The purpose of this study is to determine the safety, tolerability and pharmacokinetics of OMS643762 (the study drug) in psychiatrically stable schizophrenia patients.

Inclusion Criteria:

• Competent to provide informed consent.
• Voluntarily provide informed consent and Health Insurance Portability and Accounting Act (HIPAA) Authorization in accordance with local regulations and governing Institutional Review Board (IRB) requirements prior to any procedures or evaluations performed specifically for the sole purpose of the study.
• Have a diagnosis of schizophrenia as defined in DSM-IV-TR.
• Are from 18 to 55 years of age inclusive at the screening visit.
• Have stable schizophrenia symptomatology for greater than or equal to three months at the screening visit, in the opinion of the investigator.
• For enrollment to Cohorts 1 and 2, have not taken any oral antipsychotic medication for at least seven days or any parenteral antipsychotic medication for at least 30 days prior to randomization. Subjects should have been on a stable medication regimen for greater than or equal to two months at the screening visit.
• For enrollment to Cohorts 3, 4, and 5, have been on a stable medication regimen for greater than or equal to two months at the screening visit.
• Have normal clinical laboratory test results and ECG, or results with minor deviations, which are not considered to be clinically significant by the investigator.
• If able to reproduce, agree to use an acceptable method of birth control (e.g., condom and spermicide, oral birth control which has been stable for 30 days) or agree to remain abstinent from Visit 2 until 90 days after the last dose of study drug for males and 30 days after the last dose of study drug for females.

Exclusion Criteria:

• Have a history of lactose intolerance or allergy to dairy products.
• Are pregnant or lactating.
• Have a history or presence of significant cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrine, or neurological disorders which, in the opinion of the investigator, increases the risk of the study drug or may confound the interpretation of study measures.
• Have a history of alcohol dependence (within 12 months of screening) or abuse (within six months of screening) as defined by DSM-IV-TR or consume excessive amounts of alcohol, in the opinion of the investigator.
• Have a history of substance dependence (within 12 months of screening) or abuse (within six months of screening) as defined by DSM-IV-TR (with the exception of nicotine and caffeine). Positive results on drug screening will be exclusionary unless the patient has a valid prescription for the medication (i.e., benzodiazepines).
• Have unstable depression, in the opinion of the investigator.
• Have experienced EPS within 30 days prior to Visit 1.
• Are currently taking clozapine.
• Are currently taking aripiprazole (for enrollment to Cohorts 1 and 2).
• Have a history of blood donation in excess of 500 mL of blood within 30 days prior to Visit 1.
• Have received treatment with an investigational drug or device within 60 days prior to Visit 1.
• Have a positive test for human immunodeficiency virus (HIV) antibodies, Hepatitis B surface antigen or Hepatitis C antibody.
• Are an employee of Omeros, an investigator, a study staff member, or their immediate family member.