Classification of Penicillin. 1  Natural Penicillins (Penicillin V, Penicillin G, Benzathine, Procaine Penicillin) 2  Penicillinase-Resistant Penicillins (Oxacillin, Dicloxacillin, Cloxacillin, Methicillin, Nafcillin) 3  Aminopenicillins (Amoxicillin, Bacampicillin, Ampicillin) 4  Extended Spectrum Penicillins.