vigabatrin: clinical use

Prescribing considerations

• Initiation and follow-up require specialist supervision.
• Except for infantile spasms, vigabatrin is an adjunctive rather than initial monotherapy.
• Use only after careful benefit-risk assessment because visual-field loss can be permanent and asymptomatic.
• Withdrawal must be gradual.
• Use caution with previous psychosis, depression or behavioural disturbance.
• Renal elimination increases the risk of sedation and confusion in renal impairment and older people.

Contraindications and cautions

• Hypersensitivity to vigabatrin or a formulation excipient.
• Avoid concurrent retinotoxic medicinal products.
• Not recommended where a clinically significant pre-existing visual-field defect is present.

Monitoring

• Arrange baseline and regular ophthalmic assessment during treatment, using age-appropriate visual-field or retinal testing, with follow-up after withdrawal.
• Ask about visual symptoms, seizure worsening, mood, behaviour, cognition, sedation and movement disorders.
• Assess renal function and monitor more closely when renal clearance is reduced.
• Be aware that vigabatrin can suppress measured ALT and AST activity and interfere with some urinary amino-acid tests.
• In infants with new movement or neurological abnormalities, consider reported MRI changes or intramyelinic oedema.

Clinical pharmacology

Vigabatrin selectively and irreversibly inhibits GABA-transaminase, increasing cerebral GABA. It is rapidly absorbed, minimally protein-bound, not significantly metabolised and mainly excreted unchanged by the kidneys. Clinical effect does not correlate directly with plasma concentration.

Formulation and product differences

• Sabril is a film-coated tablet; its score assists swallowing but does not provide equal portions.
• Vigabatrin Zydus is a ready-made oral solution supplied with an oral syringe. It contains methyl and propyl parahydroxybenzoates, which can cause delayed allergic reactions.
• Kigabeq is a soluble paediatric tablet that can be divided into equal portions, dispersed only in water and given orally or through a gastric tube.
• Kigabeq tablet strengths can look similar when whole or divided, creating a risk of selection error; confirm the intended strength carefully.

Oral solution

Route: Oral

Strengths: 100 mg/mL, 500 mg

Tablet

Route: Oral

Strengths: 500 mg