Vigabatrin

How it works

It is an irreversible inhibitor of GABA transaminase, the enzyme that degrades GABA, thereby raising brain GABA concentrations and enhancing inhibitory neurotransmission.

Prescribing in practice

• It can cause permanent, irreversible concentric visual field constriction, so the benefits and risks must be discussed and vision assessed where feasible, with treatment limited to indications where the benefit justifies this risk.
• Sedation, weight gain and behavioural changes can occur, and MRI signal changes have been reported in infants.
• It should be withdrawn gradually to avoid precipitating seizures.

Monitoring

Arrange baseline and periodic visual field testing where the child or adult can cooperate, and monitor for behavioural change and excessive sedation.

Counselling the patient

• Be aware of the risk of permanent loss of peripheral vision and attend any recommended eye tests.
• Do not stop the medicine suddenly, as this can bring on seizures.

Evidence & guidelines

Its first-line role in infantile spasms and the visual field risk are reflected in NICE guidance and MHRA safety advice.