Inclusion Criteria:

• Provision of written informed consent before initiation of any study related procedures.
• Male and female subjects aged 18 to 65 years, inclusive.
• Documented clinical diagnosis meeting the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for any of the following: Schizophrenia DSM-IV, catatonic 295.20, disorganised 295.10, paranoid 295.30 and undifferentiated 295.90.
• Outpatient status.
• Subjects who in their own and/or in the Principal Investigator's opinion, consider their ongoing antipsychotic treatment inadequate because of insufficient efficacy, poor tolerance, and/or non acceptability of their actual dosage regimen (eg. b.i.d, t.i.d, etc).
• Monotherapy with current antipsychotic for at least 7 days prior to initiating treatment (ie, cannot be on more than one antipsychotic during the 7 day period prior to initiating study medication). Note: Subjects on a b.i.d regimen of seroquel IR for 7 days prior to enrolment are eligible to participate in the study.
• Female subjects of childbearing potential must have a negative serum pregnancy test at enrolment and be willing to use a reliable method of birth control, ie, barrier method, oral contraceptive, implant, dermal contraception, long-term injectable contraceptive, intrauterine device, or tubal ligation during the study.
• Capable to make treatment decisions, including being able to understand and comply with the requirements of the study, and judged as such by the Principal Investigator.
• Be able to read and write either English or French at a grade 7 proficiency level.

Exclusion Criteria:

• First episode, drug naive schizophrenic subjects.
• Meeting the criteria for any other (than schizophrenia) DSM-IV Axis I diagnosis, concomitant organic mental disorder or mental retardation that in the opinion of the Principal Investigator may interfere with study conduct or interpretation.
• Substance/alcohol dependence or abuse at enrolment [except dependence in full remission (>3 months) and except caffeine and nicotine dependence] as defined by DSM-IV criteria. A urine drug screen will be performed. The Principal Investigator will evaluate the results along with medical history to determine if the patient meets DSM-IV criteria for substance abuse or dependence. However, a single urine toxicology screen for cocaine, heroin, methamphetamine or PCP will lead to exclusion.
• Subjects requiring treatment with another antipsychotic agent than investigational product during study.
• Subjects on seroquel IR once daily.
• Known lack of response to clozapine or treatment with clozapine within 4 weeks prior to enrolment.
• Known intolerance to seroquel IR.
• Subjects requiring treatment with disallowed medication following enrolment into the study.
• Subjects requiring treatment for epilepsy.
• Subjects who pose an imminent risk of suicide or danger to themselves or others, as judged by the Principal Investigator.
• Pregnancy or lactation.
• A thyroid-stimulating hormone (TSH) concentration more than 10% above the upper limit of the normal range of the laboratory used for sample analysis whether or not the patient is being treated for hypothyroidism or hyperthyroidism.
• Use of a depot or long-acting injectable antipsychotic drug within 1 dosing interval before Day 1 of treatment or during treatment.
• Use of drugs that induce or inhibit the hepatic metabolising cytochrome P450 3A4 enzymes within 14 days of the screening assessment period (Day -7 to 0). See Table 5.
• History of idiopathic or drug-induced agranulocytosis.
• A QTc interval longer than 450 msec (calculated using the Fridericia correction for heart rate) or ECG considered to show cardiac abnormality at enrolment as determined by a centrally located, experienced cardiologist, and confirmed by the Principal Investigator as clinically significant.
• Evidence of clinically relevant disease (eg, renal, hepatic, autonomic, endocrine, hematologic or ophthalmologic impairment, significant coronary artery disease, congestive heart failure, cerebrovascular disease, viral hepatitis B or C, acquired immunodeficiency syndrome [AIDS] or cancer) or a clinical finding that is unstable or that, in the opinion of the Principal Investigator, would be negatively affected by the investigational product or that would affect the investigational product.
• Laboratory test results outside the reference range considered by the Principal Investigator to be clinically significant and potentially interfere with the study outcome.

• A patient with Diabetes Mellitus (DM) fulfilling one of the following criteria:

  • Unstable DM defined as HbA1c >8.5% at enrolment. Admitted to hospital for treatment of DM or DM related illness in past 12 weeks.
  • Not under care of physician responsible for patient's DM care.
  • Physician responsible for patient's DM care has not indicated that patient's DM is controlled.
  • Physician responsible for patient's DM care has not approved patient's participation in the study.
  • Has not been on the same dose of oral hypoglycemic drug(s) and/or diet for the four (4) weeks prior to randomisation. For thiazolidinediones (glitazones) this period should not be less than 8 weeks.
  • Taking insulin whose daily dose on one occasion in the past 4 weeks has been more than 10% above or below their mean dose in the preceding 4 weeks.

Note: If a diabetic patient meets one of these criteria the patient is to be excluded even if the treating physician believes the patient is stable and can participate in the study.

• An absolute neutrophil count (ANC) of <1.5 x 109/L
• Inability to accommodate the visit schedule.
• History of non-compliance as judged by the Principal Investigator.
• Previous enrolment in the present study.
• Participation in another clinical study or compassionate use programme within 4 weeks of screening (Day -7 to 0).
• Involvement in the planning and conduct of the study (applies to both AstraZeneca staff or staff at the study site).