Switching From Twice-Daily to Once-Daily Clozapine Dosing in Schizophrenia

Switching From Twice-Daily to Once-Daily Clozapine Dosing in Schizophrenia: A Pilot, Double-Blind, Randomized Controlled Trial

Plasma half-life has routinely been used to establish the dosing schedule of antipsychotics; for example, it is recommended that agents with a short plasma half-life be administered multiple times per day. However, to date, several randomized controlled trials (RCTs) have shown no differences in clinical outcomes between once- and twice-daily dosing of various antipsychotics, suggesting that once-daily dosing of antipsychotics is a viable option regardless of plasma half-life. This would apply to clozapine as well; however, there have been no studies comparing once-daily vs. twice-daily dosing regimens of clozapine in terms of efficacy and tolerability. To address this gap in the literature, the investigators shall conduct a pilot, double-blind, RCT to examine efficacy and tolerability following a switch to once-daily dosing regimen of clozapine in patients with schizophrenia receiving clozapine twice a day.

Plasma half-life has routinely been used to establish the dosing schedule of antipsychotics; for example, it is recommended that agents with a short plasma half-life be administered multiple times per day. To date, however, several randomized controlled trials (RCTs) have shown that once-daily dosing of antipsychotics including perphenazine, risperidone, olanzapine, quetiapine, and asenapine is comparable to twice-daily dosing in terms of efficacy and tolerability, suggesting that once-daily dosing of antipsychotics is a viable option regardless of plasma half-life. This issue applies to clozapine as well, in that it has a relatively short plasma half-life of 12-16 hours; of note, the product monographs recommends that clozapine be administered more than once daily if the dose exceeds 200 mg/day in Canada. Despite this, in clinical practice clozapine is frequently administered once daily because of convenience and side effects such as a daytime sedation or somnolence, In support of this, a cross-sectional survey done at the investigators' own centre has revealed that clozapine was prescribed once daily in 75.1% of 676 patients, even though >200 mg/day was administered in 88.6%. However, there have been no studies comparing once-daily vs. twice-daily dosing regimens of clozapine in terms of efficacy and tolerability. To address this gap in the literature, the investigators shall conduct a pilot, double-blind, RCT to examine efficacy and tolerability following a switch to once-daily dosing regimen of clozapine in patients with schizophrenia receiving clozapine twice a day.

Participants will receive clozapine once daily at evening or bedtime throughout the study period. If a participant takes ≥200 mg of clozapine at a time other than evening/bedtime, half of this dose will be switched to an evening/bedtime regimen on day 0 (baseline), then another half dose will be switched on day 7 (week 1). Participants will receive placebo in place of the clozapine dose that was switched to evening/bedtime.

Change in BPRS total scores from baseline to 12 weeks Total scores range from 18-126, higher scores represent worse clinical outcomes: <31 = Illness not significant >=31 = Mildly ill >41 = Moderately ill >53 = Markedly ill.

Detect side effects related to Clozapine from baseline to 12 weeks Higher Scores indicating worse side-effects: 0-16 (absent/mild side-effects) 17-32 (moderate side-effects) 33-48 (severe side-effects)

Assess the overall severity of five symptom domains of BE-PSD with a total score in each domain scoring from absent to very severe (i.e. 0-6 with higher scores with worse outcomes)

Change in patients social functioning scores from baseline to 12 weeks The PSP is a 100-point single item rating scale from 1-100, subdivided into 10 equal intervals with higher scores indicating better outcomes. The ratings are based on patient's functioning in four main areas: 1) socially useful activities, 2) personal and social relationships, 3) self-care; and 4) disturbing and aggressive behaviours.

Assess severity of Illness in Schizophrenia CGI scores from baseline to 12 weeks Scores ranging from normal to the most ill (i.e., scores ranging from 1-7 with higher scores with illness worsening)

The BNA is a brief neurocognitive assessment that measures global cognitive impairment in patients with schizophrenia from baseline to 12 weeks. Negative Z scores (i.e., -0.5 to -2.0 ) indicate mild to severe cognitive impairment.

Self report scale to measure well being. Study assess changes in subjective wellbeing in patients on a neuroleptic from baseline to Week 12. Higher total score indicating better outcomes

Change in the Visual Analogue Scale for Distress Associated with Symptoms (VAS-DAS) scores from baseline to 12 weeks

Assess changes in level of distress associated with symptoms from no distress to worst distress (i.e., 0-100)

Inclusion Criteria: Diagnosed with schizophrenia or schizoaffective disorder based on DSM-IV criteria Outpatient status Ages 18 years or older Has received clozapine twice a day, one of which is in the evening/bedtime, at the same dose and dosing regimen for at least 3 months Fluent in English and competent to provide written informed consent Exclusion Criteria: Having significant medical or neurological illnesses Pregnant or lactating

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