Usage
- The usual indication for Zonisamide is focal seizures and secondarily generalised seizures that have not been satisfactorily controlled by other anti-epileptic drugs.
- There is evidence that Zonisamide is an effective broad spectrum antiepileptic drug and has been used in myoclonic seizures, generalised seizures, and syndromes such as Lennox-Gastaut and Myoclonic-astatic epilepsy.
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Side effects
Possible 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 below initiation and escalation doses are only a guide and need to be individualised based on patient (age, weight, co-morbidities), disease (seizure type, frequency, duration) and medication (metabolism, interactions, side-effect profile) characteristics.
- Situations that require more careful consideration include children with higher weights, polytherapy, or multiple co-morbidities. Consultation with appropriate formularies or a paediatric neurologist may be required in specific circumstances.
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.
- Dosages per kilogram can only be used up to weights of 30-40kgs.
- 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.
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.