Evaluation of zonisamide for the treatment of focal epilepsy: a review of pharmacokinetics, clinical efficacy and adverse effects

An isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS)-based candidate reference measurement procedure for the quantification of zonisamide in human serum and plasma

OBJECTIVES

To describe and validate an isotope dilution-liquid chromatograph-tandem mass spectrometry (ID-LC-MS/MS) based reference measurement procedure (RMP) for zonisamide to accurately measure serum and plasma concentrations.

METHODS

Quantitative nuclear magnetic resonance (qNMR) spectroscopy was employed to determine the absolute content of the reference material used in order to establish traceability to SI units. Separation of zonisamide from known or unknown interferences was performed on a C8 column. For sample preparation a protocol based on protein precipitation in combination with a high dilution step was established. Assay validation and determination of measurement uncertainty were performed based on guidelines from the Clinical and Laboratory Standards Institute, the International Conference on Harmonization, and the Guide to the expression of uncertainty in measurement.

RESULTS

The RMP was proven to be highly selective and specific with no evidence of a matrix effect, allowing for quantification of zonisamide within the range of 1.50-60.0 μg/mL. Intermediate precision was <1.4 % and repeatability CV ranged from 0.7 to 1.2 % over all concentration levels. The relative mean bias ranged from 0.0 to 0.8 % for native serum levels and from 0.2 to 2.0 % for Li-heparin plasma levels. The measurement uncertainties for single measurements and target value assignment ranged from 1.1 to 1.4 % and 0.8-1.0 %, respectively.

CONCLUSIONS

We present a novel LC-MS/MS-based candidate RMP for zonisamide in human serum and plasma which provides a traceable and reliable platform for the standardization of routine assays and evaluation of clinically relevant samples.

Role of zonisamide in advanced Parkinson's disease: a randomized placebo-controlled study

BACKGROUND

Zonisamide (ZNS) has shown some efficacy in motor symptoms of PD; however, more evidence is lacking, and its effects on nonmotor symptoms (NMSs) and quality of life (QoL) remain to be investigated. This randomized double-blinded placebo-controlled crossover study investigated the effect of ZNS on motor and NMS symptoms and QoL in advanced PD.

METHODS

PD patients with Hoehn and Yahr stage ≥ 2 ("On" state) and at least 2 h off time daily were randomized to groups: ZNS 25 mg, ZNS 50 mg and placebo. Groups were assessed at baseline and at the 1- and 3-month follow-ups. The primary endpoint was the change in the total MDS-UPDRS III "On", while the secondary endpoint was the change in the total and parts I and IV MDS-UPDRS, Nonmotor Symptoms Scale and Parkinson's disease questionnaire-39 at the final assessment.

RESULTS

Sixty-nine patients were assessed for efficacy at the 1-month follow-up, and 58 patients were assessed at the 3-month follow-up. The primary endpoint showed significant improvement in the ZNS 25 mg group compared to the placebo group (p = 0.009). At the final assessment, the ZNS 25 mg group showed significant improvement of total and part VI MDS-UPDRS, bradykinesia, tremor and functional impact of fluctuations compared to placebo. There was no change in dyskinesia, NMSs, QoL or side effects except for sedation.

CONCLUSION

ZNS has a favourable effect on motor symptoms in patients with wearing off as adjunctive therapy with other dopaminergic drugs, with no exacerbation of dyskinesia and a limited impact on NMSs and QoL.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT04182399, in 24/11/2019.

Bioequivalence of Different Formulations of Zonisamide Oral Suspensions: A Short Review

To satisfy the needs of pediatric and other patients with focal onset seizures who cannot swallow solid dosage forms of zonisamide, an oral liquid form of this drug is necessary in clinical practice. Although there are two oral suspensions of zonisamide with marketing authorization (MA), there are issues of availability and high cost which limit their use and inspire extemporaneous compounding. Extemporaneously compounded oral suspensions of zonisamide are prepared according to different formulas and vary in stability; therefore it is essential to test this characteristic. Bioequivalence of extemporaneously compounded oral suspensions has never been tested, and the efficacy and safety of zonisamide oral suspensions have generally not been demonstrated in clinical trials. As a narrow therapeutic window drug, zonisamide requires precision in dosing, which could be achieved only with dosage forms with established bioavailability, efficacy, and safety. In order to avoid underdosing and toxicity with zonisamide oral suspensions and utilize their full therapeutic potential, it is necessary to perform bioequivalence studies with each variation of extemporaneously compounded oral suspension and also clinical trials with both commercial and extemporaneous oral suspensions of zonisamide.

Pharmacokinetic Drug-Drug Interactions among Antiepileptic Drugs, Including CBD, Drugs Used to Treat COVID-19 and Nutrients

Anti-epileptic drugs (AEDs) are an important group of drugs of several generations, ranging from the oldest phenobarbital (1912) to the most recent cenobamate (2019). Cannabidiol (CBD) is increasingly used to treat epilepsy. The outbreak of the SARS-CoV-2 pandemic in 2019 created new challenges in the effective treatment of epilepsy in COVID-19 patients. The purpose of this review is to present data from the last few years on drug–drug interactions among of AEDs, as well as AEDs with other drugs, nutrients and food. Literature data was collected mainly in PubMed, as well as google base. The most important pharmacokinetic parameters of the chosen 29 AEDs, mechanism of action and clinical application, as well as their biotransformation, are presented. We pay a special attention to the new potential interactions of the applied first-generation AEDs (carbamazepine, oxcarbazepine, phenytoin, phenobarbital and primidone), on decreased concentration of some medications (atazanavir and remdesivir), or their compositions (darunavir/cobicistat and lopinavir/ritonavir) used in the treatment of COVID-19 patients. CBD interactions with AEDs are clearly defined. In addition, nutrients, as well as diet, cause changes in pharmacokinetics of some AEDs. The understanding of the pharmacokinetic interactions of the AEDs seems to be important in effective management of epilepsy.

Medical Management in Focal versus Generalized Epilepsy

About 70% of children with new-onset epilepsy have the potential to become seizure-free on antiepileptic drug (AED) monotherapy with appropriately selected first-line medication. In ideal world, physician is expected to achieve best possible seizure control without impacting the quality of life. There is rapid increase in number of AEDs available over last couple of decades. Although not necessarily all of them are superior to old generation drugs in terms of seizure control, certainly there is change in landscape from perspective of tolerability and side-effect profile. Physicians must therefore be familiar with safety, tolerability, therapeutic effects, synergistic combinations as well as AEDs to avoid in specific circumstances. The article attempts to give general overview of available AEDs under broad umbrella of effectiveness against focal and generalized seizures as well as drugs with “broad spectrum.” The emergence of newer AEDs with broad spectrum and favorable side-effect profile is welcome. However, the future lies in better understanding of underlying diverse pathophysiology of clinical symptom “epilepsy” and developing new compounds acting on molecular targets as well as individualizing therapy. Technological advances in molecular genetics research are bringing precision medicine to the fore.

Pharmacological management of dementia with Lewy bodies with a focus on zonisamide for treating parkinsonism

INTRODUCTION

Dementia with Lewy bodies (DLB) has no approved symptomatic or disease-modifying treatments in the US and Europe, despite being the second most common cause of neurodegenerative dementia.

AREAS COVERED

Herein, the authors briefly review the DLB drug development pipeline, providing a summary of the current pharmacological intervention studies. They then focus on the anticonvulsant zonisamide, a benzisoxazole derivative with a sulfonamide group and look at its value for treating parkinsonism in DLB.

EXPERT OPINION

Several new compounds are being tested in DLB, the most innovative being those aimed at decreasing brain accumulation of α-synuclein. Unfortunately, new drug testing is challenging in terms of consistent diagnostic criteria and lack of reliable biomarkers. Few randomized controlled trials (RCTs) are well-designed, with enough power to detect significant drug effects. Levodopa monotherapy can treat the parkinsonism in DLB, but it can cause agitation or visual hallucination worsening. Two Phase II/III RCTs of DLB patients recently reported a statistically significant improvement in motor function in those receiving zonisamide as an adjunctive treatment to levodopa. New biomarker strategies and validated outcome measures for DLB or prodromal DLB may enhance clinical trial design for the development of specific disease-modifying treatments.