Co-amoxiclav (Amoxicillin/Clavulanic Acid)
Is It Right for You?
A complete guide to Co-amoxiclav (Amoxicillin/Clavulanic Acid) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Co-amoxiclav?
Co-amoxiclav is a combination antibiotic containing two active ingredients: amoxicillin, a broad-spectrum penicillin antibiotic, and clavulanic acid, a beta-lactamase inhibitor. Together, they form a powerful combination that is effective against a wider range of bacteria than amoxicillin alone -- including many strains that have developed resistance to standard penicillin antibiotics.
Clavulanic acid itself has little direct antibacterial activity. Its role is to block the beta-lactamase enzymes that certain bacteria produce to break down and neutralise amoxicillin. By disabling these enzymes, clavulanic acid restores amoxicillin's effectiveness against resistant organisms, significantly broadening the spectrum of treatable infections.
Co-amoxiclav is available in tablet, dispersible tablet, and oral suspension forms and is approved for use in both adults and children. It is widely available generically and under the brand name Augmentin.
Co-amoxiclav is a prescription-only medication in the UK. A licensed clinician must assess your symptoms and medical history before it can be prescribed -- which can now be done quickly and conveniently through a telehealth consultation.
What Conditions Is Co-amoxiclav Used For?
Co-amoxiclav is prescribed for bacterial infections that are caused by organisms resistant to amoxicillin alone, or where a broader spectrum of cover is required:
community-acquired pneumonia, acute exacerbations of chronic bronchitis, and lung infections caused by beta-lactamase-producing organisms.
acute bacterial sinusitis, tonsillitis, and otitis media (ear infections) that have not responded to first-line antibiotics or where resistant organisms are suspected.
including complicated UTIs and those caused by resistant bacteria not covered by simpler antibiotics such as trimethoprim.
Co-amoxiclav is an antibiotic and has no effect on viruses. It will not treat the common cold, influenza, COVID-19, or other viral illnesses. Using antibiotics unnecessarily contributes to antibiotic resistance. A clinician can help determine whether your infection is bacterial and which antibiotic is most appropriate.
How Does Co-amoxiclav Work?
Co-amoxiclav works through the combined action of its two components, each targeting bacterial resistance at a different level.
Amoxicillin is a beta-lactam antibiotic that works by binding to penicillin-binding proteins (PBPs) on the surface of bacteria. This disrupts the final stage of bacterial cell wall synthesis -- the cross-linking of peptidoglycan strands that gives the cell wall its structural integrity. Without a stable cell wall, bacteria cannot survive or divide, and the cells rupture and die. This is a bactericidal (bacteria-killing) mechanism.
Clavulanic acid works by acting as a suicide inhibitor of beta-lactamase enzymes. Many bacteria have developed resistance to penicillin antibiotics by producing these enzymes, which chemically break open the beta-lactam ring of amoxicillin and render it inactive. Clavulanic acid has a similar structure to beta-lactam antibiotics and binds irreversibly to beta-lactamase enzymes, permanently inactivating them before they can destroy amoxicillin. This restores amoxicillin's full antibacterial activity against resistant strains.
Together, this dual mechanism extends co-amoxiclav's effectiveness to include beta-lactamase-producing strains of organisms such as Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Klebsiella species, Staphylococcus aureus, and many anaerobic bacteria -- organisms that would otherwise be resistant to amoxicillin alone.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Co-amoxiclav should be taken at the start of a meal. Taking it with food significantly reduces the risk of gastrointestinal side effects -- particularly nausea and diarrhoea -- and also improves the absorption of clavulanic acid.
Space doses evenly throughout the day. If taking three times daily, try to space doses approximately 8 hours apart (e.g. 7am, 3pm, 11pm) to maintain consistent antibiotic levels.
Shake oral suspension well before each use and store in the refrigerator. Discard any unused suspension after 7 days.
Complete the full prescribed course even if symptoms improve before the course ends. Stopping early can allow surviving bacteria to multiply and potentially develop resistance, leading to a harder-to-treat relapse.
Do not take co-amoxiclav if you have had jaundice or liver problems associated with previous use of co-amoxiclav or amoxicillin, as repeated exposure significantly increases the risk of hepatotoxicity.
Side Effects of Co-amoxiclav
Co-amoxiclav is generally well tolerated, though gastrointestinal side effects are more common than with amoxicillin alone, largely due to the clavulanic acid component. Serious side effects are uncommon but require prompt medical attention.
- Diarrhoea (the most commonly reported side effect)
- Nausea or stomach upset
- Vomiting
- Skin rash
- Headache
- Oral or vaginal thrush (candidiasis)
- Indigestion or abdominal discomfort
- Severe allergic reaction (anaphylaxis) -- sudden onset hives, facial or throat swelling, difficulty breathing, or circulatory collapse; requires immediate emergency treatment
- Cholestatic jaundice and hepatitis -- jaundice, dark urine, pale stools, severe fatigue, right upper abdominal pain; can occur during or up to several weeks after completing treatment; more common in older male patients and with prolonged courses
- Severe skin reactions -- Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis; widespread blistering and peeling of skin and mucous membranes
- C. difficile-associated diarrhoea -- persistent watery or bloody diarrhoea with cramping and fever; can range from mild colitis to life-threatening pseudomembranous colitis
- Seizures -- rare; more likely at very high doses or in patients with renal impairment or pre-existing seizure disorder
Co-amoxiclav contains amoxicillin and must not be taken by anyone with a known allergy to penicillin or other beta-lactam antibiotics. Cross-reactivity with cephalosporins is possible. Always disclose all known drug allergies to your clinician before being prescribed co-amoxiclav.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting co-amoxiclav.
Co-amoxiclav can reduce the renal excretion of methotrexate, causing its levels to rise to potentially toxic concentrations. This combination requires close monitoring and should generally be avoided. If concurrent use is unavoidable, more frequent blood monitoring is essential.
As with other broad-spectrum antibiotics, there is a theoretical risk that co-amoxiclav may reduce the effectiveness of hormonal contraception by altering gut bacteria involved in oestrogen recycling. Use additional contraceptive precautions (e.g. condoms) during the course of treatment.
Co-amoxiclav, like other antibiotics, may reduce the immune response to certain live bacterial vaccines. Avoid vaccination during an antibiotic course unless clinically necessary.
Co-amoxiclav may reduce the absorption and blood levels of mycophenolate in transplant patients, potentially affecting immunosuppressive efficacy. Monitoring is advisable.
Important Warnings
Co-amoxiclav carries a higher risk of causing cholestatic jaundice and hepatitis than most other antibiotics, particularly with prolonged courses or repeat prescriptions. This reaction can occur during treatment or up to 6 weeks after completing a course. Do not take co-amoxiclav if you have previously experienced jaundice or liver dysfunction associated with its use. Report any symptoms of liver problems to your clinician immediately.
Antibiotic use can disrupt normal gut flora and allow Clostridioides difficile to overgrow, causing colitis ranging from mild diarrhoea to life-threatening pseudomembranous colitis. If you develop persistent, watery, or bloody diarrhoea during or after treatment, contact a clinician promptly. Do not use anti-diarrhoeal medications without medical advice in this context.
Patients with significantly reduced kidney function require dose adjustment, as both amoxicillin and clavulanic acid are primarily excreted by the kidneys. Accumulation can increase the risk of side effects including seizures. Always disclose your full medical history, including any kidney conditions, during your consultation.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Co-amoxiclav FAQs
Clavulanic acid is better absorbed when taken with food, and taking co-amoxiclav at the start of a meal also significantly reduces the risk of nausea and diarrhoea -- the most commonly reported side effects. Unlike many antibiotics that can be taken on an empty stomach, food intake is specifically recommended with co-amoxiclav.
No. Co-amoxiclav contains amoxicillin, which is a penicillin antibiotic. If you have a confirmed allergy to penicillin or other beta-lactam antibiotics, you must not take co-amoxiclav. Always inform your clinician of any known drug allergies so an appropriate alternative can be prescribed.