WHAT IS THIS MEDICINE AND WHAT IS IT USED FOR?
Sabril contains vigabatrin, an anticonvulsant that works by irreversibly
inhibiting GABA transaminase — the enzyme that breaks down GABA, the brain's
main inhibitory (calming) neurotransmitter.
By blocking GABA breakdown, vigabatrin increases GABA levels throughout
the brain, raising the seizure threshold and reducing seizure frequency.
Vigabatrin is used as add-on therapy (in combination with other
antiepileptics) for: complex partial seizures (focal seizures with impaired
awareness) in adults, adolescents, and children — when other antiepileptics
have been tried and are not fully effective; and as monotherapy (first-line
treatment) for infantile spasms (West syndrome) — a severe epileptic syndrome
of infancy, where vigabatrin is particularly effective.
Because of its risk of permanent visual field loss (see warnings),
vigabatrin is generally reserved for patients whose seizures cannot be
adequately controlled with safer alternatives.
3. HOW TO TAKE THIS MEDICINE
For adults with complex partial seizures: starting dose 1g daily (two
500mg tablets), increasing by 500mg per week up to a usual maintenance dose of
2 to 3g daily (4 to 6 tablets), divided into two doses. The maximum dose is 3g
per day.
Take with or without food. For infantile spasms: 50mg/kg per day in two
divided doses, adjusted by weight — managed entirely by the paediatric
neurology team.
Because of the permanent visual field risk, every patient must have
formal visual field perimetry testing (measurement of peripheral vision) before
starting vigabatrin, and then every 6 months throughout treatment. Patients who
develop visual field defects may need to stop vigabatrin — but the visual loss
is typically irreversible. This monitoring is mandatory, not optional.
⚠ PATIENT TIP: Attend every visual field test
appointment — without exception. These tests check whether vigabatrin is
affecting your peripheral (side) vision. The visual field loss caused by
vigabatrin is often unnoticed at first because it affects side vision rather
than central vision. Regular testing is the only way to detect it before it
becomes severe.
4. POSSIBLE SIDE EFFECTS
|
How Common? |
Side Effects |
|
Very Common |
Fatigue, drowsiness,
dizziness, headache, weight gain, visual field defects (peripheral vision
loss — see warning) |
|
Common |
Depression, mood
changes, memory problems, concentration difficulties, double vision, tremor,
numbness or tingling in extremities |
|
Serious — Monitoring
Required or Seek Help |
Permanent visual field
constriction (the most serious and irreversible side effect — affects up to
40% of long-term users; peripheral vision is gradually lost, which can cause
difficulty driving and navigating in busy environments). Encephalopathic
symptoms (confusion, drowsiness, abnormal movements, slowed thinking —
particularly in overdose or renal impairment — usually reversible). Severe
depression or psychosis — report immediately. MRI signal changes in basal
ganglia (seen in infants receiving vigabatrin — usually asymptomatic and
reversible). |
5. WHO SHOULD NOT TAKE THIS MEDICINE
Vigabatrin must not be used as a first-line treatment for most epilepsy
types given its visual risk — use is restricted to complex partial seizures
where other treatments have failed, and infantile spasms. It must not be used
in patients who cannot undergo regular visual field monitoring (e.g. patients
unable to cooperate with perimetry). Use with great caution in kidney disease —
dose reduction required (vigabatrin is renally cleared). Not recommended in
pregnancy — specialist guidance essential.
⚠ VISUAL FIELD DEFECTS — PERMANENT, IRREVERSIBLE
RISK: Up to 40% of patients who take vigabatrin long-term develop a permanent
visual field defect — typically a bilateral concentric constriction
(tunnel-like narrowing of peripheral vision). This is often only detected on
formal testing as it affects side vision first. The loss is irreversible even
after stopping vigabatrin. Mandatory formal perimetry every 6 months is
required throughout treatment. If visual field defects develop, the decision to
continue must be made by the neurologist weighing seizure control benefits
against the irreversible visual cost.
⚠ RENAL DOSE ADJUSTMENT: Vigabatrin is primarily
cleared by the kidneys. In any degree of kidney impairment, the dose must be
reduced to prevent drug accumulation and encephalopathic toxicity. Check
eGFR/creatinine before starting and monitor during treatment.
⚠ DRIVING: The combination of potential visual
field loss and CNS side effects (drowsiness, dizziness) means driving is
contraindicated in many patients on vigabatrin. Follow your neurologist's and
licensing authority's guidance explicitly.
6. MEDICINES THAT INTERACT WITH THIS TREATMENT
Vigabatrin reduces phenytoin plasma levels by 20 to 30% — phenytoin dose
adjustment may be needed. It has relatively few pharmacokinetic interactions
but pharmacodynamic interactions (additive CNS depression) with other
antiepileptics and CNS depressants (alcohol, sedatives) are expected.
Vigabatrin does not significantly induce or inhibit liver enzymes.
7. HOW TO STORE THIS MEDICINE
Store below 30°C. Keep in original packaging. Keep out of reach of
children.
8. PRESCRIPTION REQUIREMENT
|
Field |
Details |
|
Status |
Prescription Only
Medicine (POM) — Specialist (neurology) prescription required; subject to
restricted use guidelines in many countries |
9. GUIDANCE FOR PATIENTS & CAREGIVERS
Take your tablets as prescribed — usually twice daily, with or without
food. Never miss your 6-monthly visual field test appointments — these are
essential to detect any changes in your peripheral vision before they become
severe.
The visual changes from vigabatrin often cannot be felt or noticed in
daily life until they are advanced — only formal testing detects them early.
Tell your neurologist immediately if you notice any narrowing of your side
vision, difficulty driving, or problems navigating in crowds. Do not drive
unless your neurologist has confirmed it is safe for you. If you experience
severe mood changes, confusion, or worsening seizures, contact your neurology
team promptly.
10. PHARMACIST & PRESCRIBER NOTES
|
Field |
Details |
|
Clinical Dispensing
Notes |
Vigabatrin —
irreversible GABA transaminase inhibitor. Visual field perimetry is
mandatory: baseline before starting, then every 6 months throughout
treatment. Confirm this monitoring is in place before every dispensing —
liaise with neurology team if visual field records are absent. Visual field
defects affect up to 40% of long-term users — often asymptomatic until
advanced. Irreversible even after stopping. Renal dose adjustment is
essential: reduce by 25% for mild–moderate impairment; significant reduction
for severe impairment. Phenytoin: vigabatrin reduces phenytoin levels by
20–30% — monitor phenytoin levels after initiation. CNS depression additive
with other AEDs, alcohol, sedatives. Driving guidance: typically
contraindicated — advise patient and document. Paediatric use (infantile
spasms): weight-based dosing; MRI brain changes monitored by paediatric
neurologist. Pregnancy: specialist advice essential. Encephalopathic symptoms
at high doses or in renal failure. |
11. FREQUENTLY ASKED QUESTIONS
Q: Can I still drive while taking vigabatrin?
In most cases, driving is not permitted while taking vigabatrin — both
because of the CNS side effects (drowsiness, dizziness) and because of the risk
of visual field impairment. You must follow your neurologist's guidance and
inform the relevant driving licence authority. Do not drive until you have
received explicit clearance from your neurologist.
Q: Why does vigabatrin affect vision?
Vigabatrin accumulates in the retina — the light-sensitive layer at the
back of the eye — where it irreversibly inhibits the same enzyme (GABA
transaminase) it targets in the brain. This disrupts normal retinal function,
gradually damaging the cells responsible for peripheral vision.
Q: Is vigabatrin effective for infantile spasms?
Yes — vigabatrin is considered one of the most effective first-line
treatments for infantile spasms (West syndrome), particularly in babies with
tuberous sclerosis complex (TSC). The benefit in this severe epileptic syndrome
is considered to outweigh the visual risk, which is monitored carefully by the
paediatric neurology team.
Q: Are there alternatives if vigabatrin is damaging my vision?
Yes — your neurologist will discuss alternatives. Depending on the type
and severity of your epilepsy, other options may include different
antiepileptic medicines. The decision is made on an individual basis, balancing
seizure control against the progressive and irreversible nature of the visual
side effect.