Vigabatrin
Vigabatrin is an anticonvulsant medication primarily used as an adjunctive therapy for refractory epilepsy, particularly in cases of focal seizures that have not responded to other treatments. It is also used to treat infantile spasms (West syndrome).
Trade Names
Vigabatrin is marketed under the brand name Sabril, Sabrilex, Vigafyde, Vigadrone, and Vigpoder.
Chemical Properties
Chemical structure: Vigabatrin is a structural analog of gamma-aminobutyric acid (GABA).
Molecular formula: C₆H₁₁NO₂
Molecular weight: 129.16 g/mol
Solubility: Vigabatrin is highly soluble in water and is available as tablets and powder for oral suspension.
Biochemical Properties
Mechanism of action: Vigabatrin works by irreversibly inhibiting GABA transaminase, an enzyme that breaks down GABA. This results in increased GABA levels in the brain, which has an inhibitory effect on neuronal activity, thereby reducing seizure frequency.
Pharmacology
Administration: Vigabatrin is taken orally in tablet or powder form.
Bioavailability: Vigabatrin has high bioavailability with rapid absorption in the gastrointestinal tract.
Metabolism: Vigabatrin is not extensively metabolized by the liver; it is mainly excreted unchanged by the kidneys.
Half-life: The half-life of vigabatrin is approximately 5–8 hours, but its effects on GABA transaminase are long-lasting, allowing for once or twice daily dosing.
Clinical Indications
Refractory focal seizures: It is often used as adjunctive therapy in adults and children with focal seizures that have not responded to other treatments.
Infantile spasms (West syndrome): Vigabatrin is one of the first-line treatments for infantile spasms, a severe epilepsy syndrome that begins in infancy.
Side Effects
Visual field defects: Vigabatrin is associated with a risk of irreversible peripheral vision loss (visual field constriction), so regular visual field testing is essential during treatment.
Drowsiness and sedation: Sedation and drowsiness are common, especially when first starting treatment.
Weight gain: Some patients experience weight gain during treatment.
Mood and behavioral changes: Irritability, agitation, and depression may occur.
Fatigue and dizziness: Many patients report feeling fatigued or dizzy, especially at higher doses.
Peripheral neuropathy: Numbness, tingling, and other nerve-related symptoms may develop in some patients.
Psychiatric symptoms: In rare cases, vigabatrin can cause psychosis, hallucinations, or confusion, particularly in individuals with a history of mental health issues.
Monitoring and Considerations
Visual field monitoring: Due to the risk of irreversible visual field loss, visual field tests should be conducted at baseline and then every six months during treatment. If vision issues develop, discontinuing the drug may be considered.
Pregnancy: Vigabatrin is classified as Category C in pregnancy, indicating potential risk to the fetus. It should only be used if the potential benefits justify the risks.
Kidney function: Since vigabatrin is excreted through the kidneys, dose adjustments may be necessary in patients with kidney impairment.
Vigabatrin is an effective anticonvulsant, particularly for focal seizures that are resistant to other treatments and for managing infantile spasms. However, its use requires careful monitoring due to the significant risk of irreversible visual field loss. Regular vision testing is essential, and patients should be advised of the risks before beginning treatment.
