Zonisamide

INDICATIONS AND USAGE Zonisamide capsules USP are indicated as adjunctive therapy in the treatment of partial seizures in adults with epilepsy.

DOSAGE AND ADMINISTRATION Zonisamide capsules are recommended as adjunctive therapy for the treatment of partial seizures in adults. Safety and efficacy in pediatric patients below the age of 16 have not been established. Zonisamide capsules should be administered once or twice daily, using 25 mg, 50 mg or 100 mg capsules. Zonisamide capsules are given orally and can be taken with or without food. Capsules should be swallowed whole. Adults over Age 16: The prescriber should be aware that, because of the long half-life of zonisamide, up to two weeks may be required to achieve steady state levels upon reaching a stable dose or following dosage adjustment. Although the regimen described below is one that has been shown to be tolerated, the prescriber may wish to prolong the duration of treatment at the lower doses in order to fully assess the effects of zonisamide at steady state, noting that many of the side effects of zonisamide are more frequent at doses of 300 mg per day and above. Although there is some evidence of greater response at doses above 100 to 200 mg/day, the increase appears small and formal dose-response studies have not been conducted. The initial dose of zonisamide capsules should be 100 mg daily. After two weeks, the dose may be increased to 200 mg/day for at least two weeks. It can be increased to 300 mg/day and 400 mg/day, with the dose stable for at least two weeks to achieve steady state at each level. Evidence from controlled trials suggests that zonisamide capsules doses of 100 to 600 mg/day are effective, but there is no suggestion of increasing response above 400 mg/day (see CLINICAL PHARMACOLOGY, Clinical Studies subsection). There is little experience with doses greater than 600 mg/day. Patients with Renal or Hepatic Disease: Because zonisamide is metabolized in the liver and excreted by the kidneys, patients with renal or hepatic disease should be treated with caution, and might require slower titration and more frequent monitoring (see CLINICAL PHARMACOLOGY and PRECAUTIONS ).

CONTRAINDICATIONS Zonisamide capsules are contraindicated in patients who have demonstrated hypersensitivity to sulfonamides or zonisamide.

ADVERSE REACTIONS The most commonly observed adverse events related to treatment with zonisamide (an incidence at least 4% greater than placebo) in controlled clinical trials and shown in descending order of frequency were somnolence, anorexia, dizziness, ataxia, agitation/irritability, and difficulty with memory and/or concentration. In controlled clinical trials, 12% of patients receiving zonisamide as adjunctive therapy discontinued due to an adverse event compared to 6% receiving placebo. Approximately 21% of the 1,336 patients with epilepsy who received zonisamide in clinical studies discontinued treatment because of an adverse event. The adverse events most commonly associated with discontinuation were somnolence, fatigue and/or ataxia (6%), anorexia (3%), difficulty concentrating (2%), difficulty with memory, mental slowing, nausea/vomiting (2%), and weight loss (1%). Many of these adverse events were dose-related (see WARNINGS and PRECAUTIONS ). Adverse Event Incidence in Controlled Clinical Trials: Table 4 lists treatment-emergent adverse events that occurred in at least 2% of patients treated with zonisamide in controlled clinical trials that were numerically more common in the zonisamide group. In these studies, either zonisamide or placebo was added to the patient’s current AED therapy. Adverse events were usually mild or moderate in intensity. The prescriber should be aware that these figures, obtained when zonisamide was added to concurrent AED therapy, cannot be used to predict the frequency of adverse events in the course of usual medical practice when patient characteristics and other factors may differ from those prevailing during clinical studies. Similarly, the cited frequencies cannot be directly compared with figures obtained from other clinical investigations involving different treatments, uses, or investigators. An inspection of these frequencies, however, does provide the prescriber with one basis by which to estimate the relative contribution of drug and non-drug factors to the adverse event incidences in the population studied. Table 4 Incidence (%) of Treatment-Emergent Adverse Events in Placebo-Controlled, Add-On Trials (Events that occurred in at least 2% of Zonisamide treated patients and occurred more frequently in Zonisamide treated than placebo-treated patients) BODY SYSTEM/ PREFERRED TERM Zonisamide (n=269) % Placebo (n=230) % BODY AS A WHOLE Headache 10 8 Abdominal Pain 6 3 Flu Syndrome 4 3 DIGESTIVE Anorexia 13 6 Nausea 9 6 Diarrhea 5 2 Dyspepsia 3 1 Constipation 2 1 Dry Mouth 2 1 HEMATOLOGIS ANDA LYMPHATIC Ecchymosis 2 1 METABOLIC AND NUTRITIONAL Weight Loss 3 2 NERVOUS SYSTEM Dizziness 13 7 Ataxia 6 1 Nystagmus 4 2 Paresthesia 4 1 NEUROPSYCHIATIC AND COGNITIVE DYSFUNCTION-ALTERED COGNITIVE FUNCTION Confusion 6 3 Difficulty Concentrating 6 2 Difficulty with Memory 6 2 Mental Slowing 4 2 NEUROPSYCHIATIC AND COGNITIVE DYSFUNCTION-BEHAVIORAL ABNORMALITIES (NON-PYSCHOSIS-RELATED) Agitation/Irritability 9 4 Depression 6 3 Insomnia 6 3 Anxiety 3 2 Nervousness 2 1 NEUROPSYCHIATIC AND COGNITIVE DYSFUNCTION-BEHAVIORAL ABNORMALITIES (PYSCHOSIS-RELATED) Schizophrenic/Schizophreniform Behavior 2 0 NEUROPSYCHIATIC AND COGNITIVE DYSFUNCTION-CNS DEPRESSION Somnolence 17 7 Fatigue 8 6 Tiredness 7 5 NEUROPSYCHIATIC AND COGNITIVE DYSFUNCTION-SPEECH AND LANGUAGE ABNORMALITIES Speech Abnormalities 5 2 Difficulties in Verbal Expression 2 <1 RESPIRATORY Rhinitis 2 1 SKIN AND APPENDAGES Rash 3 2 SPECIAL SENSES Diplopia 6 3 Taste Perversion 2 0 Other Adverse Events Observed During Clinical Trials: zonisamide has been administered to 1,598 individuals during all clinical trials, only some of which were placebo-controlled. During these trials, all events were recorded by the investigators using their own terms. To provide a useful estimate of the proportion of individuals having adverse events, similar events have been grouped into a smaller number of standardized categories using a modified COSTART dictionary. Th …

Drug Interactions: Effects of zonisamide on the pharmacokinetics of other antiepilepsy drugs (AEDs): Zonisamide had no appreciable effect on the steady state plasma concentrations of phenytoin, carbamazepine, or valproate during clinical trials. Zonisamide did not inhibit mixed-function liver oxidase enzymes (cytochrome P450), as measured in human liver microsomal preparations, in vitro. Zonisamide is not expected to interfere with the metabolism of other drugs that are metabolized by cytochrome P450 isozymes. Effects of other drugs on zonisamide pharmacokinetics: Drugs that induce liver enzymes increase the metabolism and clearance of zonisamide and decrease its half-life. The half-life of zonisamide following a 400 mg dose in patients concurrently on enzyme-inducing AEDs such as phenytoin, carbamazepine, or phenobarbital was between 27 to 38 hours; the half-life of zonisamide in patients concurrently on the non-enzyme inducing AED, valproate, was 46 hours. Concurrent medication with drugs that either induce or inhibit CYP3A4 would be expected to alter serum concentrations of zonisamide. Interaction with cimetidine: Zonisamide single dose pharmacokinetic parameters were not affected by cimetidine (300 mg four times a day for 12 days). Drug Interactions with CNS Depressants: Concomitant administration of zonisamide and alcohol or other CNS depressant drugs has not been evaluated in clinical studies. Because of the potential of zonisamide to cause CNS depression, as well as other cognitive and/or neuropsychiatric adverse events, zonisamide should be used with caution if used in combination with alcohol or other CNS depressants. Other Carbonic Anhydrase Inhibitors: Concomitant use of zonisamide, a carbonic anhydrase inhibitor, with any other carbonic anhydrase inhibitor (e.g., topiramate, acetazolamide or dichlorphenamide), may increase the severity of metabolic acidosis and may also increase the risk of kidney stone formation. Therefore, if zonisamide is given concomitantly with another carbonic anhydrase inhibitor, the patient should be monitored for the appearance or worsening of metabolic acidosis (see CLINICAL PHARMACOLOGY , Interactions of Zonisamide with Other Carbonic Anhydrase Inhibitors subsection).

Mechanism of Action The precise mechanism(s) by which zonisamide exerts its antiseizure effect is unknown. Zonisamide demonstrated anticonvulsant activity in several experimental models. In animals, zonisamide was effective against tonic extension seizures induced by maximal electroshock but ineffective against clonic seizures induced by subcutaneous pentylenetetrazol. Zonisamide raised the threshold for generalized seizures in the kindled rat model and reduced the duration of cortical focal seizures induced by electrical stimulation of the visual cortex in cats. Furthermore, zonisamide suppressed both interictal spikes and the secondarily generalized seizures produced by cortical application of tungstic acid gel in rats or by cortical freezing in cats. The relevance of these models to human epilepsy is unknown. Zonisamide may produce these effects through action at sodium and calcium channels. In vitro pharmacological studies suggest that zonisamide blocks sodium channels and reduces voltage-dependent, transient inward currents (T-type Ca 2+ currents), consequently stabilizing neuronal membranes and suppressing neuronal hypersynchronization. In vitro binding studies have demonstrated that zonisamide binds to the GABA/benzodiazepine receptor ionophore complex in an allosteric fashion which does not produce changes in chloride flux. Other in vitro studies have demonstrated that zonisamide (10 mcg/mL to 30 mcg/mL) suppresses synaptically-driven electrical activity without affecting postsynaptic GABA or glutamate responses (cultured mouse spinal cord neurons) or neuronal or glial uptake of [ 3 H]-GABA (rat hippocampal slices). Thus, zonisamide does not appear to potentiate the synaptic activity of GABA. In vivo microdialysis studies demonstrated that zonisamide facilitates both dopaminergic and serotonergic neurotransmission. Zonisamide is a carbonic anhydrase inhibitor. The contribution of this pharmacological action to the therapeutic effects of zonisamide is unknown. However, as a carbonic anhydrase inhibitor, zonisamide may cause metabolic acidosis (see WARNINGS, Metabolic Acidosis subsection).

DESCRIPTION Zonisamide USP is an antiseizure drug chemically classified as a sulfonamide and unrelated to other antiseizure agents. The active ingredient is zonisamide USP, 1,2 benzisoxazole-3-methanesulfonamide. The empirical formula is C 8 H 8 N 2 O 3 S with a molecular weight of 212.23. Zonisamide USP is a white powder, pK a = 10.2, and is moderately soluble in water (0.80 mg/mL) and 0.1 N HCl (0.50 mg/mL). The chemical structure is: Zonisamide USP is supplied for oral administration as capsules containing 25 mg, 50 mg or 100 mg zonisamide USP. Each capsule contains the labeled amount of zonisamide USP plus the following inactive ingredients: microcrystalline cellulose, hydrogenated vegetable oil, and sodium lauryl sulfate. The printed capsule shell of the different strengths is made from the following ingredients: 25 mg – D&C Red #28, FD&C Blue #1, gelatin and titanium dioxide 50 mg – D&C Yellow #10, FD&C Blue #1, FD&C Red #40, gelatin and titanium dioxide 100 mg - D&C Yellow #10, FD&C Blue #1, FD&C Yellow #6, gelatin and titanium dioxide The dyes used in the printing ink are FD&C Blue #1, FD&C Blue #2, FD&C Red #40, D&C Yellow #10 aluminium lake and iron oxide black. Additionally, the printing ink also contains n-butyl alcohol, ethanol, propylene glycol and shellac. Chemical Formula of Zonisamide

OVERDOSAGE Human Experience: Experience with Zonisamide Capsules daily doses over 800 mg/day is limited. During Zonisamide Capsules clinical development, three patients ingested unknown amounts of Zonisamide Capsules as suicide attempts, and all three were hospitalized with CNS symptoms. One patient became comatose and developed bradycardia, hypotension, and respiratory depression; the zonisamide plasma level was 100.1 mcg/mL measured 31 hours post-ingestion. Zonisamide plasma levels fell with a half-life of 57 hours, and the patient became alert five days later. Management: No specific antidotes for Zonisamide Capsules overdosage are available. Following a suspected recent overdose, emesis should be induced or gastric lavage performed with the usual precautions to protect the airway. General supportive care is indicated, including frequent monitoring of vital signs and close observation. Zonisamide has a long half-life (see CLINICAL PHARMACOLOGY section). Due to the low protein binding of zonisamide (40%), renal dialysis may be effective. The effectiveness of renal dialysis as a treatment of overdose has not been formally studied. A poison control center should be contacted for information on the management of Zonisamide Capsules overdosage.

HOW SUPPLIED Zonisamide capsules USP, 25 mg are white to off white granular powder filled in size '4' hard gelatin capsules with pink colored cap printed with "ZA-31" in black ink and white colored body printed with "25 mg" in black ink, which are supplied as follows. NDC 72578-040-01 in bottles of 100's capsules with child-resistant closure NDC 72578-040-05 in bottles of 500's capsules Zonisamide capsules USP, 50 mg are white to off white granular powder filled in size '3' hard gelatin capsules with pink colored cap printed with "ZA-32" in black ink and white colored body printed with "50 mg" in black ink, which are supplied as follows. NDC 72578-041-01 in bottles of 100's capsules with child-resistant closure NDC 72578-041-05 in bottles of 500's capsules Zonisamide capsules USP, 100 mg are white to off white granular powder filled in size '1' hard gelatin capsules with pink colored cap printed with "ZA-33" in black ink and white colored body printed with "100 mg" in black ink, which are supplied as follows. NDC 72578--042-01 in bottles of 100's capsules with child-resistant closure NDC 72578-042-05 in bottles of 500's capsules NDC 72578-042-10 in bottles of 1,000's capsules Storage Store at 20 o C to 25 o C (68 o F to 77 o F) [see USP Controlled Room Temperature]. Keep in dry place and protect from light. Medication Guide available at www.vionausa.com/medguides or call 1-888-304-5011. Manufactured by: Zydus Lifesciences Ltd. Ahmedabad, India Distributed by: Viona Pharmaceuticals Inc. Cranford, NJ 07016 Rev.: 12/22