Oxacillin — Compare Prices at US & Canada Pharmacies

Oxacillin is a penicillinase-resistant penicillin, in the same family as nafcillin and dicloxacillin, used for serious infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) — bacteremia, endocarditis, osteomyelitis, and other deep-seated staph infections where a beta-lactam is preferred over vancomycin for its faster, more reliable bactericidal action against susceptible organisms. It has no activity against methicillin-resistant S. aureus (MRSA); in fact, "oxacillin-resistant S. aureus" is used interchangeably with MRSA in lab reporting, since oxacillin's chemical stability made it the preferred agent for susceptibility testing even after methicillin itself fell out of clinical use.

Compared with nafcillin, its closest clinical alternative, oxacillin is generally less irritating to veins if an IV infiltrates, but it carries a distinctly higher rate of hepatotoxicity — transient elevations in liver enzymes, and less commonly clinically apparent hepatitis, especially with higher doses or longer courses. Because of this, clinicians monitoring a patient on extended oxacillin therapy typically check liver function periodically, and unexplained nausea, fatigue, or abdominal pain during treatment is worth flagging rather than dismissing. Interstitial nephritis, an allergic-type kidney reaction, is also a recognized risk shared across this drug class.

Two interactions are worth knowing: tetracyclines can blunt oxacillin's bactericidal effect and are generally avoided together, and probenecid raises and prolongs oxacillin blood levels by blocking its kidney excretion — occasionally used intentionally when very high oxacillin levels are needed, but otherwise not combined without a specific reason.

Contraindications

CONTRAINDICATIONS A history of a hypersensitivity (anaphylactic) reaction to any penicillin is a contraindication.

Warnings

WARNINGS Serious and occasionally fatal hypersensitivity (anaphylactic shock with collapse) reactions have occurred in patients receiving penicillin. The incidence of anaphylactic shock in all penicillin-treated patients is between 0.015 and 0.04 percent. Anaphylactic shock resulting in death has occurred in approximately 0.002 percent of the patients treated. When oxacillin therapy is indicated, it should be initiated only after a comprehensive patient drug and allergy history has been obtained. If an allergic reaction occurs, oxacillin should be discontinued and appropriate therapy instituted.

Pregnancy & breastfeeding

Pregnancy Teratogenic Effects Reproduction studies performed in the mouse, rat, and rabbit have revealed no evidence of impaired fertility or harm to the fetus due to the penicillinase-resistant penicillins. Human experience with the penicillins during pregnancy has not shown any positive evidence of adverse effects on the fetus. There are, however, no adequate or well-controlled studies in pregnant women showing conclusively that harmful effects of these drugs on the fetus can be excluded.