A double-blind clinical trial of isoniazid in Huntington disease.

Isoniazid (INH) was given to nine patients with Huntington disease (HD) in a double-blind, placebo-controlled crossover trial. In an earlier open trial, three of six patients had improved, and one of them remained improved after 7 years on INH. Only one patient benefited in the present trial. All patients excreted small amounts of hydrazine in their urine while taking INH, and it is this INH metabolic that elevates GABA content in brain. GABA concentrations were markedly increased in CSF during INH therapy. Lack of clinical improvement in most HD patients despite elevation of brain GABA content suggests that in the minority who are benefited, INH may be acting by some mechanism other than increase of GABAergic neuronal function.