Talk about penicillin G.

Is the first line, and it is a narrow spectrum, and it is given parenterally, mostly against Gram+ bacteria (example: in IV, intramuscular or subcutaneous). We can add a benzene ring to penicillin G  benzathine penicillin, this give the penicillin a longer half-life (benzene ring is stable) so half-life of the medication will last longer. We use benzathine penicillin in very important infections (example: effective in treating syphilis)