It is multifactorial and a complicated MG medical treatment decision planning depending on your MG health status and what your selected treatment plan is according to your NeuroMuscular Doc.
When do you most likely need to change to IV MG therapy:
1)MG exacerbations not controlled with oral medication
2) MG IV therapy choices is often dictated by what your health insurance plans allows you to receive and must take into consideration expensive co- pays or other hidden costs.
3) Which MG IV therapy you are eligible for is dependent on your MG antibody status .
For example, certain MG IV treatments can only be given to MG antibody positive patients. If you are seronegative MG you are not eligible to receive a long list of certain IV MG treatments.
4) IVIG is commonly given when needed for MG exacerbations and as a MG improvement booster before imminent surgeries , it is easily covered by most health insurance plans and can be given to MG antibody positive and seronegative MG folks.
5) The Goal as always under the guidance of your NEUROMuscular doc is to receive the best treatment needed for your MG status in real time taking into consideration if you are MG stable or having acute MG exacerbations .
6) If you are changed to IV MG therapy , your doc will discuss with you the pros & cons of which IV MG therapy is appropriate , the expected timeline of improvement , the side effects and a hopeful move forward to a remission status with this treatment if you respond favorably.
7) Your IV MG treatment plan will change if you do not respond well and your doc will guide you to receive the best next MG cocktail treatment which can include a different IV MG treatment.
8) Remember it is not an exact science, everyone responds differently and oftentimes the worse part is the timeline of watchful waiting for improvement and of course dealing with potential side effects.

Coin toss, dart board??? I don't know...just hoping something will work.

Main thing is to find the right neurologist