain concentrations of both RMD and DGR and attenuation of the anticonvulsant effects of RMD in the maximal electroshock model. Pharmacokinetic analysis suggested that DGR was proportionately more susceptible to CYP(450) induction than the parent compound. As the principal active moiety, the selectively enhanced metabolism of DGR under induced conditions may underlie the debatable findings of add-on trials with RMD in refractory epilepsy. However, this hypothesis does not explain the similarly questionable efficacy of RMD monotherapy in newly diagnosed epilepsy, an observation that may have wider pharmacological implications.

Remacemide hydrochloride as an add-on therapy in epilepsy: a randomized, placebo-controlled trial of three dose levels (300, 600 and 800 mg/day) in a B.I.D. regimen

Remacemide hydrochloride is a low-affinity, non-competitive NMDA receptor channel blocker under investigation for the treatment of epilepsy. This double-blind, placebo-controlled, multicentre study assessed the safety and efficacy of adjunctive remacemide hydrochloride or placebo, in adult patients with refractory epilepsy who were already taking up to three antiepileptic drugs (including an enzyme-inducer). Patients (n= 262) were randomized to one of three doses of remacemide hydrochloride (300, 600 or 800 mg/day) or placebo, in a B.I.D. regimen, for up to 14 weeks. Plasma concentrations of carbamazepine (CBZ) and phenytoin (PHT) were controlled throughout. Patients recorded their seizures on a diary card. There was an increase in the percentage of responders (defined as a reduction in seizure frequency from baseline > or = 50 %), from 15 % (9/60) with placebo, to 30 % (18/60) in the 800 mg/day group. A pairwise comparison between remacemide hydrochloride 800 mg/day and placebo was statistically significant (P = 0.049). Most reported adverse events (mainly CNS and gastrointestinal) were mild or moderate in severity and dose-dependent. Adjunctive remacemide hydrochloride treatment was associated with a higher, dose-related responder rate compared with placebo. The difference reached significance at the highest dose tested (800 mg/day). Remacemide hydrochloride was well tolerated.

Remacemide hydrochloride as an add-on therapy in epilepsy: a randomized, placebo-controlled trial of three dose levels (300, 600 and 1200 mg/day) in a Q.I.D. regimen

Remacemide hydrochloride is a low-affinity, non-competitive N-methyl-D-aspartic acid (NMDA) receptor channel blocker, under investigation in epilepsy. This double-blind, placebo-controlled, multicentre study assessed the safety and efficacy of remacemide hydrochloride or placebo, as adjunctive therapy, in 252 adult patients with refractory epilepsy who were already taking up to three antiepileptic drugs (including an enzyme-inducer). Patients were randomized to one of three doses of remacemide hydrochloride (300, 600 or 1200 mg /day) or placebo Q.I.D., for up to 15 weeks. An increasing percentage of responders (defined as a reduction in seizure frequency from baseline of > or =50%) was seen with increasing remacemide hydrochloride dose. At 1200 mg /day, 23% of patients were responders compared with 7% on placebo. This difference was significant (P = 0.016), as was the overall difference between treatments (P = 0.038). Adverse events: dizziness, abnormal gait, gastrointestinal disturbance, somnolence, diplopia and fatigue were mild or moderate in severity. Carbamazepine and phenytoin plasma concentrations were well controlled and maintained within target ranges, with no evidence of improved seizure control due to increases in the concentrations of these drugs. A dose-dependent, significant, increase in responders following adjunctive remacemide hydrochloride compared with placebo was observed. Remacemide hydrochloride was well tolerated.

Evaluation of a pharmacokinetic interaction between remacemide hydrochloride and phenobarbitone in healthy males

AIMS

To determine whether there is a pharmacokinetic interaction between the antiepileptic drugs remacemide and phenobarbitone.

METHODS

In a group of 12 healthy adult male volunteers, the single dose and steady-state kinetics of remacemide were each determined twice, once in the absence and once in the presence of phenobarbitone. The effect of 7 days remacemide intake on initial steady-state plasma phenobarbitone concentrations was also investigated.

RESULTS

Apparent remacemide clearance (CL/F) and elimination half-life values were unchanged after 7 days intake of the drug in the absence of phenobarbitone (1.25 +/- 0.32 vs 1.18 +/- 0.22 l kg(-1) h(-1) and 3.29 +/- 0.68 vs 3.62 +/- 0.85 h, respectively). Concomitant administration of remacemide with phenobarbitone resulted in an increase in the estimated CL/F of remacemide (1.25 +/- 0.32 vs 2.09 +/-0.53 l kg-1 h-1), and a decreased remacemide half-life (3.29 +/- 0.68 vs 2.69 +/- 0.33 h). The elimination of the desglycinyl metabolite of remacemide also appeared to be increased after the phenobarbitone intake (half-life 14.72 +/- 2.82 vs 9.61 +/- 5.51 h, AUC 1532 +/- 258 vs 533 +/- 281 ng ml(-1) h). Mean plasma phenobarbitone concentrations rose after 7 days of continuing remacemide intake (12.67 +/- 1.31 vs 13.86 +/- 1.81 microgram ml(-1)).

CONCLUSIONS

Phenobarbitone induced the metabolism of remacemide and that of its desglycinyl metabolite. Remacemide did not induce its own metabolism, but had a modest inhibitory effect on the clearance of phenobarbitone.

Progress report on new antiepileptic drugs: a summary of the Fifth Eilat Conference (EILAT V)

The Fifth Eilat Conference on New Antiepileptic Drugs (AEDs) took place at the Dan Hotel, Eilat, Israel, 25-29 June 2000. Basic scientists, clinical pharmacologists and neurologists from 20 countries attended the conference, whose main themes included recognition of unexpected adverse effects, new indications of AEDs, and patient-tailored AED therapy. According to tradition, the central part of the conference was devoted to a review of AEDs in development, as well to updates on AEDs that have been marketed in recent years. This article summarizes the information presented on drugs in preclinical and clinical development, including AWD 131-138, DP-valproate, harkoseride, LY300164, NPS 1776, NW 1015, pregabalin, remacemide, retigabine, rufinamide and valrocemide. The potential value of an innovative strategy, porcine embryonic GABAergic cell transplants, is also discussed. Finally, updates on felbamate, fosphenytoin, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, zonisamide, and the antiepileptic vagal stimulator device are presented.

Remacemide hydrochloride: a placebo-controlled, one month, double-blind assessment of its safety, tolerability and pharmacokinetics as adjunctive therapy in patients with epilepsy

Forty patients (33 male, 7 female) with refractory epilepsy were randomized to receive ascending weekly doses of adjunctive remacemide hydrochloride in a b.i.d. or q.i.d. regimen, or placebo for up to 1 month. Assessments included routine physical examination and laboratory tests, recording of adverse events and seizure frequency, and neuropsychological tests. Trough plasma concentrations of concomitant AEDs were measured at weekly intervals. Trough plasma concentrations of remacemide and its desglycinyl metabolite were measured before each dose increment, and complete 24-hour profiles were measured at steady state following administration of 600 mg day(-1)and 1200 mg day(-1). A daily dose of 1200 mg was well tolerated in a q.i.d. regimen and up to 800 mg was well tolerated in a b.i.d. regimen. The most common adverse events were dizziness, diplopia, dyspepsia and abdominal pain. On some occasions, these were considered to be related to raised concentrations of concomitant AEDs. No adverse effects were observed on seizure frequency. Neuropsychology tests revealed no significant changes. Remacemide and the desglycinyl metabolite demonstrated dose proportional pharmacokinetics over the dose range tested.

A placebo-controlled, double-blind cross-over trial of adjunctive one month remacemide hydrochloride treatment in patients with refractory epilepsy

The efficacy, safety and pharmacokinetics of adjunctive remacemide hydrochloride, a novel, low-affinity non-competitive NMDA receptor channel blocker, were investigated in 28 adult patients with refractory epilepsy. This was a randomized double-blind placebo-controlled cross-over study with five 4-week periods (baseline, treatment 1, washout, treatment 2, washout). Baseline median seizure frequency was reduced by 33% following adjunctive remacemide hydrochloride 150 mg q.i.d. for 4 weeks compared with placebo (P= 0.041). Seizure frequency was reduced by > or =50% in 30% of patients treated with remacemide hydrochloride compared with 9% on placebo. Mean plasma concentration of concomitant carbamazepine increased by approximately 15% following adjunctive remacemide hydrochloride. There was no correlation between increased plasma carbamazepine and reduced seizure frequency. Remacemide hydrochloride was well tolerated and only three patients withdrew due to adverse events (two remacemide hydrochloride, one placebo). Two patients died unexpectedly from their epilepsy during placebo treatment; both deaths were considered by the investigators to be unrelated to earlier remacemide hydrochloride treatment. This first specific efficacy investigation with adjunctive remacemide hydrochloride demonstrated anticonvulsant effects in patients with refractory epilepsy. More extensive clinical investigation is justified.

Simultaneous determination of remacemide hydrochloride and desglycinylremacemide (AR-R12495XX) in brain tissue by high-performance liquid chromatography

Remacemide hydrochloride, a novel anticonvulsant agent, and its major active metabolite, desglycinylremacemide, were measured simultaneously in brain tissue by high-performance liquid chromatography with UV detection. Intra- and inter-assay variations for remacemide (1, 5, 10 microg/ml) were 5.1, 10.5 and 3.1% and 3.1, 4.0 and 1.3%, respectively. Intra- and inter-assay variations for desglycinylremacemide (1, 5, 10 microg/ml) were 4.2, 3.8 and 8.4% and 7.9, 8.8 and 3.1%, respectively. Limits of detection and quantification for both analytes were 4 and 31 ng/ml, respectively, with recovery consistently > or =85%. This reliable assay has applications in the pre-clinical neuropharmacokinetic and neuropharmacodynamic investigation of remacemide hydrochloride.

Remacemide: current status and clinical applications

Remacemide (RMC) is a non-competitive, low-affinity N-methyl-D-aspartate (NMDA) receptor antagonist that does not cause the behavioural and neuropathological side effects seen with other NMDA receptor antagonists. RMC and its active metabolite, AR-R 12495 AR, which has moderate affinity for the NMDA receptor, also interact with voltage-dependent neuronal sodium channels. Both agents show efficacy in a variety of animal models of epilepsy, parkinsonism and cerebral ischaemia. There is no evidence for teratogenicity or genotoxicity. RMC delays the absorption of L-dopa and elevates the concentrations of drugs metabolised by the hepatic cytochrome P450 3A4 isoform. RMC and AR-R 12495 AR have moderate protein binding and linear pharmacokinetics. Controlled studies show evidence of efficacy in treating epilepsy and Parkinson's disease. Post-surgical outcomes in RMC-treated patients at risk for intra-operative cerebral ischaemia are also encouraging. Adverse effects are related to the gastrointestinal and central nervous systems. RMC is a promising drug with numerous potential applications for both acute or chronic conditions associated with glutamate-mediated neurotoxicity.

New anti-epileptic drugs

Epilepsy represents the most common serious neurological disorder, with a prevalence of 0.4 - 1%. Approximately 30% of patients are resistant to currently available drugs. New anti-epileptic drugs are needed to treat refractory epilepsy, improve upon current therapies, improve the prognosis of epilepsy and to prevent the epileptogenic process. Designing compounds with specific physiological targets would seem the most rational method of anti-epileptic drug development, but results from this approach have been disappointing; the widespread screening of compounds in animal models has been much more fruitful. Older methods of animal screening have used acute seizure models, which bear scant relationship to the human condition. More modern methods have included the development of animal models of chronic epilepsy; although more expensive, it is likely that these models will be more sensitive and more specific in determining anti-epileptic efficacy. In this review, we consider the possible physiological targets for anti-epileptic drugs, the animal models of epilepsy, problems with clinical trials and ten promising anti-epileptic drugs in development (AWD 131-138, DP16 (DP-VPA), ganaxolone, levetiracetam, losigamone, pregabalin, remacemide, retigabine, rufinamide and soretolide). Perhaps the most important advances will come about from the realisation that epilepsy is a symptom, not a disease. Preclinical testing should be used to determine the spectrum of epilepsies that a drug can treat, and to direct later clinical trials, which need to select patients based on carefully defined epilepsy syndromes and aetiologies. Not only will such an approach improve the sensitivity of clinical trials, but also will lead to a more rational basis on which to treat.

Stereoselective pharmacokinetic analysis of the antiepileptic 10-hydroxycarbazepine in dogs

The active entity of the new antiepileptic drug, oxcarbazepine (OXC), is 10-hydroxycarbazepine (MHD). In humans, OXC undergoes rapid presystemic (first-pass) metabolic reduction to MHD. MHD is a chiral molecule with an asymmetric carbon at position 10. Previous reports have shown that in humans, the first-pass metabolic reduction of OXC into MHD is stereoselective, resulting in a 1-to-4 AUC ratio of R(-) and S(+) enantiomers. The objective of the current study was to investigate whether the pharmacokinetics of MHD was stereoselective. Racemic MHD was thus administered intravenously (i.v.) and orally to six dogs, and plasma samples were analyzed by a stereospecific, high-performance liquid chromatographic (HPLC) assay. We found that R(-)-MHD had a clearance similar to that of S(+)-MHD; however, a difference was found between the volume of distribution (Vd) and consequently, between the half-lives of the two MHD enantiomers. The main pharmacokinetic parameters of R(-)- and S(+)-MHD were as follows: A terminal half-life (t1/2) of 2.2 +/- 0.4 hours for R(-)-MHD and of 3.8 +/- 0.3 hours for S(+)-MHD; a clearance (CL) of 7.8 +/- 1.3 L/h for R(-)-MHD and of 8.6 +/- 2.1 L/h for S(+)-MHD; a Vd of 25 +/- 6 L for R(-)-MHD and of 47 +/- 14 L for S(+)-MHD; and a Vd at steady state (V(ss)) of 22.8 +/- 3.6 for R(-)-MHD and of 29.9 +/- 4.1 for S(+)-MHD. After its oral administration to dogs, the absolute bioavailability was 78.4 +/- 20.9% for R(-)-MHD and 78.5 +/- 27.3% for S(+)-MHD; t1/2 was 2.7 +/- 0.6 hours for R(-)-MHD and 4.1 +/- 0.8 hours for S(+)-MHD. These results showed stereoselectivity in the volume of distribution and consequently, the t1/2 of S(+)-MHD was longer than that of R(-)-MHD after both i.v. and oral administration to dogs.

Adjustment of carbamazepine dose to offset the effects of the interaction with remacemide hydrochloride in a double-blind, multicentre, add-on drug trial (CR2237) in refractory epilepsy

PURPOSE

The efficacy of remacemide hydrochloride (REM) as an antiepileptic drug (AED) was tested in a double-blind, add-on trial in patients with refractory epilepsy. Concurrent drugs included carbamazepine (CBZ). The interfering effects of the pharmacokinetic interaction between REM and CBZ were offset by the monitoring of plasma CBZ concentration and the appropriate reduction of CBZ dose by an unblinded observer.

METHODS

Patients taking CBZ entered a 4-week run-in period to stabilise their dosage regimen to Tegretol tablets and blinded capsules containing Tegretol tablets. They then entered an 8-week baseline period during which variation of plasma CBZ concentration was used to derive an individual Shewart Control Chart for each patient. These charts were used to define the threshold for CBZ dose reduction after the addition of trial drug. Where necessary the unblinded observer adjusted that portion of the daily dose of CBZ concealed in the opaque capsules, thereby maintaining the blind for the investigator and the patient.

RESULTS

CBZ dosage reductions ranging from 14 to 50% were required by 63% of patients who received REM. Substantial increases in plasma CBZ concentration, which would have confounded the results of the trial, were thus avoided. The small increases in CBZ concentration that occurred in spite of this procedure were of similar magnitude in responders (patients who experienced > or =50% reduction in seizure frequency during treatment) and nonresponders, and in both groups the mean increase was <1 mg/L.

CONCLUSIONS

The method is offered as a model solution for problems caused by pharmacokinetic interactions in add-on trials.

Neurochemical actions of the desglycinyl metabolite of remacemide hydrochloride (ARL 12495AA) in mouse brain

1. Remacemide hydrochloride, a recently developed antiepileptic drug, is believed to exert its effects, at least in part, via its desglycinyl metabolite, ARL 12495AA. 2. We have investigated the effects of ARL 12495AA on several neurochemical parameters in mouse brain. Adult male ICR mice were randomized into two groups and administered ARL 12495AA (0-75 mg kg-1) intraperitoneally, either as a single dose or once daily for 5 days. 3. Six hours after the final dose, animals were killed and their brains removed. Brain tissues were analysed for concentrations of gamma-aminobutyric acid (GABA), glutamine and glutamate and for the activities of GABA-transaminase (GABA-T) and glutamic acid decarboxylase (GAD). 4. Single dose ARL 12495AA was without effect on any of the parameters investigated. 5. Repeated ARL 12495AA treatment did not alter brain concentrations of GABA and glutamine, but at a high dose there was a trend toward reduced brain glutamate concentrations (P = 0.10). 6. Repeated administration of ARL 12495AA at a high dose significantly increased GABA-T activity (P < 0.05) and decreased that of GAD (P < 0.05). 7. These findings may have relevance to the clinical use of remacemide hydrochloride in human epilepsy.

Lack of pharmacokinetic interaction between remacemide hydrochloride and sodium valproate in epileptic patients

A randomized, double-blind, placebo-controlled cross-over study of adjuvant treatment with remacemide hydrochloride was carried out in 17 patients taking sodium valproate (VPA) as monotherapy. Plasma concentration profiles of VPA, remacemide, and its active desglycinyl metabolite (ARL12495XX) were determined following single (300 mg) and multiple dosing (150 or 300 mg twice daily) of remacemide hydrochloride for 14 days with a 300-mg final dose. Central nervous system side-effects were more common at the higher dose, which prompted dosage reduction to 150 mg twice daily for subsequent patients partway through the study. The mean area under the concentration-time curve, peak concentration and pre-dose concentration of VPA were unchanged by remacemide hydrochloride in three patients on the higher and in 10 patients on the lower dose of remacemide. The pharmacokinetic parameters of remacemide and its active metabolite in the VPA-treated patients were similar to those described previously in healthy volunteers. Thus, remacemide hydrochloride does not interfere with the pharmacokinetics of VPA and vice versa.

Mutual interaction between remacemide hydrochloride and phenytoin

A randomised, double-blind, placebo-controlled crossover study of add-on remacemide hydrochloride was carried out in epilepsy patients being treated with phenytoin (PHT) monotherapy. Eleven patients were recruited, ten of whom completed the study. Plasma concentration profiles of PHT, remacemide, and its active desglycinyl metabolite (ARL12495XX) were determined following single and multiple dosing with remacemide hydrochloride. Following 14 days' treatment with remacemide hydrochloride 300 mg twice daily, the mean AUC of PHT was increased by 11.5% (P = 0.33), Cmax by 13.7% (P = 0.32) and Cmin by 22.2% (P = 0.12) over placebo. There was an increase in trough concentrations of PHT averaging 20% during active treatment compared with placebo (P = 0.01). No symptoms of PHT toxicity were reported by any patient. There was no evidence of autoinduction of remacemide metabolism. However, average concentrations of remacemide and its active metabolite in PHT-treated patients were around 40 and 30% lower, respectively than in healthy volunteers previously receiving the same dose of remacemide hydrochloride. Thus, remacemide hydrochloride has a small inhibitory effect on PHT metabolism, which itself induces that of remacemide and its active metabolite. This mutual interaction is predictable and modest and should not present a barrier to their clinical use in combination.