Primidone and essential tremor.

To clarify whether primidone itself, and not only its metabolite phenobarbitone, suppresses essential tremor, the effect of a high single dose of primidone was tested. Of 11 patients, 8 showed a reduction of their tremor by 54%-69% for up to 28 h. The serum concentration of primidone was as expected, whereas those of the metabolites phenyl-ethyl-malonamide and phenobarbitone were very low. The tremor suppression can thus be considered to be an effect of primidone. Three of the 11 patients did not show a reduction of tremor.