Effect of pindolol administration on serum levels of thioridazine, haloperidol, phenytoin, and phenobarbital.

Twenty-six male patients with intermittent explosive disorder secondary to organic brain disease were studied. Each had been treated with long-term administration of thioridazine, haloperidol, phenytoin, and/or phenobarbital, either singly or in combination. The effect of adding increasing doses of pindolol--a beta-adrenergic blocking agent previously demonstrated to be effective in the treatment of intermittent explosive disorder--on serum levels of each long-term medication was determined. Moderate, dose-related increases in serum levels of thioridazine and two of its metabolites were found when pindolol was added. Conversely, higher-than-expected serum pindolol levels occurred in patients receiving thioridazine. No serum level increases were found for haloperidol, phenytoin, or phenobarbital when pindolol was added to each of these drugs individually, but serum phenytoin levels did rise in two patients receiving all three drugs simultaneously when pindolol was added. Three treatment failures with pindolol occurred in association with low serum pindolol levels.