Olanzapine, a second-generation
antipsychotic, is a first-line agent in the treatment of
schizophrenia. The objective of this review was to determine whether
olanzapine warrants clinical pharmacokinetic monitoring in patients with
schizophrenia, using a previously published decision-making algorithm. Although
olanzapine is an appropriate
therapy for patients with
schizophrenia and is readily measurable in biological fluids, significant interindividual variation exists in its pharmacokinetics. While the
duration of therapy is expected to be long term, the correlation of
olanzapine concentrations with efficacy and toxicity has not been well defined in the literature. There are multiple tools readily available for the assessment of efficacy in
schizophrenia, and clinical signs and symptoms can be used to monitor both for efficacy and for adverse effects. Therefore, routine monitoring of
olanzapine concentrations does not appear warranted in the general schizophrenic population. However, patients in whom a change in
olanzapine pharmacokinetics is expected--such as during addition or removal of an
enzyme-inducing or -inhibiting drug, or during initiation or cessation of smoking--may benefit from clinical pharmacokinetic monitoring, as would patients in whom non-compliance is suspected. Patients who fail to respond to maximum recommended doses and those who experience adverse effects from therapeutic doses may also benefit from therapeutic drug monitoring, as they may have inherent variations in hepatic
enzyme activity. However, in the population at large who suffer from
schizophrenia, monitoring of
olanzapine concentrations is not expected to offer additional benefit beyond appropriate clinical monitoring alone.