oxacillin
Brand: Bactocill
Prototype: penicillin-g
Drug Class: antibiotic (penicillin)
Drug Family: antibiotic
Subclass: antistaphylococcal (isoxazolyl) penicillin
Organ Systems: infectious-disease
Mechanism of Action
Inhibits PBPs like all penicillins; the isoxazolyl side chain provides steric protection against staphylococcal penicillinase (beta-lactamase), making it active against methicillin-susceptible Staphylococcus aureus (MSSA). Has no activity against MRSA (altered PBP2a).
penicillin-binding proteins (PBPs)
Indications
- methicillin-susceptible Staphylococcus aureus (MSSA) infections (bacteremia, endocarditis, osteomyelitis, skin/soft tissue)
- preferred over vancomycin for serious MSSA infections
Contraindications
- penicillin allergy
- MRSA infections (not active)
Adverse Effects
Common
- phlebitis at IV site
- nausea
- rash
Serious
- hepatotoxicity (elevated LFTs in up to 5%)
- interstitial nephritis (rare)
- C. difficile colitis
- anaphylaxis
Pharmacokinetics (ADME)
| Absorption | IV or oral; oral bioavailability ~30% (food reduces further); IV preferred for serious infections |
| Distribution | protein binding ~94%; penetrates bone, synovial fluid; limited CSF |
| Metabolism | hepatic (20-30%) and renal |
| Excretion | renal and biliary |
| Half-life | 0.4-0.7 hours |
| Onset | end of IV infusion |
| Peak | end of infusion (IV) |
| Duration | 4-6 hours |
| Protein Binding | 94% |
| Vd | 0.38 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| aminoglycosides | synergistic for endocarditis; physically incompatible in same line | moderate |
| rifampin | synergistic for foreign body/biofilm infections | moderate |
Nursing Considerations
- Monitor hepatic function (ALT, AST, bilirubin) during prolonged therapy; hepatotoxicity may require discontinuation.
- IV oxacillin is preferred over vancomycin for MSSA bacteremia and endocarditis because it achieves bactericidal activity more reliably and has better outcomes data.
- Severe phlebitis with peripheral IV administration; use central venous access for prolonged treatment.
- Must confirm MSSA susceptibility before using; if susceptibility unknown, use vancomycin empirically until culture results available.
Clinical Pearls
- For MSSA bacteremia and endocarditis, oxacillin (or nafcillin) reduces 30-day mortality compared to vancomycin; switching from empiric vancomycin to oxacillin upon MSSA confirmation is a quality improvement benchmark.
- Hepatotoxicity is a class-specific adverse effect of the isoxazolyl penicillins (oxacillin, nafcillin, dicloxacillin) and is not seen with other penicillins.
Safety Profile
Pregnancy safe
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.