This group, through substitution on the penicillin nucleus (6-aminopenicillanic acid [6-APA]), is refractory to a greater or lesser degree to the effects of various β-lactamase enzymes produced by resistant gram-positive organisms, particularly Staphylococcus aureus . However, penicillins in this class are not as active against many gram-positive bacteria as penicillin G and are inactive against almost all gram-negative bacteria. Acid-stable members of this group (that are used PO) include isoxazolyl penicillins, such as oxacillin, cloxacillin, dicloxacillin, and flucloxacillin. Methicillin and nafcillin are available as parenteral preparations. Temocillin is a semisynthetic penicillin that is β-lactamase stable but also active against nearly all isolates of gram-negative bacteria exceptPseudomonas spp . |
| |