I Went From 300 Mg Wellbutrin Xl To 450 Mg,

I went from 300 mg wellbutrin xl to 450 mg, but I had to drop back down to 300 mg again, because the 450 mg became unbearable. i was only on the 450 mg for 2 weeks...my question is, roughly how long before the 450 is out of system and I'm just operating on the 300mg again?? Thanks so much!