Chemical formula: C₁₉H₁₉N₃O₅S Molecular mass: 401.436 g/mol PubChem compound: 6196
Penicillinase-resistant penicillins exert a bactericidal action against penicillin susceptible microorganisms during the state of active multiplication. All penicillins inhibit the biosynthesis of the bacterial cell wall.
Oxacillin adheres to bacterial penicillin-binding proteins, thus inhibiting bacterial cell wall synthesis. Oxacillin resists the effects of penicillinases-enzymes that inactivate penicillin-and is thus active against many strains of penicillinase-producing bacteria; this activity is most important against penicillinase-producing staphylococci; some strains may remain resistant. Oxacillin is also active against a few gram-positive aerobic and anaerobic bacilli but has no significant effect on gram-negative bacilli.
Resistance to penicillins may be mediated by destruction of the beta-lactam ring by a beta-lactamase, altered affinity of penicillin for target, or decreased penetration of the antibiotic to reach the target site.
Resistance to oxacillin implies resistance to all other beta-lactam agents, except newer agents with activity against methicillin-resistant Staphylococcus aureus.
Intravenous administration provides peak serum levels approximately 5 minutes after the injection is completed. Slow I.V. administration of 500 mg gives a peak serum level of 43 mcg/mL after 5 minutes with a half-life of 20-30 minutes.
The penicillinase-resistant penicillins bind to serum protein, mainly albumin. The degree of protein binding reported for oxacillin is 94.2% ± 2.1%. Reported values vary with the method of study and the investigator.
The penicillinase-resistant penicillins vary in the extent to which they are distributed in the body fluids. With normal doses, insignificant concentrations are found in the cerebrospinal fluid and aqueous humor. All the drugs in this class are found in therapeutic concentrations in the pleural, bile, and amniotic fluids.
The penicillinase-resistant penicillins are rapidly excreted primarily as unchanged drug in the urine by glomerular filtration and active tubular secretion. The elimination half-life for oxacillin is about 0.5 hours. Nonrenal elimination includes hepatic inactivation and excretion in bile.
Probenecid blocks the renal tubular secretion of penicillins. Therefore, the concurrent administration of probenecid prolongs the elimination of oxacillin and, consequently, increases the serum concentration.
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