In patients who then had an actual ( last ) dose of 12mg during the extension blinded Conversion Period ( n = 217 ) , median percent change in seizure frequency per 28days improved from -32.4 % ( 8mg , phase III Maintenance Period ) to -44.2 % ( 12mg , extension blinded Conversion Period ) ; 50 % responder rates increased slightly from 37.3 % to 42.9 % .