Conventional and sustained-release valproate in children with newly diagnosed epilepsy: a randomized and crossover study comparing clinical effects, patient preference and pharmacokinetics

Population pharmacokinetics of valproic acid in children with epilepsy: Implications for dose tailoring when switching from oral syrup to sustained-release tablets

Significant pharmacokinetic (PK) differences exist between different forms of valproic acid (VPA), such as syrup and sustained-release (SR) tablets. This study aimed to develop a population pharmacokinetic (PopPK) model for VPA in children with epilepsy and offer dose adjustment recommendation for switching dosage forms as needed. The study collected 1411 VPA steady-state trough concentrations (Ctrough) from 617 children with epilepsy. Using NONMEM software, a PopPK model was developed, employing a stepwise approach to identify possible variables such as demographic information and concomitant medications. The final model underwent internal and external evaluation via graphical and statistical methods. Moreover, Monte Carlo simulations were used to generate a dose tailoring strategy for typical patients weighting 20-50 kg. As a result, the PK characteristics of VPA were described using a one-compartment model with first-order absorption. The absorption rate constant (ka) was set at 2.64 and 0.46 h-1 for syrup and SR tablets. Body weight and sex were identified as significant factors affecting VPA's pharmacokinetics. The final PopPK model demonstrated acceptable prediction performance and stability during internal and external evaluation. For children taking syrup, a daily dose of 25 mg/kg resulted in the highest probability of achieving the desired target Ctrough, while a dose of 20 mg/kg/day was appropriate for those taking SR tablets. In conclusion, we established a PopPK model for VPA in children with epilepsy to tailor VPA dosage when switching between syrup and SR tablets, aiming to improve plasma VPA concentrations fluctuations.

Efficacy, Safety, and Retention Rate of Extended-Release Divalproex Versus Conventional Delayed-Release Divalproex: A Meta-Analysis of Controlled Clinical Trials

Purpose: A novel once-daily divalproex-extended release (ER) dose formulation has been developed; this formulation prolongs the therapeutic serum levels of the drug, compared with the twice-daily conventional divalproex-delayed release (DR) formulation. This study aimed to systematically examine and compare the efficacy, safety, and retention rates of the ER divalproex (VPA-ER) and conventional DR divalproex (VPA-DR) formulations.

Methods: Randomized control trials (RCTs) reporting the efficacy, adverse events (AEs), and medication compliance of ER and DR divalproex were searched in online databases, including PubMed, Embase, and Cochrane Library databases, by searching MeSH words and term words. Observational studies with potential biases were excluded. The meta-analysis was performed using Stata 16.0 software.

Findings: Thirteen RCTs, involving 1,028 participants, were included in this meta-analysis. Efficacy, AEs, and drug retention rates were the main study outcomes. According to our study, VPA-ER presented clinically significant benefits compared with the placebo in the population with bipolar disorder (BD) (39.5% versus 27.2%, p < 0.001). A similar efficacy of VPA-ER and VPA-DR in controlling seizures was observed in epilepsy patients (87.4% versus 86.5%, p = 0.769). A significantly lower incidence of AEs was reported in the VPA-ER group than in the placebo group (26.8% versus 34.8%, p = 0.003). By contrast, there was no evidence of difference in safety between VPA-ER and VPA-DR (29.4% versus 30.5%, p = 0.750). In addition, the drug retention rate was significantly lower in the VPA-ER group than in the placebo group (76.0% versus 82.7%, p = 0.020), especially in migraine patients (p = 0.022) and in patients who were treated for fewer than 4 weeks (p = 0.018).

Implications: The efficacy of VPA-ER was significantly superior to that of the placebo treatment, which provided efficacy similar to that of conventional VPA-DR. VPA-ER is well tolerated with a low rate of AEs compared to the placebo. In addition, the acceptable medicine compliance of VPA-ER was conducive to the long-term maintenance treatment of chronic diseases. Although we analyzed open labels and crossover design RCTs, large-scale multicenter studies on the efficacy and medicine compliance of new ER formulations with less AEs are required to validate our conclusion.

KOMET: an unblinded, randomised, two parallel-group, stratified trial comparing the effectiveness of levetiracetam with controlled-release carbamazepine and extended-release sodium valproate as monotherapy in patients with newly diagnosed epilepsy

OBJECTIVE

To compare the effectiveness of levetiracetam (LEV) with extended-release sodium valproate (VPA-ER) and controlled-release carbamazepine (CBZ-CR) as monotherapy in patients with newly diagnosed epilepsy.

METHODS

This unblinded, randomised, 52-week superiority trial (NCT00175903) recruited patients (≥16 years of age) with ≥2 unprovoked seizures in the previous 2 years and ≥1 in the previous 6 months. The physician chose VPA or CBZ as preferred standard treatment; each patient was randomised to standard treatment or LEV. The primary outcome was time to treatment withdrawal (LEV vs standard antiepileptic drugs (AEDs)). Analyses also compared LEV with VPA-ER, and LEV with CBZ-CR.

FINDINGS

1688 patients (mean age 41 years; 44% female) were randomised to LEV (n=841) or standard AEDs (n=847). Time to treatment withdrawal was not significantly different between LEV and standard AEDs: HR (95% CI) 0.90 (0.74 to 1.08). Time to treatment withdrawal (HR (95% CI)) was 1.02 (0.74 to 1.41) for LEV/VPA-ER and 0.84 (0.66 to 1.07) for LEV/CBZ-CR. Time to first seizure (HR, 95% CI) was significantly longer for standard AEDs, 1.20 (1.03 to 1.39), being 1.19 (0.93 to 1.54) for LEV/VPA-ER and 1.20 (0.99 to 1.46) for LEV/CBZ-CR. Estimated 12-month seizure freedom rates from randomisation: 58.7% LEV versus 64.5% VPA-ER; 50.5% LEV versus 56.7% CBZ-CR. Similar proportions of patients within each stratum reported at least one adverse event: 66.1% LEV versus 62.0% VPA-ER; 73.4% LEV versus 72.5% CBZ-CR.

CONCLUSIONS

LEV monotherapy was not superior to standard AEDs for the global outcome, namely time to treatment withdrawal, in patients with newly diagnosed focal or generalised seizures.

Strategies for improving adherence to antiepileptic drug treatment in patients with epilepsy

BACKGROUND

Poor adherence to antiepileptic medications is associated with increased mortality and morbidity. In this review we focus on interventions designed to assist patients with adherence to antiepileptic medications.

OBJECTIVES

To determine the effectiveness of interventions aimed at improving adherence to antiepileptic medications in adults and children with epilepsy.

SEARCH STRATEGY

We searched the Epilepsy Group's Specialised Register (24 June 2010), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 2) and electronic databases: MEDLINE (OVID) (1950 to June 2010); EMBASE (OVID) (1980 to 2010 Week 24); CINAHL (1982 to June 2010) and PsycINFO (22 June 2010), and the reference lists of relevant articles. 

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials of adherence-enhancing interventions aimed at patients with clinical diagnosis of epilepsy (as defined in individual studies), of any age and of either gender, treated with antiepileptic drugs in a primary care, outpatient or other community setting.

DATA COLLECTION AND ANALYSIS

We screened titles and abstracts for eligibility. Two review authors independently extracted data and assessed each study according to the Cochrane criteria. The studies differed widely according to intervention and measures of adherence, therefore combining data was not appropriate.

MAIN RESULTS

Six trials met our inclusion criteria: five targeted adult epileptic patients with a combined patient number of 222 and one targeted parents of children with epilepsy (n = 51). Follow-up time was generally short: from one to six months. Two main types of intervention were examined: educational and behavioural modification. Each study compared treatment with no intervention 'usual care'. None compared one intervention with another. Due to heterogeneity between studies in terms of interventions and the methods used to measure adherence, we did not pool the results. Education and counselling of patients with epilepsy have shown mixed success. Behavioural interventions such as the use of intensive reminders and 'implementation intention' interventions provided more positive effects on adherence.

AUTHORS' CONCLUSIONS

Intensive reminders and 'implementation intention' interventions appear promising in enhancing adherence to antiepileptic mediations, however we need more reliable evidence on their efficacy from carefully designed randomised controlled trials before a firm conclusion can be reached.

Extended-release formulations of antiepileptic drugs: rationale and comparative value

Extended-release products are designed to prolong the absorption of drugs with short half-lives, thereby allowing longer dosing intervals while minimizing fluctuations in serum drug levels. The relationship between serum drug concentration and clinical effects of antiepileptic drugs (AEDs) can be complex and reducing fluctuations in serum drug levels is not equally advantageous for all AEDs. Extended-release formulations have been shown to be particularly valuable for carbamazepine, whereas for other AEDs advantages, other than prolongation of the dosing interval, have not been clearly demonstrated. Differences in bioavailability may exist between extended-release and immediate-release formulations and among different brands of extended-release products. Therefore, when switching from one formulation to another, careful monitoring of clinical response and attention to the need for dose adjustment are warranted.

Extended-release formulations for the treatment of epilepsy

This review analyses the concept of extended-release (ER) formulations in epilepsy and evaluates ER formulations of carbamazepine, valproic acid and a modified-release (MR) formulation of oxcarbazepine. ER formulations are usually designed to reduce dose frequency and maintain relatively constant or flat plasma drug concentration. It is questionable whether flat plasma concentrations of an antiepileptic drug (AED) improve antiepileptic efficacy compared with fluctuating plasma concentrations. More certainly, they minimise concentration-related adverse effects, and the dosing flexibility and consistency of plasma concentrations may simplify the management of antiepileptic drug therapy. Neurologists would like ER formulations that can be administered once- and/or twice-daily to tailor therapy for the individual patient; however, switching dosage schedules from multiple dosages per day to once daily, although more convenient, will not generally improve therapeutic coverage (maintenance of effective drug concentration in biological fluids and tissue). Pharmacokinetically, the impact of a missed dose is greater the larger the dose and the less frequent the administration. Therefore, the risk of breakthrough seizure is higher during AED once-daily administration than twice-daily administration. Consequently, the increased compliance observed with fewer dosages per day should be weighed against the impact or forgiveness of omitted dose(s) and the shorter 'forgiveness' period associated with once-daily administration. Currently, the trend is to treat patients with epilepsy with ER formulations because of the better compliance, convenience and flat plasma concentration versus time curve. Thus, it seems that the term 'flatter is better' for AED plasma profiles has precipitated in the last 10-15 years among neurologists and epilepsy caregivers, and is being promoted by marketing forces of pharmaceutical companies. Data from the literature support the trend to treat epileptic patients with twice-daily administration of the existing ER formulations of valproic acid and carbamazepine, and oxcarbazepine-MR; however, the author of this article is not convinced that these ER formulations can guarantee a complete therapeutic coverage throughout the 24-hour dosing interval following once-daily administration. Epilepsy is a single-episode disease, and the convenience and possible better compliance associated with once-daily administration must be weighed against the shorter 'forgiveness' period and possible higher risk of breakthrough seizure due to sub-therapeutic plasma levels and/or omitted doses. Data suggest just a small difference in compliance between once- and twice-daily administration, with no significant difference in efficacy. Therefore, the increased compliance following once-daily administration may be counter-productive in minimising the occurrence of sub-therapeutic drug concentrations. Weighing up the advantages and disadvantages for once- versus twice-daily administration of ER formulations in epilepsy leads to a conclusion in favour of twice-daily administration.