Extended-release antiepileptic drugs: a comparison of pharmacokinetic parameters relative to original immediate-release formulations

Pharmacokinetic profile of phenytoin in dried blood spot with high-performance liquid chromatography-photodiode array

Phenytoin is a first-line antiepileptic drug with narrow therapeutic range and follows non-linear pharmacokinetics. Pharmacokinetics of phenytoin have been studied in plasma matrix before, however, there were several disadvantages. This study aimed to obtain partial validation data of the analytical method and the pharmacokinetic profile of phenytoin in Dried Blood Spot (DBS) of six healthy subjects. DBS has the advantage of only requiring small sample volumes and could be transported more efficiently. Phenytoin along with carbamazepine as the chosen internal standard was analyzed with a reversed-phase high performance-liquid chromatography system and a photodiode array detector at 205 nm. The results of partial validation, which evaluated the linearity, within-run accuracy, and precision, were within the criteria acceptance range. The pharmacokinetic profile showed that average AUC0-t was 83.81 ± 37.32 μg.h/mL and AUC0-∞ was 83.65 ± 38.89 μg.h/mL with an average ratio of 93%. Previous study quantifying phenytoin in the plasma matrix found the average AUC0-t was 39.41 ± 8.57 µg.h/mL and AUC0-∞ was 42.94 ± 9.55 µg.h/mL. Despite the difference between parameters of phenytoin analyzed in DBS and plasma matrices, the pharmacokinetic profiles obtained from both matrices were similar indicated by comparable concentration-time curves, thus, proving that DBS matrix can be used interchangeably with the plasma matrix as a more comfortable and effective alternative to phenytoin quantification in blood.

Retrospective analysis of the biopharmaceutics characteristics of solid oral Modified-Release drug products in approved US FDA NDAs designated as Extended-Release or Delayed-Release formulations

BACKGROUND

Modified Release (MR) orally administered drugs products [Extended-Release (ER) and Delayed-Release (DR)] differ from Immediate-Release (IR) drug products in their drug release site and/or rate to offer therapeutic advantages. It is important to understand the biopharmaceutics factors that determine how a drug works in the gastrointestinal tract and the various pharmacokinetic properties that determine a drug's rate of absorption and release in the human body. To better understand the biopharmaceutics characteristics of ER and DR drug products, this study retrospectively analyzed submissions approved by the US Food and Drug Administration (FDA), from 2001 to 2021, and their corresponding review documents. This review work is expected to enhance the readers' understanding regarding the biopharmaceutics properties that supported approval of these products' ER claims, as per 21 CFR 320.25(f), and DR claims.

METHODS

A comprehensive search was conducted using the FDA's internal New Drug Application (NDA) database for ER and DR oral drug products approved between 2001 and 2021. The search yielded 87 ER applications (23 ER capsules and 64 ER tablets) and 21 DR applications (10 DR capsules, 11 DR tablets) for which electronic records were accessible. These products were analyzed for overall drug product design, dosing frequency compared to the reference (if applicable), degree of fluctuation, dissolution method, and alcohol dose-dumping.

RESULTS

Out of 87 total applications for ER drug products that were assessed, 62% of the ER tablets contained a polymer matrix formulation, and hypromellose (HPMC) was used in 50% of these products. 52% of the ER capsules consisted of polymer beads while about half of the DR drug products contained a non-bead formulation with a combination of polymers. The majority of ER drug products were found to have a reduction in dosing frequency and a decrease in the degree of fluctuation when compared to the IR reference product. The 13 ER drug products that exhibited an increase in degree of fluctuation exhibited general and pharmacodynamic benefits, such as reduced dosing frequency and reduced pill burden. The majority of DR formulations were developed to prevent drug degradation in the stomach, followed by to decrease potential stomach irritation, and lastly for localized release in the colon. The majority of ER drug products had 1:1 ratios of dissolution duration compared to dosing frequency (i.e., the majority of ER drug products had a dissolution duration of 24 h and were dosed every 24 h while those with a dissolution duration of 12 h were dosed every 12 h). The majority of ER applications had single-stage dissolution methods while most DR drug products used biphasic dissolution methods. All of the DR dissolution methods incorporated an acid stage of 2 h and a buffer stage with various timeframes. 53% the DR drug products had a ratio of dissolution duration to dosing frequency of 1:4 (e.g. a dissolution duration of 2 h to a dosing frequency of 8 h) or 1:8 (e.g. a dissolution duration of 2 h to a dosing frequency of 16 h). Of the ER tablets and DR drug products, 72% exhibited no alcohol dose-dumping under in vitro testing conditions. ER capsules, however, did not yield similar results-most of which exhibited alcohol induced dose-dumping. Alcohol dose dumping was mitigated by either in vivo studies or warnings on the drug product label.

CONCLUSION

The results of this study help the reader understand the design, characteristics, and pharmacological advantages of the ER and DR drug products for patient benefit; as well as the regulations governing the FDA's assessment of ER claims.

Emerging frontiers in drug delivery with special focus on novel techniques for targeted therapies

The management and treatment of disease are achieved via the use of pharmacologically active substances or drugs. Drugs do not, however, have an intrinsic ability to be effective; rather, how well they work depends on how they are administered or supplied. Treatment of a variety of biological illnesses, such as autoimmune disorders, cancer, and bacterial infections, requires effective drug delivery. Drug absorption, distribution, metabolism, duration of therapeutic impact, pharmacokinetics, excretion, and toxicity can all be impacted by drug administration. Improved chemistry and materials are required for the delivery of therapeutic concentration of novel treatments to the specified targets within the body, as well as for the necessary duration of time. This requirement is accompanied by the development of new therapeutics. Formulating a medication as a DDS is a promising strategy for directly addressing numerous typical barriers to adherence, such as frequent dosage, such as frequent dosage, side effects, and a delayed beginning of the action. In the current review, we give a compendium of drug delivery and controlled release and subsequently highlight some of the newest developments in the realm, with a particular emphasis on cutting-edge methods for targeted therapy. In each instance, we outline the obstacles to efficient drug administration as well as the chemical and material developments that are allowing the sector to overcome these obstacles and have a positive clinical impact.

Overcoming barriers to patient adherence: the case for developing innovative drug delivery systems

Poor medication adherence is a pervasive issue with considerable health and socioeconomic consequences. Although the underlying reasons are generally understood, traditional intervention strategies rooted in patient-centric education and empowerment have proved to be prohibitively complex and/or ineffective. Formulating a pharmaceutical in a drug delivery system (DDS) is a promising alternative that can directly mitigate many common impediments to adherence, including frequent dosing, adverse effects and a delayed onset of action. Existing DDSs have already positively influenced patient acceptability and improved rates of adherence across various disease and intervention types. The next generation of systems have the potential to instate an even more radical paradigm shift by, for example, permitting oral delivery of biomacromolecules, allowing for autonomous dose regulation and enabling several doses to be mimicked with a single administration. Their success, however, is contingent on their ability to address the problems that have made DDSs unsuccessful in the past.

Generic lamotrigine extended-release tablets are bioequivalent to innovator drug in fully replicated crossover bioequivalence study

OBJECTIVE

Lamotrigine is a commonly prescribed antiepileptic drug. U.S. Food and Drug Administration (FDA)-funded clinical studies have demonstrated bioequivalence (BE) for generic lamotrigine immediate-release (IR) products in epilepsy patients with generic substitution. To address the potential concerns about the risk of generic-brand substitution of lamotrigine extended-release (ER) products, considering the complexity of controlled release systems and pharmacokinetic variations associated with possible within-subject variability (WSV), this prospective study assessed (1) BE of generic and brand lamotrigine ER products in a fully replicated BE study design in healthy subjects and (2) whether such fully replicated study design and WSV data can better support the approval of generic lamotrigine ER products.

METHODS

This open-label, single-dose, two-treatment, four-period, two-sequence, fully replicated crossover BE study compared generic lamotrigine ER tablet to brand Lamictal XR (200 mg) in 30 healthy subjects under fed conditions. Pharmacokinetics (PK) profiles were generated based on intensive blood sampling up to 144 h.

RESULTS

The two products showed comparable peak plasma concentration (C_max ), area under the concentration-time curve (AUC) from time zero to the last measurable time point (AUC_0-t ) and AUC extrapolated to infinity (AUC_0-inf ), whereas median time to C_max (T_max ) values differed, that is, 10 h for generic and 22 h for brand products, respectively. WSVs for PK metrics were small (~8% of C_max and ~6% of AUC) and similar between these two products. PK simulation predicted equivalent PK measurements of both products at steady state and after brand-to-generic switch, except the first day upon switching. No serious adverse events were reported.

SIGNIFICANCE

The generic lamotrigine ER tablet product demonstrates BE to the brand product in a fully replicated BE study design with healthy subjects, supporting the adequacy of the two-way crossover study design to demonstrate BE and generic-brand substitution of lamotrigine ER products.

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.

Efficacy, safety, and retention rate of extended-release divalproex versus conventional delayed-release divalproex: A protocol for systematic review and meta-analysis

BACKGROUND

A novel once-daily divalproex-extended release (VPA-ER) dose formulation has been developed, which prolongs therapeutic serum levels compared with that of twice-daily conventional divalproex-delayed release (VPA-DR). Currently, there is lack of meta-analysis focusing on drug retention rate between VPA-ER and VPA-DR. Thus, our study is the first one that aims to systematically examine and compare the efficacy, safety, and retention rate of VPA-ER and VPA-DR.

METHODS

Online databases including MEDLINE via PubMed, Cochrane Library, Embase (up to October 30, 2021) will be applied for literature screen. We will conduct meta-analysis by using Stata16.0 software.

RESULTS

This study aims to evaluate the efficacy, safety, and drug retention rate of VPA-ER versus conventional VPA-DR.

CONCLUSION

Once-daily VPA-ER may present a positive efficacy and not increase the incidence of AEs and has a higher retention rate for patients, which can be used as a substitute for conventional VPA-DR.INPLASY registration number: INPLASY2021110090(DOI: 10.37766/inplasy2021.11.0090).

A Pharmacokinetic Evaluation of a Pectin-Based Oral Multiparticulate Matrix Carrier of Carbamazepine

Background

Carbamazepine is a drug used in the treatment of neurological disorders such as epilepsy. However, due to its erratic absorption, oral bioavailability is often poor. There is, therefore, the need to develop alternative formulations for carbamazepine with better pharmacokinetic characteristics.

Aim

The aim of this study was to formulate an oral modified-release multiparticulate matrix of carbamazepine from cocoa pod husk (CPH) pectin and evaluate the pharmacokinetic profile of this formulation using in vitro and in vivo models.

Methods

CPH pectin was extracted from cocoa pod husks with hot aqueous and citric acid solutions. Oral multiparticulate carbamazepine matrices were formulated from CPH pectin cross-linked with calcium. The formulation was evaluated for carbamazepine content and release profile in vitro. For in vivo pharmacokinetic profile estimation, rats were put into 4 groups of 5 animals each to receive carbamazepine multiparticulate matrix formulations A and B, carbamazepine powder, and Tegretol CR^®. Animals in each group received 200 mg/kg of each drug via the oral route. Maximum plasma concentration (C_max), area under the concentration-time curve (AUC), elimination rate constant (K_e), and terminal half-life (t_1/2) of the formulations were estimated by noncompartmental analysis.

Results

The pectin extraction from fresh cocoa pod husks using hot aqueous and citric acid solutions gave pectin yields of 9.63% and 11.54%, respectively. The drug content of carbamazepine in CPH pectin formulations A and B was 95% and 96%, respectively. There was controlled and sustained release of carbamazepine for both formulations A and B in vitro. AUC_0⟶36 (176.20 ± 7.97 µg.h/mL), C_max (8.45 ± 0.71 μg/mL), T_max (12 ± 1.28 h), and t_1/2 (13.75 ± 3.28 h) of formulation A showed a moderately enhanced and comparable pharmacokinetic profile to Tegretol CR^® (AUC_0⟶36: 155 ± 7.15 µg.h/mL, C_max: 8.24 ± 0.45 μg/mL, T_max: 8.0 ± 2.23 h, and t_1/2: 13.51 ± 2.87 h).

Conclusion

Findings from the study suggest that formulations of CPH pectin had the potential to control and maintain therapeutic concentrations of carbamazepine in circulation over a period of time in the rat model.

Use of extended-release and immediate-release anti-seizure medications with a long half-life to improve adherence in epilepsy: A guide for clinicians

Poor adherence to anti-seizure medications (ASMs) is associated with breakthrough seizures and potentially increased toxicity in patients with epilepsy. Extended-release (ER) drugs and immediate-release (IR) drugs with a long half-life (t_1/2) that permit once-daily dosing (such as, perampanel, zonisamide, lamotrigine [IR, ER] and topiramate [ER]) have a number of advantages over short t_1/2 ASMs that require multiple daily dosing. These advantages include simplification of dosing regimens, reduction in pill burden, and a decrease in the peak-to-trough fluctuations in serum drug concentration that may be associated with a decreased risk of adverse effects and seizures. Such properties have wider implications in improving patient adherence to treatment. This article is intended as a practical guide for clinicians that provides an overview of the features of ER ASMs and long t_1/2 IR ASMs that are advantageous in the context of patient adherence and pharmacokinetic "forgiveness" (after missing a dose). In addition, we note that efforts to improve adherence should not depend solely on drug dosing regimens and drug pharmacokinetics, but should be part of a wider strategy that includes therapeutic drug monitoring, improved healthcare provider-patient dialogue, patient education, and the use of "reminder" technology.

Usefulness of extended-release topiramate in patients with epilepsy: A two-year retention study

WHAT IS KNOWN AND OBJECTIVE

Extended-release topiramate (TPM-XR) was recently approved for the treatment of epilepsy, but there is only limited real-world information on the clinical usefulness of TPM-XR in epilepsy patients. We investigated the usefulness of TPM-XR in clinical practice by analysing the retention of TPM-XR in adult epilepsy patients.

METHODS

We performed a single-centre retrospective study covering two years. Epilepsy patients taking TPM-XR were included in the study and classified into one of three groups: the monotherapy group, in which patients took only TPM-XR; the adjunctive therapy group, in which patients took TPM-XR concomitant with other AEDs; and the switching AED regimen group, in which patient's AED was switched from immediate-release TPM (TPM-IR) to TPM-XR. We evaluated the retention rates of TPM-XR and analysed the differences in retention rate among the three patient groups.

RESULTS AND DISCUSSION

We included 164 epilepsy patients who received TPM-XR for the treatment of epilepsy. The overall retention rate of TPM-XR was generally favourable: 79.1% after one year and 77.7% after two years. The switching AED regimen group had a better retention rate than the other two groups (p = 0.04), with a one-year retention rate of 90.6% and a two-year retention rate of 88.1%.

WHAT IS NEW AND CONCLUSION

The favourable retention rate of TPM-XR shows that TPM-XR can be an effective treatment option for epilepsy patients, as either a monotherapy or as an adjunctive therapy. Additionally, switching AED regimen to TPM-XR from TPM-IR can be considered in selected epilepsy patients with poor adherence to TPM-IR.

Genetic and Non-genetic Factors Contributing to the Significant Variation in the Plasma Trough Concentration-to-Dose Ratio of Valproic Acid in Children With Epilepsy

Objective: This study was conducted to evaluate the potential genetic and non-genetic factors contributing to plasma trough concentration-to-dose (C ₀/D) ratio of valproic acid (VPA) in pediatric patients with epilepsy. Study Design: A single-center, retrospective cohort study was performed by collecting data from 194 children aged 1-14 years between May 2018 and November 2018. The oral solution (n = 135) group and the sustained-release (SR) tablet group (n = 59) were defined, and the plasma VPA C ₀ was measured. Twenty-six single-nucleotide polymorphisms (SNPs) were chosen for genotyping with the MassARRAY system. A multiple logistic regression model was used for data analysis. Results: Body weight (BW) and age were positively correlated with the C ₀/D ratio in 194 patients, but the positive correlation disappeared after the patients were divided into oral solution and SR tablet subgroups. The average C ₀/D ratio was significantly increased by 2.11-fold (P = 0.000) in children who took VPA SR tablets compared with children who were administered VPA oral solutions. No significant association between genetic variants and the C ₀/D ratio was found, even for the five well-studied SNPs, namely UGT2B7 G211T, C802T, C161T, T125C, and CYP2C9 ^* 3 A1075C. However, a significant association between the C ₀/D ratio and UGT1A6/9 Del>A (rs144486213) was observed in the VPA oral solution group, but not in the VPA SR tablet group. Conclusions: The dosage forms of sodium valproate, rather than BW, age, or genetic polymorphisms, significantly affected the VPA C ₀/D ratios in pediatric patients with epilepsy. Based on our findings, switching the dosage form between solution and SR tablet should be performed cautiously. Total daily dose adjustment should be considered, and the plasma concentration, seizure-control effect, and adverse drug reaction should also be monitored very closely.

Refining General Principles of Antiepileptic Drug Treatments for Epilepsy

Antiepileptic drugs (AEDs) are the primary treatment strategy for epilepsy. As the use of AEDs has become more widespread and diverse over the past century, it has become necessary to refine the associated prescription strategies. This prompted the Drug Committee of the Korean Epilepsy Society to perform a systemic review of both international and domestic guidelines as well as literature related to medical treatment of epilepsy, and prepared a series of reviews to provide practical guidelines for clinicians to follow. This article is the first in a series on AED treatments for epilepsy in South Korea.

Pharmacokinetics of a commercially available product and a compounded formulation of extended-release levetiracetam after oral administration of a single dose in cats

OBJECTIVE

To compare pharmacokinetics of levetiracetam in serum and CSF of cats after oral administration of extended-release (ER) levetiracetam.

ANIMALS

9 healthy cats.

PROCEDURES

Cats received 1 dose of a commercially available ER levetiracetam product (500 mg, PO). Thirteen blood and 10 CSF samples were collected over a 24-hour period for pharmacokinetic analysis. After 1 week, cats received 1 dose of a compounded ER levetiracetam formulation (500 mg, PO), and samples were obtained at the same times for analysis.

RESULTS

CSF concentrations of levetiracetam closely paralleled serum concentrations. There were significant differences between the commercially available product and the compounded formulation for mean ± SD serum maximum concentration (C_max; 126 ± 33 μg/mL and 169 ± 51 μg/mL, respectively), C_max corrected for dose (0.83 ± 0.10 μg/mL/mg and 1.10 ± 0.28 μg/mL/mg, respectively), and time to C_max (5.1 ± 1.6 hours and 3.1 ± 1.5 hours, respectively). Half-life for the commercially available product and compounded formulation of ER levetiracetam was 4.3 ± 2.0 hours and 5.0 ± 1.6 hours, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The commercially available product and compounded formulation of ER levetiracetam both maintained concentrations in healthy cats 12 hours after oral administration that have been found to be therapeutic in humans (ie, 5 μg/mL). Results of this study supported dosing intervals of 12 hours, and potentially 24 hours, for oral administration of ER levetiracetam to cats. Monitoring of serum concentrations of levetiracetam can be used as an accurate representation of levetiracetam concentrations in CSF of cats.

Lamotrigine in the Prevention of Migraine With Aura: A Narrative Review

BACKGROUND

Lamotrigine is not recommended in the prevention of migraine in general but some reports suggest that it might be effective for treating specifically migraine with aura (MA). This review aims to summarize the related data from the literature and to better understand this discrepancy.

METHODS

All reports from the literature related to the use of lamotrigine in migraine with or without aura published prior to February 2019 found using PUBMED and the 2 keywords "migraine" AND "lamotrigine" were reviewed. Original studies, published in full, systematic reviews, and all case reports were synthetized. We also examined the risk profile, pharmacokinetics, and mode of action of lamotrigine in view of the presumed mechanism of MA.

RESULTS

Lamotrigine was tested in different populations of migraineurs, but previous studies had small sample sizes (n < 35) and might not have been powered enough for detecting a potential benefit of lamotrigine in MA. Accumulating data suggest that the drug can reduce both the frequency and severity of aura symptoms in multiple conditions and is well tolerated.

CONCLUSION

Lamotrigine appears promising for treating attacks of MA and related clinical manifestations because of its high potential of efficacy, low-risk profile, and cost. Additional studies are needed for testing lamotrigine in patients with MA.

A randomized, double-blind, double-dummy, multicenter trial comparing the efficacy and safety of extended- and immediate-release levetiracetam in people with partial epilepsy

PURPOSE

The aim of this trial was to compare the efficacy and safety of two formulations of levetiracetam in people with partial epilepsy over a 12-week treatment period.

METHODS

We performed a randomized, paralleled, and multicenter trial that consisted of a 4-week single-blind placebo run-in, followed by a 12-week double-blind, double-dummy treatment phase to compare the efficacy and safety of levetiracetam extended-release (LEV-ER) and immediate-release (LEV-IR) tablets as an adjunctive treatment in adult patients with uncontrolled epilepsy.

RESULTS

The median partial-onset seizure (POS) frequency per week (min-max) was 0.3 (0.0, 17.4; 95% confidence interval [95% CI] 1.3, 4.8) in the LEV-ER group and 0.3 (0.0, 31.4; 95% CI - 0.1, 4.3) in the LEV-IR group. No serious adverse events occurred during the trial period. Both groups had the same responder rate (58.6%), while a higher rate of seizure freedom over the treatment period was noted in the LEV-ER group compared with the LEV-IR group (27.6% vs. 13.8%, respectively). The European Quality of Life-5 Dimensions scores significantly increased in the LEV-ER-treated group, in contrast to the scores in the LEV-IR group, which decreased (7.2 vs. - 1.5, p = 0.03).

CONCLUSION

These results suggest that LEV-ER is equivalent to LEV-IR in reducing the frequency of POS and has a similar tolerability as LEV-IR as an add-on therapy. In addition, LEV-ER treatment improved the health-related quality of life of people with uncontrolled partial epilepsy.

Population pharmacokinetics of extended-release levetiracetam in epileptic dogs when administered alone, with phenobarbital or zonisamide

BACKGROUND

Extended-release levetiracetam (LEV-XR) has gained acceptance as an antiepileptic drug in dogs. No studies have evaluated its disposition in dogs with epilepsy.

HYPOTHESIS/OBJECTIVES

To evaluate the pharmacokinetics of LEV-XR in epileptic dogs when administered alone or with phenobarbital or zonisamide.

ANIMALS

Eighteen client-owned dogs on steady-state maintenance treatment with LEV-XR (Group L, n = 6), LEV-XR and phenobarbital (Group LP, n = 6), or LEV-XR and zonisamide (Group LZ, n = 6).

METHODS

Pharmacokinetic study. Blood samples were collected at 0, 2, 4, 8, and 12 hours after LEV-XR was administered with food. Plasma LEV concentrations were determined by high-pressure liquid chromatography. A population pharmacokinetic approach and nonlinear mixed effects modeling were used to analyze the data.

RESULTS

Treatment group accounted for most of the interindividual variation. The LP group had lower CMAX (13.38 μg/mL) compared to the L group (33.01 μg/mL) and LZ group (34.13 μg/mL), lower AUC (134.86 versus 352.95 and 452.76 hours·μg/mL, respectively), and higher CL/F (0.17 versus 0.08 and 0.07 L/kg/hr, respectively). The half-life that defined the terminal slope of the plasma concentration versus time curve (~5 hours) was similar to values previously reported for healthy dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Considerable variation exists in the pharmacokinetics of LEV-XR in dogs with epilepsy being treated with a common dose regimen. Concurrent administration of phenobarbital contributed significantly to the variation. Other factors evaluated, including co-administration of zonisamide, were not shown to contribute to the variability. Drug monitoring may be beneficial to determine the most appropriate dose of LEV-XR in individual dogs.

Pharmacokinetics of Rytary®, An Extended-Release Capsule Formulation of Carbidopa-Levodopa

Parkinson's disease (PD) is a chronic progressive neurological disorder characterized by resting tremor, rigidity, bradykinesia, gait disturbance, and postural instability. Levodopa, the precursor to dopamine, coadministered with carbidopa or benserazide, aromatic amino acid decarboxylase inhibitors, is the most effective and widely used therapeutic agent in the treatment of PD. With continued levodopa treatment, a majority of patients develop motor complications such as dyskinesia and motor 'on-off' fluctuations, which are, in part, related to the fluctuations in plasma concentrations of levodopa. A new extended-release (ER) carbidopa-levodopa capsule product (also referred to as IPX066) was developed and approved in the US as Rytary^® and in the EU as Numient^®. The capsule formulation is designed to provide an initial rapid absorption of levodopa comparable to immediate-release (IR) carbidopa-levodopa, and to subsequently provide stable levodopa concentrations with reduced peak-to-trough excursions in plasma concentrations in order to reduce motor fluctuations associated with pulsatile stimulation of dopamine receptors and to minimize dyskinesia. Phase III studies of this ER carbidopa-levodopa capsule formulation in patients with PD have shown a significant reduction in 'off' time compared with IR carbidopa-levodopa and carbidopa-levodopa-entacapone. We present a review of the clinical pharmacokinetics and pharmacodynamics of this ER product of carbidopa-levodopa in healthy subjects and in patients with PD.

A Clinician's Guide to Oral Extended-Release Drug Delivery Systems in Epilepsy

Epilepsy is one of the most common chronic neurologic disorders that affects individuals of all ages. It is primarily managed with antiepileptic drugs (AEDs), with the goal of maintaining complete seizure control combined with minimal or no adverse effects. Oral administration is the mainstay of AED delivery for patients with chronic epilepsy and consists essentially of immediate-release (IR) and modified-release (delayed-release and extended-release [ER]) dosage formulations. Extended-release formulations (hydrophilic or hydrophobic matrix systems, reservoir systems, and osmotic-release systems) release a drug in a controlled manner during an extended period of time following administration. Extended-release formulations have many advantages compared with IR formulations, including simplification of dosing regimens, reduction in pill burden, and reduction in the peak-to-trough fluctuations in serum drug concentration that may be associated with a decreased risk of adverse effects and of seizures. These advantages have the potential to increase adherence to antiepileptic therapy, improve the quality of life of patients, and reduce health care costs. This article, which is intended as a practical guide for clinicians, reviews the properties of the different ER AED formulations currently available and discusses the advantages of ER over IR formulations. Subsequently, an explanation of the technologic basis of the different oral ER formulations, the critical attributes that differentiate ER products, and their individual strengths and weaknesses is provided. Specific recommendations to practitioners on treating patients with ER formulations are included.

Clinical Use and Monitoring of Antiepileptic Drugs

Background

Antiepileptic drugs (AEDs) have been used for the treatment of epilepsy and other neurological disorders since the late 19th century. There are currently several classes of AEDs available for epilepsy management, many of which are also used to treat migraines, bipolar disorder, schizophrenia, depression, and neuropathic pain. Because of their molecular and mechanistic diversity, as well as the potential for drug–drug interactions, AEDs are prescribed and monitored in a highly personalized manner.

Content

This review provides a general overview of the use of AEDs with a focus on the role of therapeutic drug monitoring. Discussed topics include mechanisms of action, guidelines on the clinical applications of AEDs, clinical tests available for AED monitoring, and genetic factors known to affect AED efficacy.

Summary

Implementation of AED therapies is highly individualized, with many patient-specific factors considered for drug and dosage selection. Both therapeutic efficacy and target blood concentrations must be established for each patient to achieve seizure mitigation or cessation. The use of an AED with any additional drug, including other AEDs, requires an evaluation of potential drug–drug interactions. Furthermore, AEDs are commonly used for nonepilepsy indications, often in off-label administration to treat neurological or psychiatric disorders.

Serum levetiracetam concentrations and adverse events after multiple dose extended release levetiracetam administration to healthy cats

BACKGROUND

Multiple dose administration of antiepileptic drugs to cats presents a challenge for owners. Extended release levetiracetam (XRL) has once daily recommended dosing interval, but multiple dose administration of XRL has not been evaluated in cats.

OBJECTIVE

Evaluate serum levetiracetam concentrations and adverse clinical effects after 11 days of once daily XRL administration to healthy cats.

ANIMALS

Nine healthy privately owned cats, body weight ≥ 5 kg METHODS: Extended release levetiracetam (500 mg/cat) was administered PO q24h for 10 days. On day 11, blood was collected at trough, 4, 6, and 8 hours after tablet administration. Owners maintained records of adverse effects throughout study. Levetiracetam was quantitated in serum using immunoassay validated in cats.

RESULTS

Median dose 94.3 mg/kg q24h. Median (range) trough, 4, 6, and 8 hour serum levetiracetam concentrations were 7.0 (2.3-14.1), 82.6 (7.8-125.3), 92.3 (13.3-97.3), and 72 (22.8-96.4) μg/mL, respectively. Peak was not observed in 4 cats because of missed samples (n = 2) and failure to reach maximal concentration (C_max ) by 8 hours (n = 2). Median time of maximal concentration (T_max ) for the remaining 5 cats 5.2 (range 4-6) hours. Adverse effects were minimal and included ataxia (n = 1), sedation (n = 1), and vomiting or regurgitation (n = 1). All signs resolved without dose adjustment or additional treatment.

CONCLUSIONS AND CLINICAL IMPORTANCE

Mean trough serum levetiracetam concentrations were ≥5 μg/mL and adverse effects were minimal throughout dosing period, indicating that the drug was well tolerated. Once daily XRL (500 mg/cat) administration may provide an easier alternative to 3 times daily dosing of intermediate-release levetiracetam for epileptic cats.

Pharmacokinetics of Single Oral Dose Extended-Release Levetiracetam in Healthy Cats

BACKGROUND

Repeated PO dosing of anti-epileptic drugs may contribute to poor compliance in treated cats. Intermediate-release levetiracetam has been used safely in cats, but must be given q8h to maintain serum concentrations in the therapeutic interval for humans (5-45 μg/mL). Approved extended-release levetiracetam (XRL) for human use may require less frequent dosing, but the large dosing unit has limited its use in cats.

HYPOTHESES

In healthy cats, serum levetiracetam concentration will remain above 5 μg/mL for at least 24 hours after administration of a single dose of XRL PO and will be well tolerated.

ANIMALS

7 healthy cats.

METHODS

Extended-release levetiracetam (500 mg) was administered PO. Blood was collected and neurologic examination findings recorded at scheduled times over 30 hours. Serum levetiracetam concentration was quantitated by an immunoassay validated in cats. Data were subjected to noncompartmental analysis. Descriptive statistics were reported.

RESULTS

The median dosage of 86.2 mg/kg, (range, 80-94.3) achieved a mean maximum concentration (C_max ) of 89.8 ± 25.8 μg/mL at 4.9 ±1.57 hours. Serum levetiracetam was >5 μg/mL in all cats by 90 minutes. Mean concentrations were 43.7 ± 18.4 and 4.9 ± 3.4 μg/mL at 12 and 24 hours, respectively. The half-life was 4.1 ± 1.0 hours. The drug was well tolerated.

CONCLUSIONS AND CLINICAL IMPORTANCE

A single 500 mg PO dose of XRL safely maintained serum levetiracetam concentration ≥5 μg/mL in healthy cats for at least 21 hours. Clinical efficacy studies in epileptic cats receiving XRL are indicated; however, monitoring should be implemented for individual cats.

Development of Extended-Release Oral Flexible Tablet (ER-OFT) Formulation for Pediatric and Geriatric Compliance: an Age-Appropriate Formulation

Development of age-appropriate formulation suitable for pediatric and geriatric patients involves various challenges. The objective of this research was to develop extended-release oral flexible tablet (ER-OFT) formulation using carbamazepine (CBZ) as model drug for pediatric and geriatric compliance. ER-microparticles of carbamazepine, a BCS class 2, and narrow therapeutic index (NTI) drug, were prepared using ethyl cellulose as matrixing polymer and hypromellose as hydrophilic pore former. Microparticles were prepared using high-shear granulator fitted with an atomizing spray system. Granulation of carbamazepine and ethyl cellulose (EC-FP) with ethanolic binder solution resulted in ER-microparticles with extended-release >16 h. Release kinetics of ER microparticles showed Higuchi model by drug diffusion and erosion. Korsemeyer-peppas release exponent "n" value 0.42 suggested Fickian diffusion. ER-OFT was prepared by blending of ER-microparticles with water-insoluble compressible aid and disintegrating agent. ER-OFT was characterized for performance characteristics and elemental impurities. As the polymer content in formulation was <10%, the size of ER-OFT was smaller compared to marketed ER-formulations. ER-OFT showed in vitro disintegration time of <30 s as per USP and dispersion time of ∼60 to 180 s in 5 to 10 mL of water. Drug release profiles of ER-microparticles and ER-OFT were comparable as f2 values were >50. In vitro dissolution of ER-OFT was comparable to the marketed ER formulation in the pH range of GIT. ER-OFT can be orally swallowed, orally disintegrating, and used as dispersible tablets. Compared to non-disintegrating type ER-formulations, ER-OFT would provide uniform drug release in GIT with low within-subject variability an essential criterion for NTI drug.

Application of Pharmacokinetics and Pharmacodynamics in Product Life Cycle Management. A Case Study with a Carbidopa-Levodopa Extended-Release Formulation

Increasing costs in discovering and developing new molecular entities and the continuing debate on limited company pipelines mean that pharmaceutical companies are under significant pressure to maximize the value of approved products. Life cycle management in the context of drug development comprises activities to maximize the effective life of a product. Life cycle approaches can involve new formulations, new routes of delivery, new indications or expansion of the population for whom the product is indicated, or development of combination products. Life cycle management may provide an opportunity to improve upon the current product through enhanced efficacy or reduced side effects and could expand the therapeutic market for the product. Successful life cycle management may include the potential for superior efficacy, improved tolerability, or a better prescriber or patient acceptance. Unlike generic products where bioequivalence to an innovator product may be sufficient for drug approval, life cycle management typically requires a series of studies to characterize the value of the product. This review summarizes key considerations in identifying product candidates that may be suitable for life cycle management and discusses the application of pharmacokinetics and pharmacodynamics in developing new products using a life cycle management approach. Examples and a case study to illustrate how pharmacokinetics and pharmacodynamics contributed to the selection of dosing regimens, demonstration of an improved therapeutic effect, or regulatory approval of an improved product label are presented.

Topiramate Extended Release: A Review in Epilepsy

Once-daily oral topiramate extended release (USL255; hereafter referred to as topiramate XR) [QUDEXY(®) XR] is approved in the USA for use as initial monotherapy and adjunctive therapy in patients aged ≥2 years with partial-onset seizures (POS) or primary generalized tonic-clonic seizures and as adjunctive therapy in patients aged ≥2 years with seizures associated with Lennox-Gastaut syndrome. Compared with twice-daily topiramate immediate release at the same total daily dose, topiramate XR provided bioequivalent exposure, an extended absorption rate (permitting convenient once-daily dosing) and more constant therapeutic plasma concentrations (potentially minimizing topiramate-associated adverse events). Switching between the two formulations did not affect the maintenance of topiramate concentrations. Moreover, the contents of a topiramate XR capsule may be sprinkled on to soft food for patients who have difficulty swallowing. In a multinational phase III study in adults with refractory POS, adjunctive topiramate XR was associated with significantly greater improvements from baseline in weekly median seizure frequency and the proportion of patients achieving a ≥50 % reduction in seizure frequency compared with placebo. These benefits were sustained during a 55-week open-label extension study. Adjunctive topiramate XR was generally well tolerated in these studies, with the majority of treatment-emergent adverse events being mild or moderate in intensity. In conclusion, current evidence suggests once-daily topiramate XR extends the treatment options currently available for patients aged ≥2 years with epilepsy, with its dosing regimen potentially delivering tolerability and adherence advantages over AEDs that require more frequent administration.

Ghost-Pill-Buster: A Case Study of Intact Levetiracetam Extended-Release Tablets after Dissolution Testing

BACKGROUND

Orally administered medications in extended-release (ER) dosage forms continue to play a pivotal role in the treatment of various central nervous system disorders. For certain ER dosage forms, pharmaceutical scientists have been familiar with the passage of intact tablet-like objects in patients' feces after administration of ER tablets or capsules based on water-insoluble or slowly dissolving excipients. Nevertheless, because of lack of awareness of the "ghost pill" phenomenon, anxiety has ensued among some patients and clinicians, who have less understanding of how drugs are released from these tablets once ingested. It has been brought to the attention of the US Food and Drug Administration (FDA) that epilepsy patients administered with Teva's levetiracetam ER tablets have noticed intact tablets in their stools and been concerned that they were not getting the needed dose of the drug. In response to neurologists' clinical reporting, the FDA has conducted investigations to confirm a minimal risk of incomplete drug release of Teva's drug product.

OBJECTIVE

The objective of this study was to evaluate the risks of incomplete drug release associated with the passing of intact levetiracetam ER tablets, by conducting in vitro dissolution testing.

METHODS

Dissolution testing of Teva's drug product was performed in accordance with the US Pharmacopeia monograph for levetiracetam ER tablets in phosphate buffer and bio-relevant buffers at different pH values. In addition, dissolution testing was conducted with split and crushed tablets. At the end of the dissolution testing, all samples were visually inspected for any undissolved pieces.

RESULTS

Approximately 90 % of levetiracetam had been released in all dissolution media after 8 h of dissolution. The levetiracetam ER tablets after dissolution testing remained fully intact in all dissolution media. The rates of drug release were significantly faster from split and crushed tablets than that from whole tablets.

CONCLUSION

On the basis of these findings, Teva's levetiracetam ER tablets may appear intact in the stools but have released the drug successfully. The FDA has requested Teva to revise its product labeling to include remarks regarding the potential passing of intact tablets. Since patients who notice ghost pills in their stools may impetuously crush or split the tablets of subsequent doses on their own, healthcare providers should instruct patients to swallow whole tablets throughout the treatment, in accordance with the drug label.

Assessing bioequivalence of generic modified-release antiepileptic drugs

OBJECTIVES

The purpose of this study was to determine how closely generic modified-release antiepileptic drugs (MR-AEDs) resemble reference (brand) formulations by comparing peak concentrations (Cmax), total absorption (area under the curve [AUC]), time to Cmax (Tmax), intersubject variability, and food effects between generic and reference products.

METHODS

We tabulated Cmax and AUC data from the bioequivalence (BE) studies used to support the approvals of generic Food and Drug Administration-approved MR-AEDs. We compared differences in 90% confidence intervals of the generic/reference AUC and Cmax geometric mean ratios, and intersubject variability, Tmax and delivery profiles and food effects.

RESULTS

Forty-two MR-AED formulations were studied in 3,175 healthy participants without epilepsy in 97 BE studies. BE ratios for AUC and Cmax were similar between most generic and reference products: AUC ratios varied by >15% in 11.4% of BE studies; Cmax varied by >15% in 25.8% of studies. Tmax was more variable, with >30% difference in 13 studies (usually delayed in the fed compared to fasting BE studies). Generic and reference MR products had similar intersubject variability. Immediate-release AEDs showed less intersubject variability in AUC than did MR-AEDs.

CONCLUSIONS

Most generic and reference MR-AEDs have similar AUC and Cmax values. Ratios for some products, however, are near acceptance limits and Tmax values may vary. Food effects are common with MR-AED products. High variability in pharmacokinetic values for once-a-day MR-AEDs suggests their major advantage compared to immediate-release AED formulations may be the convenience of less frequent dosing to improve adherence.

Relationship between mono-hydroxy-carbazepine serum concentrations and adverse effects in patients on oxcarbazepine monotherapy

PURPOSE

To evaluate the relationship between serum concentrations of mono-hydroxy-carbazepine (MHD), the main metabolite of oxcarbazepine (OXC), and the occurrence of adverse effects (AE) in a large group of patients on OXC monotherapy.

METHODS

An antiepileptic drug (AED) therapeutic drug monitoring (TDM) database was analyzed especially with regard to OXC dosage, MHD serum concentration, and the occurrence of AE. In total, 893 blood samples of 442 patients were included in this retrospective study. The statistical evaluation was performed by means of Kaplan-Meier estimates, log-rank tests and generalized estimating equations (GEE).

RESULTS

At least one AE was reported in 78 (17.6%) of the 442 patients. At MHD serum concentrations of 30.0 μg/ml and 43.7 μg/ml and OXC dosages of 33.1 mg/kg and 62.3 mg/kg, 25% and 75% of patients, respectively, experienced at least one AE. Log-rank tests indicated that younger patients (<18 years) may be able to tolerate higher MHD serum levels (p = 0.006) and higher OXC dosages per body weight (p < 0.001) compared to adult patients (≥ 18 years). Furthermore, AEs occurred at higher body-weight adjusted OXC dosages of extended release formulations compared to immediate-release formulations (p = 0.010), whereas MHD serum levels at which AEs occurred did not differ significantly between formulations (p = 0.125). Multivariate GEE confirmed the results.

CONCLUSION

The occurrence of AEs is significantly (and non-linearly) dependent on MHD serum level, whereas the dependence of OXC dosage is less distinctive. But, tolerability of OXC seems to depend on age of the patients as well as on pharmaceutical formulation of OXC.

Steady-state pharmacokinetics and bioavailability of immediate-release and extended-release formulations of lamotrigine in elderly epilepsy patients: Use of stable isotope methodology

A classic 2-period crossover bioavailability study was conducted to evaluate the relative and absolute bioavailability of immediate-release (IR) and extended-release (XR) lamotrigine formulations under steady-state conditions in elderly patients with epilepsy. On treatment days, each subject's morning dose (IR or XR lamotrigine) was replaced with an intravenous 50-mg dose of stable-labeled lamotrigine. Lamotrigine concentrations were measured at 13 points between 0 and 96 hours. XR and IR lamotrigine formulations were similar with respect to steady-state area under the concentration-time curve from 0 to 24 hours (AUC0-24 h ss), average concentration (Cavg, ss), and trough concentration (Cτ, ss). A 33% lower fluctuation in concentrations with XR was observed relative to IR lamotrigine. The time to peak concentration (Tmax, ss) was delayed for XR lamotrigine (3.0 vs 1.3 hours) with lower peak concentration (15% lower). The absolute bioavailability for IR and XR formulations was 73% and 92%, respectively. The formulations were bioequivalent with respect to AUC0-24 h ss, Cτ, ss, and Cavg, ss indicating that it may be possible to switch directly from IR to XR lamotrigine without changes in the total daily dose.

Modified-Release Formulations of Second-Generation Antiepileptic Drugs: Pharmacokinetic and Clinical Aspects

Modified-release or extended-release (XR) formulations are used to decrease the frequency of dosing for drugs with rapid elimination, to improve convenience and adherence. Use of a modified-release formulation can decrease the peak to trough fluctuations in serum concentrations and theoretically improve the therapeutic benefit of the drug, by decreasing adverse events associated with the higher peak concentrations. Once-daily formulations of lamotrigine (Lamictal XR(®)), levetiracetam (Keppra XR(®)), oxcarbazepine (Oxtellar XR(®), Apydan(®) extent) and topiramate (Qudexy XR™, Trokendi XR™) are approved for the treatment of focal and/or generalized onset seizures. Other seizure medications have been approved for non-epileptic symptoms. Gabapentin XR (Gralise(®)) is approved for the treatment of post-herpetic neuralgias. Gabapentin enacarbil XR (Horizant(®)) is a prodrug of gabapentin and is indicated for treatment of post-herpetic neuralgia and restless leg syndrome, a novel indication. For all but Qudexy XR™, the tablets/capsules must be swallowed whole, without cutting, crushing or chewing, in order to maintain the XR properties of the formulation. Qudexy XR™ can be swallowed intact or the capsules can be opened and sprinkled onto soft food for those with swallowing difficulties, for example, children and the elderly. The bioavailability of Gralise(®) and Horizant(®) is significantly affected by food, specifically fat content, and should be taken with a meal to maximize absorption. Overall, the primary advantage of the newly released XR formulations is the once-daily dosing to improve convenience and adherence, with very limited data suggesting improved tolerability.

Generic lamotrigine versus brand-name Lamictal bioequivalence in patients with epilepsy: A field test of the FDA bioequivalence standard

OBJECTIVE

To test the current U.S. Food and Drug Administration (FDA) bioequivalence standard in a comparison of generic and brand-name drug pharmacokinetic (PK) performance in "generic-brittle" patients with epilepsy under clinical use conditions.

METHODS

This randomized, double-blind, multiple-dose, steady-state, fully replicated bioequivalence study compared generic lamotrigine to brand-name Lamictal in "generic-brittle" patients with epilepsy (n = 34) who were already taking lamotrigine. Patients were repeatedly switched between masked Lamictal and generic lamotrigine. Intensive PK blood sampling at the end of each 2-week treatment period yielded two 12-h PK profiles for brand-name and generic forms for each patient. Steady-state area under the curve (AUC), peak plasma concentration (Cmax ), and minimum plasma concentration (Cmin ) data were subjected to conventional average bioequivalence (ABE) analysis, reference-scaled ABE analysis, and within-subject variability (WSV) comparisons. In addition, generic-versus-brand comparisons in individual patients were performed. Secondary clinical outcomes included seizure frequency and adverse events.

RESULTS

Generic demonstrated bioequivalence to brand. The 90% confidence intervals of the mean for steady-state AUC, Cmax , and Cmin for generic-versus-brand were 97.2-101.6%, 98.8-104.5%, and 93.4-101.0%, respectively. The WSV of generic and brand were also similar. Individual patient PK ratios for generic-versus-brand were similar but not identical, in part because brand-versus-brand profiles were not identical, even though subjects were rechallenged with the same product. Few subjects had seizure exacerbations or tolerability issues with product switching. One subject, however, reported 267 focal motor seizures, primarily on generic, although his brand and generic PK profiles were practically identical.

SIGNIFICANCE

Some neurologists question whether bioequivalence in healthy volunteers ensures therapeutic equivalence of brand and generic antiepileptic drugs in patients with epilepsy, who may be at increased risk for problems with brand-to-generic switching. Bioequivalence results in "generic-brittle" patients with epilepsy under clinical conditions support the soundness of the FDA bioequivalence standards. Adverse events on generic were not related to the small, allowable PK differences between generic and brand.

A review of the efficacy and safety of extended-release topiramate in the adjunctive treatment for refractory partial-onset seizures

Topiramate has been widely utilized worldwide as an effective medication against partial- and generalized-onset seizures. Extended-release topiramate was developed to provide patients with the convenience of once-daily dosing and potentially improved tolerability by reducing serum concentration fluctuation. USL255 is a once-daily, extended-release formulation of topiramate, which was recently approved in the USA. Compared with immediate-release topiramate taken twice daily, once-daily USL255 provides equivalent topiramate exposure with a 26% reduction in plasma fluctuations. A multinational, phase III, randomized, double-blind, placebo-controlled clinical trial in patients with refractory partial-onset seizures demonstrated that USL255 (200 mg/day) significantly improved seizure control and was well tolerated with low overall neuropsychiatric and neurocognitive adverse events.

USL255 extended-release topiramate for the treatment of epilepsy

USL255 is a once-daily, extended-release formulation of the well-established antiepileptic drug topiramate that was recently approved by the US FDA. As a capsule formulation, USL255 can be swallowed intact or opened and sprinkled onto soft food for patients with swallowing difficulties, including children (≥2 years old) and older patients. USL255 has been evaluated in seven key Phase I and III studies. Compared with immediate-release topiramate taken twice daily, once-daily USL255 provides equivalent topiramate exposure with a 26% reduction in plasma fluctuations. A multinational, Phase III, randomized, double-blind, placebo-controlled clinical trial in patients with refractory partial-onset seizures (PREVAIL) demonstrated that USL255 (200 mg/day) significantly improved seizure control and clinical outcomes versus placebo. USL255 is generally safe and well-tolerated, with a low incidence of neuropsychiatric and neurocognitive adverse events. These data suggest that USL255 may provide a useful treatment option for seizure control with convenient once-daily dosing.

Conversion from immediate-release to extended-release lamotrigine improves seizure control

BACKGROUND

Immediate release lamotrigine (LTG-IR) dosing can be limited by peak toxicity. It is thought that peak levels are responsible for some adverse effects such as dizziness, blurred vision, double vision and unsteadiness. At the same time, trough levels may be associated with reduced seizure threshold. The use of extended release lamotrigine (LTG-XR) to replace LTG-IR will be associated with less fluctuation in drug levels-lower peak levels may reduce adverse effects and higher trough levels may improve seizure control. This hypothesis was tested by analyzing seizure control and adverse effects before and after conversion from LTG-IR to LTG-XR in patients who underwent such conversion in 2009-2011.

METHODS

We searched our patient database to identify patients converted from LTG-IR to LTG-XR for persistent seizures or adverse effects from August 2009 until December 31, 2011. We included only patients who took LTG-IR and LTG-XR for at least 6 months each. We excluded patients with nonepileptic seizures, progressive cause of epilepsy, or not keeping a seizure record. We collected the following parameters: age at conversion, LTG-IR dose and dosing schedule, duration on that dose, LTG-XR dose and dosing schedule, LTG serum level before and after conversion, duration of LTG-XR treatment, seizure frequency before and after conversion, and change in adverse experience profile. We also recorded baseline AEDs and any AED change during the course of the analysis.

RESULTS

Fifty five patients (26 female) satisfied the inclusion/exclusion criteria. Their mean age was 45 years (range 23 to 86). Ten were on LTG-IR monotherapy, 24 took LTG-IR plus one other AED, most commonly levetiracetam, and the remaining 21 took LTG-IR plus at least 2 other AEDs. The mean LTG-IR dose was 544 mg/day (range 150-1100 mg/day). The mean LTG-IR serum level was 11.6 (available in 53 patients-range 4.6-21 mcg/ml). Twenty six patients were converted to the same dose and one patient took a mixture of LTG-XR and LTG-IR at the same total daily dose, while 21 had their dose slightly increased and 7 had their dose slightly decreased due to adverse effects. The mean serum level after conversion was 11.8 (available in 49 patients-range 2.6-21.2 mcg/ml). As a result of the conversion, 26 patients (47%) experienced >50% reduction in seizure frequency. There was a 46% median reduction in seizure frequency overall. Seven patients reported improvement in adverse effects.

CONCLUSION

A conversion from LTG-IR to LTG-XR can help improve seizure control in some individuals with drug-resistant epilepsy, in addition to improving tolerability. While it is indicated in individuals experiencing peak adverse effects, it should also be considered in patients who have received incomplete seizure control from LTG-IR.

Once-daily USL255 as adjunctive treatment of partial-onset seizures: randomized phase III study

OBJECTIVE

To evaluate the efficacy and safety of USL255, Qudexy(™) XR (topiramate) extended-release capsules, as an adjunctive treatment for refractory partial-onset seizures (POS) in adults taking one to three concomitant antiepileptic drugs.

METHODS

In this global phase III study (PREVAIL; NCT01142193), 249 adults with POS were randomized 1:1 to once-daily USL255 (200 mg/day) or placebo. The primary and key secondary efficacy endpoints were median percent reduction in weekly POS frequency and responder rate (proportion of patients with ≥ 50% reduction in seizure frequency). Seizure freedom was also assessed. Safety (adverse events, clinical and laboratory findings), as well as treatment effects on quality of life (QOLIE-31-P) and clinical global impression of change (CGI-C), were evaluated.

RESULTS

Across the entire 11-week treatment phase, USL255 significantly reduced the median percent seizure frequency and significantly improved responder rate compared with placebo. Efficacy over placebo was observed early in treatment, in patients with highly refractory POS, and in those with the most debilitating seizure types (i.e., complex partial, partial secondarily generalized). USL255 was safe and generally well tolerated with a low incidence of neurocognitive adverse events. USL255 was associated with significant clinical improvement without adversely affecting quality of life.

SIGNIFICANCE

The PREVAIL phase III clinical study demonstrated that once-daily USL255 (200 mg/day) significantly improved seizure control and was safe and generally well tolerated with few neurocognitive side effects.

The practical impact of altered dosing on perampanel plasma concentrations: pharmacokinetic modeling from clinical studies

RATIONALE

Perampanel is a selective AMPA receptor antagonist approved for adjunctive therapy in patients with refractory partial-onset seizures. Perampanel is metabolized primarily via CYP3A4, yet it has a relatively long half-life of 105h; it is, therefore, recommended that perampanel be given once daily (preferably at bedtime). Many patients occasionally have less-than-perfect adherence to their drug regimen, and given the known pharmacokinetic interactions of perampanel with commonly used enzyme-inducing antiepileptic drugs (EIAEDs), we explored the effects of a missed dose on steady-state perampanel plasma concentrations and the ramifications of "make up" doses in these patients. Although perampanel is approved for once-daily dosing, some clinicians may elect to give perampanel as a divided dose (i.e., twice daily), so we also sought to examine the pharmacokinetic impact of twice- versus once-daily dosing.

METHODS

Pharmacokinetic simulations were performed using validated perampanel pharmacokinetic parameters, derived from 19 phase I studies in 606 subjects, to investigate the effect on perampanel plasma concentration of (1) missing a dose of perampanel followed by delayed replacement of the missed dose, (2) missing a dose followed by resumption of scheduled therapy, and (3) missing a dose in the presence/absence of carbamazepine. Simulations were done for a typical patient receiving an 8-mg once-daily or a 4-mg twice-daily dose using the nonlinear mixed effects program, NONMEM v7.2, in conjunction with PDx-pop v5.

RESULTS

Our results corroborate that given the pharmacokinetic characteristics of perampanel, a missed dose is unlikely to cause as much fluctuation in plasma concentration as would be expected for a drug with a short half-life. Importantly, simulations suggest that supplementing a missed dose 6-12h later, followed by continuation of the regular schedule, may not result in any significant "spikes" in perampanel plasma concentrations. Simulations demonstrated that twice-daily dosing offered little advantage in further flattening the concentration-time profile of perampanel in the adherent patient. However, fluctuations in plasma concentrations are minimized by twice-daily dosing in patients receiving concomitant EIAEDs.

CONCLUSIONS

These pharmacokinetic simulations suggest that the long half-life of perampanel may be advantageous in conferring a relatively smooth concentration-time profile with a once-daily or twice-daily dosing, even in the presence of concomitant EIAEDs. However, the results of the present study suggest that perampanel replacement is recommended for patients taking an EIAED to mitigate the potential risks associated with reduced exposure. Confirmation of the ultimate clinical impact of these findings will require further study.

USL255 extended-release topiramate: dose-proportional pharmacokinetics and tolerability in healthy volunteers

Objective

Evaluate the pharmacokinetics (PK), safety, and tolerability of single doses of once-daily USL255, Qudexy XR (topiramate) extended-release capsules, over a wide dosing range.

Methods

Two single-dose, phase I studies in healthy adults were used to evaluate the PK profile and maximum tolerated dose (MTD) of USL255 from 25–1,400 mg. Standard PK parameters assessed included area under the plasma concentration-time curve (AUC) and maximum plasma concentration (C_max). Dose proportionality, linearity, and intersubject and intrasubject variability (coefficient of variation [%CV]) of AUC and C_max were evaluated. Investigator-reported adverse events (AEs) were obtained throughout the studies.

Results

After the initial increase in plasma concentration levels immediately following administration of USL255 25–1,400 mg, plasma topiramate concentration-time profiles were flat up to 24 h after dosing. AUC was dose proportional from 25–1,400 mg, and C_max was dose proportional from 50–1,400 mg; both AUC and C_max were linear across the entire dose range. Low intersubject and intrasubject %CV values were observed for AUC_0−t, AUC_0−∞, and C_max (intersubject %CV: 20.2, 19.6, and 22.4%, respectively; intrasubject %CV of dose-normalized mean values: 10.8, 8.2, and 13.2%, respectively). USL255 was generally safe and well tolerated with MTD established at 1,200 mg.

Significance

These results demonstrate that USL255 provides consistent plasma topiramate exposure across an extended-dosing interval and predictable plasma topiramate concentrations over a wide dosing range. Overall, the favorable safety profile and consistency of exposure suggest once-daily USL255 can be a useful treatment option for patients with epilepsy.

Valproyl-CoA inhibits the activity of ATP- and GTP-dependent succinate:CoA ligases

BACKGROUND

Valproic acid (VPA) is an effective antiepileptic drug that may induce progressive microvesicular steatosis. The impairment of mitochondrial function may be an important metabolic effect of VPA treatment with potential adverse consequences.

OBJECTIVE

To investigate the influence of VPA on the activity of GTP- and ATP-specific succinate:CoA ligases (G-SUCL and A-SUCL).

METHODS

The GTP- and ATP-specific SUCL activities were measured in human fibroblasts in the reverse direction, i.e. the formation of succinyl-CoA. These were assessed at different concentrations of succinate in the presence of VPA, valproyl-CoA and zinc chloride, an established inhibitor of the enzymes. Activities were measured using an optimized HPLC procedure.

RESULTS

Valproyl-CoA (1 mM) inhibited the activity of A-SUCL and G-SUCL by 45-55% and 25-50%, respectively. VPA (1 mM) had no influence on the activity of the two enzymes.

DISCUSSION

Valproyl-CoA appears to affect the activity of SUCL, especially with the ATP-specific enzyme. Considering the key role of SUCL in the Krebs cycle, interference with its activity might impair the cellular energy status. Moreover, A-SUCL is bound to the nucleoside diphosphate kinase (NDPK), which is responsible for the mitochondrial (deoxy)nucleotide synthesis. An inhibition of A-SUCL might influence the activity of NDPK inducing an imbalance of nucleotides in the mitochondria and eventually mitochondrial DNA depletion. This may account for the potential liver failure associated with valproate therapy, reported in patients with deficiencies within the mitochondrial DNA replicase system such as polymerase gamma 1.

Perspective on the use of perampanel and intravenous carbamazepine for generalized seizures

INTRODUCTION

Several antiepileptic drugs are available for the treatment of epileptic patients. However, the treatment of some seizure types and novel drug formulations deserve further advances in epilepsy research.

AREAS COVERED

The authors analyze the published evidence on the efficacy of perampanel against secondarily generalized seizures (SGS) and report the currently available development of intravenous (IV) formulations of carbamazepine (CBZ), commenting on their potential in the clinical setting.

EXPERT OPINION

Perampanel is the first noncompetitive AMPA receptor antagonist to be approved as adjunctive treatment in patients with partial-onset (focal) seizures (POS) with or without secondary generalization. Apart from its efficacy and safety on POS, a consistent body of evidence supports its efficacy in SGS at a minimum dose of 8 mg/day; however, such dose appears close to the best-tolerated dose. CBZ is a poorly water-soluble compound; many efforts to develop a parenteral formulation have not been successful so far. Novel IV CBZ formulations seem to exhibit favorable pharmacokinetics along with good tolerability in animal models and in patients taking oral CBZ. Further studies are needed to assess whether larger doses will be as well tolerated, allowing IV CBZ to be used as bridge therapy when the oral route is not feasible or in patients naïve to CBZ.