I gave my two months old preemie one drop of formula milk prepared 5 hours ago.but she spitted up after 5 minutes (nothing unusual).will she be ok?

Will be fine: Many infants have reflux. Doubt seriously that formula had anything to do with spitting up. Try again. Burping regularly is important

Should be o.k.: Formula prepared 5 hours back ,if kept in the refrigerator is fit to be given to the baby . The preterm baby usually spit because their stomach is small and spitting is like overflow or change in position of the baby .This is not an illness .Moreover a drop of formula will not make your baby sick .Feed the baby as you do .

Spoiled milk?: Generally speaking, if milk is left out at room temperature for over an hour, you should discard the milk. However, I do not feel that one drop of milk should cause any significant harm to your baby. Watch out for vomiting or diarrhea or fever. If your baby displays any of these symptoms, call your pediatrician for further advice.

Mgt/feedings: If she continues to vomit with feedings this pattern may be related to reflux. There are medications that can be used to treat reflux, which is a common problem among premature infants. I would suggest feeding her with her head at least at a 30 degree angle upward to help prevent vomiting with feedings. Frequent small feedings are usually easier for the premature infant rather than a larger volume