Tiagabine add-on for drug-resistant partial epilepsy

Tiagabine add-on therapy for drug-resistant focal epilepsy

BACKGROUND

Epilepsy is a common neurological condition that affects up to 1% of the population. Nearly 30% of people with epilepsy are resistant to currently available antiepileptic drugs (AEDs) and require treatment with multiple antiepileptic drugs in combination. Tiagabine is one of the newer AEDs that can be used as an adjunct (add-on) to standard AEDs.

OBJECTIVES

To evaluate the efficacy and tolerability of tiagabine when used as an add-on treatment for people with drug-resistant focal seizures.

SEARCH METHODS

This is an updated Cochrane review, last published in 2014. For the latest update, we searched the following databases on 22 January 2019: Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group's Specialized Register and the Cochrane Central Register of Controlled Trials, MEDLINE (Ovid, 1946 to January 21, 2019), ClinicalTrials.gov, and the WHO International Clinical Trials Registry Platform. We imposed no language restrictions. We also contacted the manufacturers of tiagabine and experts in the field to identify any ongoing or unpublished studies.

SELECTION CRITERIA

We included randomised placebo-controlled add-on trials conducted in people of any age with focal epilepsy. The studies could be double-, single-, or unblinded and of parallel or cross-over design. They had to have a minimum treatment period of eight weeks. We also included trials using an active drug control group.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and extracted data according to the standard methodological procedures expected by the Cochrane Collaboration for this review update. We resolved disagreements by discussion. Outcomes investigated included 50% or greater reduction in seizure frequency, treatment withdrawal, adverse effects, effects on cognition and quality of life. The primary analyses were performed by intention-to-treat. We calculated worst-case and best-case analyses for seizure outcomes. We evaluated dose response using regression models. Two review authors assessed risk of bias in each study using the Cochrane 'Risk of bias' tool.

MAIN RESULTS

No further studies were added since the previous update in 2014. The review included six trials (four parallel-group and two cross-over group trials) consisting of 948 participants. For the main comparison, tiagabine versus placebo, all participants were aged between 12 and 77 years and the study treatment periods ranged from 12 to 22 weeks. The overall risk ratio (RR) with 95% confidence intervals (CIs) for a 50% or greater reduction in seizure frequency (tiagabine versus placebo) was 3.16 (95% CI 1.97 to 5.07; 3 trials; 769 participants; high-certainty evidence). Because of differences in response rates among trials, regression models were unable to provide reliable estimates of response to individual doses. The RR for treatment withdrawal (tiagabine versus placebo) was 1.81 (95% CI 1.25 to 2.62; 3 trials, 769 participants; moderate-certainty evidence). Dizziness and tremor were significantly associated with tiagabine therapy. For cognitive and quality-of-life outcomes, the limited available data suggested no significant effects on cognition, mood, or adjustment. One trial comparing tiagabine with an active drug control group (tiagabine versus topiramate) found no significant differences between the two add-on drugs for a 50% or greater reduction in seizure frequency (RR 0.54, 95% CI 0.19 to 1.58; 1 trial; 41 participants) or for treatment withdrawal (RR 1.43, 95% CI 0.74 to 2.74; one trial; 41 participants). We judged two of the six included studies to have low risk of bias, three studies to have an unclear risk of bias, and one study to have a high risk of bias. Methods for randomisation sequence generation were the least reported trial design factor and generated the most concerns regarding risk of bias. We rated the overall certainty of the evidence as largely moderate to high using the GRADE approach. We rated the evidence for two of the adverse effect outcomes, nausea and tremor, as low certainty.

AUTHORS' CONCLUSIONS

Tiagabine reduced seizure frequency but was associated with some adverse effects when used as an add-on treatment in people with drug-resistant focal epilepsy. The findings of the current review are mainly applicable to adults and adolescents, and may not necessarily be applicable to children as none of the trials included participants aged under 12 years. We found no significant differences between tiagabine and topiramate as add-on drugs; however, evidence was provided by a single trial and was therefore limited.

Emerging drugs for partial-onset epilepsy: a review of brivaracetam

There are more than 12 new antiepileptic drugs approved in the last 2 decades. Even with these newer agents, seizure remission is still unachievable in around 30% of patients with partial-onset seizures (POS). Brivaracetam (BRV) is chemically related to levetiracetam (LEV) and possesses a strong binding affinity for the synaptic vesicle protein 2A tenfold above that of LEV, and other possible modes of antiepileptic actions. BRV is now under Phase III development for POS, but data from one Phase III trial also suggested its potential efficacy for primary generalized seizures. The purpose of this review is to provide updated information on the mechanisms of action of the available antiepileptic drugs, with a focus on BRV to assess its pharmacology, pharmacokinetics, clinical efficacy, safety, and tolerability in patients with uncontrolled POS. To date, six Phase IIb and III clinical trials have been performed to investigate the efficacy, safety, and tolerability of BRV as an adjunctive treatment for patients with POS. Generally, BRV was well tolerated and did not show significant difference in safety profile, compared to placebo. The efficacy outcomes of BRV, although not consistent across trials, did indicate that BRV was a promising add-on therapy for patients with POS. In conclusion, the many favorable attributes of BRV, like its high oral efficacy, good tolerability, dosing regimen, and minimal drug interaction, make it a promising antiepileptic therapy for patients with uncontrolled partial-onset epilepsy.

Selection of antiepileptic drugs in older people

OPINION STATEMENT

Elderly people are one of the fastest-growing populations in the United States, and the incidence of epilepsy in older people is much higher than in other population subgroups. This age group is the most vulnerable because of the increased incidence of multiple medical comorbidities, including stroke. The diagnosis of epilepsy is extremely challenging and often delayed in this age group because of an atypical presentation. Seizures are manifest through extremely vague complaints, such as episodes of altered mental status or memory lapses. Once the diagnosis is established by careful history taking and diagnostic testing, anticonvulsants are the mainstay of treatment. The choice of anticonvulsants in elderly patients requires careful evaluation of medical comorbidities, which vary on an individual basis. This subgroup also is more susceptible to adverse effects because of the physiologic changes in the body due to older age, which affect the pharmacokinetics of most anticonvulsants. The ideal drug in this age group should have linear pharmacokinetics, fewer adverse effects, minimal or no drug-drug interactions, no enzyme induction/inhibition, a long half-life, and minimal protein binding, and should be cost-effective. As such, there is no ideal drug for this patient population, although both older- and newer-generation anticonvulsants are used for long-term treatment. Most newer anticonvulsants have the advantage of a favorable pharmacokinetic profile, minimal or no drug-drug interactions, and fewer adverse events, as well as being well tolerated. The older anticonvulsants still are widely used, because the newer anticonvulsants are much more expensive.

Role of Cochrane reviews in pediatric neurology

Evidence-based medicine in pediatric neurology is considered an important contributor to the best quality of care. We performed a literature review of all Cochrane reviews from 1996-2010 in pediatric neurology. Some reviews concluded that a certain intervention provided benefits, some concluded that certain interventions should not be performed, and some concluded that the current level of evidence was inconclusive. One hundred and twelve reviews were enrolled; only 17 exclusively involved children. In 33/112, a clear recommendation in favor of a certain intervention was given, 11/112 issued a conditionally positive recommendation, and 32/112 concluded that certain interventions should not be performed. Six concluded that no differences were evident between different therapeutic/treatment options. Thirty were inconclusive. The proportion of inconclusive reviews increased during three a priori defined time intervals. Common criticisms regarding quality of enrolled studies included heterogeneous study populations (49/112), a small number of participants (48/112), and a lack of comparability of studies (40/112). An ongoing need exists for high-quality research to reduce the proportion of inconclusive meta-analyses. Further randomized, controlled trials should involve only pediatric populations.

Retention rates of new antiepileptic drugs in localization-related epilepsy: a single-center study

OBJECTIVES

We evaluated long-term retention rates of newer antiepileptic drugs (AED) in adults with localization-related epilepsy retrospectively.

METHODS

We estimated retention rates by Kaplan-Meier method in all 222 patients (age > or = 16) with localization-related epilepsy exposed to new AED at the Tampere University Hospital.

RESULTS

There were 141 patients exposed to lamotrigine, 78 to levetiracetam, 97 to topiramate, 68 to gabapentin, and 69 to tiagabine. Three-year retention rate for lamotrigine was 73.5%, levetiracetam 65.4%, topiramate 64.2%, gabapentin 41.7%, and tiagabine 38.2%. The most common cause for withdrawal of these AED was lack of efficacy.

CONCLUSIONS

Our study suggests that there are clinically significant differences among gabapentin, lamotrigine, levetiracetam, tiagabine, and topiramate as treatment for focal epilepsy in everyday practice. Gabapentin and tiagabine seem to be less useful than the other three AED. Furthermore, our study supports the value of retention rate studies in assessing outcome of the drugs in clinical practice.

Greater response to placebo in children than in adults: a systematic review and meta-analysis in drug-resistant partial epilepsy

BACKGROUND

Despite guidelines establishing the need to perform comprehensive paediatric drug development programs, pivotal trials in children with epilepsy have been completed mostly in Phase IV as a postapproval replication of adult data. However, it has been shown that the treatment response in children can differ from that in adults. It has not been investigated whether differences in drug effect between adults and children might occur in the treatment of drug-resistant partial epilepsy, although such differences may have a substantial impact on the design and results of paediatric randomised controlled trials (RCTs).

METHODS AND FINDINGS

Three electronic databases were searched for RCTs investigating any antiepileptic drug (AED) in the add-on treatment of drug-resistant partial epilepsy in both children and adults. The treatment effect was compared between the two age groups using the ratio of the relative risk (RR) of the 50% responder rate between active AEDs treatment and placebo groups, as well as meta-regression. Differences in the response to placebo and to active treatment were searched using logistic regression. A comparable approach was used for analysing secondary endpoints, including seizure-free rate, total and adverse events-related withdrawal rates, and withdrawal rate for seizure aggravation. Five AEDs were evaluated in both adults and children with drug-resistant partial epilepsy in 32 RCTs. The treatment effect was significantly lower in children than in adults (RR ratio: 0.67 [95% confidence interval (CI) 0.51-0.89]; p = 0.02 by meta-regression). This difference was related to an age-dependent variation in the response to placebo, with a higher rate in children than in adults (19% versus 9.9%, p < 0.001), whereas no significant difference was observed in the response to active treatment (37.2% versus 30.4%, p = 0.364). The relative risk of the total withdrawal rate was also significantly lower in children than in adults (RR ratio: 0.65 [95% CI 0.43-0.98], p = 0.004 by metaregression), due to higher withdrawal rate for seizure aggravation in children (5.6%) than in adults (0.7%) receiving placebo (p < 0.001). Finally, there was no significant difference in the seizure-free rate between adult and paediatric studies.

CONCLUSIONS

Children with drug-resistant partial epilepsy receiving placebo in double-blind RCTs demonstrated significantly greater 50% responder rate than adults, probably reflecting increased placebo and regression to the mean effects. Paediatric clinical trial designs should account for these age-dependent variations of the response to placebo to reduce the risk of an underestimated sample size that could result in falsely negative trials.

Introduction to zonisamide

Zonisamide (Zonegran), a novel antiepileptic drug (AED) approved recently in Europe as adjunctive therapy for refractory partial seizures in adults, has been used extensively in Japan and the United States. A substantial body of clinical experience has accumulated over a 14-year period, allowing the properties and pharmacologic/clinical profiles of zonisamide to be clearly defined. Zonisamide is structurally distinct from other AEDs and has multiple and complementary mechanisms of action, which likely contribute to its efficacy across a broad range of epilepsy types. Zonisamide has a long T1/2 enabling once-daily dosing, linear pharmacokinetics and minimal interaction with other drugs; plasma levels of commonly administered AEDs and oral contraceptives are unaffected by concomitant zonisamide. Effective control of partial seizures (up to 51% decrease in seizure frequency) is attained at doses of >or=300 mg/day, and optimal titration and maintenance dosing schedules have been established. The adverse event profile is well defined; in common with most AEDs, most adverse events are central nervous system-related (e.g. somnolence, dizziness, tiredness). Adverse events may be minimised with appropriate patient management. Zonisamide therefore has many characteristics considered desirable in an AED and represents a valuable addition to the therapeutic options for treating epilepsy in Europe.