What are you getting out of it at 50-75mg, therapeutically speaking?
Obiter: NueDexta is a new pharm, 20mg dxm/10mg quinidine (a cardiac medication at far lower than cardiac dose levels used to alter DXM metabolism), taken b.i.d. for pseudobulbar affect (you may have seen the commercials) which sees already some off label use for different psych indications (mood stabilizer, etc.)