• Somnolence/sedation (rarely Vigabatrin may cause encephalopathic symptoms)
• Weight gain
• Dizziness
• Double vision
• Fatigue
• Headaches
• Nausea and abdominal pain
• Behavioural disturbance (excitation/agitation/irritability)
• Cognitive change (thought disturbance/psychosis)

Other notable side effects:

Peripheral visual field loss

• Vigabatrin is associated with a significant incidence of visual field constriction on testing, though the clinical significance in all patients is often not stated in the literature.
• Some patients are, however, at risk of significant visual compromise that is irreversible.
• Licensing of Vigabatrin in the USA was delayed until 2009 and mandatory baseline testing and serial data entry was conducted through to 2016.
• Across all 9423 patients enrolled for serial testing, the risk of clinical vision impact appears low (no patient had documented visual loss).
• 37% had clinically significant pathology affecting their visual system before vigabatrin was commenced. Test results of 1509 patients (OCT, ERG, VF) was available. The risk of change on tests was low - 2%3 .
• However, regular monitoring is strongly recommended (see MIMS: Precautions in usage and USA FDA advice). It is critical to do baseline testing, collaborate with an ophthalmologist and discuss monitoring in the very young with a paediatric neurologist, where perimetry is not possible and ERG utilized.
• Decisions are based on risk-benefit ratio noting the significant impact of drug resistant epilepsy and epileptic encephalopathy.
• Further data is required, particularly in patients with infantile spasms, determining pre vigabatrin retinal function, optimal monitoring and longitudinal follow-up on visual function.

MRI abnormality 

• Vigabatrin may cause prominent signal abnormality in basal ganglia and upper brain stem, especially in infants.
• These abnormalities are usually reversible and may even remit with continued drug usage.
• They are known as VABAM (vigabatrin associated brain abnormalities on magnetic resonance imaging). In the majority of circumstances, the patient is asymptomatic.
• In 2020, attention was drawn to movement disorder, encephalopathy and dysautonomia in 3 patients where combined hormonal and vigabatrin treatment was used, with Down Syndrome patients at particular risk.
• Again further data is required particularly to determine causation.
• Rarely: Optic neuritis, rash, urticaria and angioedema.

All anti-seizure medications are potentially teratogenic and this is often dose related. For a complete list of adverse effects, appropriate formularies should be consulted.

Precautions

• Use with caution in patients with a history of behavioural problems, depression, or psychosis.
• Vigabatrin may worsen absence and myoclonic seizures.
• Renal impairment: As Vigabatrin is renally excreted, consult formularies and neurology if there is renal impairment.

Pregnancy

• Usage in pregnancy needs to be discussed with a neurologist.
• There is limited data on the safety of Vigabatrin in pregnancy.
• All anti-seizure medications are potentially teratogenic and this is often dose related

• PBS (Pharmaceutical Benefits Scheme)
• MIMS (Monthly Index of Medical Specialties)
• AMH (Australian Medicines Handbook)