Formula changes  

For the most part you will want to choose one formula and stick with it.  It is ok to change between powder, concentrate, and ready-to-feed.  If for convenience sake you need to make a change, you can substitute one cow's milk formula for another or one soy formula for another. Similac, Enfamil, and Carnation Good Start are cow's milk formulas.  Prosobee, Isomil and Nursoy are soy formulas.  Low iron formulas should never be used.

If your baby seems very spitty, gassy, or uncomfortable you can try substituting a soy formula for a cow's milk formula.  If these symptoms do not improve within a week, they were probably not caused by the formula (frequently it is just colic) and you can return to cow's milk formula

Follow-up formulas are unnecessary.  Whole milk should not be substituted for breast milk or formula until one year old.