Q: in game purchase using itunes gift card

Before i was living in malaysia, now i already move to us. So i changed the app store to us store, but the game that i purchase in malaysia app store can still be played ? how about the in game purchase? because i have a itunes gift card that my friend gave me. i heard that the itunes gift card can only be use in us only. So can i use the itunes gift card to purchse the game that i downloaded using malaysia app store ? thx for helping =)