You are correct in that the plasmaphersis will undo the IVIG, so you really can't do them together.

As far as dosage on the IVIG, my understanding is the normal dosage is 2.0 gms per kilogram of weight per month. After discussing with my neuro, I spread mine out over the month and get .4/gms per kg once weekly. This means I go in weekly, but it does a better job of managing my mg. You could also possibly do .4/gms per kg for 2 days every 2 weeks, or whatever works for you. My neuro is willing to work with me on the timing as long as it equals out to 2.0 gms/kg monthly.

Hope this helps.