Istopen (Oxacillin)

Oxacillin is used to treat infections caused by susceptible Gram‑positive bacteria, particularly in serious or deep‑seated infections.

• Skin and soft‑tissue infections: effective against Staphylococcus aureus and other susceptible organisms, reducing lesion size and preventing spread.
• Bone and joint infections: eradicates pathogens in osteomyelitis and septic arthritis, promoting healing of bone tissue.
• Endocarditis: eliminates susceptible bacteria from heart valves, aiding recovery and preventing complications.

• Oxacillin binds irreversibly to penicillin‑binding proteins on the bacterial cell wall, inhibiting the transpeptidation step of peptidoglycan synthesis. This disruption weakens the cell wall, leading to osmotic instability and bacterial lysis, particularly in penicillinase‑producing Gram‑positive organisms.

Oxacillin may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Injection site pain: mild discomfort at the infusion site.
• Diarrhea: loose stools occurring during therapy.
• Nausea: feeling of sickness or urge to vomit.
• Rash: mild skin erythema or itching.
• Fever: elevated body temperature.
• Elevated liver enzymes: transient increase in hepatic transaminases.

Serious or Rare Side Effects

• Anaphylaxis: severe, potentially life‑threatening allergic reaction.
• Clostridioides difficile colitis: severe intestinal infection causing diarrhea and colitis.
• Severe neutropenia: marked reduction in neutrophil count increasing infection risk.

When using Oxacillin, clinicians should observe several precautionary measures to ensure safety and efficacy.

• Renal function: assess creatinine clearance and adjust dose if impaired.
• Allergy history: avoid in patients with known penicillin hypersensitivity.
• Concurrent antibiotics: monitor for antagonistic effects when combined with bacteriostatic agents.
• Pregnancy and lactation: use only if benefits outweigh potential risks, as safety data are limited.
• Therapeutic monitoring: observe clinical response and consider susceptibility testing.
• Store at ambient temperature: keep below 25 °C, protect from moisture and light in original packaging.

Oxacillin can interact with other medicines, affecting its efficacy or safety.

Major Interactions (Avoid)

• Aminoglycosides: increased risk of nephrotoxicity when combined; avoid if possible.
• Oral contraceptives: may reduce efficacy; consider alternative contraception.

Moderate Interactions (Monitor Closely)

• Bacteriostatic antibiotics (e.g., chloramphenicol, tetracyclines): may antagonize bactericidal activity; monitor response.
• Loop diuretics: may increase risk of ototoxicity with high‑dose penicillins; monitor hearing.
• Warfarin: possible alteration of INR; monitor coagulation parameters.