Just a few additional notes about diabetes management in general.  It's
important to know why specifically the medication is being changed.  Is
it because the blood sugars are not in ideal control (this is important
because over the years with less than tight control there is a great risk
of serious kidney and eye complications, among others), or is it because
her sugars are so high that she could be hospitalized acutely.  If the
latter, then clearly it's important to treat promptly with whatever
medication will get those sugars down (if she wants to continue
breastfeeding, insulin may be a good choice).  If the former, then a lot
depends on how long her diabetes has been poorly controlled and how long
she plans to breastfeed.  If her diabetes has not been too bad for more
than a couple of years, then she may be able to continue on her current
regimen (and of course take extra care with her diet, weight loss and
exercise to optimize their effects in addition to the benefit of
breastfeeding itself) while she continues to breastfeed, and switch to
metformin after weaning.  If, however, she has several years of poorly
controlled diabetes and is starting to show signs of kidney or eye
disease or other complications, she may need to go for tighter control
(again, insulin might be an option if she wanted to continue nursing).
Hope this helps.  Alicia.  [log in to unmask]