(R)-Baclofen (STX209) suppresses audiogenic seizures in the Fmr1 -knockout mouse on the seizure-resistant C57BL/6 background with an effective dose of 1 mg/kg . Acute intraperitoneal administration of (R)-Baclofen (STX209) significantly reduces the percent of mice displaying seizures (seizure incidence), with a minimum effective dose (MED) of 1.5 mg/kg.