Impact of clinical pharmacokinetics on neuroleptic therapy in patients with schizophrenia

Abstract

This review covers some recent work on: 1. The effects of route of administration on the pharmacokinetics of fluphenazine and some of its metabolites; 2. The clinical pharmacokinetics of fluphenazine in acute patients medicated with oral fluphenazine; 3. The clinical pharmacokinetics of haloperidol in acute patients medicated with oral haloperidol; 4. The clinical pharmacokinetics of fluphenazine in the maintenance of individuals with chronic schizophrenia with fluphenazine decanoate; 5. A systematic dose reduction study in maintenance treatment refractory patients with oral haloperidol. A study in which plasma levels of fluphenazine and fluphenazine sulfoxide were measured in a group of DSM-III-R patients with schizophrenia before and after switching from oral fluphenazine to depot fluphenazine, decanoate revealed much higher levels of fluphenazine sulfoxide with oral medication compared with those found with depot fluphenazine. These data illustrate the effect of "first pass" metabolism after oral fluphenazine. Thus in a group of 33 patients randomly assigned to receive 5 mg, 10 mg or 25 mg oral fluphenazine daily, steady state plasma fluphenazine levels at each dose were significantly lower that those of fluphenazine sulfoxide or 7-hydroxy-fluphenazine, although there were no significant differences between the levels of fluphenazine and fluphenazine N4-oxide. On the other hand, plasma levels of the parent drug were significantly higher than those of any metabolite in a corresponding group of patients at steady state on depot medication. These observations underscore the importance of route dependent differences in the pharmacokinetics of fluphenazine which can lead to problems when switching patients from oral to depot neuroleptics. The concept of "disabling side-effects" is an important development in understanding relationships between plasma levels of neuroleptic drugs and clinical response in patients with schizophrenia. Risk-benefit analysis shows clearly that evaluation of relationships between plasma levels and clinical response must take into account the consequences of side-effects which the patient feels have a negating effect on therapy. Emerging data on putative therapeutic plasma level ranges in maintenance therapy are potentially important and may be particularly useful in the maintenance of patients on low dose therapy. It is noteworthy that in a carefully executed dose reduction study in treatment resistant patients under medication with haloperidol, the mean lowest effective dose (8.7 ng/mL) lay within the optimal therapeutic range (5 ng/mL to 12 ng/mL) found in acutely psychotic patients. The study showed that gradual dose reduction of neuroleptic was possible in chronic treatment resistant patients with schizophrenia who were originally thought by ward staff to require high doses of neuroleptic.(ABSTRACT TRUNCATED AT 400 WORDS)