Vigabatrin

Vigabatrin is now a second line treatment for patients with partial seizures. It is, however, still a first-line treatment for infantile spasms, particularly those associated with tuberous sclerosis. It has no use in primary generalised epilepsy and may worsen myoclonic seizures. Tolerance may develop in up to one-third of initial responders.

• Adjunctive treatment in combination with other antiepileptic treatment for partial seizures with or without secondary generalisation not satisfactorily controlled with other antiepileptics. Its use is restricted to patients in whom all other combinations are inadequate or are not tolerated.
• Monotherapy for management of infantile spasms (West's syndrome)

• Visual field defects

• Visual field defects:
  • About one-third of patients develop visual field defects
  • The CSM has advised that onset of symptoms varies from 1 month to several years after starting
  • In most cases, visual field defects have persisted despite discontinuation
  • Visual fields should be tested before treatment and at 6-month intervals
  • Patients should be warned to report any new visual symptoms that develop; those with symptoms should be referred for an urgent ophthalmological opinion and gradual withdrawal of vigabatrin should be considered.
• Elderly
• Closely monitor neurological function
• Avoid sudden withdrawal (taper off over a 2-4 week period)
• History of psychosis, depression or behavioural problems
• Absence seizures (may be exacerbated)
• Pregnancy (congenital anomalies have been reported)
• Breast-feeding (present in breast milk and so advice is to avoid)

• The addition of vigabatrin reduces plasma concentrations of phenytoin. Usually this has no clinical significance, but occasionally an increase in phenytoin dose is necessary.
• Vigabatrin has no other known interactions

• Sedation, dizziness and headache particularly occur when doses are being increased. The symptoms are usually temporary and self-limiting. These symptoms can usually be prevented by introducing the drug gradually.
• Up to 10% of patients develop a change in mood, such as agitation, disturbed behaviour or depression. Paranoid and psychotic symptoms occur but only rarely.
• Visual field defects

• Treatment should be started with a low dose (250-500 mg/day), and titrated slowly upwards over a period of several weeks until therapeutic response is achieved.
• Too rapid titration may be associated with an increased incidence of adverse events
• With current antiepileptic therapy, initially 1 g daily in single or 2 divided doses then increased according to response in steps of 500 mg at weekly intervals.
• The usual range is 2-3 g daily (maximum 3 g daily)
• Infantile spasms (West's syndrome): 50 mg/kg daily, adjusted according to response over 7 days up to 150 mg/kg daily

• Other than checking for compliance, there is no value in measuring the plasma concentration