4. On a stable regimen of treatment to include quetiapine fumarate for 3 months minimum prior to screening, and on a dose of quetiapine fumarate totaling 600 mg total per day for a minimum of 1 month prior to screening. Patients who are on qd dosing of daily quetiapine fumarate must be willing to convert to 300 mg bid dosing for the duration of the study.