Drug Interaction Report

GENERALLY AVOID: Theoretical concerns exist that oculotoxic effects of vigabatrin may be additive with those of other drugs that are associated with serious adverse ophthalmic effects. Vigabatrin causes permanent bilateral concentric visual field constriction in 30% or more of patients, with severity ranging from mild to severe. Vigabatrin can also damage the central retina and decrease visual acuity. The onset of vision loss is unpredictable, occurring within weeks of starting treatment to months or even years later. The risk of vision loss increases with increasing dose and cumulative exposure, although there is no dose or exposure known to be risk-free. It is possible that vision loss can worsen even after discontinuation of vigabatrin.

MANAGEMENT: Vigabatrin should generally not be used with other drugs associated with serious adverse ophthalmic effects such as retinopathy or glaucoma unless the benefits clearly outweigh the risks. These drugs may include amiodarone, deferoxamine, ethambutol, quinine derivatives, tamoxifen, and long-term corticosteroids. Vision testing at baseline (no later than 4 weeks after starting vigabatrin) and at least every 3 months during therapy is required for adults. Vision testing is also required about 3 to 6 months after the discontinuation of vigabatrin therapy. Due to the risk of irreversible vision loss, vigabatrin should be withdrawn from patients who fail to show substantial clinical benefit within 3 months of initiation, or sooner if treatment failure becomes obvious. The patient's response and continued need for vigabatrin should be periodically reassessed. The lowest dosage and shortest duration of treatment consistent with clinical objectives should be employed.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.