<qa>  What is the acute efficacy determined by demonstrating a greater response rate?Patients, ages 18 to 70 years with a diagnosis of bipolar disorder I or II current episode depressed without psychotic features, will be randomized to double-blind treated to receive either riluzole 50-200 mgday or placebo for a period of 8 weeks. Acute efficacy will be determined by demonstrating a greater response rate using specified criteria. 