slowly start mixing them. so if baby takes a 4 oz bottle then do 3 parts old formula 1 part new kind. Then after a few times do half and half and so on. baby will adjust

I tried calling her dr but they were closed

@lizramos1, we did a different formula at first an than switched her over she did fine with the transition

My sister said no cuz the babies tummy got used to similac formula and it would upset her stomach

You can use whatever formula you like, unless you get wic then you'll have to get a paper from your pediatrician to give to the wic office. @lizramos1