RISPERIDONE DOSE AND BLOOD LEVEL VARIABILITY - ACCUMULATION EFFECTS AND INTERINDIVIDUAL AND INTRAINDIVIDUAL VARIABILITY IN THE NONRESPONDERPATIENT IN THE CLINICAL-PRACTICE SETTING

Risperidone blood levels mere measured every 2 weeks after initiation of therapy in 24 refractory chronic schizophrenic patients referred to a locked, skilled nursing facility for long-term treatment. Blood lev els were assessed on 285 occasions over a 1- to 16-month treatment pro gram. Drug plasma level increases peaked by 2 months for risperidone a t 334% and by 6 months for 9-hydroxy-risperidone at 104% over the base line levels. Total blood levels (risperidone plus 9-hydroxy-risperidon e) peaked at 111% increase at 6 months and then declined 8% per month to 12 months, stabilizing at a value 31% higher than the initial value . Significant dose to blood level interindividual variation was noted. Considerable blood level variation was evident in single blood level sample determinations. The results suggest the value of risperidone bl ood levels, consideration of reduction of initial recommended starting dosages, and a need to optimize risperidone dosage approaches individ ually to patients.