The partner in co-amoxiclav that protects amoxicillin
Clavulanic acid
A partner ingredient combined with amoxicillin (as co-amoxiclav) to overcome resistance and help the antibiotic work.
What is Clavulanic acid?
Clavulanic acid (clavulanate) is not really an antibiotic on its own; it is a 'beta-lactamase inhibitor' given together with the antibiotic amoxicillin, and the combination is called co-amoxiclav. Many bacteria defend themselves by making an enzyme that breaks down amoxicillin; clavulanate blocks that enzyme so the amoxicillin can work. The combination treats infections that ordinary amoxicillin cannot, but it is more likely to cause diarrhoea and, rarely, liver problems, so it is used when it is genuinely needed.
Education and reference only. This is a plain-language guide to Clavulanic acid — 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
Clavulanic acid, often called clavulanate, is the partner ingredient in the combination antibiotic co-amoxiclav. By itself it has very little effect on bacteria; its job is to protect the antibiotic it is paired with, amoxicillin. Some bacteria produce an enzyme that destroys amoxicillin and similar penicillins, making them resistant; clavulanate is added to overcome that. So when you take co-amoxiclav, you are taking two ingredients working as a team: amoxicillin to kill the bacteria and clavulanate to stop the bacteria disabling it.
How it works
Certain bacteria make an enzyme called beta-lactamase that breaks open and inactivates amoxicillin before it can do its job, which is how they become resistant. Clavulanate works by latching onto this enzyme and blocking it, so the enzyme is kept busy and cannot destroy the amoxicillin. With the enzyme out of action, the amoxicillin is free to attack the bacteria's cell walls and clear the infection. This is why clavulanate is described as protecting the partner antibiotic rather than killing bacteria itself.
Company & origin
Originated / developed by: Generic (long-established).
Used in the UK as the partner ingredient in co-amoxiclav, where it is combined with amoxicillin to overcome bacterial resistance.
Practical use
How to take Clavulanic acid
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as co-amoxiclav exactly as prescribed and finish the whole course, even once you feel better.
- Take it with or just before food to reduce the chance of stomach upset.
- Space the doses out evenly through the day as directed.
- Tell your prescriber if you have ever had a reaction to penicillin or to co-amoxiclav before.
- Report yellowing of the skin or eyes, dark urine, severe diarrhoea or itching, even after the course has finished.
Weighing it up
Advantages & disadvantages of Clavulanic acid
Advantages
- Allows amoxicillin to work against bacteria that would otherwise resist it, widening the range of infections treated.
- Taken by mouth as the combination co-amoxiclav, or given by injection in hospital.
- A long-established, well-understood way to overcome a common type of antibiotic resistance.
Disadvantages
- Has little antibacterial effect on its own; it only works as a partner to amoxicillin.
- More likely than plain amoxicillin to cause diarrhoea and stomach upset.
- Carries a rare risk of liver problems, which can appear after the course has finished.
Practical use
Good to know
The most useful thing to understand is that clavulanate is a helper, not the main antibiotic: it is given as part of co-amoxiclav specifically to overcome resistance when plain amoxicillin would be broken down. Because of the clavulanate part, co-amoxiclav is more likely than amoxicillin alone to cause diarrhoea and tummy upset, and taking it with food can help. A rare but important risk is liver problems, which can sometimes appear days or even weeks after finishing the course, so report yellowing of the skin or eyes, dark urine or itching. As with all penicillins, allergy matters: anyone who has had a serious reaction to penicillin should not take it. It is best reserved for infections that genuinely need it, to help keep antibiotics working in the long run.
Who should not take it / use with caution
- People who have had a serious allergic reaction to penicillin or to co-amoxiclav must not take it.
- People who have had liver problems or jaundice linked to co-amoxiclav before should not take it again.
- It is used with care in people with kidney or liver problems, under medical guidance.
Monitoring
- Reviewing how well the infection responds to treatment.
- Watching for severe or lasting diarrhoea, which occasionally signals a gut infection needing attention.
- Checking for signs of liver problems, especially yellowing of the skin or eyes, during or after treatment.
Side effects
- Diarrhoea, nausea or stomach upset, which is more common than with amoxicillin alone.
- Thrush (a fungal infection) in the mouth or vagina after a course.
- Skin rash, which can sometimes signal an allergy and should be checked.
- Rarely, liver problems with yellowing of the skin or eyes, or serious allergic reactions, which need urgent attention.
Key interactions
- It can interact with the blood thinner warfarin, sometimes affecting clotting tests, so this may be monitored.
- Taking it with the gout medicine allopurinol may make a rash more likely.
- Tell your prescriber about all your medicines, including any other antibiotics.
Available as: Tablets, an oral liquid (as co-amoxiclav), and a form for injection given in hospital.
Answers
Clavulanic acid: frequently asked questions
What does clavulanate actually do?
On its own it has little effect on bacteria; it blocks an enzyme that bacteria use to destroy amoxicillin, so it protects and allows the amoxicillin to work.
Is it the same as co-amoxiclav?
Co-amoxiclav is the combination of amoxicillin and clavulanate together; clavulanate is the partner ingredient that overcomes resistance.
Why does it upset my stomach more?
The clavulanate part makes diarrhoea and stomach upset more likely than with plain amoxicillin; taking it with food can help reduce this.
Can it affect my liver?
Rarely it can cause liver problems, which may appear even after the course has finished, so report yellowing of the skin or eyes, dark urine or itching.
Can I take it if I am allergic to penicillin?
No. Co-amoxiclav contains a penicillin, so anyone who has had a serious reaction to penicillin should not take it; tell your prescriber about any allergy.
The wider class
About Beta-lactamase inhibitor (given with amoxicillin)
Clavulanic acid belongs to the beta-lactamase inhibitor (given with amoxicillin) 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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