Sequential neuropathology of dogs treated with vigabatrin, a GABA-transaminase inhibitor.

Abstract

Vigabatrin (Sabril) is a gamma-aminobutyric acid-transaminase (GABA-T) inhibitor that is effective in the treatment of certain types of drug-resistant or uncontrolled epilepsy but is known to cause microscopic vacuolation (intramyelinic edema) in the brains of treated rats, mice, and dogs. The effects of high oral doses (300 mg/kg/day) of vigabatrin administered orally to Beagle dogs were studied during treatment weeks 1-12 and recovery weeks 13, 14, 16, 20, 24, and 28. Emesis, loose stools, and anorexia and 3 drug-related deaths were observed during the first 4 wk of treatment but were virtually nonexistent thereafter because of adaptation to the drug aided by food supplementation. In more sensitive areas of the brain (columns of the fornix, thalamus, and hypothalamus), microscopic quantitative differences between background vacuolation in controls and drug-related vacuolation in treated dogs could be delineated after 4 wk, generally reached highest levels of severity between 8 and 12 wk, and were reversible upon cessation of dosing. Inhibition of brain GABA-T and elevation of brain GABA were noted after 1 wk of treatment. During the course of treatment vigabatrin ranged between 4-17 nmol/ml (plasma) and 42-1,570 nmol/ml [cerebrospinal fluid (CSF)] while CSF GABA concentrations were 4-32 nmol/ml (treated dogs) and 0.1-0.6 nmol/ml (control dogs). Although the cause of vigabatrin-induced microvacuolation is unknown, the results of the study demonstrated that GABA-T inhibition with subsequent GABA elevation occurred within the first week of treatment and was followed by the onset of detectable microvacuolation several weeks later.

• Authors: J T Yarrington, J P Gibson, J E Dillberger, G Hurst, B Lippert, N M Sussman, W E Heydorn, R J Marler
• Journal: Toxicologic pathology (Toxicol Pathol) 1993 Sep-Oct Vol. 21 Issue 5 Pg. 480-9 ISSN: 0192-6233 [Print] United States
• PMID: 8115824 (Publication Type: Journal Article)

Chemical References

• Aminocaproates
• gamma-Aminobutyric Acid
• 4-Aminobutyrate Transaminase
• Glutamate Decarboxylase
• Vigabatrin

Topics

• 4-Aminobutyrate Transaminase (antagonists & inhibitors, metabolism)
• Aminocaproates (blood, cerebrospinal fluid, toxicity)
• Animals
• Behavior, Animal (drug effects)
• Brain (drug effects, metabolism, pathology)
• Dogs
• Female
• Glutamate Decarboxylase (drug effects)
• Male
• Vigabatrin
• gamma-Aminobutyric Acid (metabolism)