Several penicillins are now available for clinical use. They may be classified into 4 groups. The first is represented by the original penicillin G, which is sensitive to penicillinase and to acid. This penicillin is generally used as a standard to which later developed penicillins are compared. The second group, which might be called the penicillin V group, besides the old penicillin V, includes the new phenethicillin and propylcillin (phenoxypropyl penicillin, propicillin).* They have an antibacterial activity similar to penicillin G, but they resist acid and are readily absorbed after oral administration. The 2 new ones have a somewhat higher resistance to penicillinase than does penicillin G. The third group includes methicillin and oxacillin (phenylmethylisoxazolylpenicillin), often referred to as P-12. These 2 penicillins are highly resistant to penicillinase and have a fairly uniform activity on staphylococci. The fourth group, finally, has hitherto only one member, ampicillin (α-aminobenzylpenicillin), characterized by a
WALLMARK G. Comparison in Vitro of New Penicillins: Special Reference to Methicillin-Resistant Staphylococci. Arch Intern Med. 1962;110(5):787–793. doi:10.1001/archinte.1962.03620230233032
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