I've had IVIG several times for exascerbations. I can no longer do IVSM. The infusion takes longer (4-5 hours), but the only side effect I ever had was a headache . They can pre-medicate you with tylenol and benadryl. I got a 5 day tx each time. It was just as effective as IVSM for recovering from a flare. It is alot more expensive, but my insurance covered it.Thank Goodness!! I would have no problems doing it again, if I had too.