Amoxicillin with clavulanic acid
Co-amoxiclav
A broad-spectrum penicillin combination used for infections likely to be resistant to amoxicillin alone.
What is Co-amoxiclav?
Co-amoxiclav is a combination antibiotic that pairs amoxicillin, a penicillin, with clavulanic acid, which blocks an enzyme bacteria use to resist penicillins. It is used for chest, urine, dental, skin and other infections where the bacteria are likely to be resistant to amoxicillin on its own. Because it is broad-spectrum, it is usually reserved for situations where a narrower antibiotic would not be enough.
Education and reference only. This is a plain-language guide to Co-amoxiclav — 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
Co-amoxiclav is a combination antibiotic widely prescribed across the UK health service. It contains two ingredients: amoxicillin, a penicillin that kills bacteria, and clavulanic acid, which protects the amoxicillin from being broken down by certain resistant bacteria. This combination broadens what amoxicillin can treat, so co-amoxiclav is used for infections that are more serious or more likely to be resistant. Because it is broad-spectrum, it is generally a second-line choice, used when a narrower antibiotic is unsuitable or has not worked.
How it works
Amoxicillin kills bacteria by stopping them building their cell walls, which causes them to break apart. Many resistant bacteria defend themselves by producing an enzyme (beta-lactamase) that destroys amoxicillin before it can act. Clavulanic acid mops up that enzyme, leaving the amoxicillin free to work. Together they cover a wider range of bacteria than amoxicillin alone.
Company & origin
Originated / developed by: Beecham (now GSK).
Developed by Beecham Research Laboratories in the UK and introduced as Augmentin in the early 1980s, it pairs the penicillin amoxicillin with clavulanic acid to overcome a common form of bacterial resistance.
Practical use
How to take Co-amoxiclav
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it with or just before food to reduce stomach upset and help it work well.
- Space the doses evenly through the day, as directed on the label, to keep a steady level in the body.
- Complete the whole course even if you feel better, unless a clinician tells you to stop.
- Report severe, watery or bloody diarrhoea, which may continue after the course — it can signal a gut infection (Clostridioides difficile) that needs different treatment.
- Tell your prescriber about any previous reaction to penicillins or other antibiotics before starting.
Weighing it up
Advantages & disadvantages of Co-amoxiclav
Advantages
- Broad-spectrum cover that works against many bacteria resistant to amoxicillin alone.
- A familiar, well-established option for chest, urine, dental, bite and skin infections when a narrower antibiotic is not enough.
- Available as both tablets and a liquid, so it suits adults and children.
Disadvantages
- More likely than narrower penicillins to cause diarrhoea and to upset the gut, including Clostridioides difficile infection.
- Can rarely cause a cholestatic liver injury (jaundice with itching), which is more likely with longer or repeated courses and in older people.
- Not suitable for people with a true penicillin allergy, and overuse drives antibiotic resistance, so it is reserved rather than first-line.
Practical use
Good to know
It is a broad-spectrum antibiotic, so it disturbs the natural gut bacteria more than narrower penicillins and is more likely to cause diarrhoea. It is best taken with food to reduce stomach upset. As with all antibiotics, the full course should be completed even once you feel better, and it should never be shared or saved for another time.
Who should not take it / use with caution
- Anyone who has had a serious allergic reaction (such as rash, swelling or anaphylaxis) to penicillins or to co-amoxiclav itself.
- People who have previously had jaundice or liver problems caused by co-amoxiclav or a related penicillin.
- Used with caution in significant kidney or liver disease, and the prescriber checks suitability in pregnancy and breastfeeding.
Monitoring
- Mainly clinical — checking the infection is settling and watching for diarrhoea or allergic reactions.
- Liver and kidney function with longer courses or in people with existing liver or kidney problems.
- Closer INR checks if taken with warfarin.
Side effects
- Diarrhoea, nausea and thrush are the most common — taking it with food helps.
- Skin rash; a widespread rash with swelling, breathlessness or feeling faint needs urgent attention as it may be an allergic reaction.
- Rarely, jaundice or liver inflammation (yellowing of skin or eyes, dark urine, itching) and, rarely, severe or persistent diarrhoea from a gut infection — both should be reported.
Key interactions
- Can increase the effect of warfarin, so blood-clotting (INR) may need closer checking.
- Used with care alongside methotrexate, as levels of methotrexate can rise.
- Allopurinol taken at the same time can increase the chance of a skin rash.
Available as: Tablets and an oral suspension (liquid); a form for hospital drip use also exists.
Answers
Co-amoxiclav: frequently asked questions
Why is co-amoxiclav given instead of plain amoxicillin?
Many bacteria resist amoxicillin by making an enzyme that destroys it. Co-amoxiclav adds clavulanic acid, which blocks that enzyme, so the amoxicillin can work against those resistant bacteria. It is usually kept for infections that are more serious or more likely to be resistant, rather than used as a first choice.
Why does it cause diarrhoea more often than other antibiotics?
Co-amoxiclav is broad-spectrum, so as well as the bacteria causing your infection it disturbs the helpful bacteria that live in the gut. This imbalance commonly causes loose stools. Taking it with food helps, but report any severe, watery or bloody diarrhoea, as it can occasionally signal a more serious gut infection.
Can I take co-amoxiclav if I am allergic to penicillin?
No. Co-amoxiclav contains amoxicillin, which is a penicillin, so it must be avoided by anyone who has had a genuine allergic reaction to penicillins. Always tell your prescriber and pharmacist about any previous antibiotic reactions so a safe alternative can be chosen.
Should I take it with food?
Yes, it is best taken with or just before a meal. Food reduces the stomach upset that co-amoxiclav can cause and helps it be absorbed well. Spacing the doses evenly through the day keeps a steady amount in your body.
What is the difference between co-amoxiclav and Augmentin?
They are the same medicine. Co-amoxiclav is the generic name (amoxicillin with clavulanic acid) and Augmentin is the original brand name. Generic co-amoxiclav contains the identical active ingredients.
The wider class
About Penicillins
Co-amoxiclav belongs to the penicillins class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF: Co-amoxiclav.
- NICE CKS: Co-amoxiclav.
- MHRA Drug Safety Update: co-amoxiclav and cholestatic jaundice.
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.