(2S, 5R, 6R ) -6 - [(2,6 -dimethoxy- benzoyl) amino] -3,3- dimethyl- 7- oxo-4 -thia -1 -azabicyclo [ 3.2.0] - heptane-2 -carboxylic acid
- 132-92-3 (sodium salt)
2000 mg · kg -1 ( LD50, rat, oral)
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Is the first so-called methicillin penicillinasefeste penicillin with a narrow bandwidth in therapy. It was developed by Beecham in 1959. In contrast to benzylpenicillin (penicillin G) of the β -lactam ring is sterically shielded, so they can be worse by penicillinases ( formed by bacterial enzymes ) is cleaved and inactivated. Methicillin is no longer commercially available. In its place, oxacillin, dicloxacillin and flucloxacillin be used.
Oxacillin, dicloxacillin and flucloxacillin are acid-resistant, so they can be administered parenterally and orally. Their potency is approximately one percent of benzylpenicillin. They also induce the synthesis of β -lactamases ( penicillinases ).
They act only against gram-positive pathogens; Gram- negative bacteria are primarily resistant. If Staphylococcus aureus resistant to methicillin (so-called MRSA ', better, ORSA ' because oxacillin is still being used ), it can be assumed that the strain is also resistant to all other beta-lactam antibiotics. A therapy is then usually with vancomycin, alternatively, of course, according to antibiogram, because even to vancomycin resistance has already occurred. The reserve antibiotic of choice is therefore currently linezolid.
MRSA / ORSA are often resistant to antibiotics of other groups ( quinolones, tetracyclines, aminoglycosides, erythromycin, sulfonamides ).