Figure 1 presents the proportion of patients (X-axis) whose percentage
reduction from baseline in the all partial seizure rate was at least as great as
that indicated on the Y-axis in the second and third placebo-controlled trials.
A positive value on the Y-axis indicates an improvement from baseline (i.e., a
decrease in seizure rate), while a negative value indicates a worsening from
baseline (i.e., an increase in seizure rate). Thus, in a display of this type,
the curve for an effective treatment is shifted to the left of the curve for
placebo. The proportion of patients achieving any particular level of reduction
in seizure rate was consistently higher for the zonisamide groups compared to
the placebo groups. For example, Figure 1 indicates that approximately 27% of
patients treated with zonisamide experienced a 75% or greater reduction,
compared to approximately 12% in the placebo groups.
Figure 1 Proportion of Patients Achieving Differing Levels of Seizure Reduction in Zonisamide and Placebo Groups in Studies 2 and 3.
No differences in efficacy based on age, sex or race, as measured by a change
in seizure frequency from baseline, were detected.
Suicidal Behavior and IdeationAntiepileptic drugs (AEDs), including zonisamide, 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 to 100 years) in the clinical trials analyzed.
Table 3 shows absolute and relative risk by indication for
all evaluated AEDs.
Table 3. Risk by indication for antiepileptic drugs in the pooled analysis
| Placebo Patients with Events |
| Drug Patients with Events |
| Relative Risk: Incidence of Events in Drug |
| Risk Difference: Additional Drug
Patients |
| Indication | Per 1000 Patients |
| Per 1000 Patients |
| Patients / Incidence in Placebo Patients |
| with Events Per 1000 Patients |
|
|
|
|
|
|
|
|
| Epilepsy | 1 |
| 3.4 |
| 3.5 |
| 2.4 |
| Psychiatric | 5.7 |
| 8.5 |
| 1.5 |
| 2.9 |
| Other | 1 |
| 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 zonisamide 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.
Patients, their caregivers, and families should be informed that AEDs
increase the risk of suicidal thoughts and behavior and should be advised of the
need to be alert for the emergence or worsening of the signs and 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, Cognitive/Neuropsychiatric Adverse Events
subsection below).
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) (see PRECAUTIONS, Laboratory Tests subsection). 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 to be 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 (see PRECAUTIONS,
Kidney Stones subsection).
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 (see PRECAUTIONS, Laboratory Tests
subsection).
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.
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 zonisamide (using dose tapering).
If the decision is made to continue patients on zonisamide in the face of
persistent acidosis, alkali treatment should be considered.
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 to 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.
Seizures on WithdrawalAs with other AEDs, abrupt withdrawal of zonisamide in patients
with epilepsy may precipitate increased seizure frequency or status epilepticus.
Dose reduction or discontinuation of zonisamide should be done
gradually.
TeratogenicityWomen of child bearing potential who are given zonisamide should
be advised to use effective contraception. Zonisamide was teratogenic in mice,
rats, and dogs and embryolethal in monkeys when administered during the period
of organogenesis. A variety of fetal abnormalities, including cardiovascular
defects, and embryo-fetal 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 (see PRECAUTIONS, Pregnancy
subsection). Zonisamide should be used during pregnancy only if the potential
benefit justifies the potential risk to the fetus.
Cognitive/Neuropsychiatric Adverse Events
Use of zonisamide was frequently associated with central nervous
system-related adverse events. The most significant of these can be classified
into three general categories: 1) psychiatric symptoms, including depression and
psychosis, 2) psychomotor slowing, difficulty with concentration, and speech or
language problems, in particular, word-finding difficulties, and 3) somnolence
or fatigue.
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% were
hospitalized because of reported depression or suicide attempts. In
placebo-controlled trials, 2.2% of patients discontinued zonisamide or were
hospitalized due to psychosis or psychosis-related symptoms compared to none of
the placebo patients. Among all epilepsy patients treated with zonisamide, 0.9%
were discontinued and 1.4% were hospitalized because of reported psychosis or
related symptoms.
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 to 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 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 to 500 mg/day. Patients should be
cautioned about this possibility and special care should be taken by patients if
they drive, operate machinery, or perform any hazardous task.
Other Adverse Events Observed During Clinical TrialsZonisamide 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. The frequencies represent the
proportion of the 1,598 individuals exposed to zonisamide who experienced an
event on at least one occasion. All events are included except those already
listed in the previous table or discussed in WARNINGS or PRECAUTIONS, 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 patient; 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.