Predicting Plasma Olanzapine Concentration Following a Change in Dosage: A Population Pharmacokinetic Study

Model-Guided Antipsychotic Dose Reduction in Schizophrenia: A Pilot, Single-Blind Randomized Controlled Trial

PURPOSE/BACKGROUND

Patients with schizophrenia as well as their psychiatrists are hesitant to reduce the antipsychotic dose in fear of relapse. To overcome such dilemmas, we developed models to individually calculate an oral dose that corresponds to a given target dopamine D2 receptor occupancy.

METHODS/PROCEDURES

In this pilot, 52-week single-blind randomized controlled trial, 35 clinically stable patients with schizophrenia receiving either risperidone or olanzapine monotherapy were randomly assigned to dose reduction (n = 17) or dose maintenance group (n = 18). In the former group, baseline doses were reduced to the doses corresponding to 65% D2 occupancy (the lower end of therapeutic window) at trough that were calculated from randomly collected plasma concentrations using our models.

FINDINGS/RESULTS

In the dose reduction group, doses of risperidone and olanzapine were decreased from 4.2 ± 1.9 to 1.4 ± 0.4 and 12.8 ± 3.9 to 6.7 ± 1.8 mg/d, whereas the doses in the dose maintenance group were 4.3 ± 1.9 and 15.8 ± 4.6 mg/d, respectively. Twelve subjects (70.5%) and 13 subjects (72.2%) in the dose reduction and dose maintenance groups completed the study (P = 0.604), whereas 3 subjects (18.8%) and none dropped out because of clinical worsening in the dose reduction and dose maintenance groups, respectively. There were not significant differences in score changes in Positive and Negative Syndrome Scale between the 2 groups but in Positive subscale scores in the Clinical Global Impression-Schizophrenia (0.4 ± 0.7 in the dose reduction group vs -0.1 ± 0.7 in the dose maintenance group, P = 0.029).

IMPLICATIONS/CONCLUSIONS

Although our model-guided dose reduction strategy was found to be comparable with no-dose change in terms of dropout rates, safety issues have to be further examined.

Circadian patterns of hallucinatory experiences in patients with schizophrenia: Potentials for chrono-pharmacology

The objective of this study was to investigate possible circadian pattern of psychotic symptoms in patients with schizophrenia, which could be reflected on the dosing schedule/regimen, i.e. chrono-pharmacology. Patients with schizophrenia (ICD-10) who reported having auditory hallucination, receiving monotherapy with risperidone, olanzapine or paliperidone for at least two weeks were included. The subjects were provided a diary and asked to record the time and duration of auditory hallucinations during the eight time periods (i.e. 00:00-03:00, 03:00-06:00, 06:00-09:00, 09:00-12:00, 12:00-15:00, 15:00-18:00, 18:00-21:00, and 21:00-24:00). In the diary, times of medication doses and sleep were also recorded. Time and degree of peak and trough dopamine D₂ receptor blockade with antipsychotics were estimated from 2 sparsely collected plasma drug concentrations. The prevalence and duration of auditory hallucinations were statistically examined among the eight time periods, respectively. Forty-nine patients participated in this study (mean ± SD age, 50.7 ± 14.8 years; 36 men (73.5%); 34 inpatients (69.4%)). Auditory hallucinations occurred most frequently and lasted for the longest duration in the period of 18:00-21:00 (75.5% (37/49) and 1.37 ± 1.67 h). This happened despite the fact that the difference in D₂ receptor occupancy between the peak and trough was less than 2%, indicating a stable drug delivery. Since the dopamine D₂ receptor blockade by antipsychotics was stable, the nocturnal circadian pattern found in this study may reflect intrinsic dopaminergic fluctuation or generally quieter environments at night. These circadian patterns may be considered to devise individualized treatment approach in the context of "chrono-pharmacology" for patients with schizophrenia.

The effects of illness severity, cognition, and estimated antipsychotic dopamine receptor occupancy on insight into the illness in schizophrenia: An analysis of clinical antipsychotic trials of intervention effectiveness (CATIE) data

BACKGROUND

The relationship between dopamine D₂ receptor (D₂R) occupancy and impaired illness awareness (IIA) remains unclear. While IIA is associated with illness severity and cognitive dysfunction, antipsychotic medication, the principal treatment for schizophrenia, indirectly improves IIA, but may simultaneously contribute to cognitive dysfunction at supratherapeutic doses.

AIM AND METHODS

We investigated the influence of estimated D₂R (Est.D₂R) occupancy by antipsychotics on the relationships between IIA and illness severity, and IIA and cognition. IIA was assessed in 373 adult patients with schizophrenia (18-62 years) using data from CATIE. IIA was measured using the Positive and Negative Syndrome Scale (PANSS) item G12. D₂R occupancy levels were estimated from plasma concentrations for risperidone, olanzapine, and ziprasidone. Correlation, regression, and path analyses were performed to examine IIA's relationship to illness severity, cognition, and Est.D₂R.

RESULTS

Illness severity was predictive of IIA. However, premorbid IQ, cognition, and Est.D₂R did not predict IIA, and Est.D₂R did not serve either a moderating or mediating role in both regression and path analyses.

CONCLUSIONS

Consistent with previous literature, our results suggest that IIA is a function of illness severity in adult patients with schizophrenia. Future studies should explore whether D₂R occupancy mediates the relationships between IIA and illness severity, and IIA and cognitive dysfunction, in late-life schizophrenia (i.e. ≥60 years) given the effects of aging on cognition, IIA, and antipsychotic sensitivity.