Zonisamide

Side effects

Common side effects

• Dizziness
• Drowsiness/fatigue
• Psychomotor slowing
• Behavioural changes (aggression/agitation/irritability or psychiatric adverse effects)
• Insomnia
• Double vision
• Weight/appetite loss
• GI disturbance
• Ataxia

Other notable side effects

• Hypersensitivity reaction (fever, rash, lymphadenopathy, haematuria, deranged liver function tests)
• Reduced sweating and heat tolerance
• Metabolic acidosis
• Increased incidence of kidney stones (1-2%)
• Paraesthesia
• Rarely: blood dyscrasia, oligohidrosis, hyperthermia
• All anticonvulsants are potentially teratogenic and this is often dose related (see section: AED Prescribing - Pregnancy)

For a complete list of adverse effects, appropriate formularies should be consulted

Dosing

• The initiation and escalation dose depends upon age, weight, syndrome, seizure frequency and severity, and side effect profile.
• Unfortunately, a one dose regime does not fit all.
• A Paediatric Neurologist should be consulted if there is uncertainty.

Commonly used regime

• Initial dose: 1mg/kg once daily for 2 weeks, then increase as needed and tolerated in steps of 1-2mg/kg/day as tolerated every 2 weeks.
• A reasonable maintenance dose is 6-8mg/kg/day
• Zonisamide can be taken with food
• Capsules can be opened and sprinkled onto food or mixed with juice
• In view of its long half-life, Zonisamide can be administered once or twice daily.
• Dosages per kilogram can only be used in children of weight approximately up to 30-40kgs. Consult appropriate formularies for higher weights and in the adult range.

These dosages are only a guideline and appropriate formularies should be consulted as needed.
 
Preparations

• Capsules: 25mg, 50mg, 100mg

Interactions | Precautions

Precautions

• With increased incidence of renal stones, patients are encouraged to drink liberally.
• If possible, Zonisamide should not be used with Acetazolamide, Topiramate, the Ketogenic Diet, or treatments that may also lead to metabolic acidosis or increased incidence of kidney stones.
• Hepatic impairment: No data. Advised not to use in severe hepatic impairment and use with caution in mild-moderate impairment.
• Renal impairment: Limited data. Slower dose titration may be required.
• Enzyme inducing drugs can increase the clearance of Zonisamide and decrease plasma levels.

Weaning

When ceasing Zonisamide it is important to withdraw slowly (over a minimum of several weeks, recommended rate of reduction of 1mg/kg/week) to minimize the potential of increased seizure frequency.
 

Pregnancy

• All anticonvulsants are potentially teratogenic and this is often dose related (see section: AED Prescribing - Pregnancy)
• Usage in pregnancy needs to be discussed with a neurologist.
• There is limited data of the safety of Zonisamide in pregnancy.