what kind of ear infection? the only one that may benefit from an injection of a potent steroid would be an inner ear infection (dizzy vertigo vomiting etc. ). cortisporin eardrops will only help otitis externa (swimmer's ear). since i don't know the reason for the steroid the type or severity of your ear infection ther is really no way to predict when (or even "if") this treatment will work.
how long does it take for a methylprednisolone injection to take effect? i got it 30 hours ago for an ear infection. they have an cortisporin ear drop waiting for me at the pharmacy. should i pick it up now or give the infection more time to work?