ZONISAMIDE: 4,764 Adverse Event Reports & Safety Profile

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

AND USAGE ZONISADE is indicated as adjunctive therapy for the treatment of partial-onset seizures in adults and pediatric patients 16 years and older. ZONISADE is indicated as adjunctive therapy for the treatment of partial-onset seizures in adults and pediatric patients 16 years of age and older ( 1 ).

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 ).

ZONISADE is contraindicated in patients who have demonstrated hypersensitivity to sulfonamides or zonisamide. ZONISADE is contraindicated in patients who have demonstrated hypersensitivity to sulfonamides or zonisamide ( 4 ).

REACTIONS The following clinically signification adverse reactions are described elsewhere in the labeling:

• Potentially Fatal Reactions to Sulfonamides [see Warnings and Precautions ( 5.1 )]
• Serious Skin Reactions [see Warnings and Precautions ( 5.2 )]
• Serious Hematologic Events [see Warnings and Precautions ( 5.3 )]
• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multi-Organ Hypersensitivity [see Warnings and Precautions ( 5.4 )]
• Oligohidrosis and Hyperthermia in Pediatric Patients [see Warnings and Precautions ( 5.5 )]
• Acute Myopia and Secondary Angle Closure Glaucoma [see Warnings and Precautions ( 5.6 )]
• Suicidal Behavior and Ideation [see Warnings and Precautions ( 5.7 )]
• Metabolic Acidosis [see Warnings and Precautions ( 5.8 )]
• Seizures on Withdrawal of Antiepileptic Drugs [see Warnings and Precautions ( 5.9 )]
• Teratogenicity [see Warnings and Precautions ( 5.10 )]
• Cognitive/Neuropsychiatric Adverse Reactions [see Warnings and Precautions ( 5.11 )]
• Hyperammonemia and Encephalopathy [see Warnings and Precautions ( 5.12 )]
• Kidney Stones [see Warnings and Precautions ( 5.13 )]
• Effect on Renal Function [see Warnings and Precautions ( 5.14 )]
• Status Epilepticus [see Warnings and Precautions ( 5.15 )] The most common adverse reactions with ZONISADE (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 ( 6 ). To report SUSPECTED ADVERSE REACTIONS, contact Azurity Pharmaceuticals, Inc., at 1-800-461-7449 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

Adverse

Reactions in Placebo-Controlled Trials with Zonisamide Capsules [see Clinical Studies ( 14 )] The most common adverse reactions with zonisamide capsules (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 because of an adverse reaction 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 reaction. The most common adverse reactions leading to 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 reactions were dose-related [see Warnings and Precautions ( 5 )] .

Table

2 lists adverse reactions that occurred in at least 2% of patients treated with zonisamide capsules 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.

Table

2.

Adverse

Reactions that Occurred in at least 2% of Patients Treated with Zonisamide Capsules and More Frequently than in Patients who Received Placebo in Placebo-Controlled, Adjunctive Trials BODY SYSTEM/Adverse Reaction Zonisamide Capsules (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 HEMATOLOGIC AND 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 NEUROPSYCHIATRIC AND COGNITIVE DYSFUNCTION-ALTERED COGNITIVE FUNCTION Confusion 6 3 Difficulty Concentrating 6 2 Difficulty with Memory 6 2 Mental Slowing 4 2 NEUROPSYCHIATRIC AND COGNITIVE DYSFUNCTION-BEHAVIORAL ABNORMALITIES (NON-PSYCHOSIS-RELATED)

Agitation/Irritability

9 4 Depression 6 3 Insomnia 6 3 Anxiety 3 2 Nervousness 2 1 NEUROPSYCHIATRIC AND COGNITIVE DYSFUNCTION-BEHAVIORAL ABNORMALITIES (PSYCHOSIS-RELATED)

Schizophrenic/Schizophreniform

Behavior 2 0 NEUROPSYCHIATRIC AND COGNITIVE DYSFUNCTION-CNS DEPRESSION Somnolence 17 7 Fatigue 8 6 Tiredness 7 5 NEUROPSYCHIATRIC 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 Laboratory Tests Zonisamide increases serum chloride and alkaline phosphatase and decreases serum bicarbonate [see Warnings and Precautions ( 5.8 )] , phosphorus, calcium, and albumin.

Other Adverse

Reactions in Clinical Trials of Zonisamide Capsules Zonisamide capsules have been administered to 1,598 individuals during all clinical trials, only some of which were placebo-controlled. The frequencies represent the proportion of the 1,598 individuals exposed to zonisamide capsules who experienced an event on at least one occasion. All events are included except those already listed in the previous table or discussed in [see Warnings and Precautions ( 5 )] , trivial events, those too general to be informative, and those not reasonably associated with zonisamide. Events are further classified within each category and listed in order of decreasing frequency as follows: frequent occurring in at least 1:100 patients; infrequent occurring in 1:100 to 1:1000 patients; rare occurring in fewer than 1:1000 patients. Body as a Whole : Frequent: Accidental injury, asthenia. Infrequent: Chest pain, flank pain, malaise, allergic reaction, face edema, neck rigidity. Rare: Lupus erythematosus. Cardiovascular : Infrequent: Palpitation, tachycardia, vascular insufficiency, hypotension, hypertension, thrombophlebitis, syncope, bradycardia. Rare: Atrial fibrillation, heart failure, pulmonary embolus, ventricular extrasystoles. Digestive : Frequent: Vomiting. Infrequent: Flatulence, gingivitis, gum hyperplasia, gastritis, gastroenteritis, stomatitis, cholelithiasis, glossitis, melena, rectal hemorrhage, ulcerative stomatitis, gastro-duodenal ulcer, dysphagia, gum hemorrhage. Rare: Cholangitis, hematemesis, cholecystitis, cholestatic jaundice, colitis, duodenitis, esophagitis, fecal incontinence, mouth ulceration. Hematologic and Lymphatic : Infrequent: Leukopenia, anemia, immunodeficiency, lymphadenopathy. Rare: Thrombocytopenia, microcytic anemia, petechia. Metabolic and Nutritional : Infrequent: Peripheral edema, weight gain, edema, thirst, dehydration. Rare: Hypoglycemia, hyponatremia, lactic dehydrogenase increased, SGOT increased, SGPT increased. Musculoskeletal : Infrequent: Leg cramps, myalgia, myasthenia, arthralgia, arthritis.

Nervous

System : Frequent: Tremor, convulsion, abnormal gait, hyperesthesia, incoordination. Infrequent: Hypertonia, twitching, abnormal dreams, vertigo, libido decreased, neuropathy, hyperkinesia, movement disorder, dysarthria, cerebrovascular accident, hypotonia, peripheral neuritis, reflexes increased. Rare: Dyskinesia, dystonia, encephalopathy, facial paralysis, hypokinesia, hyperesthesia, myoclonus, oculogyric crisis.

Behavioral

Abnormalities –Non-Psychosis-Related : Infrequent: Euphoria. Respiratory : Frequent: Pharyngitis, cough increased. Infrequent: Dyspnea. Rare: Apnea, hemoptysis. Skin and Appendages : Frequent: Pruritus. Infrequent: Maculopapular rash, acne, alopecia, dry skin, sweating, eczema, urticaria, hirsutism, pustular rash, vesiculobullous rash.

Special

Senses : Frequent: Amblyopia, tinnitus. Infrequent: Conjunctivitis, parosmia, deafness, visual field defect, glaucoma. Rare: Photophobia, iritis. Urogenital : Infrequent: Urinary frequency, dysuria, urinary incontinence, hematuria, impotence, urinary retention, urinary urgency, amenorrhea, polyuria, nocturia. Rare: Albuminuria, enuresis, bladder pain, bladder calculus, gynecomastia, mastitis, menorrhagia.

6.2 Postmarketing Experience The following serious adverse reactions have been reported since approval and use of zonisamide worldwide. These reactions are reported voluntarily from a population of uncertain size; therefore, it is not possible to estimate their frequency or establish a causal relationship to drug exposure. Acute pancreatitis, rhabdomyolysis, increased creatine phosphokinase, and drug reaction with eosinophilia and systemic symptoms (DRESS), acute myopia and secondary angle closure glaucoma, and hyperammonemia and encephalopathy <span class="opacity-50 text-xs">[see Warnings and Precautions ( 5 )]</span> .

AND PRECAUTIONS

• Potentially Fatal Reactions to Sulfonamides: Fatalities have occurred as a result of severe reactions to sulfonamides (zonisamide is a sulfonamide) including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias ( 5.1 ).
• Serious Skin Reactions: Discontinue ZONISADE at the first sign of rash unless clearly not drug related ( 5.2 ).
• Serious Hematologic Events: Aplastic anemia and agranulocytosis have been reported with zonisamide treatment ( 5.3 ).
• Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multi-Organ Hypersensitivity: DRESS, also known as multiorgan hypersensitivity, has occurred with zonisamide ( 5.4 ).
• Oligohidrosis and Hyperthermia in Pediatric Patients: Oligohidrosis, sometimes resulting in heat stroke and hospitalization, is seen in association with zonisamide in pediatric patients ( 5.5 ).
• Acute Myopia and Secondary Angle Closure Glaucoma: If occurs, primary treatment is discontinuation of ZONISADE ( 5.6 ).
• Suicidal Behavior and Ideation: Monitor patients for suicidal behavior or ideation ( 5.7 ).
• Metabolic Acidosis: Baseline and periodic measurement of serum bicarbonate is recommended; consider dose reduction or discontinuation if appropriate ( 5.8 ).
• Seizures on Withdrawal of Antiepileptic Drugs: Withdraw ZONISADE gradually ( 5.9 ).
• Teratogenicity: Based on animal data, may cause fetal harm. Advise females of reproductive potential of the potential risk to a fetus and to use an effective method of contraception during ZONISADE treatment and for one month after discontinuation ( 5.10 , 8.1 , 8.3 ).

5.1 Potentially Fatal Reactions to Sulfonamides Fatalities have occurred as a result of severe reactions to sulfonamides (zonisamide is a sulfonamide) including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias <span class="opacity-50 text-xs">[see Warnings and Precautions ( 5.2 , 5.3 , 5.4 )]</span> . Such reactions may occur when a sulfonamide is readministered irrespective of the route of administration. If signs of hypersensitivity or other serious reactions occur, discontinue ZONISADE immediately. Specific experience with sulfonamide-type adverse reaction to zonisamide is described below.

5.2 Serious Skin Reactions Seven deaths from severe rash [i.e., Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN)] were reported in the first 11 years of marketing in Japan. All of the patients were receiving other drugs in addition to zonisamide. In postmarketing experience from Japan, a total of 49 cases of SJS or TEN have been reported, a reporting rate of 46 per million patient-years of exposure. Although this rate is greater than background, it is probably an underestimate of the true incidence because of under-reporting. There were no confirmed cases of SJS or TEN in the US, European, or Japanese development programs. In the US and European randomized controlled trials <span class="opacity-50 text-xs">[see Clinical Studies ( 14 )]</span> , 6 of 269 (2.2%) patients who received zonisamide discontinued treatment because of rash compared to no patients who received placebo. Across all trials during the US and European development, rash that led to discontinuation of zonisamide was reported in 1.4% of patients (12.0 events per 1000 patient-years of exposure).

During

Japanese development, serious rash or rash that led to discontinuation of zonisamide was reported in 2.0% of patients (27.8 events per 1000 patient-years). Rash usually occurred early in treatment, with 85% reported within 16 weeks in the US and European studies and 90% reported within two weeks in the Japanese studies. There was no apparent relationship of dose to the occurrence of rash. Discontinue ZONISADE at the first sign of rash, unless the rash is clearly not drug-related. If signs or symptoms suggest SJS/TEN, use of ZONISADE should not be resumed and alternative therapy should be considered.

5.3 Serious Hematologic Events Two confirmed cases of aplastic anemia and one confirmed case of agranulocytosis were reported in the first 11 years of marketing in Japan, rates greater than generally accepted background rates. There were no cases of aplastic anemia and two confirmed cases of agranulocytosis in the US, European, or Japanese development programs. There is inadequate information to assess the relationship, if any, between dose and duration of treatment and these events.

5.4 Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multi-Organ Hypersensitivity Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multi-organ hypersensitivity, has occurred with zonisamide, the active ingredient in ZONISADE. Some of these events have been fatal or life-threatening. DRESS typically, although not exclusively, presents with fever, rash, lymphadenopathy and/or facial swelling, in association with other organ system involvement, such as hepatitis, nephritis, hematologic abnormalities, myocarditis, or myositis, sometimes resembling an acute viral infection. Eosinophilia is often present. This disorder is variable in its expression, and other organ systems not noted here may be involved. It is important to note that early manifestations of hypersensitivity (e.g., fever, lymphadenopathy) may be present even though rash is not evident. If such signs or symptoms are present, the patient should be evaluated immediately. ZONISADE should be discontinued if an alternative etiology for the signs or symptoms cannot be established.

5.5 Oligohidrosis and Hyperthermia in Pediatric Patients ZONISADE is not approved for use in patients below 16 years of age. Oligohidrosis, sometimes resulting in heat stroke and hospitalization, is seen in association with zonisamide in pediatric patients. During the pre-approval development program in Japan, one case of oligohidrosis was reported in 403 pediatric patients, an incidence of 1 case per 285 patient-years of exposure. While there were no cases reported in the US or European development programs, fewer than 100 pediatric patients participated in these trials. In the first 11 years of marketing in Japan, 38 cases were reported, an estimated reporting rate of about 1 case per 10,000 patient-years of exposure. In the first year of marketing in the US, 2 cases were reported, an estimated reporting rate of about 12 cases per 10,000 patient-years of exposure. These rates are underestimates of the true incidence because of under-reporting. There has also been one report of heat stroke in an 18-year-old patient in the US. Decreased sweating and an elevation in body temperature above normal characterized these cases. Many cases were reported after exposure to elevated environmental temperatures. Heat stroke, requiring hospitalization, was diagnosed in some cases. Pediatric patients appear to be at an increased risk for zonisamide-associated oligohidrosis and hyperthermia. Patients, especially pediatric patients, treated with ZONISADE should be monitored closely for evidence of decreased sweating and increased body temperature, especially in warm or hot weather. Caution should be used when ZONISADE is prescribed with other drugs that predispose patients to heat-related disorders; these drugs include, but are not limited to, carbonic anhydrase inhibitors and drugs with anticholinergic activity.

5.6 Acute Myopia and Secondary Angle Closure Glaucoma Acute myopia and secondary angle closure glaucoma have been reported in patients receiving zonisamide, the active ingredient in ZONISADE. Elevated intraocular pressure can lead to serious sequelae, including permanent vision loss, if left untreated. Symptoms in reported cases have included acute onset of decreased visual acuity and/or ocular pain. Ophthalmologic findings can include myopia, anterior chamber shallowing, ocular hyperemia (redness), and increased intraocular pressure. Mydriasis may or may not be present. This syndrome may be associated with ciliochoroidal effusion resulting in anterior displacement of the lens and iris, with secondary angle closure glaucoma. Symptoms typically occur within one month after initiating zonisamide therapy. In contrast to primary narrow angle glaucoma, which is rare under 40 years of age, secondary angle closure glaucoma associated with zonisamide has been reported both in pediatric patients and in adults. ZONISADE is not approved for use in patients below 16 years of age. The primary treatment to reverse symptoms is discontinuation of ZONISADE as rapidly as possible, according to the judgment of the treating physician. Other therapeutic measures, in conjunction with discontinuation of ZONISADE, may be helpful. Myopia and secondary angle closure glaucoma usually resolve or improve after discontinuation of zonisamide.

5.7 Suicidal Behavior and Ideation Antiepileptic drugs (AEDs), including ZONISADE, increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior. Pooled analyses of 199 placebo-controlled clinical trials (mono- and adjunctive therapy) of 11 different AEDs showed that patients randomized to one of the AEDs had approximately twice the risk (adjusted Relative Risk 1.8, 95% CI:1.2, 2.7) of suicidal thinking or behavior compared to patients randomized to placebo. In these trials, which had a median treatment duration of 12 weeks, the estimated incidence rate of suicidal behavior or ideation among 27,863 AED-treated patients was 0.43%, compared to 0.24% among 16,029 placebo-treated patients, representing an increase of approximately one case of suicidal thinking or behavior for every 530 patients treated. There were four suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide. The increased risk of suicidal thoughts or behavior with AEDs was observed as early as one week after starting drug treatment with AEDs and persisted for the duration of treatment assessed. Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed. The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed. The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5-100 years) in the clinical trials analyzed.

Table

1 shows absolute and relative risk by indication for all evaluated AEDs.

Table

1. Risk by Indication for Antiepileptic Drugs in the Pooled Analysis Indication Placebo Patients with Events Per 1000 Patients Drug Patients with Events Per 1000 Patients Relative Risk: Incidence of Events in Drug Patients/Incidence in Placebo Patients Risk Difference: Additional Drug Patients with Events Per 1000 Patients Epilepsy 1.0 3.4 3.5

2.4 Psychiatric 5.7 8.5 1.5

2.9 Other 1.0 1.8 1.9

0.9 Total 2.4 4.3 1.8

1.9 The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications. Anyone considering prescribing ZONISADE or any other AED must balance the risk of suicidal thoughts or behavior with the risk of untreated illness. Epilepsy and many other illnesses for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Should suicidal thoughts and behavior emerge during treatment, the prescriber needs to consider whether the emergence of these symptoms in any given patient may be related to the illness being treated.

5.8 Metabolic Acidosis Zonisamide causes hyperchloremic, non-anion gap, metabolic acidosis (i.e., decreased serum bicarbonate below the normal reference range in the absence of chronic respiratory alkalosis). This metabolic acidosis is caused by renal bicarbonate loss due to the inhibitory effect of zonisamide on carbonic anhydrase. Generally, zonisamide-induced metabolic acidosis occurs early in treatment, but it can develop at any time during treatment. Metabolic acidosis generally appears dose-dependent and can occur at doses as low as 25 mg daily. Conditions or therapies that predispose to acidosis (such as renal disease, severe respiratory disorders, status epilepticus, diarrhea, ketogenic diet, or specific drugs) may be additive to the bicarbonate lowering effects of zonisamide. Some manifestations of acute or chronic metabolic acidosis include hyperventilation, nonspecific symptoms such as fatigue and anorexia, or more severe sequelae including cardiac arrhythmias or stupor. Chronic, untreated, metabolic acidosis may increase the risk for nephrolithiasis or nephrocalcinosis. Nephrolithiasis has been observed in the clinical development program in 4% of adults treated with zonisamide, has also been detected by renal ultrasound in 8% of pediatric treated patients who had at least one ultrasound prospectively collected, and was reported as an adverse event in 3% (4/133) of pediatric patients <span class="opacity-50 text-xs">[see Warnings and Precautions ( 5.15 )]</span>. Metabolic acidosis can also increase the risk for hyperammonemia, particularly in the presence of drugs which can cause hyperammonemia. Chronic, untreated metabolic acidosis may result in osteomalacia (referred to as rickets in pediatric patients) and/or osteoporosis with an increased risk for fracture. Of potential relevance, zonisamide treatment was associated with reductions in serum phosphorus and increases in serum alkaline phosphatase, changes that may be related to metabolic acidosis and osteomalacia. Chronic, untreated metabolic acidosis in pediatric patients may reduce growth rates. A reduction in growth rate may eventually decrease the maximal height achieved. The effect of zonisamide on growth and bone-related sequelae has not been systematically investigated. ZONISADE is not approved for use in patients below 16 years of age. Serum bicarbonate was not measured in the adjunctive controlled trials of adults with epilepsy. However, serum bicarbonate was studied in three clinical trials for indications which have not been approved: a placebo-controlled trial for migraine prophylaxis in adults, a controlled trial for monotherapy in epilepsy in adults, and an open label trial for adjunctive treatment of epilepsy in pediatric patients (3-16 years). In adults, mean serum bicarbonate reductions ranged from approximately 2 mEq/L at daily doses of 100 mg to nearly 4 mEq/L at daily doses of 300 mg. In pediatric patients, mean serum bicarbonate reductions ranged from approximately 2 mEq/L at daily doses from above 100 mg up to 300 mg, to nearly 4 mEq/L at daily doses from above 400 mg up to 600 mg. In two controlled studies in adults, the incidence of a persistent treatment-emergent decrease in serum bicarbonate to less than 20 mEq/L (observed at 2 or more consecutive visits or the final visit) was dose-related at relatively low zonisamide doses. In the monotherapy trial of epilepsy, the incidence of a persistent treatment-emergent decrease in serum bicarbonate was 21% for daily zonisamide doses of 25 mg or 100 mg, and was 43% at a daily dose of 300 mg. In a placebo-controlled trial for prophylaxis of migraine, the incidence of a persistent treatment-emergent decrease in serum bicarbonate was 7% for placebo, 29% for 150 mg daily, and 34% for 300 mg daily. The incidence of persistent markedly abnormally low serum bicarbonate (decrease to less than 17 mEq/L and more than 5 mEq/L from a pretreatment value of at least 20 mEq/L) in these controlled trials was 2% or less. In the pediatric study, the incidence of persistent, treatment-emergent decreases in serum bicarbonate to levels less than 20 mEq/L was 52% at doses up to 100 mg daily, was 90% for a wide range of doses up to 600 mg daily, and generally appeared to increase with higher doses. The incidence of a persistent markedly abnormally low serum bicarbonate value was 4% at doses up to 100 mg daily, was 18% for a wide range of doses up to 600 mg daily, and generally appeared to increase with higher doses. Some patients experienced moderately severe serum bicarbonate decrements down to a level as low as 10 mEq/L. The relatively high frequencies of varying severities of metabolic acidosis observed in this study of pediatric patients (compared to the frequency and severity observed in various clinical trial development programs in adults) suggest that pediatric patients may be more likely to develop metabolic acidosis than adults. Measurement of baseline and periodic serum bicarbonate during treatment is recommended. If metabolic acidosis develops and persists, consideration should be given to reducing the dose or discontinuing ZONISADE (using dose tapering). If the decision is made to continue patients on ZONISADE in the face of persistent acidosis, alkali treatment should be considered.

5.9 Seizures on Withdrawal of Antiepileptic Drugs As with most antiepileptic drugs, ZONISADE should generally be withdrawn gradually because of the risk of increased seizure frequency and status epilepticus <span class="opacity-50 text-xs">[see Dosage and Administration ( 2.3 )]</span> . However, if withdrawal is needed because of a serious adverse event, rapid discontinuation can be considered. In these situations, appropriate monitoring is recommended.

5.10 Teratogenicity Women of childbearing potential who are given ZONISADE should be advised to use effective contraception. Zonisamide produced fetal malformations in mice, rats, and dogs and was embryolethal in monkeys when administered during the period of organogenesis. A variety of fetal abnormalities, including cardiovascular defects and embryofetal deaths, occurred at maternal plasma levels similar to or lower than therapeutic levels in humans. These findings suggest that the use of zonisamide during pregnancy in humans may present a significant risk to the fetus <span class="opacity-50 text-xs">[see Use in Specific Populations ( 8.1 )]</span>. Although human data to confirm findings in animals is limited, ZONISADE should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

5.11 Cognitive/Neuropsychiatric Adverse Reactions Use of zonisamide was frequently associated with central nervous system-related adverse reactions <span class="opacity-50 text-xs">[see Adverse Reactions ( 6.1 )]</span> . The most significant of these can be classified into three general categories: 1) psychiatric symptoms, including depression and psychosis, 2) cognitive dysfunction, and 3) somnolence or fatigue.

Psychiatric

Symptoms In placebo-controlled trials, 2.2% of patients discontinued zonisamide or were hospitalized for depression compared to 0.4% of placebo patients. Among all epilepsy patients treated with zonisamide, 1.4% were discontinued and 1.0% were hospitalized because of reported depression or suicide attempts. In placebo-controlled trials, 2.2% of patients discontinued zonisamide or were hospitalized because of psychosis or psychosis-related symptoms compared to no patients who received placebo. Among all epilepsy patients treated with zonisamide, 0.9% discontinued treatment and 1.4% were hospitalized because of reported psychosis or related symptoms.

Cognitive Dysfunction

Zonisamide, the active ingredient in ZONISADE, causes adverse reactions related to cognitive dysfunction (e.g., psychomotor slowing, difficulty with concentration, and speech or language problems, in particular, word-finding difficulties). In placebo-controlled trials with zonisamide, psychomotor slowing and difficulty with concentration occurred in the first month of treatment and were associated with doses above 300 mg/day. Speech and language problems tended to occur after 6–10 weeks of treatment and at doses above 300 mg/day. Although in most cases these events were of mild to moderate severity, they at times led to withdrawal from treatment. Somnolence and Fatigue Somnolence and fatigue were frequently reported CNS adverse events during clinical trials with zonisamide. Although in most cases these events were of mild to moderate severity, they led to withdrawal from treatment in 0.2% of the patients enrolled in controlled trials. Somnolence and fatigue tended to occur within the first month of treatment. Somnolence and fatigue occurred most frequently at doses of 300–500 mg/day.

Risk Amelioration

Prescribers should advise patients against engaging in hazardous activities requiring mental alertness, such as operating motor vehicles or dangerous machinery, until the effect of ZONISADE is known. Patients should be carefully observed for signs of central nervous system (CNS) depression, such as somnolence and sedation, when ZONISADE is used with other drugs with sedative properties because of potential additive effects.

5.12 Hyperammonemia and Encephalopathy Hyperammonemia and encephalopathy have been reported with the postmarketing use of zonisamide. Zonisamide, the active ingredient in ZONISADE, treatment inhibits carbonic anhydrase activity, which may cause metabolic acidosis that is associated with an increased risk for developing hyperammonemia. Hyperammonemia resulting from zonisamide can also be asymptomatic. The risks of hyperammonemia and various manifestations of encephalopathy may be increased in patients treated with zonisamide and concomitantly taking other medications that can cause hyperammonemia, including valproic acid or topiramate <span class="opacity-50 text-xs">[see Warnings and Precautions ( 5 )]</span>. Patients with inborn errors of metabolism or reduced hepatic mitochondrial activity may be at an increased risk for hyperammonemia with or without encephalopathy and this risk may be increased by zonisamide use. Measure serum ammonia concentration if signs or symptoms (e.g., unexplained change in mental status, vomiting, or lethargy) of encephalopathy occur. Hyperammonemia resulting from zonisamide resolves when zonisamide is discontinued. Hyperammonemia from zonisamide may resolve or decrease in severity with a decrease of the daily dose.

5.13 Kidney Stones Zonisamide, the active ingredient in ZONISADE, may cause kidney stones.

Among

991 patients treated during the development of zonisamide, 40 patients (4.0%) with epilepsy receiving zonisamide developed clinically possible or confirmed kidney stones (e.g., clinical symptomatology, sonography, etc.), at rate of 34 per 1000 patient-years of exposure (40 patients with 1168 years of exposure). Of these, 12 were symptomatic, and 28 were described as possible kidney stones based on sonographic detection. In nine patients, the diagnosis was confirmed by a passage of a stone or by a definitive sonographic finding. The rate of occurrence of kidney stones was 28.7 per 1000 patient-years of exposure in the first six months, 62.6 per 1000 patient-years of exposure between 6 and 12 months, and 24.3 per 1000 patient-years of exposure after 12 months of use. There are no normative sonographic data available for either the general population or patients with epilepsy. Although the clinical significance of the sonographic findings may not be certain, the development of nephrolithiasis may be related to metabolic acidosis [see Warnings and Precautions ( 5.8 )] . The analyzed stones were composed of calcium or urate salts. In general, increasing fluid intake and urine output can help reduce the risk of stone formation, particularly in those with predisposing risk factors. It is unknown, however, whether these measures will reduce the risk of stone formation in patients treated with ZONISADE. Although not approved in pediatric patients, sonographic findings consistent with nephrolithiasis were also detected in 8% of a subset of zonisamide treated pediatric patients who had at least one renal ultrasound prospectively performed in a clinical development program investigating open-label treatment. The incidence of kidney stone as an adverse event was 3% [see Warnings and Precautions ( 5.8 )] .

5.14 Effect on Renal Function Zonisamide, the active ingredient in ZONISADE, can have an effect on renal function. In several clinical studies, zonisamide was associated with a statistically significant 8% mean increase from baseline of serum creatinine and blood urea nitrogen (BUN) compared to essentially no change in the placebo patients. The increase appeared to persist over time but was not progressive; this has been interpreted as an effect on glomerular filtration rate (GFR). There were no episodes of unexplained acute renal failure in clinical development in the US, Europe, or Japan. The decrease in GFR appeared within the first 4 weeks of treatment. In a 30-day study, the GFR returned to baseline within 2–3 weeks of drug discontinuation. There is no information about reversibility, after drug discontinuation, of the effects on GFR after long-term use. ZONISADE should be discontinued in patients who develop acute renal failure or a clinically significant sustained increase in the creatinine/BUN concentration. Avoid use of ZONISADE in patients with renal failure (estimated GFR &lt; 50 mL/min) since there is insufficient experience concerning drug dosing and toxicity <span class="opacity-50 text-xs">[see Use in Specific Populations ( 8.6 )]</span> . Consideration should be given to monitoring renal function periodically .

5.15 Status Epilepticus Estimates of the incidence of treatment emergent status epilepticus in patients treated with zonisamide, the active ingredient in ZONISADE, are difficult because a standard definition was not employed. Nonetheless, in controlled trials, 1.1% of patients treated with zonisamide had an event labeled as status epilepticus compared to none of the patients treated with placebo. Among patients treated with zonisamide across all epilepsy studies (controlled and uncontrolled), 1.0% of patients had an event reported as status epilepticus.

PRECAUTIONS General: Somnolence is commonly reported, especially at higher doses of zonisamide (see WARNINGS: Cognitive/ Neuropsychiatric Adverse Events subsection). Zonisamide is metabolized by the liver and eliminated by the kidneys; caution should therefore be exercised when administering zonisamide to patients with hepatic and renal dysfunction (see CLINICAL PHARMACOLOGY , Special Populations subsection).

Kidney

Stones: Among 991 patients treated during the development of zonisamide, 40 patients (4.0%) with epilepsy receiving zonisamide developed clinically possible or confirmed kidney stones (e.g. clinical symptomatology, sonography, etc.), a rate of 34 per 1000 patient-years of exposure (40 patients with 1168 years of exposure). Of these, 12 were symptomatic, and 28 were described as possible kidney stones based on sonographic detection. In nine patients, the diagnosis was confirmed by a passage of a stone or by a definitive sonographic finding. The rate of occurrence of kidney stones was 28.7 per 1000 patient-years of exposure in the first six months, 62.6 per 1000 patient-years of exposure between 6 and 12 months, and 24.3 per 1000 patient-years of exposure after 12 months of use. There are no normative sonographic data available for either the general population or patients with epilepsy. Although the clinical significance of the sonographic findings may not be certain, the development of nephrolithiasis may be related to metabolic acidosis (see WARNINGS , Metabolic Acidosis subsection). The analyzed stones were composed of calcium or urate salts. In general, increasing fluid intake and urine output can help reduce the risk of stone formation, particularly in those with predisposing risk factors. It is unknown, however, whether these measures will reduce the risk of stone formation in patients treated with zonisamide. Although not approved in pediatric patients, sonographic findings consistent with nephrolithiasis were also detected in 8 % of a subset of zonisamide treated pediatric patients who had at least one renal ultrasound prospectively performed in a clinical development program investigating open-label treatment. The incidence of kidney stone as an adverse event was 3 % (see WARNINGS , Metabolic Acidosis subsection). Effect on Renal Function: In several clinical studies, zonisamide was associated with a statistically significant 8% mean increase from baseline of serum creatinine and blood urea nitrogen (BUN) compared to essentially no change in the placebo patients. The increase appeared to persist over time but was not progressive; this has been interpreted as an effect on glomerular filtration rate (GFR). There were no episodes of unexplained acute renal failure in clinical development in the US, Europe, or Japan. The decrease in GFR appeared within the first 4 weeks of treatment. In a 30-day study, the GFR returned to baseline within 2 to 3 weeks of drug discontinuation. There is no information about reversibility, after drug discontinuation, of the effects on GFR after long-term use. Zonisamide should be discontinued in patients who develop acute renal failure or a clinically significant sustained increase in the creatinine/BUN concentration. Zonisamide should not be used in patients with renal failure (estimated GFR < 50 mL/min) as there has been insufficient experience concerning drug dosing and toxicity.

Status

Epilepticus: Estimates of the incidence of treatment emergent status epilepticus in zonisamide -treated patients are difficult because a standard definition was not employed. Nonetheless, in controlled trials, 1.1% of patients treated with zonisamide had an event labeled as status epilepticus compared to none of the patients treated with placebo. Among patients treated with zonisamide across all epilepsy studies (controlled and uncontrolled), 1.0% of patients had an event reported as status epilepticus. Information for Patients: Patients should be informed of the availability of a Medication Guide, and they should be instructed to read the Medication Guide prior to taking zonisamide. Patients should be instructed to take zonisamide only as prescribed. Patients should be advised as follows: (See Medication Guide ) Zonisamide may produce drowsiness, especially at higher doses. Patients should be advised not to drive a car or operate other complex machinery until they have gained experience on zonisamide sufficient to determine whether it affects their performance. 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. Patients should contact their physician immediately if a skin rash develops or seizures worsen. Instruct patients to seek immediate medical attention if they experience blurred vision, visual disturbances, or periorbital pain (see WARNINGS, Acute Myopia and Secondary Angle Closure Glaucoma subsection). Patients should contact their physician immediately if they develop signs or symptoms, such as sudden back pain, abdominal pain, and/or blood in the urine, that could indicate a kidney stone. Increasing fluid intake and urine output may reduce the risk of stone formation, particularly in those with predisposing risk factors for stones (see PRECAUTIONS, Kidney Stones subsection). Patients should contact their physician immediately if a child has been taking zonisamide and is not sweating as usual with or without a fever (see WARNINGS, Oligohidrosis and Hyperthermia in Pediatric Patients subsection). Because zonisamide can cause hematological complications, patients should contact their physician immediately if they develop a fever, sore throat, oral ulcers, or easy bruising. (see WARNINGS, Serious Hematologic Events subsection). Counsel patients and caregivers that AEDs, including zonisamide, may increase the risk of suicidal thoughts and behavior and advise them of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers (see WARNINGS, Suicidal Behavior and Ideation subsection). Warn patients about the possible development of hyperammonemia with or without encephalopathy. Although hyperammonemia may be asymptomatic, clinical symptoms of hyperammonemic encephalopathy often include acute alterations in level of consciousness and/or cognitive function with lethargy and/or vomiting. Instruct patients to contact their physician if they develop unexplained lethargy, vomiting, or changes in mental status (see WARNINGS, Hyperammonemia and Encephalopathy subsection). Patients should contact their physician immediately if they develop fast breathing, fatigue/tiredness, loss of appetite, or irregular heart beat or palpitations, which are possible manifestations of metabolic acidosis (see WARNINGS, Metabolic Acidosis subsection). As with other AEDs, patients should contact their physician if they intend to become pregnant or are pregnant during zonisamide therapy. Patients should notify their physician if they intend to breast-feed or are breast-feeding an infant. (see PRECAUTIONS, Use in Nursing Mothers subsection). Encourage patients to enroll in the North American Antiepileptic Drug (NAAED)

Pregnancy

Registry if they become pregnant. This registry is collecting information about the safety of antiepileptic drugs during pregnancy. To enroll, patients can call the toll-free number 1-888-233-2334 (see PRECAUTIONS, Pregnancy subsection).

Laboratory

Tests: In several clinical studies, zonisamide was associated with a mean increase in the concentration of serum creatinine and blood urea nitrogen (BUN) of approximately 8% over the baseline measurement. Consideration should be given to monitoring renal function periodically (see PRECAUTIONS, Effect on Renal Function subsection). Zonisamide increases serum chloride and alkaline phosphatase and decreases serum bicarbonate (see WARNINGS, Metabolic Acidosis subsection), phosphorus, calcium, and albumin.

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).

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). Carcinogenesis, Mutagenesis, Impairment of Fertility: No evidence of carcinogenicity was found in mice or rats following dietary administration of zonisamide for two years at doses of up to 80 mg/kg/day. In mice, this dose is approximately equivalent to the maximum recommended human dose (MRHD) of 400 mg/day on a mg/m2 basis. In rats, this dose is 1 to 2 times the MRHD on a mg/m2 basis. Zonisamide was mutagenic in an in vitro chromosomal aberration assay in CHL cells. Zonisamide was not mutagenic or clastogenic in other in vitro assays (Ames, mouse lymphoma tk assay, chromosomal aberration in human lymphocytes) or in the in vivo rat bone marrow cytogenetics assay. Rats treated with zonisamide (20, 60, or 200 mg/kg) before mating and during the initial gestation phase showed signs of reproductive toxicity (decreased corpora lutea, implantations, and live fetuses) at all doses. The low dose in this study is approximately 0.5 times the maximum recommended human dose (MRHD) on a mg/m 2 basis. Pregnancy: Pregnancy Category C (see WARNINGS , Teratogenicity subsection): Zonisamide may cause serious adverse fetal effects, based on clinical and nonclinical data. Zonisamide was teratogenic in multiple animal species. Zonisamide treatment causes metabolic acidosis in humans. The effect of zonisamide induced metabolic acidosis has not been studied in pregnancy; however, metabolic acidosis in pregnancy (due to other causes) may be associated with decreased fetal growth, decreased fetal oxygenation, and fetal death, and may affect the fetus’ ability to tolerate labor. Pregnant patients should be monitored for metabolic acidosis and treated as in the non-pregnant state. (See WARNINGS , Metabolic Acidosis subsection.) Newborns of mothers treated with zonisamide should be monitored for metabolic acidosis because of transfer of zonisamide to the fetus and possible occurrence of transient metabolic acidosis following birth. Transient metabolic acidosis has been reported in neonates born to mothers treated during pregnancy with a different carbonic anhydrase inhibitor. Zonisamide was teratogenic in mice, rats, and dogs and embryolethal in monkeys when administered during the period of organogenesis. Fetal abnormalities or embryo-fetal deaths occurred in these species at zonisamide dosage and maternal plasma levels similar to or lower than therapeutic levels in humans, indicating that use of this drug in pregnancy entails a significant risk to the fetus. A variety of external, visceral, and skeletal malformations was produced in animals by prenatal exposure to zonisamide. Cardiovascular defects were prominent in both rats and dogs. Following administration of zonisamide (10, 30, or 60 mg/kg/day) to pregnant dogs during organogenesis, increased incidences of fetal cardiovascular malformations (ventricular septal defects, cardiomegaly, various valvular and arterial anomalies) were found at doses of 30 mg/kg/day or greater. The low effect dose for malformations produced peak maternal plasma zonisamide levels (25 mcg/mL) about 0.5 times the highest plasma levels measured in patients receiving the maximum recommended human dose (MRHD) of 400 mg/day. In dogs, cardiovascular malformations were found in approximately 50% of all fetuses exposed to the high dose, which was associated with maternal plasma levels (44 mcg/mL) approximately equal to the highest levels measured in humans receiving the MRHD. Incidences of skeletal malformations were also increased at the high dose, and fetal growth retardation and increased frequencies of skeletal variations were seen at all doses in this study. The low dose produced maternal plasma levels (12 mcg/mL) about 0.25 times the highest human levels. In cynomolgus monkeys, administration of zonisamide (10 or 20 mg/kg/day) to pregnant animals during organogenesis resulted in embryo-fetal deaths at both doses. The possibility that these deaths were due to malformations cannot be ruled out. The lowest embryolethal dose in monkeys was associated with peak maternal plasma zonisamide levels (5 mcg/mL) approximately 0.1 times the highest levels measured in patients at the MRHD. In a mouse embryo-fetal development study, treatment of pregnant animals with zonisamide (125, 250, or 500 mg/kg/day) during the period of organogenesis resulted in increased incidences of fetal malformations (skeletal and/or craniofacial defects) at all doses tested. The low dose in this study is approximately 1.5 times the MRHD on a mg/m 2 basis. In rats, increased frequencies of malformations (cardiovascular defects) and variations (persistent cords of thymic tissue, decreased skeletal ossification) were observed among the offspring of dams treated with zonisamide (20, 60, or 200 mg/kg/day) throughout organogenesis at all doses. The low effect dose is approximately 0.5 times the MRHD on a mg/m 2 basis. Perinatal death was increased among the offspring of rats treated with zonisamide (10, 30, or 60 mg/kg/day) from the latter part of gestation up to weaning at the high dose, or approximately 1.4 times the MRHD on a mg/m 2 basis. The no effect level of 30 mg/kg/day is approximately 0.7 times the MRHD on a mg/ m 2 basis. There are no adequate and well-controlled studies in pregnant women. Zonisamide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. To provide information regarding the effects of in utero exposure to zonisamide, physicians are advised to recommend that pregnant patients taking zonisamide enroll in the NAAED Pregnancy Registry. This can be done by calling the toll free number 1-888-233-2334, and must be done by patients themselves. Information on the registry can also be found at the website http://www.aedpregnancyregistry.org/. Labor and Delivery: The effects of zonisamide on labor and delivery in humans are unknown. Use in Nursing Mothers: Zonisamide is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from zonisamide, a decision should be made whether to discontinue nursing or to discontinue drug, taking into account the importance of the drug to the mother.

Pediatric

Use: The safety and effectiveness of zonisamide in children under age 16 have not been established. Cases of oligohidrosis and hyperpyrexia have been reported (see WARNINGS , Oligohidrosis and Hyperthermia in Pediatric Patients subsection). Zonisamide commonly causes metabolic acidosis in pediatric patients (see WARNINGS , Metabolic Acidosis subsection). Chronic untreated metabolic acidosis in pediatric patients may cause nephrolithiasis and/or nephrocalcinosis, osteoporosis and/or osteomalacia (potentially resulting in rickets), and may reduce growth rates. A reduction in growth rate may eventually decrease the maximal height achieved. The effect of zonisamide on growth and bone-related sequelae has not been systematically investigated.

Geriatric

Use: Single dose pharmacokinetic parameters are similar in elderly and young healthy volunteers (see CLINICAL PHARMACOLOGY , Special Populations subsection). Clinical studies of zonisamide did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

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).