Effects of vigabatrin and of GABA on myelinated rat cerebellar cultures: preliminary data

1. The aim of this study was to evaluate the effect of high concentrations of vigabatrin (gamma-vinyl GABA) and of GABA on myelin of the central nervous system cultures. 2. Explants of rat cerebellum were cultured for 14-19 days in vitro on collagen-coated coverslips in Leighton tubes. They were exposed for up to 14 days to 500 nmol ml-1 vigabatrin or to 1000 nmol ml-1 GABA. 3. Qualitative and quantitative blind examination of living cultures and of Sudan black B-stained slides showed mild toxicity of both drugs for myelinated fibres. No clear-cut differences could be demonstrated between the two compounds, although vigabatrin seemed slightly more toxic than GABA at these doses. 4. In electron microscopy, no patent intramyelinic oedema nor primary demyelination were seen. On the contrary, some degenerating myelinated fibres and astrocytic gliosis were seen in both experimental conditions. The changes involved axons as well as myelin sheaths. 5. The toxicity of GABA and vigabatrin was surprisingly mild in this very sensitive model.

Effects of long term vigabatrin on somatosensory evoked potentials in epileptic patients

1. Vigabatrin has proved to be a very effective antiepileptic in clinical trials, with excellent long term tolerability. 2. The purpose of this study was to test the central nervous system (CNS) safety of the drug during long term clinical use, due to the existence of species-dependent intramyelinic oedema in animal toxicology studies. 3. Somatosensory evoked potentials were recorded repeatedly over a mean period of 11 months, in 54 adult patients with refractory epilepsy who received vigabatrin as add-on therapy to their current antiepileptic regime. 4. There was no suggestion throughout the study that vigabatrin could lead to a prolongation of neuronal conduction times within the CNS pathways. 5. The results are consistent with previous studies of somatosensory, visual and brainstem auditory evoked potentials in patients. In view of the results observed in the dog, where increases in central latencies of somatosensory evoked potentials were clearly apparent, these data provide strong reassurance about the neurological safety of vigabatrin in the treatment of epileptic patients.