Overview
11 DESCRIPTION VIGADRONE (vigabatrin, USP) is an oral antiepileptic drug and is available as a white, film- coated 500 mg tablet. The chemical name of vigabatrin, a racemate consisting of two enantiomers, is (±) 4-amino-5-hexenoic acid. The molecular formula is C 6 H 11 NO 2 and the molecular weight is 129.16.
Mechanism of Action
12 CLINICAL PHARMACOLOGY 12.1 Mechanism of Action The precise mechanism of vigabatrin's anti-seizure effect is unknown, but it is believed to be the result of its action as an irreversible inhibitor of γ-aminobutyric acid transaminase (GABA-T), the enzyme responsible for the metabolism of the inhibitory neurotransmitter GABA. This action results in increased levels of GABA in the central nervous system. No direct correlation between plasma concentration and efficacy has been established. The duration of drug effect is presumed to be dependent on the rate of enzyme re-synthesis rather than on the rate of elimination of the drug from the systemic circulation. 12.
Indications
- 1 INDICATIONS AND USAGE VIGADRONE is indicated for the treatment of: Refractory Complex Partial Seizures as adjunctive therapy in patients 2 years of age and older who have responded inadequately to several alternative treatments; VIGADRONE is not indicated as a first line agent ( 1.1 ) Infantile Spasms – monotherapy in infants 1 month to 2 years of age for whom the potential benefits outweigh the potential risk of vision loss ( 1.2 ) 1.
Common Doses
- 000 mg
- 500 mg
- 50 mg
- 25 mg
Dosage
2 DOSAGE AND ADMINISTRATION Refractory Complex Partial Seizures Adults (17 years of age and older): Initiate at 1,000 mg/day (500 mg twice daily); increase total daily dose weekly in 500 mg/day increments, to the recommended dose of 3,000 mg/day (1,500 mg twice daily) ( 2.2 ) Pediatric (2 to 16 years of age): The recommended dosage is based on body weight and administered as two divided doses ( 2.2 ) The dosage may be increased in weekly intervals, depending on response ( 2.2 ) Dose patients weighing more than 60 kg according to adult recommendations ( 2.
Black Box Warning
WARNING: PERMANENT VISION LOSS VIGADRONE can cause permanent bilateral concentric visual field constriction, including tunnel vision that can result in disability. In some cases, VIGADRONE also can damage the central retina and may decrease visual acuity [see Warnings and Precautions (5.1) ]. The onset of vision loss from VIGADRONE is unpredictable and can occur within weeks of starting treatment or sooner, or at any time after starting treatment, even after months or years.
Contraindications
- 4 CONTRAINDICATIONS None. None ( 4 )
Side Effects
- 6 ADVERSE REACTIONS The following serious and otherwise important adverse reactions are described elsewhere in labeling: Permanent Vision Loss [see BOXED WARNING , Warnings and Precautions (5.1) ] Magnetic Resonance Imaging (MRI) Abnormalities in Infants [see Warnings and Precautions (5.3) ] Neurotoxicity [see Warnings and Precautions (5.4) ] Suicidal Behavior and Ideation [see Warnings and Precautions (5.5) ] Withdrawal of Antiepileptic Drugs (AEDs) [see Warnings and Precautions (5.6) ] Anemia [see Warnings and Precautions (5.7) ] Somnolence and Fatigue [see Warnings and Precautions (5.
Interactions
- 7 DRUG INTERACTIONS Decreased phenytoin plasma levels: dosage adjustment may be needed ( 7.1 ) 7.1 Antiepileptic Drugs Phenytoin Although phenytoin dose adjustments are not routinely required, dose adjustment of phenytoin should be considered if clinically indicated, since VIGADRONE may cause a moderate reduction in total phenytoin plasma levels [see Clinical Pharmacology (12.3) ]. Clonazepam VIGADRONE may moderately increase the C max of clonazepam resulting in an increase of clonazepam-associated adverse reactions [see Clinical Pharmacology (12.3) ].