A penicillinase-resistant penicillin antibiotic
Oxacillin
A penicillin antibiotic, given by injection, used to treat infections caused by staph bacteria.
What is Oxacillin?
Oxacillin is a penicillin antibiotic of the penicillinase-resistant type, given by injection to treat infections caused by staphylococcus (staph) bacteria, including skin, bone and bloodstream infections. It is the US equivalent of flucloxacillin, which is used in the UK. As a penicillin, it must not be given to anyone with a penicillin allergy, especially those who have had a severe reaction such as anaphylaxis. It can occasionally affect the liver, so this is monitored. It is given in hospital under medical supervision.
Education and reference only. This is a plain-language guide to Oxacillin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Oxacillin is an antibiotic from the penicillin family, in a group designed to work against staphylococcus bacteria that produce an enzyme able to destroy ordinary penicillin. It is used to treat staph infections such as skin and soft-tissue infections, bone and joint infections, and infections in the blood. It is given by injection, usually in hospital. It is closely related to flucloxacillin, the medicine used for the same job in the UK, and the two are essentially equivalents used in different countries.
How it works
Oxacillin kills bacteria by stopping them building their cell walls, the protective outer layer they need to survive; without a proper wall, the bacteria burst and die. Its special feature is that it resists penicillinase, an enzyme that staph bacteria make to break down ordinary penicillin, so it stays effective against those staph bugs. This makes it well suited to staph infections. Like all penicillins, it works against the bacteria and does not affect viruses, so it is no use for colds or flu.
Company & origin
Originated / developed by: Various manufacturers.
A penicillin antibiotic given by injection for staph infections; it is the US equivalent of flucloxacillin used in the UK.
Practical use
How to take Oxacillin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by injection by healthcare staff, usually in hospital.
- Tell the team about any allergy to penicillin or other antibiotics before it is given.
- Complete the full course as directed, even once you feel better, to clear the infection fully.
- Report yellowing of the skin or eyes, dark urine or pale stools, as these can signal a liver effect.
- Report severe or persistent diarrhoea, as this needs checking.
Weighing it up
Advantages & disadvantages of Oxacillin
Advantages
- Effective against staph infections, including those that destroy ordinary penicillin.
- Well suited to skin, bone and bloodstream infections caused by staph.
- A long-established antibiotic, closely related to flucloxacillin used in the UK.
Disadvantages
- Cannot be used by people with a penicillin allergy.
- Can occasionally affect the liver, sometimes after treatment has finished.
- Given by injection, usually needing hospital care.
Practical use
Good to know
The most important safety point is allergy: because oxacillin is a penicillin, it must not be given to anyone who is allergic to penicillins, and a previous severe reaction such as anaphylaxis is especially important to know about, so always tell the team about any antibiotic allergy. Like flucloxacillin, it can occasionally upset the liver, sometimes appearing after treatment has finished, so the team may check liver blood tests and you should report yellowing of the skin or eyes, dark urine or pale stools. It is given by injection in hospital, and finishing the full course as directed matters even once you feel better, to clear the infection fully and help prevent resistance. Diarrhoea is a common antibiotic side effect; severe or persistent diarrhoea should be reported.
Who should not take it / use with caution
- People allergic to penicillins must not be given it, especially those who have had a severe reaction such as anaphylaxis.
- It is used with caution in people who have had liver problems with this type of antibiotic before.
- It is used with care in people with kidney problems, under medical guidance.
- It does not work against viruses, so it is not used for colds or flu.
Monitoring
- Watching how well the infection responds to treatment.
- Checking liver blood tests where appropriate, especially with longer courses.
- Watching for allergic reactions and for severe diarrhoea.
Side effects
- Diarrhoea, nausea or stomach upset.
- Rash and other allergic-type reactions.
- Occasionally, liver effects, sometimes appearing after treatment has finished.
- Rarely but seriously, a severe allergic reaction (anaphylaxis) or severe gut infection, which need urgent attention.
Key interactions
- Tell the team about all medicines you take, as a few can interact with penicillins.
- It can affect some blood tests and may interact with certain other antibiotics.
- Live vaccines and some other treatments may need timing advice during antibiotic use.
Available as: A powder made up into a solution for injection into a vein or muscle.
Answers
Oxacillin: frequently asked questions
What is oxacillin used for?
It is a penicillin antibiotic used to treat infections caused by staphylococcus (staph) bacteria, such as skin, bone and bloodstream infections.
Is it the same as flucloxacillin?
It is very closely related; oxacillin is essentially the US equivalent of flucloxacillin, which is used in the UK for the same kinds of staph infections.
Can I have it if I am allergic to penicillin?
No. Oxacillin is a penicillin, so it must not be given to anyone with a penicillin allergy, especially if they have had a severe reaction.
Why might my liver be checked?
Like flucloxacillin, it can occasionally affect the liver, sometimes after treatment finishes, so report yellowing of the skin or eyes, dark urine or pale stools.
Will it help a cold or flu?
No. It is an antibiotic that works only against bacteria, so it does not work against viruses such as colds or flu.
The wider class
About Penicillinase-resistant penicillin (anti-staph)
Oxacillin belongs to the penicillinase-resistant penicillin (anti-staph) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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