resistant class disc may be used to determine microbial susceptibility to cloxacillin, dicloxacillin, methicillin, nafcillin, and oxacillin. With this procedure, employing a 5 microgram methicillin sodium disc, a report from the laboratory of “susceptible” (zone of at least 14 mm) indicates that the infecting organism is likely to respond to therapy. A report of “resistant” (zone of less than 10 mm) indicates that the infecting organism is not likely to respond to therapy. A report of “intermediate susceptibility” (zone of 10 to 13 mm) suggests that the organism might be susceptible if high doses of the antibiotic are used, or if the infection is confined to tissues and fluids (e.g. urine), in which high antibiotic levels are attained.
In general, all staphylococci should be tested against the penicillin G disc and against the methicillin disc. Routine methods of antibiotic susceptibility testing may fail to detect strains of organisms resistant to the penicillinase-resistant penicillins. For this reason, the use of large inocula and 48-hour incubation periods may be necessary to obtain accurate susceptibility studies with these antibiotics. Bacterial strains which are resistant to one of the penicillinase-resistant penicillins should be considered resistant to all of the drugs in the class.
Pharmacokinetics
Oxacillin Sodium, with normal doses, has insignificant concentrations in the cerebrospinal and ascitic fluids. It is found in therapeutic concentrations in the pleural, bile, and amniotic fluids. Oxacillin Sodium is rapidly excreted as unchanged drug in the urine by glomerular filtration and active tubular secretion.
Oxacillin Sodium binds to serum protein, mainly albumin. The degree of protein binding reported varies with the method of study and the investigator, but generally has been found to be 94.2 ± 2.1%.
Intravenous injection gives a peak serum level about 5 minutes after the injection is completed. Slow IV dosing with 500 mg gives a 5 minute peak of 43 mcg/mL with a half-life of 20 to 30 minutes.
INDICATIONS AND USAGEOxacillin is indicated in the treatment of infections caused by penicillinase producing staphylococci which have demonstrated susceptibility to the drug. Cultures and susceptibility tests should be performed initially to determine the causative organism and its susceptibility to the drug. (See CLINICAL PHARMACOLOGY: Susceptibility Plate Testing).
Oxacillin may be used to initiate therapy in suspected cases of resistant staphylococcal infections prior to the availability of susceptibility test results. Oxacillin should not be used in infections caused by organisms susceptible to penicillin G. If the susceptibility tests indicate that the infection is due to an organism other than a resistant Staphylococcus , therapy should not be continued with oxacillin.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of Oxacillin for Injection, USP and other antibacterial drugs, Oxacillin for Injection, USP should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.
CONTRAINDICATIONSA history o
