There are risks of anaphylactic shock if you get all your needed iron in one big infusion. Many doctors don't like to take that risk (although the percentage of people who have that reaction is pretty small)--and they recommend getting a weekly IV of a much lesser amount of iron, so that it takes you a few months to get the entire dose. It takes about 90 minutes a week, but the risks are much much smaller. I had 16 IV infusions of Ferrlecit, and, after that, another 16. As long as the nurses are skilled at placing the needle, it isn't bad at all--kind of an enforced rest period surrounded by courageous, funny oncology patients, who help you put your own medical problems in perspective. I had no discernable side effects either.
Ask your GP about the benefits of not getting all your iron in one big dose.