This is a an open-label (all patients will know the name of the study drug that they are receiving), randomized (patients will selected by "chance" or like "flipping a coin" to administration of study drug by intramuscular \[i.m.\] injection into the gluteal \[buttocks\] or deltoid \[upper arm\] muscle of the body) study in patients with schizophrenia. A minimum of 40 patients (20 patients per group \[1 group of patients to be administered study drug by injection in the gluteal muscle and 1 group of patients to be administered study drug by injection in the deltoid muscle\]) will participate in this study, including at least 4 women in each group. The study will consist of a screening period that will occur within 21 days before the first study drug administration, an open-label treatment period during which patients will receive a total of 4 injections of study drug (paliperidone palmitate) either in the deltoid or gluteal muscle, and an end-of-study visit where final study evaluations will be performed. At the screening visit, if a patient has been treated with an antipsychotic medication before study entry, the medication may be continued during the study except for medications specified in the exclusion criteria for the study. If patients have not been previously treated with 1 of the following antipsychotic drugs: risperidone, paliperidone, or paliperidone palmitate, they will undergo a 4-day evaluation period where they will be given a 3 mg/day dose of an extended release (ER) formulation of paliperidone to evaluate their ability to tolerate study drug. Patients who meet all entry criteria for the study will be randomly assigned to 1 of 2 treatment groups in which they will receive 100 mg equivalent of paliperidone palmitate by i.m. injection in either the gluteal muscle or the deltoid muscle. Blood samples for pharmacokinetics (ie, to test the concentration of study drug in the blood) will be collected at specified times before and after each dose of study drug. A single blood sample may also be collected at any time during screening or before the first day of i.m. administration of study drug for patients who agree to participate in an optional part of the study called a pharmacogenomic evaluation which is an evaluation where genetic information obtained from the patient's blood is used to predict whether or not study drug will help make the patient well. During the study, the patient's psychiatric symptoms, severity of symptoms, and injection site reactions will be evaluated. The primary outcome measure in the study will be the determination of the concentration of paliperidone in the patient's blood before study drug administration at protocol-specified time points during the study. The patient's safety will be monitored throughout the study by performing physical examinations, vital signs measurements, clinical laboratory tests, electrocardiograms (ECGs), monitoring of extrapyramidal symptoms (ie, symptoms that can be associated with taking antipsychotic medications), injection site evaluations, and recording of adverse events (side effects). Each patient will receive a total of 4 paliperidone palmitate 100 mg equivalent injections in the gluteal or deltoid muscle on Day 1, 8, 36, and 64.
