Co-Amoxiclav is one of the most commonly prescribed antibiotics in the UK, especially for infections that don’t respond to plain amoxicillin. You might have heard your doctor call it Augmentin, Clavamox, or just "amoxicillin with clavulanic acid." But what exactly is it, and why does it work when other antibiotics fail?
What is Co-Amoxiclav?
Co-Amoxiclav is a combination antibiotic made of two active ingredients: amoxicillin and clavulanic acid. Amoxicillin is a penicillin-type antibiotic that kills bacteria by stopping them from building their cell walls. But many bacteria have evolved a defense - they produce an enzyme called beta-lactamase that breaks down amoxicillin before it can work.
That’s where clavulanic acid comes in. It doesn’t kill bacteria itself. Instead, it blocks beta-lactamase, letting amoxicillin do its job. Think of it like giving amoxicillin a shield against the bacteria’s weapons. Together, they form a powerful team that works against a wider range of infections than amoxicillin alone.
This combination is used for infections caused by bacteria that are resistant to standard penicillins. It’s not a magic bullet - it won’t work on viruses like colds or flu - but when used correctly, it’s highly effective against stubborn bacterial infections.
How does Co-Amoxiclav work?
Co-Amoxiclav works in two steps. First, clavulanic acid binds to and disables beta-lactamase enzymes produced by resistant bacteria. These enzymes would normally destroy amoxicillin. Once they’re neutralized, amoxicillin can freely enter bacterial cells and interfere with their ability to make cell walls. Without strong cell walls, the bacteria swell up and burst.
This dual-action mechanism makes Co-Amoxiclav effective against a broad spectrum of bacteria, including:
- Staphylococcus aureus (including some penicillin-resistant strains)
- Escherichia coli
- Klebsiella species
- Haemophilus influenzae
- Proteus mirabilis
- Prevotella and Fusobacterium (common in dental and sinus infections)
It’s especially useful for infections where resistance is suspected - like recurring sinusitis, complicated urinary tract infections, or infected wounds after animal bites. In hospitals, it’s often the go-to for moderate to severe infections before lab results come back.
When is Co-Amoxiclav prescribed?
Doctors in the UK typically prescribe Co-Amoxiclav for infections that either didn’t improve with standard amoxicillin or are likely to involve resistant bacteria. Common uses include:
- Sinus infections that last more than 10 days or get worse after initial improvement
- Ear infections in children who haven’t responded to first-line antibiotics
- Urinary tract infections with fever or signs of kidney involvement
- Dental abscesses - especially when swelling or fever is present
- Skin and soft tissue infections like cellulitis or infected cuts
- Animal bites (especially cat bites, which often carry resistant bacteria)
- Pneumonia in patients with risk factors like recent hospital stays or chronic lung disease
In the NHS, Co-Amoxiclav is usually reserved for cases where first-choice antibiotics like amoxicillin or doxycycline have failed. It’s not a starter drug - it’s a second-line option, which helps reduce the risk of antibiotic resistance.
Dosage and how to take it
Co-Amoxiclav comes in tablets, liquid suspension, and intravenous form. The most common oral doses in the UK are:
- 375 mg (250 mg amoxicillin + 125 mg clavulanate)
- 625 mg (500 mg amoxicillin + 125 mg clavulanate)
- 1000 mg (875 mg amoxicillin + 125 mg clavulanate)
For adults, the usual dose is one 625 mg tablet every 12 hours, or one 1000 mg tablet every 12 hours for more serious infections. Children get doses based on weight - usually 20-40 mg/kg per day divided into two or three doses.
It’s best taken at the start of a meal. Food helps reduce stomach upset and improves absorption. Don’t skip doses, even if you start feeling better. Stopping early can let the toughest bacteria survive and multiply.
The course usually lasts 5-10 days, depending on the infection. Always finish the full course unless your doctor says otherwise. In hospital settings, intravenous Co-Amoxiclav is given every 8 hours for severe infections like sepsis or deep tissue abscesses.
Side effects and risks
Most people tolerate Co-Amoxiclav well, but side effects are common. About 1 in 10 people experience:
- Diarrhoea
- Nausea or vomiting
- Stomach pain
- Rash
Diarrhoea is the most frequent issue. In some cases, it can be caused by Clostridioides difficile - a serious gut infection that can happen after antibiotics disrupt normal bacteria. If you get watery or bloody diarrhoea, fever, or severe stomach cramps, stop taking it and see a doctor immediately.
Less common but serious side effects include:
- Allergic reactions (hives, swelling, trouble breathing) - especially if you’re allergic to penicillin
- Liver problems (yellow skin or eyes, dark urine, extreme tiredness)
- Severe skin reactions like Stevens-Johnson syndrome
If you’ve ever had a rash or swelling after taking penicillin, tell your doctor before taking Co-Amoxiclav. About 10% of people with penicillin allergies will react to it too.
Who should avoid Co-Amoxiclav?
Co-Amoxiclav isn’t safe for everyone. Avoid it if you:
- Have a known allergy to penicillin or any beta-lactam antibiotic
- Have had liver damage from Co-Amoxiclav in the past
- Have severe kidney disease - your dose may need adjusting
- Have mononucleosis (glandular fever) - you’re much more likely to get a severe rash
It’s generally safe in pregnancy and breastfeeding, but only if the benefits outweigh the risks. Always tell your doctor if you’re pregnant, planning to be, or nursing.
Older adults and people with long-term illnesses may need lower doses or closer monitoring. Co-Amoxiclav can interact with other drugs - especially allopurinol (used for gout), which increases the chance of rash, and oral contraceptives, which may become less effective.
How does it compare to other antibiotics?
Here’s how Co-Amoxiclav stacks up against other common antibiotics used for similar infections:
| Antibiotic | Best for | Resistance coverage | Common side effects | Penicillin allergy safe? |
|---|---|---|---|---|
| Co-Amoxiclav | Sinus, ear, dental, skin, animal bites | High - covers beta-lactamase producers | Diarrhoea, nausea, rash | No |
| Amoxicillin | Simple ear, throat, urinary infections | Low - ineffective against resistant strains | Mild stomach upset | No |
| Doxycycline | Lyme disease, acne, respiratory infections | Moderate - good for atypical bacteria | Stomach upset, sun sensitivity | Yes |
| Cephalexin | Skin, bone, urinary infections | Moderate - broader than amoxicillin | Diarrhoea, nausea | Maybe - 10% cross-reactivity |
| Clarithromycin | Respiratory, H. pylori, some skin infections | Moderate - good for atypical pathogens | Altered taste, stomach cramps | Yes |
Co-Amoxiclav has the broadest coverage against resistant bacteria among these options, but it also has the highest risk of diarrhoea. Doxycycline or clarithromycin are often preferred for people with penicillin allergies. Cephalexin is a good alternative for skin infections, but it won’t work on the same range of gut or dental bugs.
What to do if it doesn’t work
If you’ve taken Co-Amoxiclav for 48-72 hours and your symptoms haven’t improved - or if they’ve gotten worse - contact your doctor. Possible reasons include:
- The infection is viral, not bacterial
- The bacteria are resistant to Co-Amoxiclav (rare, but possible)
- You didn’t take it correctly (missed doses, didn’t take with food)
- There’s an abscess or foreign object that needs drainage
Your doctor may order a culture - taking a swab or sample to identify the exact bacteria and test which antibiotics it’s sensitive to. In hospital settings, this is standard practice. At home, it’s usually only done if the infection is severe or recurrent.
Don’t try to switch antibiotics on your own. Taking the wrong one can make things worse or cause dangerous side effects.
Preventing resistance and using Co-Amoxiclav responsibly
Antibiotic resistance is one of the biggest public health threats in the UK. The NHS has strict guidelines to limit unnecessary use of Co-Amoxiclav. You can help by:
- Never asking for antibiotics for colds or flu
- Always finishing your full course, even if you feel better
- Never sharing your antibiotics with others
- Not saving leftover tablets for next time
Studies show that up to 30% of antibiotic prescriptions in primary care are unnecessary. Co-Amoxiclav is often overprescribed for mild sinus infections that would clear on their own. If your doctor says you don’t need it, trust them - your body’s immune system can often handle it.
When to seek help
Call 111 or see a doctor immediately if you experience:
- Severe diarrhoea with blood or mucus
- Difficulty breathing, swelling of face or throat
- Yellowing of skin or eyes
- Unexplained bruising or bleeding
- Severe skin rash or blisters
These are signs of serious reactions that need urgent care. Don’t wait.
Is Co-Amoxiclav the same as amoxicillin?
No. Co-Amoxiclav contains amoxicillin plus clavulanic acid. Amoxicillin alone doesn’t work against bacteria that produce beta-lactamase enzymes. Co-Amoxiclav is designed to overcome that resistance. If your infection doesn’t respond to amoxicillin, your doctor may switch you to Co-Amoxiclav.
Can I take Co-Amoxiclav if I’m allergic to penicillin?
No. Co-Amoxiclav contains amoxicillin, which is a penicillin-type antibiotic. If you’ve ever had a rash, swelling, or breathing trouble after taking penicillin or amoxicillin, you should not take Co-Amoxiclav. Tell your doctor about your allergy - they’ll choose a different antibiotic like doxycycline or clarithromycin.
How long does it take for Co-Amoxiclav to work?
Most people start to feel better within 2-3 days. But it can take up to 5 days for symptoms like fever or swelling to fully improve. Don’t stop taking it just because you feel better. Stopping early can cause the infection to come back stronger.
Can Co-Amoxiclav cause yeast infections?
Yes. Like other antibiotics, Co-Amoxiclav can disrupt the natural balance of bacteria in your body, which can lead to yeast overgrowth. Women may develop vaginal thrush, and some people get oral thrush. Symptoms include itching, white patches in the mouth, or thick discharge. Over-the-counter antifungal treatments usually help, but talk to your pharmacist or doctor if it’s severe.
Can I drink alcohol while taking Co-Amoxiclav?
Yes, alcohol doesn’t interact with Co-Amoxiclav in a dangerous way. But drinking while you’re unwell can make you feel worse and slow your recovery. It’s best to avoid alcohol until you’re feeling better. Plus, alcohol can irritate your stomach - and Co-Amoxiclav already causes stomach upset in some people.
Is Co-Amoxiclav safe for children?
Yes. Co-Amoxiclav is commonly prescribed for children with ear infections, sinus infections, or dental abscesses. It comes in a liquid form that’s easy to give. Doses are based on the child’s weight. Always use the measuring device that comes with the medicine - kitchen spoons aren’t accurate enough.
Next steps if you’ve been prescribed Co-Amoxiclav
If you’ve been given Co-Amoxiclav:
- Take it exactly as directed - don’t skip doses.
- Take it with food to reduce stomach upset.
- Drink plenty of water.
- Watch for diarrhoea, rash, or signs of allergic reaction.
- Finish the full course, even if you feel better.
- Call your doctor if symptoms don’t improve in 2-3 days.
- Don’t save leftovers - dispose of them safely at your pharmacy.
Antibiotics like Co-Amoxiclav save lives - but only when used correctly. Understanding how it works, when it’s needed, and how to take it safely means you’re not just following a prescription. You’re helping protect yourself and others from the growing threat of antibiotic resistance.
