Vigabatrin

Drug Information: Vigabatrin

Detailed information regarding Vigabatrin, a medication commonly used in clinical settings. Vigabatrin is an anticonvulsant drug used primarily in the treatment of epilepsy. Specifically, it’s often prescribed for infantile spasms (West syndrome) and as adjunctive therapy for refractory partial seizures in adults and children. It functions by irreversibly inhibiting GABA transaminase, the enzyme responsible for breaking down GABA (gamma-aminobutyric acid), the brain’s primary inhibitory neurotransmitter. This results in increased GABA levels in the synaptic cleft, leading to enhanced inhibitory neurotransmission and a reduction in seizure activity.

Category

Neurological Drugs – Anticonvulsant

Mechanism of Action

Vigabatrin’s mechanism of action centers around enhancing GABAergic neurotransmission in the brain. GABA, or gamma-aminobutyric acid, is the primary inhibitory neurotransmitter in the central nervous system. It functions by binding to GABA receptors on neurons, leading to hyperpolarization of the neuronal membrane and thus inhibiting neuronal firing. Vigabatrin acts as an irreversible inhibitor of GABA transaminase (GABA-T). GABA-T is the enzyme responsible for the breakdown of GABA. By inhibiting GABA-T, Vigabatrin reduces the degradation of GABA, leading to an increase in the concentration of GABA in the synaptic cleft. This elevated GABA concentration enhances the activation of GABA receptors, prolonging their inhibitory effect on neuronal excitability and reducing the likelihood of seizures. This mechanism is particularly important in controlling seizures associated with epilepsy, where an imbalance between excitatory and inhibitory neurotransmission contributes to seizure activity. The irreversible nature of the inhibition means that the enzyme activity can only be restored by the synthesis of new GABA-T molecules.

Clinical Uses

Vigabatrin is primarily indicated for the treatment of seizures, particularly in specific patient populations. One of its major uses is in the treatment of infantile spasms (West syndrome), especially when other treatments have been ineffective. Infantile spasms are a type of seizure disorder that occurs in infants, characterized by sudden, repetitive muscle spasms. Vigabatrin is also used as adjunctive therapy for adults and children with refractory partial seizures who have not responded adequately to other antiepileptic drugs. Refractory seizures are those that are difficult to control with standard medications. The drug’s ability to increase GABA levels in the brain helps to reduce the frequency and severity of seizures in these patients. Due to the risk of vision loss (peripheral visual field constriction), the use of vigabatrin is often reserved for cases where other treatments have failed to provide adequate seizure control.

Dosage

Adults (Refractory Partial Seizures):

• Initial Dose: 1000 mg orally per day, administered in one or two divided doses.
• Maintenance Dose: May be increased in increments of 500 mg to 1000 mg per day at weekly intervals, depending on response and tolerability. The usual maintenance dose ranges from 2000 mg to 3000 mg per day.
• Maximum Dose: Do not exceed 3000 mg per day.

Pediatrics (Infantile Spasms):

• Initial Dose: 50 mg/kg per day, administered in two divided doses.
• Maintenance Dose: May be increased gradually as needed, up to a maximum of 150 mg/kg per day, administered in two divided doses.

Route of Administration: Oral. Vigabatrin is available as tablets and oral solution.

Indications

• Infantile Spasms (West Syndrome)
• Adjunctive therapy for refractory partial seizures in adults and children

Contraindications

• Known hypersensitivity to Vigabatrin or any of its components
• Pre-existing visual field defects: Vigabatrin can cause or worsen visual field constriction

FAQ

1. What is Vigabatrin used for?

   Vigabatrin is primarily used to treat infantile spasms (West syndrome) and as adjunctive therapy for refractory partial seizures in adults and children.

2. How does Vigabatrin work?

   Vigabatrin works by irreversibly inhibiting GABA transaminase, an enzyme that breaks down GABA. This increases GABA levels in the brain, reducing neuronal excitability and decreasing the likelihood of seizures.

3. What are the common side effects of Vigabatrin?

   Common side effects include drowsiness, fatigue, dizziness, weight gain, and visual field defects.

4. What is the most serious side effect of Vigabatrin?

   The most serious side effect is progressive and permanent bilateral concentric visual field constriction (peripheral vision loss).

5. How often should I have my vision checked while taking Vigabatrin?

   Regular eye exams, including visual field testing, are essential before starting Vigabatrin and periodically during treatment to monitor for visual field defects.

6. Can Vigabatrin be used during pregnancy?

   Vigabatrin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Discuss this thoroughly with your doctor.

7. What should I do if I miss a dose of Vigabatrin?

   If you miss a dose, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not double the dose to catch up.

8. Can Vigabatrin cause behavioral changes?

   Yes, some patients may experience behavioral changes, including agitation, irritability, or psychosis. Report any significant behavioral changes to your healthcare provider immediately.