- Topiramate has a broad range of seizure efficacy and on the Australian PBS can be considered in treatment for partial epileptic seizures, primary generalised tonic-clonic seizures and seizure of Lennox Gastaut Syndrome not controlled satisfactorily by other antiepileptic drugs.
- Side effects (irritability, anorexia, sedation) should be considered before prescribing.
- It has been used in neonates and infants.
NOTABLE Side Effects:
- Marked loss of appetite/loss of weight may require cessation of drug.
- Metabolic acidosis (topiramate is a carbonic anhydrase inhibitor) is a common finding in young infants. Blood bicarbonate levels around 16-18mmol/L are to be expected and usually cause no significant problems. Lower levels may require treatment.
- Nephrocalcinosis can occur and patients on long term treatment or who have other risk factors can be monitored with urine studies and renal ultrasound.
- Reduced sweating may cause heat intolerance which is manageable with simple measures. Care must be taken in warm climates. In the very young heat intolerance can be a more serious side effect and overheating must be avoided.
- Word finding difficulty and language impairment may be pronounced and are more of a risk with higher doses.
- Sedation can occur but is more common with higher doses.
- Mood disturbance (irritability, crankiness, depression) can occur.
- Glaucoma is a contraindication. Advise urgent review if painful eyes develop.
- Rarely, visual field defect is described.
- Paraesthesia’s and hand tingling can occur but are uncommon.
- All anticonvulsants are potentially teratogenic and this is often dose related (see section: Pregnancy and AEDs)
- For a complete list of adverse effects, appropriate formularies should be consulted.
- The initiation and escalation dose depends upon age, weight, syndrome, seizure frequency and intensity, and side effect profile.
- Unfortunately, a one dose regime does not fit all. A Paediatric Neurologist should be consulted if there is uncertainty.
A commonly used regime is below:
- Typical dosage is approximately 5mg/kg/day in two divided doses. Some patients may respond to 2mg/kg/day. Dose can be increased to 8-9mg/kg/day in refractory cases (a patient is probably failing the drug if there is no significant effect on seizures above 7mg/kg/day). Advice from a Paediatric Neurologist may be helpful.
- Starting dose 0.5-1mg/kg/day in two divided doses increasing either weekly or fortnightly by 0.5mg/kg/day to target. In certain acute situations such as an epileptic encephalopathy or status, initiating dose can be higher (e.g. 2mg/kg/day) and rate of escalation faster. Consultation with Paediatric Neurology may be helpful.
- 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.
- Tablets 25mg, 50mg, 100mg, 200mg; Topamax Sprinkle Capsule 15mg, 25mg, 50mg. Tablets or capsule contents can be dissolved to make a liquid form. It can be given rectally if a patient is fasting.
Monitoring and Levels:
- Drug level monitoring is not routinely utilized or readily available.
- Blood bicarbonate should be checked within a month as a guide and then at intervals with escalation. This is particularly important in the infant.
- Renal ultrasound and urine testing are considered as necessary, particularly if back pain or haematuria
- Topiramate may decrease serum concentrations of oestrogens.
- Topiramate may increase toxicity of sodium valproate.
- Topiramate concentration may be decreased by carbamazepine.
This website was created in March 2012. This page was last modified in December 2017.