Harnessing the clinical potential of antiepileptic drug therapy: dosage optimisation

Determination of levetiracetam by GC-MS and effects of storage conditions and gastric digestive systems on drug samples

Background: Epilepsy is a neurologic condition that is occurs globally and is associated with various degrees of seizures. Levetiracetam is an approved drug that is commonly used to treat seizures in juvenile epileptic patients. Accurate quantification of the drug's active compound and determining its stability in the stomach after oral administration are important tasks that must be performed. Results & methodology: Levetiracetam was extracted from drug samples and quantified by gas chromatography mass spectrometry using calibration standards. Stability of levetiracetam was studied under various storage conditions and in simulated gastric conditions. The calibration plot determined for levetiracetam showed good linearity with a coefficient of determination value of 0.9991. The limits of detection and quantification were found to be 0.004 and 0.014 μg·ml^-1, respectively. The structural integrity of levetiracetam did not change within a 4-h period under the simulated gastric conditions, and no significant degradation was observed for the different storage temperatures tested. Discussion & conclusion: An accurate and sensitive quantitative method was developed for the determination of levetiracetam in drug samples. The stability of the drug active compound was monitored under various storage and gastric conditions. The levetiracetam content determined in the drug samples were within ±10% of the value stated on the drug labels.

Cytochrome P450-mediated estrogen catabolism therapeutic avenues in epilepsy

Epilepsy is a neuropsychiatric disorder, which does not have any identifiable cause. However, experimental and clinical results have asserted that the sex hormone estrogen level and endocrine system function influence the seizure and epileptic episodes. There are available drugs to control epilepsy, which passes through the metabolism process. Cytochrome P-450 family 1 (CYP1A1) is a heme-containing mono-oxygenase that are induced several folds in most of the tissues and cells contributing to their differential expression, which regulates various metabolic processes upon administration of therapeutics. CYP1A1 gene family has been found to metabolize estrogen, a female sex hormone, which plays a central role in maintaining the health of brain altering the level of estrogen active neuropsychiatric disorder like epilepsy. Hence, in this article, we endeavor to provide an opinion of estrogen, its effects on epilepsy and catamenial epilepsy, their metabolism by CYP1A1 and new way forward to differential diagnosis and clinical management of epilepsy in future.

Changing the neurology policy landscape in the United States: Misconceptions and facts about epilepsy

Epilepsy has a relatively high prevalence, and diagnosis and treatment are often challenging. Seizure freedom without significant side effects is the ultimate goal for both physicians and patients, but not always achievable. In those cases, the treatment goals of patients and providers may differ. In the United States, many clinicians continue to prescribe older AEDs, even though newer AEDs have a more desirable safety and tolerability profile, fewer drug-drug interactions, and are associated with lower epilepsy-related hospital visits. Newer AEDs are more commonly prescribed by neurologists and epilepsy center physicians, highlighting the importance of access to specialty care. We report that antiepileptic drugs are not the dominant cost driver for patients with epilepsy and costs are considerably higher in patients with uncontrolled epilepsy. Poor drug adherence is considered a main cause of unsuccessful epilepsy treatment and is associated with increases in inpatient and emergency department admissions and related costs. Interventions and educational programs are needed to address the reasons for nonadherence. Coverage policies placing a higher cost burden on patients with epilepsy lead to lower treatment adherence, which can result in higher future health care spending. Epilepsy is lagging behind other neurological conditions in terms of funding and treatment innovation. Increased investment in epilepsy research may be particularly beneficial given current funding levels and the high prevalence of epilepsy.

An Updated Overview on Therapeutic Drug Monitoring of Recent Antiepileptic Drugs

Given the distinctive characteristics of both epilepsy and antiepileptic drugs (AEDs), therapeutic drug monitoring (TDM) can make a significant contribution to the field of epilepsy. The measurement and interpretation of serum drug concentrations can be of benefit in the treatment of uncontrollable seizures and in cases of clinical toxicity; it can aid in the individualization of therapy and in adjusting for variable or nonlinear pharmacokinetics; and can be useful in special populations such as pregnancy. This review examines the potential for TDM of newer AEDs such as eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, perampanel, pregabalin, rufinamide, retigabine, stiripentol, tiagabine, topiramate, vigabatrin, and zonisamide. We describe the relationships between serum drug concentration, clinical effect, and adverse drug reactions for each AED as well as the different analytical methods used for serum drug quantification. We discuss retrospective studies and prospective data on the serum drug concentration-efficacy of these drugs and present the pharmacokinetic parameters, oral bioavailability, reference concentration range, and active metabolites of newer AEDs. Limited data are available for recent AEDs, and we discuss the connection between drug concentrations in terms of clinical efficacy and nonresponse. Although we do not propose routine TDM, serum drug measurement can play a beneficial role in patient management and treatment individualization. Standardized studies designed to assess, in particular, concentration-efficacy-toxicity relationships for recent AEDs are urgently required.

Influence of titration schedule and maintenance dose on the tolerability of adjunctive eslicarbazepine acetate: An integrated analysis of three randomized placebo-controlled trials

OBJECTIVE

To examine the influence of titration schedule and maintenance dose on the incidence and type of treatment-emergent adverse events (TEAEs) associated with adjunctive eslicarbazepine acetate (ESL).

METHODS

Data from three randomized, double-blind, placebo-controlled trials were analyzed. Patients with refractory partial-onset seizures were randomized to maintenance doses of ESL 400, 800, or 1200mg QD (dosing was initiated at 400 or 800mg QD) or placebo. The incidence of TEAEs was analyzed during the double-blind period (2-week titration phase; 12-week maintenance phase), according to the randomized maintenance dose and the titration schedule.

RESULTS

1447 patients were included in the analysis. During the first week of treatment, 62% of patients taking ESL 800mg QD had ≥1 TEAE, vs 35% of those taking 400mg QD and 32% of the placebo group; dizziness, somnolence, nausea, and headache were numerically more frequent in patients taking ESL 800mg than those taking ESL 400mg QD. During the double-blind period, the incidences of common TEAEs were lower in patients who initiated ESL at 400mg vs 800mg QD. For the 800 and 1200mg QD maintenance doses, rates of TEAEs leading to discontinuation were lower in patients who began treatment with 400mg than in those who began taking ESL 800mg QD.

CONCLUSIONS

Initiation of ESL at 800mg QD is feasible. However, initiating treatment with ESL 400mg QD for 1 or 2 weeks is recommended, being associated with a lower incidence of TEAEs, and related discontinuations. For some patients, treatment may be initiated at 800mg QD, if the need for more immediate seizure reduction outweighs concerns about increased risk of adverse reactions during initiation.

Patient emotions and perceptions of antiepileptic drug changes and titration during treatment for epilepsy

OBJECTIVE

To investigate the impact of antiepileptic drug (AED) change and dose titration on the emotional well-being of patients with epilepsy.

METHODS

Members of an online epilepsy community were invited to voluntarily participate in an online survey. The cross-sectional anonymous survey consisted of 31 multiple choice questions balanced in terms of variety and positivity/negativity of emotions concerning participants' most recent AED change. To substantiate survey results, spontaneous comments from epilepsy-related online forums and social media websites that mentioned participants' experiences with AED medication changes (termed passive listening statements) were analyzed and categorized by theme.

RESULTS

All 345 survey participants (270 [78.3%] female; 172 [49.9%] were 26-45years old) self-reported an epilepsy/seizure diagnosis and were currently taking seizure medication; 263 (76.2%) were taking ≥2 AEDs and 301 (87.2%) had ≥1 seizure in the previous 18months. All participants reported a medication change within the previous 12months (dose increased [153 participants (44.3%)], medication added [105 (30.4%)], dose decreased [49 (14.2%)], medication removed [38 (11.0%)]). Improving seizure control (247 [71.6%]) and adverse events (109 [31.6%]) were the most common reasons for medication change. Primary emotions most associated (≥10% of participants) with an AED regimen change were (before medication change; during/after medication change) hopefulness (50 [14.5%]; 43 [12.5%]), uncertainty (50 [14.5%]; 69 [20.0%]), and anxiety (35 [10.1%]; 45 [13.0%]), and were largely due to concerns whether the change would work (212/345 [61.4%]; 180/345 [52.2%]). In the text analysis segment aimed at validating the survey, 230 participants' passive listening statements about medication titration were analyzed; additional seizure activity during dose titration (93 [40.4%]), adverse events during titration (71 [30.9%]), higher medication dosages (33 [14.3%]), and drug costs (25 [10.9%]) were the most commonly noted concerns.

CONCLUSION

Although the emotional well-being of patients with epilepsy is complex, our study results suggest that participants report their emotional well-being as negatively affected by changes in AED regimen, with most patients reporting uncertainty regarding the outcome of such a change. Future research is warranted to explore approaches to alleviate patient concerns associated with AED medication changes.

[Algorithms of mono- and polytherapy in clinical epileptology]

The large number of antiepileptic drugs (AEDs) at the physician's disposal provides not only a broad therapeutic potential in the treatment of epilepsy (EP), but creates difficulties in the adequate choice of AED. The sufficient experience in the management of patients with epilepsy has been gained so far in the world, based on which the International League Against Epilepsy (ILAE), updated classification, adopted the basic definition of efficiency, remission, resistance, evidence of research on the effectiveness of AED therapy, and introduced the concept of "resolved" epilepsy. In this article, a group of Russian experts suggest recommendations on the main steps in the choice of therapy in epilepsy. Possible drug interactions between different AEDs and other drugs as well as main characteristics of mono- and polytherapy of epilepsy are described. Some features of the use of AEDs in the elderly, characteristics of the "female" epilepsy related to the reproductive function and basic requirements for the therapy of epilepsy in children are presented.

[Algorithms of mono- and polytherapy in clinical epileptology. Part 1. General principles of drug choice]

The large number of antiepileptic drugs (AEDs) at the physician's disposal provides not only a broad therapeutic potential in the treatment of epilepsy (EP), but creates difficulties in the adequate choice of AED. The sufficient experience in the management of patients with epilepsy has been gained so far in the world, based on which the International League Against Epilepsy (ILAE), updated classification, adopted the basic definition of efficiency, remission, resistance, evidence of research on the effectiveness of AED therapy, and introduced the concept of "resolved" epilepsy. In this article, a group of Russian experts suggest recommendations on the main steps in the choice of therapy in epilepsy. Possible drug interactions between different AEDs and other drugs as well as main characteristics of mono- and polytherapy of epilepsy are described. Some features of the use of AEDs in the elderly, characteristics of the "female" epilepsy related to the reproductive function and basic requirements for the therapy of epilepsy in children are presented.

Comparative Long-Term Effectiveness of a Monotherapy with Five Antiepileptic Drugs for Focal Epilepsy in Adult Patients: A Prospective Cohort Study

Objective

To evaluate and compare long-term effectiveness of five antiepileptic drugs (AEDs) for monotherapy of adult patients with focal epilepsy in routine clinical practice.

Methods

Adult patients with focal epilepsy, who were prescribed with carbamazepine (CBZ), valproate (VPA), lamotrigine (LTG), topiramate (TPM), or oxcarbazepine (OXC) as monotherapy, during the period from January 2004 to June 2012 registered in Wenzhou Epilepsy Follow Up Registry Database (WEFURD), were included in the study. Prospective long-term follow-up was conducted until June 2013. The endpoints were time to treatment failure, time to seizure remission, and time to first seizure.

Results

This study included 654 patients: CBZ (n=125), VPA (n=151), LTG (n=135), TPM (n=76), and OXC (n=167). The retention rates of CBZ, VPA, LTG, TPM, and OXC at the third year were 36.1%, 32.4%, 57.6%, 37.9%, and 41.8%, respectively. For time to treatment failure, LTG was significantly better than CBZ and VPA (LTG vs. CBZ, hazard ratio, [HR] 0.80 [95% confidence interval: 0.67-0.96], LTG vs. VPA, 0.53 [0.37-0.74]); TPM was worse than LTG (TPM vs. LTG, 1.77 [1.15-2.74]), and OXC was better than VPA (0.86 [0.78-0.96]). After initial target doses, the seizure remission rates of CBZ, VPA, LTG, TPM, and OXC were 63.0%, 77.0%, 83.6%, 67.9%, and 75.3%, respectively. LTG was significantly better than CBZ (1.44 [1.15-1.82]) and OXC (LTG vs. OXC, 0.76 [0.63-0.93]); OXC was less effective than LTG in preventing the first seizure (1.20 [1.02-1.40]).

Conclusion

LTG was the best, OXC was better than VPA only, while VPA was the worst. The others were equivalent for comparisons between five AEDs regarding the long-term treatment outcomes of monotherapy for adult patients with focal epilepsy in a clinical practice. For selecting AEDs for these patients among the first-line drugs, LTG is an appropriate first choice; others are reservation in the first-line but VPA is not.

Off-label prescribing of antiepileptic drugs in pharmacoresistant epilepsy: a cross-sectional drug utilization study of tertiary care centers in Italy

PURPOSE

To assess the extent of off-label prescribing of antiepileptic drugs (AEDs) and associated variables in a large population of patients with pharmacoresistant epilepsy.

METHODS

Descriptive analysis of data recorded from consecutively enrolled patients with pharmacoresistant epilepsy attending 11 tertiary referral centers in Italy. Off-label use was stratified by therapeutic indication, dose, and age. Multivariate logistic regression was used to identify variables associated with off-label prescription.

RESULTS

Of a total of 1,124 patients enrolled between November 2006 and August 2007, 53 % (101/191) of children and 31 % (287/933) of adults were receiving at least one off-label AED prescription. Among adults, off-label use was related primarily to indication and was highest for clobazam (100 %) and ethosuximide (40 %), followed by lamotrigine (25 %), and vigabatrin (25 %). In children, clobazam (100 %), lamotrigine (79 %), vigabatrin (55 %), ethosuximide (46 %), and levetiracetam (43 %) were most frequently used off-label, with indication or age being the main causes depending on the specific AED. Logistic regression analysis indicated that higher rates of off-label use were associated with a polytherapy regimen (odds ratio [OR] 2.50, 95 % confidence interval [95 % CI], 1.55-4.03), pediatric age (2.49, 1.66-3.76), having failed ≥3 AEDs (2.16, 1.04-4.48), a diagnosis of generalized epilepsy with structural/metabolic or unknown etiology (2.97, 1.25-7.04), and increasing seizure frequency (1.07, 1.01-1.14).

CONCLUSIONS

Off-label prescribing of AEDs is common among patients with pharmacoresistant epilepsy and is influenced by demographic and disease-related characteristics. Studies are needed to improve the quality of evidence guiding epilepsy treatment, and to evaluate the risks and benefits of off-label prescribing in epilepsy.

Inhibition of excitatory synaptic transmission in hippocampal neurons by levetiracetam involves Zn²⁺-dependent GABA type A receptor-mediated presynaptic modulation

Levetiracetam (LEV) is an antiepileptic drug with a unique but as yet not fully resolved mechanism of action. Therefore, by use of a simplified rat-isolated nerve-bouton preparation, we have investigated how LEV modulates glutamatergic transmission from mossy fiber terminals to hippocampal CA3 neurons. Action potential-evoked excitatory postsynaptic currents (eEPSCs) were recorded using a conventional whole-cell patch-clamp recording configuration in voltage-clamp mode. The antiepileptic drug phenytoin decreased glutamatergic eEPSCs in a concentration-dependent fashion by inhibiting voltage-dependent Na⁺ and Ca²⁺ channel currents. In contrast, LEV had no effect on eEPSCs or voltage-dependent Na⁺ or Ca²⁺ channel currents. Activation of presynaptic GABA type A (GABA(A)) receptors by muscimol induced presynaptic inhibition of eEPSCs, resulting from depolarization block. Low concentrations of Zn²⁺, which had no effect on eEPSCs, voltage-dependent Na⁺ or Ca²⁺ channel currents, or glutamate receptor-mediated whole cell currents, reduced the muscimol-induced presynaptic inhibition. LEV applied in the continuous presence of 1 µM muscimol and 1 µM Zn²⁺ reversed this Zn²⁺ modulation on eEPSCs. The antagonizing effect of LEV on Zn²⁺-induced presynaptic GABA(A) receptor inhibition was also observed with the Zn²⁺ chelators Ca-EDTA and RhodZin-3. Our results clearly show that LEV removes the Zn²⁺-induced suppression of GABA(A)-mediated presynaptic inhibition, resulting in a presynaptic decrease in glutamate-mediated excitatory transmission. Our results provide a novel mechanism by which LEV may inhibit neuronal activity.

Outcome prediction of initial lamotrigine monotherapy in adult patients with newly diagnosed localization related epilepsies

OBJECTIVE

To develop and test model to predict outcome of treatment with initial lamotrigine monotherapy in adult patients with newly diagnosed localization - related epilepsy, using data available at the time of diagnosis.

METHODS

Prospective longitudinal study included consecutive series of adult patients with newly diagnosed localization - related epilepsy started of lamotrigine monotherapy. Logistic regression analysis using backward procedure was performed with treatment failure as the outcome variable. We evaluated both calibration and discrimination of the model. Internal validation of the model was performed with bootstrapping techniques.

RESULTS

A total of 159 patients on lamotrigine monotherapy have been included in final analysis. Among them 78 (49.06%) patients had persistent seizures. Finally fitted multivariate model included: 1) age at therapy start, 2) presence of complex partial seizures, 3) aetiology of epilepsy and 4) interaction of age and epilepsy aetiology. Estimated odds ratio for seizure relapse in old patients with symptomatic epilepsy is lower than for the old patients with cryptogenic epilepsy, despite strong positive covariate effect of epilepsy aetiology. The model correctly classified 69.23% patients with seizure relapses and 81.48% of patients with seizure freedom, with estimated c - statistic of 0.80. Testing practical application we observed threefold increase or reduction of odds for the seizure relapse after model's positive or negative prediction respectively.

CONCLUSION

Standard clinical data were modesty adequate to predict response to the initial trial of lamotrigine in adult patients with localization related epilepsy. Better markers of antiepileptic failure are required to guide optimal patient counselling and clinical decisions. Formal interaction analysis of variables improves outcome prediction and may be a key to correct interpretation of data.

Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies

To improve patient care and facilitate clinical research, the International League Against Epilepsy (ILAE) appointed a Task Force to formulate a consensus definition of drug resistant epilepsy. The overall framework of the definition has two "hierarchical" levels: Level 1 provides a general scheme to categorize response to each therapeutic intervention, including a minimum dataset of knowledge about the intervention that would be needed; Level 2 provides a core definition of drug resistant epilepsy using a set of essential criteria based on the categorization of response (from Level 1) to trials of antiepileptic drugs. It is proposed as a testable hypothesis that drug resistant epilepsy is defined as failure of adequate trials of two tolerated, appropriately chosen and used antiepileptic drug schedules (whether as monotherapies or in combination) to achieve sustained seizure freedom. This definition can be further refined when new evidence emerges. The rationale behind the definition and the principles governing its proper use are discussed, and examples to illustrate its application in clinical practice are provided.

Designing clinical trials to assess antiepileptic drugs as monotherapy : difficulties and solutions

Designing monotherapy trials in epilepsy is fraught with many hurdles, including diagnostic and classification difficulties, sparse information regarding the natural history of the disorder, and ethical objections to the use of placebo or a suboptimal comparator in a condition where the consequences of therapeutic failure can be serious. These issues are further complicated by regulatory differences between the US and the EU.In the US, the FDA considers that evidence of efficacy requires demonstration of superiority to a comparator. Because available antiepileptic drugs possess relatively high efficacy, in most settings it is unrealistic to expect that a new treatment will be superior to a standard treatment used at optimized dosages. To circumvent this problem, trial designs have been developed whereby patients in the control group are assigned to receive a suboptimal comparator and are required to exit from the trial if seizure deterioration occurs. This allows demonstration of a between-group difference in efficacy endpoints, such as time to exit or time to first seizure. Although these trials have come under increasing criticism because of ethical concerns, extensive information is now available on the outcome of patients with chronic epilepsy randomized to suboptimal treatment in similarly designed conversion to monotherapy trials. This has allowed the construction of a dataset of historical controls against which response to a fully active treatment can be compared. A number of studies using this novel approach are now in progress.In the EU, in addition to requiring data on conversion to monotherapy in refractory patients, the European Medicines Agency stipulates that a monotherapy indication in newly diagnosed epilepsy can only be granted if a candidate drug has shown at least a similar benefit/risk balance compared with an acknowledged standard at its optimal use during an assessment period of no less than 1 year. This has led to the implementation of noninferiority trials, one of which has been completed and which led to approval of the monotherapy indication for levetiracetam in the EU. Noninferiority trials provide valuable data in a setting that most closely resembles routine clinical practice, but their interpretation can be complicated by uncertainties on assay sensitivity.Major evidence gaps in the treatment of epilepsy still remain and it is hoped that these will be addressed in the near future. High quality monotherapy trials are particularly needed to assess the comparative efficacy of older and newer drugs in less common epilepsy syndromes, including most generalized epilepsies, and to investigate the different treatment options in populations homogeneous not only in terms of syndromic classification, but also in terms of underlying aetiology and associated phenotypes.

Potential drug-drug interactions with antiepileptic drugs in Medicaid recipients

PURPOSE

The frequency of potential drug-drug interactions (DDIs) between antiepileptic drugs (AEDs) and other (non-AED) medications in Medicaid patients taking newer AED monotherapy, older AED monotherapy, and combinations of AED treatment was studied.

METHODS

A retrospective, observational study was conducted using administrative claims obtained from South Carolina Medicaid. Patients were included in the analysis if they (1) had at least one prescription for an AED between January 1, 2004, and December 31, 2004, (2) were taking a specific AED for at least 60 days, (3) had at least one epilepsy diagnosis during the 6 months before or during the enrollment period, and (4) were enrolled in Medicaid for at least 11 of the 12 months of the follow-up period. Possible DDI exposure was defined as 10 days of overlap between an AED and a non-AED known to have the potential to cause a clinically relevant interaction.

RESULTS

A total of 4955 patients met the inclusion criteria. Approximately 45% of patients receiving monotherapy with an older AED had a potential DDI, compared with 3.9% receiving a newer AED. An average of 0.08 potential DDI per year of exposure occurred in the newer AED monotherapy cohort compared with 1.18 in the older AED monotherapy cohort. The most common potential interaction category was a decreased concentration of the non-AED.

CONCLUSION

Older AEDs were associated with a greater likelihood of a potential DDI than were newer AEDs. Further research is needed to elucidate the relationship between the occurrence of potential DDIs and actual clinically relevant consequences.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Management of common neurologic symptoms in pediatric palliative care: seizures, agitation, and spasticity

Palliative care for children is complex and focuses on patients' comfort. Some of the most troublesome symptoms as patients approach the end of life are seizures, agitation, and spasticity. Many doctors caring for children at the end of life are uncomfortable or untrained in managing these symptoms in children. Our goal is to help physicians recognize and treat these neurologic symptoms optimally.

Idiosyncratic adverse reactions to antiepileptic drugs

Idiosyncratic drug reactions may be defined as adverse effects that cannot be explained by the known mechanisms of action of the offending agent, do not occur at any dose in most patients, and develop mostly unpredictably in susceptible individuals only. These reactions are generally thought to account for up to 10% of all adverse drug reactions, but their frequency may be higher depending on the definition adopted. Idiosyncratic reactions are a major source of concern because they encompass most life-threatening effects of antiepileptic drugs (AEDs), as well as many other reactions requiring discontinuation of treatment. Based on the underlying mechanisms, idiosyncratic reactions can be differentiated into (1) immune-mediated hypersensitivity reactions, which may range from benign skin rashes to serious conditions such as drug-related rash with eosinophilia and systemic symptoms; (2) reactions involving unusual nonimmune-mediated individual susceptibility, often related to abnormal production or defective detoxification of reactive cytotoxic metabolites (as in valproate-induced liver toxicity); and (3) off-target pharmacology, whereby a drug interacts directly with a system other than that for which it is intended, an example being some types of AED-induced dyskinesias. Although no AED is free from the potential of inducing idiosyncratic reactions, the magnitude of risk and the most common manifestations vary from one drug to another, a consideration that impacts on treatment choices. Serious consequences of idiosyncratic reactions can be minimized by knowledge of risk factors, avoidance of specific AEDs in subpopulations at risk, cautious dose titration, and careful monitoring of clinical response.

Therapeutic Monitoring of Antiepileptic Drugs: A Comparison Between a Czech and a Swedish University Hospital

Plasma concentrations obtained during routine therapeutic monitoring of antiepileptic drugs (AED) (N03A ATC group) were compared in patients treated with one or several AED in the University Hospitals in Ostrava, Czech Republic and Huddinge, Sweden. Request and reply forms for therapeutic drug monitoring (TDM) were used as a source of mean plasma concentrations (PC). The study included 2,824 adult out- and inpatients in Huddinge treated from 1995 to 1999 and 1,268 outpatients treated in Ostrava from 1993 to 2004. PC of valproic acid in Huddinge and all AED except clonazepam in Ostrava were analyzed with gas-liquid chromatography. Plasma concentrations of clonazepam in Ostrava and all AED except valproic acid in Huddinge were analyzed by HPLC. The differences in PC were tested by Student's t-test. Chi(2) method was used for the differences in the distribution of PC relative to the therapeutic window. The mean plasma concentrations generally reached the apparent therapeutic ranges but were below the range in the cases of phenytoin monotherapy in both hospitals, and clonazepam, phenobarbital and phenytoin in polytherapy in Ostrava. In monotherapy 33% of the analyses showed sub-therapeutic concentrations in Huddinge, compared to 38% in Ostrava. Eight percent of the analyses showed potentially toxic concentrations in Huddinge, but only 3% in Ostrava. The highest number of sub-therapeutic concentrations was detected for phenytoin in both hospitals: 59% in Huddinge, 78% in Ostrava. In polytherapy only slight differences between the hospitals were found. PC/dose ratios were significantly lower in polytherapy than in monotherapy for carbamazepine and valproic acid in both hospitals. In contrast a higher PC/dose ratio was found in polytherapy for phenytoin in both cohorts and for lamotrigine in Ostrava. Drug treatment of epilepsy in our two hospitals is surprisingly similar in terms of achieved plasma concentrations, in spite of socioeconomic and cultural differences between our two countries. This may be explained by the long experience with TDM in both hospitals, which has the inherent capacity to promote evidence based drug therapy.

Assessment of a dose–response relationship of levetiracetam

The aim of this study was to assess the relationship between levetiracetam dose and both efficacy and safety in adult patients with refractory partial epilepsy. Dose-response relationships for levetiracetam efficacy were evaluated using pooled data from three trials including adults with refractory partial epilepsy. Two were randomized, double-blind, placebo-controlled, parallel-group trials in which doses of 1000-3000 mg/day of levetiracetam were administered as adjunctive therapy. The third consisted of the two parts of a crossover randomized, double-blind study in which levetiracetam (1000 or 2000 mg/day) or placebo was added to ongoing therapy. Data from each part of the crossover trial were included as if it was an independent parallel-group study. A fourth randomized double-blind trial was added for the safety evaluation. It included data from adults receiving placebo or 2000 mg/day of levetiracetam as adjunctive therapy for refractory partial seizures. The combined analysis showed an increasing effect with increasing dose. The responder rates (> or = 50% reduction in seizures) for placebo and levetiracetam 1000, 2000, and 3000 mg/day were 13.1%, 28.5%, 34.3%, and 41.3%, respectively. The respective values for seizure freedom were 0.8%, 4.7%, 6.3%, and 8.6%. There was no evidence of a dose-response relationship with regard to adverse events, including those (asthenia, dizziness, somnolence) most commonly associated with this antiepileptic drug. Patients who do not become seizure-free at the lowest recommended levetiracetam dose (1000 mg/day) should be titrated to 2000 or 3000 mg/day to provide the greatest opportunity for efficacy with little or no increased risk for adverse events.

Clinically relevant drug interactions with antiepileptic drugs

Some patients with difficult-to-treat epilepsy benefit from combination therapy with two or more antiepileptic drugs (AEDs). Additionally, virtually all epilepsy patients will receive, at some time in their lives, other medications for the management of associated conditions. In these situations, clinically important drug interactions may occur. Carbamazepine, phenytoin, phenobarbital and primidone induce many cytochrome P450 (CYP) and glucuronyl transferase (GT) enzymes, and can reduce drastically the serum concentration of associated drugs which are substrates of the same enzymes. Examples of agents whose serum levels are decreased markedly by enzyme-inducing AEDs, include lamotrigine, tiagabine, several steroidal drugs, cyclosporin A, oral anticoagulants and many cardiovascular, antineoplastic and psychotropic drugs. Valproic acid is not enzyme inducer, but it may cause clinically relevant drug interactions by inhibiting the metabolism of selected substrates, most notably phenobarbital and lamotrigine. Compared with older generation agents, most of the recently developed AEDs are less likely to induce or inhibit the activity of CYP or GT enzymes. However, they may be a target for metabolically mediated drug interactions, and oxcarbazepine, lamotrigine, felbamate and, at high dosages, topiramate may stimulate the metabolism of oral contraceptive steroids. Levetiracetam, gabapentin and pregabalin have not been reported to cause or be a target for clinically relevant pharmacokinetic drug interactions. Pharmacodynamic interactions involving AEDs have not been well characterized, but their understanding is important for a more rational approach to combination therapy. In particular, neurotoxic effects appear to be more likely with coprescription of AEDs sharing the same primary mechanism of action.

Does It Really Matter When a Blood Sample for Valproic Acid Concentration is Taken Following Once-Daily Administration of Divalproex-ER?

Divalproex sodium extended-release (divalproex-ER) is a novel formulation intended for once-daily oral administration, either morning or evening. Questions have risen concerning the optimal time for obtaining a blood sample for valproic acid (VPA) concentration in relation to the dose. Trough sampling is easily achieved just before a morning daily dose, but the best time to sample after an evening daily dose is unclear, because collecting a blood sample 21 to 24 hours later may be limited by the operational hours of the laboratory. This investigation provides practical guidance regarding blood sample timing. Steady-state plasma VPA concentration-time profiles from 5 published divalproex-ER studies (healthy subjects and epilepsy patients) were analyzed. The concentration-time profile for each subject/patient was expressed as a percentage of his/her trough concentration and summary statistics computed. Typically, when taking divalproex-ER once daily in the morning, a blood sample collected 21 to 24 hours later is expected to have a concentration within 3% of the trough value. Conversely, for divalproex-ER dosed once-daily in the evening, for example 8 PM, a blood draw 12 to 15 hours later (ie, 8 to 11 AM) will give a plasma VPA concentration value that is 18% to 25% higher, on average, than the trough value. However, waiting longer, (for example 18 to 21 hours, ie 2 to 5 PM) will result in concentration values that are merely 3% to 13% higher than trough values, which may provide acceptable information for monitoring purposes. The greatest deviation from trough VPA concentration occurs around the peak, that is 3 to 15 hours after a once-daily divalproex-ER dose; sampling during this time period is recommended only if a clinical need exists to test for a higher VPA concentration. Despite the apparent smoothness of the VPA concentration-time profile after a once-daily divalproex-ER dose, the timing of the blood sample does matter and impacts the proper interpretation of the VPA concentration.

Epileptogenesis and rational therapeutic strategies

The understanding of neurobiological mechanisms of epileptogenesis is essential for rational approaches for a possible disease modification as well as treatment of underlying causes of the epilepsies. More effort is necessary to translate results from basic investigations into new approaches for clinical research and to better understand a relationship with findings from clinical studies. The following report is a condensed synapsis in which molecular mechanisms of epileptogenesis, pharmacological modulation of epileptogenesis, evidence based therapy, refractoriness and prediction of outcome is provided in order to stimulate further collaborative international research.

Overtreatment in epilepsy: how it occurs and how it can be avoided

In pharmacotherapy, overtreatment may be defined as an excessive drug load (that is, excessive drug dosages or unnecessary polypharmacy) leading to a suboptimal risk-to-benefit ratio. The risk of overtreatment in the pharmacological management of epilepsy is substantial and may have serious consequences in terms of a greater incidence and severity of adverse effects. These effects can range from subtle CNS impairment to overt toxic effects, including teratogenicity. Overtreatment also causes increased treatment costs and may even lead to a paradoxical deterioration in seizure control. The prevention and correction of overtreatment requires a thorough understanding of the situations and mechanisms that lead to inappropriate prescribing of antiepileptic drugs. These include initiating treatment in conditions where it is not indicated (for example, long-term prophylaxis after head trauma or supratentorial surgery in seizure-free patients), use of excessively fast titration rates, prescription of excessively high initial target dosages, failure to consider conditions associated with reduced dosage requirements (for example, old age or comorbidities associated with impaired drug clearance), and failure to consider the dose-response characteristics of the selected drug. Many patients whose seizures do not respond to the initially prescribed medication can be optimally managed by switching to monotherapy with an alternative agent; premature use of combination therapy represents another common form of overtreatment. Overtreatment may also result from a failure to adjust the dosage to prevent or compensate for adverse pharmacokinetic or pharmacodynamic drug interactions, and from a failure to reduce drug load in patients who have not benefited from high dosages or polypharmacy. While the measurement of drug concentrations can aid in minimising adverse effects, there is also a danger of overtreatment resulting from inappropriate interpretation of drug concentration data. Continuation of drug therapy in seizure-free patients in whom the risk-benefit ratio is in favour of gradual withdrawal may also be regarded as overtreatment. Tailoring therapy to the needs of the individual patient is the key to the successful management of epilepsy. Even though the importance of complete seizure control cannot be overemphasised, no patient should be made to suffer more from the adverse effects of treatment than from the manifestations of the seizure disorder.

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.

Adverse effects of antiepileptic drugs

Adverse effects of antiepileptic drugs (AEDs) are common, can have a considerable impact on quality of life and contribute to treatment failure in up to 40% of patients. The adverse effect profiles of AEDs differ greatly and are often a determining factor in drug selection because of the similar efficacy rates shown by most AEDs. The most common adverse effects are dose dependent and reversible. Cognitive impairment is of particular concern, especially for patients who work or study. Idiosyncratic effects, such as skin rashes, and chronic effects, such as weight gain, can lead to high rates of treatment discontinuation and complicate clinical management. Nearly all conventional AEDs increase the risk of congenital malformations when taken during pregnancy, with valproate posing a potentially greater risk, whereas the potential teratogenicity of new generation AEDs is largely unknown. Most conventional AEDs have a poor record when it comes to drug interactions, largely because of their tendency to interfere with hepatic drug metabolism. Some newer AEDs have no effect on hepatic drug metabolizing enzymes and are renally excreted, resulting in a lower potential for drug interactions. However, further research is needed to confirm the apparent improvement in tolerability offered by some of the newer AEDs.

Zonisamide: a review of its use in the management of partial seizures in epilepsy

Zonisamide (Zonegran, Excegran) is a new-generation, broad-spectrum antiepileptic drug (AED) currently approved as adjunctive therapy for the treatment of medically refractory partial seizures in adults in the US and as adjunctive therapy or monotherapy in the control of partial and generalised seizures in adults and children in Japan and Korea. Either as adjunctive therapy or monotherapy, zonisamide effectively reduces the frequency of partial seizures, with or without secondary generalisation to tonic-clonic seizures, in adults and children with epilepsy. The drug is generally well tolerated and, additionally, has a favourable pharmacokinetic profile permitting once- or twice-daily administration. Direct head-to-head comparisons with other AEDs would be beneficial in fully defining the place of zonisamide in therapy. In the meantime, adjunctive therapy or monotherapy with zonisamide is a convenient, useful option for the management of partial seizures, including those refractory to other AEDs.

An Introduction to Antiepileptic Drugs

In recent years, the number of commercially available antiepileptic drugs (AEDs) has increased steadily. Although this may complicate management choices, it also offers welcome new options to individualize treatment more effectively. Because each of the available AEDs differs from others in many clinically relevant properties, opportunities to tailor drug treatment to the characteristics of the individual patient have never been greater. Properties that are especially important in drug selection in patients with epilepsy include spectrum of efficacy in different seizure types, adverse effects profile, pharmacokinetic properties, susceptibility to cause or be a target of clinically important drug-drug interactions, ease of use, and cost. Other factors that need to be considered in tailoring drug choice include availability of user-friendly pediatric formulations, and potentially favorable effects on co-morbid conditions. In fact, a number of AEDs are efficacious and widely prescribed in additional indications, particularly psychiatric disorders, migraine prophylaxis, and neuropathic pain. Recently, advances have been made in understanding the mechanisms of actions of AEDs at the molecular level. While a fully mechanistic approach to the clinical use of these agents is not yet feasible, knowledge of mechanisms of action offers useful clues in predicting their efficacy profile and spectrum of potential adverse effects.

Antiepileptic drug monotherapy: pediatric concerns

Selecting the optimal antiepileptic drug (AED) begins with accurate epilepsy classification, including seizure type and epilepsy syndrome if possible. Based on the available data, children with focal epilepsy, with or without secondary generalization, can be treated with a traditional or newer narrow-spectrum or broad-spectrum AED. Children with generalized convulsive epilepsy, mixed epilepsy, or seizures of an unknown type are best treated with a broad-spectrum AED. Children with childhood absence epilepsy can be treated with ethosuximide, valproate, or lamotrigine. In all cases, the best choice among the various AED options requires consideration of factors such as seizure frequency, seizure severity, AED adverse event profile, AED titration schedule, patient comorbidities, prescription plan coverage, and cost. Most children with epilepsy achieve the goal of "no seizures and no side effects" and most children eventually become seizure free without AEDs. If accurate epilepsy classification is made, clear differences in efficacy are not evident among the multiple available AEDs. Better comparative data emphasizing adverse event profiles, comorbidities and longer-term outcome are needed between the traditional and newer AEDs.

P450 enzyme inducing and non-enzyme inducing antiepileptics in glioblastoma patients treated with standard chemotherapy

The co-administration of antiepileptic drugs (AED) and chemotherapeutic agents in patients with glioblastoma multiforme (GBM) is common. Interactions of chemotherapeutic agents and AED have not been investigated sufficiently. The purpose of this study is to evaluate the effects of enzyme inducing (EI-AED) and non-EI-AED in patients with GBM treated with standard chemotherapeutic agents on survival and haematotoxicity. One hundred and sixty eight glioblastoma patients with standard treatment including surgery, radiotherapy and chemotherapy were retrospectively analysed. Patients were separated into three groups: Group A patients without AED (n=88), Group B patients with EI-AED (n=43), and Group C patients with non-EI-AED (n=37). CCNU was the most frequently used first-line drug in all three groups (Group A: 77%; Group B: 81%; Group C: 78%). Second line treatment, mainly temozolomide, was applicated in 58 of patients and third-line treatment in 9. Carbamazepine was the most frequently administered AED in Group B (81%) and valproic acid in Group C (85%). For statistical analysis, only patients with CCNU first line treatment were calculated. A significant difference regarding survival was detected between Group B (10.8 month) and Group C (13.9 month), as well as increased haematotoxicity for Group C. These results indicate that AED influence the pharmacokinetics of chemotherapeutic drugs in patients with GBM. Valproic acid might be responsible for increasing haematotoxicity. Whether the difference regarding survival between Group B and Group C is due to a decrease of efficacy of chemotherapeutic agents by EI-AED, or due to increased efficacy of chemotherapeutic agents caused by the enzyme inhibiting properties of valproic acid, has to be evaluated in future studies.

The Use of Antiepileptic Drugs-Principles and Practice

Up to 70% of people developing epilepsy may expect to become seizure free with optimum antiepileptic drug (AED) therapy. The remaining 30% are the most difficult to treat. Most patients are controlled on a single AED, but a small proportion requires a combination of two agents. Add-on therapy with a second drug, rather than substitution, may be a viable and rational approach in some patients, particularly if the first drug is relatively well tolerated. Precise classification of the type of seizures, as well as the epilepsy syndrome, together with careful recording of both seizures and adverse effects, are essential if rational management decisions are to be made. The goal of therapy should be complete seizure freedom with a single drug taken once or twice a day and without adverse effects. If control is difficult to achieve, the maximum tolerated dose of each drug should be explored, but a balance needs to be struck between adverse effects and control of seizures. In patients in whom treatment appears to be ineffective, the diagnosis of epilepsy and adherence to therapy should be reviewed. Drugs used in combination must be carefully selected, as poor adherence, drug interactions, and toxicity are more likely if more than one drug is prescribed. Agents are usually chosen according to seizure type, patient characteristics, and often by clinician preference. Those that are better tolerated have a low potential for pharmacokinetic and pharmacodynamic interactions, and those that can be easily introduced without any complicated titration schedule have an advantage.

Influence of aging on serum phenytoin concentrations: a pharmacokinetic analysis based on therapeutic drug monitoring data

The influence of aging on the pharmacokinetics of phenytoin at steady-state was evaluated retrospectically by comparing apparent oral clearance values (CL/F) in 75 patients aged 65-90 years (mean, 71.7 +/- 5.3 years) receiving phenytoin alone (n = 58) or in combination with phenobarbital (n = 17) and in an equal number of control patients aged 20-50 years (mean, 36.7 +/- 8.5 years) matched for gender, body weight, and comedication. All data were derived from the database of the therapeutic drug monitoring service (TDMS) of an academic neurological hospital. On average, elderly patients were found to exhibit slightly higher CL/F values compared with controls (14.6 +/- 4.7 ml h(-1) kg(-1) versus 13.1 +/- 4.2 ml h(-1) kg(-1), P < 0.05), the difference being probably related to the dose-dependent nature of phenytoin metabolism and the fact that elderly patients received lower dosages (4.4 +/- 1.1 mg kg(-1)day(-1) versus 5.3 +/- 1.1 mg kg(-1) day(-1), P < 0.001) and had lower serum phenytoin concentrations (14.1 +/- 5.7 microg ml(-1) versus 18.6 +/- 6.8 microg ml(-1), P < 0.0001). Gender and phenobarbital comedication were not found to exert any statistically significant influence on phenytoin CL/F. By contrast, in the elderly group, CL/F values were negatively correlated with age. On average, CL/F values decreased by about one-third between 65 and 85 years of age, but interindividual variability was considerable and age explained only 7.8% of the variation in CL/F in the elderly group. Overall, these findings indicate that aging is associated with a progressive decline in phenytoin clearance, presumably as a result of decreased drug metabolizing capacity. Because assessment was based on total serum phenytoin concentrations and the unbound fraction of phenytoin is known to decrease in old age, the influence of aging as quantified in this study may underestimate the magnitude of changes in the clearance of unbound, pharmacologically active drug. Based on these data, it is prudent to utilize initially smaller phenytoin dosages in old patients, and to make subsequent dose adjustments based on clinical response and serum drug level measurements. Interpretation of the latter, however, should take into account the possibility of an increase in the fraction of unbound drug.

Adjunctive therapy versus alternative monotherapy in patients with partial epilepsy failing on a single drug: a multicentre, randomised, pragmatic controlled trial

OBJECTIVE

To evaluate the value of alternative monotherapy versus adjunctive therapy in partial epilepsy refractory to single antiepileptic drug (AED) therapy.

DESIGN AND METHODS

In a multicentre, parallel-group, open-label study, patients with cryptogenic or symptomatic partial epilepsy not controlled after single or sequential AED monotherapies were randomised to monotherapy with an alternative AED or to adjunctive therapy with a second AED. The AED to be added/substituted and dose adjustments were determined by the physician's best judgement. Patients were followed up until withdrawal from the allocated treatment or for 12 months, whichever first. Outcome measures included proportion of patients continuing on the assigned treatment strategy, proportion of patients seizure-free after achieving the target maintenance dose, and adverse effects rates. Data were analysed by actuarial life tables, Kaplan-Meier survival analysis and Cox proportional hazard regression model.

RESULTS

Of a total of 157 patients (including 94 previously exposed to only one AED), 76 were randomised to alternative monotherapy and 81 to adjunctive therapy. The two groups were balanced in clinical characteristics. The 12-month cumulative probability of remaining on the assigned treatment was 55% in patients randomised to alternative monotherapy and 65% in those randomised to adjunctive therapy (P=0.74). The 12-month probability of remaining seizure-free was 14 and 16%, respectively (P=0.74). Adverse effects were similar in the two groups. No significant differences in outcome within or between groups were identified based on etiology of epilepsy and previous AED exposure.

CONCLUSIONS

Although these findings should be interpreted with caution due to the low statistical power resulting from the relatively small sample size, alternative monotherapy and adjunctive therapy were associated with similar outcomes. Further work is required to determine whether outcome could be improved through identification of specific AED combinations with synergistic activity.

What Is the Best Strategy for Converting from Twice-Daily Divalproex to a Once-Daily Divalproex ER Regimen?

OBJECTIVE

To examine if, during conversion from conventional divalproex to once-daily divalproex extended-release (ER) tablets, plasma valproic acid (VPA) concentrations in the first 48 hours after conversion are maintained within the accepted therapeutic range (50-100 mg/L).

METHODS

Four distinct 12-hourly (q12h) divalproex to once-daily divalproex ER conversion strategies were explored: immediate, delayed, stepwise and mixed conversion. These strategies were each used in simulations for hypothetical adult patients being treated under different conditions: monotherapy (uninduced, at 1500 mg/day divalproex ER) and polytherapy on enzyme-inducing co-medications (induced, at 3000 and 4500 mg/day divalproex ER).

RESULTS

The proportion of uninduced patients expected to have minimum VPA concentrations (C(min)) >50 mg/L was 90% for immediate, 83% for stepwise and 82% for mixed-conversion strategies; only 52% undergoing a delayed-conversion strategy had C(min) >50 mg/L. More importantly, 33% of induced patients under-going delayed conversion to 3000 mg/day divalproex ER maintained an adequate VPA C(min). Maximum VPA concentrations (C(max)) attained after conversion to divalproex ER are unlikely to rise beyond the steady-state C(max) observed with divalproex q12h regimens with any conversion strategy tested in uninduced or induced patients. Marked perturbation in VPA concentration is not likely when converting to once-daily divalproex ER 'all-at-once' 12 hours after the last divalproex q12h dose. Stepwise and mixed-conversion strategies do not offer any advantage; delayed conversion may produce a large drop in VPA concentration.

CONCLUSIONS

An ideal conversion strategy for q12h divalproex to once-daily divalproex ER appears to be an immediate conversion 12 hours after the last divalproex q12h dose; it causes the least perturbation in plasma VPA, even for patients required to take high divalproex ER doses.

Current trends in antiepileptic drug therapy

Over the last two decades, drug therapy for epilepsy has improved substantially. This can be ascribed to a large extent to three factors, including the demonstration of the advantages of monotherapy; the realization of the need for dosage tailoring, coupled [for some antiepileptic drugs (AEDs)] with control of pharmacokinetic variability through therapeutic drug monitoring; and the introduction of newer agents with improved tolerability profiles. What further advances should we expect for the future? Current trends that are expected to increasingly affect our prescribing patterns include greater reliance on evidence-based medicine and treatment guidelines, a trend that will be facilitated by completion of therapeutically meaningful randomized trials (including cost-effectiveness studies) and high-quality observational studies (including multinational pregnancy registries), as well as initiatives from scientific societies and government organizations aimed at condensing the most relevant information into therapeutic guidelines. The explosion in communication technology will accelerate dissemination of this information and its application to clinical practice. Other factors include a more rational patient-tailored AED selection and dose individualization, aided by characterization of predictors of outcome as defined by clinical parameters (sex, age, epilepsy syndrome, and etiology), pathophysiological mechanisms, and newly discovered genetic markers of outcome; improved definition of the role of new AEDs, resulting in their increased use in newly diagnosed epilepsy; and reappraisal of the value of combination therapy in refractory epilepsies, based on evidence produced by experimental and clinical studies designed to identify favorable pharmacodynamic interactions. Additional important developments may come from the discovery of novel, more efficacious AEDs and from exploration of potential new targets, such as prevention of epileptogenesis.

Clinically important drug interactions in epilepsy: general features and interactions between antiepileptic drugs

There are two types of interactions between drugs, pharmacokinetic and pharmacodynamic. For antiepileptic drugs (AEDs), pharmacokinetic interactions are the most notable type, but pharmacodynamic interactions involving reciprocal potentiation of pharmacological effects at the site of action are also important. By far the most important pharmacokinetic interactions are those involving cytochrome P450 isoenzymes in hepatic metabolism. Among old generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone induce the activity of several enzymes involved in drug metabolism, leading to decreased plasma concentration and reduced pharmacological effect of drugs, which are substrates of the same enzymes (eg, tiagabine, valproic acid, lamotrigine, and topiramate). In contrast, the new AEDs gabapentin, lamotrigine, levetiracetam, tiagabine, topiramate, vigabatrin, and zonisamide do not induce the metabolism of other AEDs. Interactions involving enzyme inhibition include the increase in plasma concentrations of lamotrigine and phenobarbital caused by valproic acid. Among AEDs, the least potential interaction is associated with gabapentin and levetiracetam.