Pharmacokinetics and clinical effects of amantadine in drug-induced extrapyramidal symptoms

Plasma amantadine concentrations were assessed in a series of hospitalized schizophrenic patients receiving this drug during a double-blind trial of amantadine and benztropine in the treatment of neuroleptic-induced extrapyramidal symptoms (EPS). Mean (+/- S.E.) plasma amantadine concentrations were 0.54 +/- 0.08 microgram/ml on day 7 and 0.43 +/- 0.08 microgram/ml on day 14. Overall improvement of EPS was not correlated with plasma level, but improvement in the target EPS of rigidity was correlated with plasma amantadine concentration on day 7 (r = 0.75) and day 14 (r = 0.68). There was no evidence that the overall improvement in schizophrenic symptomatology was influenced by plasma amantadine concentrations.