minocycline and amoxicillin?

Hi. I found this for you on drugs.com (drug interaction checker):

GENERALLY AVOID: Tetracyclines may reduce the effect of penicillins by inhibiting cellular protein synthesis which is necessary for cell wall synthesis inhibition by penicillins. Antagonism is more likely when low doses of either agent are administered. Therapeutic failure may result.

MANAGEMENT: This combination should be avoided if possible.

The fact that it is an injection won't change how it works against the bacteria.

Found this:
Minocin (minocycline) and penicillin G benzathine-penicillin G procaine (penicillin) (Moderate Drug-Drug)

GENERALLY AVOID: Tetracyclines may reduce the effect of penicillins by inhibiting cellular protein synthesis which is necessary for cell wall synthesis inhibition by penicillins. Antagonism is more likely when low doses of either agent are administered. Therapeutic failure may result.

MANAGEMENT: This combination should be avoided if possible.