I wonder if there is a bit of confusion here, GG. If you had 600mg then that is not determined by your body surface area, it is just 600mg.
My understanding is that this is the formula that is currently used to calculate dosing in autoimmunity but that some doctors and studies do not use this formula and give 1 gram regardless of BSA. In general, my doctor was using one gram for most ritux patients but in my case felt the 375 mg/BSA was safer for me b/c I did not need as high of a dose and do not do well with IV fluids based on my history.
* I am always speaking about my own case and never that the decisions made with my two doctors apply to anyone else.