Oxacillin

Pronunciation: pronunciation varies by local usage.

Generic name: oxacillin
Brand names: Oxacillin for Injection, USP
Drug class: Penicillinase-resistant penicillin antibiotic
Form: Powder for solution for injection
Route: Intramuscular or intravenous injection
Legal status: Administered as an injectable antibiotic; a specific legal/prescription classification was not explicitly stated in the source reviewed for this page.

Availability and supply rules vary by country

Trade names by country:

What oxacillin is and how it works

Oxacillin is a penicillinase-resistant penicillin antibiotic. It is active against infections caused by penicillinase-producing staphylococci that have demonstrated susceptibility to the drug. (1)

Oxacillin is given by intramuscular or intravenous injection. The source reviewed for this page characterizes it as generally administered in a clinical setting rather than as a patient-self-administered oral medicine.

Mechanism of action: how oxacillin works

Oxacillin is classified as a penicillinase-resistant penicillin. Detailed mechanism-of-action wording beyond this classification was not established in the source reviewed for this page. (1)

What oxacillin is used for

Infections caused by penicillinase-producing staphylococci

Oxacillin is indicated for the treatment of infections caused by penicillinase-producing staphylococci that have demonstrated susceptibility to the drug. (1)

Before taking oxacillin

Do not take / not appropriate for

If you have a history of a hypersensitivity (anaphylactic) reaction to any penicillin, tell the prescribing clinician before treatment; this is a contraindication that they must assess. (all formulations) (1)

Tell your clinician about

Any previous allergic reaction to penicillin. (Allergy screening for other medicine classes was not specifically established in the source reviewed for this page; mention any other medicine allergies too, so your clinician can assess them.)
Current or planned pregnancy, breastfeeding, or kidney problems.
All current medicines, especially probenecid or tetracycline antibiotics.

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How to take oxacillin

Oxacillin is given as an intramuscular (IM) or intravenous (IV) injection.
The dose, frequency, and duration depend on the severity of the infection, body weight, and kidney function.
Do not change the prescribed regimen without consulting your clinician.

(1)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)

Missed dose

Because oxacillin is given by injection, typically in a clinical setting, a missed dose would ordinarily be managed by the treating clinical team rather than the patient.

Overdose

Management would be expected to be supportive, under medical supervision. (1)

Side effects

The reviewed FDA label lists several reported adverse reactions; a specific, frequency-ranked list of common side effects, or detailed patient-facing symptom descriptions for each, was not itemized in this source. The following reactions have been reported:

Blood cell effects (agranulocytosis, neutropenia)

What to do: Contact your treating clinician promptly about any new or concerning symptom. (1)

Kidney effects (renal tubular damage, interstitial nephritis)

What to do: Contact your treating clinician promptly about any new or concerning symptom. (1)

Pseudomembranous colitis (C. difficile-associated diarrhea)

What to notice: Diarrhea; this can appear over two months after antibacterial administration.

What to do: Contact a clinician promptly if diarrhea develops, even after finishing treatment. (1)

Serious warnings

Anaphylaxis — emergency

Symptoms: Anaphylaxis is a recognized, potentially fatal reaction to penicillins, and anaphylactic shock resulting in death has occurred in approximately 0.002% of treated patients per the reviewed label.

Action: Seek emergency medical attention immediately if a severe allergic reaction is suspected. (1)

Clostridioides difficile-associated diarrhea (CDAD) — urgent

Symptoms: Diarrhea; can occur over two months after treatment ends. Specific additional symptom details were not established in the source reviewed for this page.

Action: Contact a clinician promptly. (1)

Hepatotoxicity — urgent

Symptoms: Fever, nausea, and vomiting, associated with abnormal liver-function tests.

Action: Report these symptoms to your healthcare team promptly. (1)

Interactions

Medicine or test	Effect	Action
Tetracycline antibiotics	Concurrent use of tetracycline (a bacteriostatic antibiotic) may antagonize the bactericidal effect of oxacillin.	Tell your prescriber about any tetracycline-class antibiotic use; they will decide whether combination therapy is appropriate. (1)
Probenecid	Probenecid blocks renal excretion of oxacillin, raising oxacillin blood levels.	Tell your prescriber if you are taking probenecid. (1)

Pregnancy, breastfeeding, kidney/liver function, age

Children (under 40 kg)

Mild to moderate infections: 50 mg/kg/day IM or IV in equally divided doses every 6 hours. Severe infections: 100 mg/kg/day IM or IV in equally divided doses every 4 to 6 hours. Renal-function-specific adjustment for children was not established in the source reviewed for this page. (1)

Neonates and premature infants

A dosage of 25 mg/kg/day IM or IV is provided; the reviewed source did not further specify a dividing schedule beyond this daily total, and that remains unresolved. (1)

Pregnancy

Pregnancy Category B per the reviewed source, which found no evidence of impaired fertility or fetal harm. Discuss with your clinician if you are pregnant or planning pregnancy. (1)

Breastfeeding

Penicillins, including oxacillin, are excreted in human milk. Discuss with your prescriber if you are breastfeeding. (1)

Renal impairment

If any impairment of renal function is suspected or known, a reduction in total dosage should be considered. A specific creatinine-clearance-based adjustment table was not provided in the source reviewed for this page. (1)

Monitoring

Before starting

Confirm a history of penicillin hypersensitivity is screened for, since anaphylactic hypersensitivity to any penicillin is a contraindication.
Assess renal function; a total dosage reduction should be considered if impairment is suspected or known.

During treatment

Be aware of the risks of anaphylaxis, hepatotoxicity, delayed C. difficile-associated diarrhea, agranulocytosis, neutropenia, renal tubular damage, and interstitial nephritis, which have all been reported with oxacillin.
Specific monitoring schedules (such as baseline or periodic laboratory testing) were not established in the source reviewed for this page and should follow clinician judgment and institutional protocols.

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Storage

Store unreconstituted powder at 20°C-25°C (68°F-77°F). For IM reconstituted solutions, the reviewed source gives examples of 3 days at room temperature (70°F) or 1 week under refrigeration. Stability windows for IV solutions were not detailed in the source reviewed for this page.

Study the drug class: Penicillins

Professional information

Clinician-facing context only. Use the current local product label, institutional susceptibility data, and relevant guidelines.

United States

Indication: Staphylococcal infections susceptible to oxacillin

Dose summary: Adults: mild-moderate infections 250-500 mg IM/IV q4-6h; severe infections 1 g IM/IV q4-6h. Children under 40 kg: mild-moderate 50 mg/kg/day in divided doses q6h; severe 100 mg/kg/day in divided doses q4-6h. Neonates/preterm: 25 mg/kg/day IM/IV (no further dividing schedule provided in the reviewed source).

Renal context: If renal impairment exists, a reduction in total dosage should be considered. No specific creatinine-clearance-based adjustment table was provided in the reviewed source. (1)

Mechanism of action

Hepatic guidance

Hepatotoxicity has been reported as an adverse effect; a specific hepatic-impairment dosing adjustment was not found in the source reviewed for this page.

Overdose note

No specific antidote or overdose-management protocol was identified in the source reviewed for this page. Management would be expected to be supportive, under medical supervision. (1)

Frequently asked questions

Can I use oxacillin if I am allergic to penicillin?

A history of a hypersensitivity (anaphylactic) reaction to any penicillin is a contraindication to oxacillin. Always tell your clinician about any penicillin allergy so they can assess whether oxacillin is safe for you. (1)

Can oxacillin cause liver problems?

Hepatotoxicity has been associated with oxacillin, characterized by fever, nausea, and vomiting together with abnormal liver-function tests. Notify your healthcare team if you develop these symptoms. (1)

Can oxacillin cause diarrhea that starts after I stop the medicine?

Yes. Clostridioides difficile-associated diarrhea has been reported and can occur over two months after antibacterial administration. If you develop diarrhea, even after finishing treatment, contact a clinician promptly. (1)

What is the mechanism of action of oxacillin?