Third-generation antiepileptic drugs: mechanisms of action,pharmacokinetics and interactions

This review briefly summarizes the information on the molecular mechanisms of action, pharmacokinetic profiles and drug interactions of novel (third-generation) antiepileptic drugs, including brivaracetam, carabersat, carisbamate, DP-valproic acid, eslicarbazepine, fluorofelbamate, fosphenytoin, ganaxolone, lacosamide, losigamone, pregabalin, remacemide, retigabine, rufinamide, safinamide, seletracetam, soretolide, stiripentol, talampanel, and valrocemide. These novel antiepileptic drugs undergo intensive clinical investigations to assess their efficacy and usefulness in the treatment of patients with refractory epilepsy.     

The promise of new antiepileptic drugs

Epilepsy is the most common serious disorder of the brain and comprises a wide range of different conditions with varying aetiologies. The long-established antiepileptic drugs (AEDs) control seizures in 50% of patients developing partial seizures, and 60-70% of those developing generalized seizures. Several AEDs were made available in the 1990s. These drugs have efficacy, but have had only a modest impact on those with refractory epilepsies. A 50% seizure reduction, which is commonly used as an endpoint in clinical trials, confers little benefit to a patient. Of the newer AEDs, lamotrigine and oxcarbazepine are now licensed for use as monotherapy and vigabatrin has a monotherapy licence for infantile spasms. Careful and prolonged postmarketing surveillance is essential to detect adverse effects, which may not be evident in premarketing clinical trials. At this time, there are 10 AEDs currently in varying stages of clinical development. Current strategies for selecting an AED for a particular patient are crude. Magnetic resonance spectroscopic measures of cerebral neuro-transmitters and genetic analysis may allow better prediction of which drug is most likely to be efficacious and to have low risk of adverse effects. Present AEDs suppress the occurrence of seizures. Agents that prevent the development of epilepsy and which protect the brain from the consequences of seizures would be of great value, but it will be difficult to prove their effectiveness. At present AEDs are given continually and systemically. Local drug delivery is feasible and could avoid the adverse effects of AEDs. The combination of local drug delivery with prediction of seizure occurrence could revolutionize the treatment of currently refractory epilepsies.     

The new antiepileptic drugs: pharmacological and clinical aspects

In recent years several new drugs (oxcarbazepine, lamotrigine, topiramate, gabapentin, zonisamide, tiagabine, fosphenytoin, vigabatrin and felbamate) have been added to the therapeutic armamentarium against epilepsy. Some of these represent structural modifications of pre-existing compounds, others were developed with the specific objective of modifying neurotransmitter function, and many more were found to be clinically useful even though their mode of action is unclear or differs from that originally planned. The pharmacokinetics of these drugs differ widely from one agent to another. Some (gabapentin and vigabatrin) are eliminated unchanged in urine and have little or no interaction potential; others (tiagabine, lamotrigine, topiramate, oxcarbazepine, zonisamide, felbamate) are subject to induction of metabolism by concomitant anticonvulsants; lamotrigine is vulnerable to metabolic inhibition by valproate, and felbamate is a powerful enzyme inhibitor in addition to being an inducer of the metabolism of carbamazepine and steroid oral contraceptives. All new antiepileptic drugs have been found to be effective in improving seizure control in patients with partial and secondarily generalized seizures. However, lamotrigine, topiramate, zonisamide and felbamate appear to have broader efficacy against both partial and many generalized seizure types, while vigabatrin is also valuable in the management of infantile spasms. In monotherapy studies, new drugs have not been found to be more efficacious than older agents, but some may offer limited advantages in terms of improved tolerability. On the other hand, serious toxicity restricts considerably the use of vigabatrin and felbamate. Overall, new drugs represent valuable tools in the fight against epilepsy, but because of limited experience and cost considerations their first-line use cannot be recommended in most situations.     

新型抗癫痫药之间及其与传统抗癫痫药的相互作用和机制*

分别综述了几种新型抗癫痫药（托吡酯、非氨酯、奥卡西平、拉莫三嗪、唑尼沙胺、左乙拉西坦、噻加宾、加巴喷丁及氨己烯酸）与传统抗癫痫药联合应用时以及这些新型抗癫痫药之间的相互作用及其发生机制，阐明细胞色素P450酶和葡萄糖苷酸转移酶在新型抗癫痫药的相互作用中的意义及重要性。为临床合理联合应用提供理论依据，提高抗癫痫治疗的可靠性、安全性和有效性。     

Basic mechanisms of antiepileptic drugs and their pharmacokinetic/pharmacodynamic interactions: an update

This article aims to summarize the current views of AED action and the promising new targets for the pharmacotherapy of epilepsy. In the first section of this paper, a neurobiological basis of epilepsy treatment and brief pharmacological characteristics of classical and new AEDs will be presented. In the second part, the results of experimental studies that have combined AEDs with similar or different mechanisms of action will be discussed.     

New antiepileptic drugs: review on drug interactions.

During the Past decade, nine new antiepileptic drugs (AEDs) namely, Felbamate, Gabapentin, Levetiracetam, Lamotrigine, Oxcarbazepine, Tiagabine, Topiramate, Vigabatrin and Zonisamide have been marketed worldwide. The introduction of these drugs increased appreciably the number of therapeutic combinations used in the treatment of epilepsy and with it, the risk of drug interactions. In general, these newer antiepileptic drugs exhibit a lower potential for drug interactions than the classic AEDs, like phenytoin, carbamazepine and valproic acid, mostly because of their pharmacokinetic characteristics. For example, vigabatrin, levetiracetam and gabapentin, exhibit few or no interactions with other AEDs. Felbamate, tiagabine, topiramate and zonisamide are sensitive to induction by known anticonvulsants with inducing effects but are less vulnerable to inhibition by common drug inhibitors. Felbamate, topiramate and oxcarbazepine are mild inducers and may affect the disposition of oral contraceptives with a risk of failure of contraception. These drugs also inhibit CYP2C19 and may affect the disposition of phenytoin. Lamotrigine is eliminated mostly by glucuronidation and is susceptible to inhibition by valproic acid and induction by classic AEDs such as phenytoin, carbamazepine, phenobarbital and primidone.     

抗癫痫药物与华法林相互作用的研究进展

口服抗凝药华法林的抗凝作用受很多因素的影响,如患者的年龄、体重、合并症等。与其他药物的相互作用也是影响华法林抗凝作用的重要因素之一,其中一些抗癫痫药物对华法林的影响较大且机制复杂,作用持续时间也较长,对于联用华法林的癫痫患者,抗癫痫药物的选择与监测更为重要。本文通过整合国内外相关研究,探讨和总结华法林与抗癫痫药物间的相互作用机制和应对策略,比较不同抗癫痫药物的药代动力学特性及与华法林相互作用的差异,从而为抗癫痫药物的选择和相应剂量的调整提供参考,以降低用药风险。     

Adverse effects of new antiepileptic drugs

Starting with phenobarbital in the 1900s, it took almost 70-80 years to introduce old-generation agents for the treatment of epilepsy. Then, in eleven years, nine more new antiepileptic drugs were added to the armamentarium. These drugs produce a nearly 40-50% decrease in seizure incidence in refractory patients, but few patients have been able to achieve complete freedom from seizures. So the search for more effective drugs with minimal adverse effect profiles will continue. Although the new antiepileptic drugs do not demonstrate a superior efficacy compared to the older ones, they do offer some advantages in terms of tolerability, fewer drug interactions and simpler pharmacokinetics. However, our knowledge concerning their safety profiles can not yet be considered adequate due to the relatively short time these drugs have been on the market and to the limited number of patients exposed to them. The fact that the serious side effects of felbamate and vigabatrine appeared late after marketing should be taken as an important lesson because it implies the potential for unknown side effects at any time during treatment. Antiepileptic drug treatment should begin with diagnosis of the seizure and epileptic syndrome, followed by selection of the drug most appropriate for treatment of the individual patient, and continued with monitoring of not only the seizures but the adverse effect profile as well.     

新型抗癫痫药的安全性评价

新型抗癫痫药与传统抗癫痫药相比,具有较理想的药代动力学特性,不良反应和药物相互作用较少,耐受性和安全性较好。由于新型抗癫痫药上市时间较短,临床资料和用药经验相对较少,其安全性问题尤其值得人们关注。本文对9种新型抗癫痫药从作用机制、药代动力学、不良反应、相互作用等方面作一综合评价。     

格列奈类药物的药动学及与其他药物的相互作用

格列奈类药物吸收迅速,t_(1/2)短,单一疗法耐受性良好,不良反应发生率低于磺脲类药物,但与其他药物联用时,可能发生与CYP3A4、CYP2C8及CYP2C9同工酶和有机阴离子转运多肽1B1(OATP1B1)转运体相关的药动学相互作用,从而降低药物疗效或增加低血糖等不良事件的风险。本文就格列奈类药物的药动学性质及与其他药物的药动学相互作用作一综述。     

Neuroteratogens in man: an overview with special emphasis on the teratogenicity of antiepileptic drugs in pregnancy

The most active growth and development of the human cerebrum and cerebellum occurs in the second half of pregnancy and in the first year of life. It is therefore not surprising that many teratogens may also affect development causing slight, moderate or even severe brain damage. The "classical" antiepileptic drugs (AEDs) valproic acid (VPA), phenytoin, phenobarbital, primidone and carbamazepine are all considered to be teratogenic. They may increase the rate of major congenital anomalies including neural tube defects (NTD), cause specific facial and other dysmorphic features--the "Anti Epileptic Drug Syndrome" (AEDS) and often some degree of mental impairment. Of these AEDs, the most teratogenic seems to be valproic acid, causing about 2% of NTD and an additional increase of 4-8% in major congenital anomalies. Phenytoin also increases the rate of various anomalies, but apparently not of NTD. Phenobarbital primidone and carbamazepine are also teratogenic and impair intellectual function but to a lesser extent than VPA and phenytoin. Cognition is mainly impaired in the children that also exhibit the AEDS. The impairment is slight to moderate, leaving the affected children with a close to borderline intelligence. Lamotrigine monotherapy in pregnancy seems to be relatively safe. In general, polytherapy is more dangerous to the fetus than monotherapy and, at least for VPA and lamotrigine, there seems to be a "threshold effect".     

Foetal safety of old and new antiepileptic drugs

Introduction: Drugs teratogenicity has been studied for many years, especially teratogenic effects of antiepileptic drugs, because of the important impact that epilepsy has always had for young women, but data from literature are often conflicting.

Areas covered: We have carried out a critical review of all human studies about the antiepileptic drugs teratogenicity. A systematic search was performed in Medline and PubMed up to May 1, 2015. The use of older antiepileptic drugs in pregnancy is associated with an increased risk of fetus malformations; in particular, Valproate can determine neural-tube-like defects; in Phenytoin and Phenobarbital-exposed pregnancies, orofacial clefts, cardiac and genitourinary malformations are the major anomalies described. Spina bifida is the only specific major congenital malformation significantly associated with exposure to Carbamazepine monotherapy Despite the small number of studies on the teratogenic effects of new antiepileptic drugs, the analysis of the literature shows that exposure of the fetus to the new antiepileptic drugs is associated with a lower risk of major congenital malformations compared to the use of older drugs.

Expert opinion: Where possible, Valproate should be avoided in women of childbearing potential. Results about the safety of newer antiepileptic drugs require validation and further investigation.     

Pharmacodynamics and common drug-drug interactions of the third-generation antiepileptic drugs

Introduction: Anticonvulsants that belong to the third generation are considered as ‘newer’ antiepileptic drugs, including: eslicarbazepine acetate, lacosamide, perampanel, brivaracetam, rufinamide and stiripentol.

Areas covered: This article reviews pharmacodynamics (i.e. mechanisms of action) and clinically relevant drug-drug interactions of the third-generation antiepileptic drugs.

Expert opinion: Newer antiepileptic drugs have mechanisms of action which are not shared with the first and the second generation anticonvulsants, like inhibition of neurotransmitters release, blocking receptors for excitatory amino acids and new ways of sodium channel inactivation. New mechanisms of action increase chances of controlling forms of epilepsy resistant to older anticonvulsants. Important advantage of the third-generation anticonvulsants could be their little propensity for interactions with both antiepileptic and other drugs observed until now, making prescribing much easier and safer. However, this may change with new studies specifically designed to discover drug-drug interactions. Although the third-generation antiepileptic drugs enlarged therapeutic palette against epilepsy, 20–30% of patients with epilepsy is still treatment-resistant and need new pharmacological approach. There is great need to explore all molecular targets that may directly or indirectly be involved in generation of seizures, so a number of candidate compounds for even newer anticonvulsants could be generated.     

Therapeutic monitoring of the new antiepileptic drugs

Objective: To discuss the potential value of therapeutic drug monitoring (TDM) of the new antiepileptic drugs gabapentin, lamotrigine, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide. Methods: A review of studies of the relationship between plasma concentrations and effects of new antiepileptic drugs is provided. Furthermore, the potential value of TDM of these drugs is discussed in relation to their mode of action and their pharmacokinetic properties. The various methods that are available for analysing plasma concentrations of the new antiepileptic drugs are also briefly reviewed. Results: The available information on the relationship between plasma concentrations and effects of the new drugs is scarce. For most drugs, wide ranges in concentrations associated with seizure control are reported, and a considerable overlap with drug levels among non-responders and also with concentrations associated with toxicity is often noted. However, very few studies have been designed primarily to explore the relationship between drug plasma concentrations and effects. Consequently, there are no generally accepted target ranges for any of the new antiepileptic drugs. Although the available documentation clearly is insufficient, the pharmacological properties of some of the drugs, in particular lamotrigine, zonisamide and, possibly, oxcarbazepine, topiramate and tiagabine, suggest that they may be suitable candidates for TDM. Conclusion: TDM of some of the new antiepileptic drugs may be of value in selected cases, although routine monitoring in general cannot be recommended at this stage. Further systematic studies designed specifically to investigate concentration–effect relationships of the new antiepileptic drugs are urgently needed. Received: 16 September 1999 / Accepted in revised form: 9 October 1999     

Investigation of phenobarbital-carbamazepine-valproic acid interactions using population pharmacokinetic analysis for optimisation of antiepileptic drug therapy: an overview

Antiepileptic drugs are associated with a wide range of drug interactions. Although monotherapy with antiepileptic drugs is preferred, patients with multiple seizure types or refractory disease generally require various combinations of antiepileptic drugs. Pharmacokinetic interactions between antiepileptic drugs represent a major complication of epilepsy treatment with polytherapy. It is important to be aware of possible interactions, so as to anticipate clinical effects and to reduce the risk of both toxicity and seizures worsening when a drug is added to, or withdrawn from, the patient's antiepileptic drug regimen. This report is an overview of the drug-drug interactions between antiepileptic drugs (phenobarbital<-->carbamazepine, carbamazepine<-->valproic acid and phenobarbital<-->valproic acid) by population pharmacokinetic analysis.     

Methodologies used to identify and characterize interactions among antiepileptic drugs

Polytherapy antiepileptic drug (AED) regimens are prevalent in the treatment of epilepsy and the potential for AEDs to interact results in many challenges. Understanding the underlying mechanism of an interaction, along with the magnitude and its time course of presentation can allow a graded and informed therapeutic adjustment so as to minimize the adverse consequences (breakthrough seizures, increased adverse effects) of the interaction. The purpose of the present review is to address the importance of characterizing interactions among AEDs and to emphasize how preclinical studies, both in vitro and in animal models, can help inform the design of clinical studies and the characterization of potential interactions in patients with epilepsy. In addition, we review and discuss methodological issues of how case studies, population pharmacokinetic data and data from therapeutic drug-monitoring databases can provide invaluable signals regarding potential interactions that have yet to be investigated in formal clinical trials.     

Behavioral interactions between opiate and antiepileptic drugs in the mouse

Morphine and related opioid compounds are known to possess proconvulsant activity based upon both electroencephalographic and behavioral criteria. The present authors previously suggested that opiate-related seizures were behaviorally inhibitory, and this was further investigated in the present study. The effects of pretreatment with three pharmacologically distinct compounds (sodium valproic acid, trimethadione, taurine) upon normal behavioral activation to systemic morphine were examined in the mouse. Morphine consistently increased activity levels in comparison with vehicle. Each of the three experimental compounds itself was behaviorally inhibitory; nonetheless both sodium valproate and trimethadione facilitated behavioral responses to morphine. The effects of the same drugs upon activation produced by central administration of a long-lasting enkephalin analog (d-ala²-leu-enkephalinamide) were investigated, with similar results. These findings confirm a behavioral interaction between opiate and anticonvulsant drugs, although it may be selective for certain classes of anticonvulsant compounds.     

Clinical pharmacokinetics of new-generation antiepileptic drugs at the extremes of age

In recent years, several new-generation antiepileptic drugs (AEDs) have been introduced in clinical practice. These agents, which include felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, tiagabine, topiramate, vigabatrin and zonisamide, are being increasingly used in the treatment of epilepsy at the extremes of age. For a rational prescribing of these drugs in specific age groups, major pharmacokinetic changes that occur during development and aging need to be taken into consideration. A review of available evidence indicates that the apparent oral clearance (CL/F) of new-generation AEDs in children is increased by 20-170% (depending on the type of drug and characteristics of the patients studied) compared with adults, with the highest CL/F values usually being observed in the youngest age groups. These findings do not necessarily apply to the first weeks of life, when drug eliminating capacity is still undergoing maturation, as in the case of lamotrigine for which preliminary data suggest that CL/F in neonates aged <2 months can be much lower than in infants aged 2-12 months. At the other extreme of age, in the elderly, CL/F is almost invariably reduced (on average by 10-50%) compared with values found in non-elderly adults. Age-related CL/F changes, together with the large interindividual pharmacokinetic variability, contribute to the need for individualised dosage requirements in these patients. Measurement of serum drug concentrations can be useful as an aid to dosage individualization in these age groups but interpretation of therapeutic drug monitoring data should also take into account the possibility of age-related changes in pharmacodynamic sensitivity and, for neonates and the elderly, alterations in drug binding to serum proteins.