Q&A: Formula For Extra Vitamins?
Should I occasionally give my baby formula for the extra vitamins?
Nope. Your breast milk contains everything baby needs. Ignore formula advertisements. Unless there is a medical reason that your baby can't get enough milk from your breasts, she'll never need so much as a sip of the stuff.
If your pediatrician feels that baby needs a vitamin supplement (recent studies have some doctors recommending adding Vitamin D), liquid infant vitamins are available at most local drugstores.