6-amino-penicillanic acid is a common parent amine of various penicillins. 6-amino-penicillinic acid possesses definite antibacterial properties but these are much lower order than these of benzylpenicillin. It is destroyed by penicillinase (Beta-lactamase). The first penicillins to appear as derivatives of 6-APA were in fact phenethicillin and propicillin.

Bacampicillin is a penicillin antibiotic. It is a prodrug of ampicillin with improved oral bioavailability. It exerts bactericidal activity via inhibition of bacterial cell wall synthesis by binding one or more of the penicillin binding proteins (PBPs). Spectrobid is used to treat bacterial infections such as tonsillitis, pneumonia (lung infection), bronchitis (inflammation of airway), urinary tract infections, gonorrhea, and infections of the skin. Adverse effects are: anemia, thrombocytopenia, neutropenia, agranulocytosis, seizures, nephrotoxicity, Jarisch-Herxheimer Reaction (fever, chills, sweating, tachycardia, hyperventilation, flushing, and myalgia). Drug interactions: Contraceptives - decreased contraceptive effectiveness; Live Typhoid Vaccine - decreased immunological response to the typhoid vaccine; Probenecid - increased bacampicillin levels.

Sultamicillin is the mutual prodrug of sulbactam and ampicillin. It is the tosylate salt of the double ester of sulbactam plus ampicillin. Sulbactam is a semisynthetic ß-lactamase inhibitor which, in combination with ampicillin, extends the antibacterial activity of the latter to include some ß-lactamase-producing strains of bacteria that would otherwise be resistant. The combination of sulbactam plus ampicillin for parenteral use has previously been shown to be clinically and bacteriologically effective in a variety of infections. Sultamicillin is marketed under a trade name Unasyn among others.