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Oxacillin (Oxacillin Sodium) - Description and Clinical Pharmacology

 
 



PHARMACY BULK PACKAGE – NOT FOR DIRECT INFUSION

To reduce the development of drug-resistant bacteria and maintain the effectiveness of Oxacillin for Injection and other antibacterial drugs, Oxacillin for Injection should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.

DESCRIPTION

Oxacillin for Injection, USP is a semisynthetic antibiotic substance derived from 6-amino-penicillanic acid. It is the sodium salt in a parenteral dosage form. The pharmacy bulk package contains oxacillin sodium monohydrate equivalent to 10 grams oxacillin. It also contains approximately 2.5 mEq of sodium and 20 mg dibasic sodium phosphate (as a buffer) per gram of oxacillin.

OXACILLIN SODIUM

C<sub>19</sub>H<sub>18</sub>N<sub>3</sub>NaO<sub>5</sub>S • H<sub>2</sub>O                MW=441.43

C19H18N3NaO5S • H2O                MW=441.43

4-Thia-1-azabicyclo [3.2.0]heptane-2-carboxylic acid, 3,3-dimethyl-6-[[(5-methyl-3-phenyl-4-isoxazolyl) carbonyl] amino]-7-oxo-,monosodium salt, monohydrate, [2S(2α,5α,6β)].

A pharmacy bulk package bottle is a container of a sterile preparation for intravenous use that contains many single doses. The contents of this pharmacy bulk package bottle are intended for use by a pharmacy admixture service for addition to suitable parenteral fluids in the preparation of admixtures for intravenous infusion. (See DOSAGE AND ADMINISTRATION: Directions For Proper Use of Pharmacy Bulk Package).

FURTHER DILUTION IS REQUIRED. NOT FOR DIRECT INFUSION.


CLINICAL PHARMACOLOGY

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 µg/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.

Microbiology

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.

The drugs in this class are highly resistant to inactivation by staphylococcal penicillinase and are active against penicillinase-producing and nonpenicillinase-producing strains of Staphylococcus aureus.

The penicillinase-resistant penicillins are active in vitro against a variety of other bacteria.

Susceptibility Plate Testing

Quantitative methods of susceptibility testing that require measurement of zone diameters or minimal inhibitory concentrations (MIC’s) give the most precise estimates of antibiotic susceptibility. One such procedure has been recommended for use with discs to test susceptibility to this class of drugs. Interpretations correlate diameters on the disc test with MIC values. A penicillinase-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.

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