Co-amoxiclav
Is It Right for You?
A complete guide to Co-amoxiclav — 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 and clavulanic acid. Amoxicillin is a broad-spectrum penicillin antibiotic that targets a wide range of bacteria, while clavulanic acid is a beta-lactamase inhibitor – a compound that protects amoxicillin from being destroyed by the enzymes produced by resistant bacteria. Together, they form a significantly more powerful antibiotic than amoxicillin alone, effective against a broader range of bacterial infections including those caused by organisms that would otherwise resist standard penicillin treatment.
Co-amoxiclav is widely available under the brand name Augmentin and has been in clinical use since the 1980s. It is one of the most commonly prescribed antibiotics in UK primary and secondary care settings and is available in tablet, dispersible tablet, and oral suspension forms, as well as intravenous preparations for hospital use. It is suitable for adults and children of all ages.
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 a wide range of bacterial infections where organisms resistant to standard amoxicillin are suspected or confirmed:
acute otitis media, particularly where first-line treatment has failed or where a more resistant organism is suspected.
acute bacterial sinusitis, including cases caused by beta-lactamase-producing organisms.
community-acquired pneumonia, including aspiration pneumonia; acute exacerbations of chronic bronchitis; hospital-acquired pneumonia in step-down oral therapy.
Complicated UTIs and those caused by beta-lactamase-producing organisms such as Klebsiella and E. coli strains resistant to amoxicillin alone.
cellulitis, infected wounds, animal and human bites (a key indication), and diabetic foot infections where mixed bacterial flora including resistant organisms is likely.
dental abscesses and severe dental infections caused by oral bacteria including anaerobes.
osteomyelitis and septic arthritis in combination or as step-down oral therapy.
pelvic inflammatory disease and post-surgical infections in combination with other antibiotics.
used as part of combination regimens for peritonitis and abdominal sepsis.
Co-amoxiclav does not cover meticillin-resistant Staphylococcus aureus (MRSA). If MRSA is suspected or confirmed, specialist antibiotics will be required. Your clinician will assess the likelihood of MRSA based on your history and circumstances.
How Does Co-amoxiclav Work?
Co-amoxiclav works through a dual mechanism combining the antibacterial activity of amoxicillin with the protective action of clavulanic acid.
Amoxicillin is a beta-lactam antibiotic that works by binding to penicillin-binding proteins (PBPs) on the bacterial cell surface. These proteins are essential enzymes involved in the synthesis and cross-linking of peptidoglycan – the structural material that gives bacterial cell walls their strength and rigidity. By inhibiting these enzymes, amoxicillin prevents bacteria from building intact cell walls, causing them to become structurally unstable and ultimately rupture and die. This is a bactericidal mechanism of action.
Clavulanic acid is not itself a significant antibiotic, but it plays a critical role in protecting amoxicillin from destruction. Many bacteria produce enzymes called beta-lactamases, which break open the beta-lactam ring of penicillin antibiotics, rendering them inactive. Clavulanic acid binds irreversibly to these beta-lactamase enzymes, disabling them and allowing amoxicillin to reach its bacterial targets unimpeded. This combination effectively restores amoxicillin's activity against organisms that would otherwise be resistant, significantly widening the spectrum of bacteria that can be treated.
The result is an antibiotic that covers a broader range of bacteria than amoxicillin alone – including beta-lactamase-producing strains of Staphylococcus aureus, Haemophilus influenzae, Moraxella catarrhalis, Klebsiella species, and many anaerobes.
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
Always take co-amoxiclav at the start of a meal or with food. This is important for two reasons: it significantly reduces the risk of gastrointestinal side effects (particularly diarrhoea and nausea, which are more common with co-amoxiclav than with amoxicillin alone), and it improves the absorption of clavulanic acid.
Take doses at evenly spaced intervals throughout the day – three-times-daily dosing works best when spread approximately every 8 hours to maintain consistent antibiotic blood levels.
Shake oral suspension well before each use and store in the refrigerator. Discard unused suspension after 7 days.
Always complete the full prescribed course even if symptoms improve. Stopping early risks relapse and may contribute to antibiotic resistance.
Do not crush or chew modified-release tablets if prescribed in this form. Swallow whole with a glass of water.
Side Effects of Co-amoxiclav
Co-amoxiclav has a higher rate of gastrointestinal side effects than amoxicillin alone, primarily due to the clavulanic acid component. Most side effects are mild and manageable. Serious reactions are uncommon but require prompt medical attention.
- Diarrhoea (more common than with amoxicillin alone)
- Nausea
- Vomiting
- Abdominal discomfort or bloating
- Indigestion
- Oral or vaginal thrush (yeast overgrowth)
- Mild skin rash
- Severe allergic reaction (anaphylaxis) – sudden onset hives, facial or throat swelling, difficulty breathing, collapse
- Cholestatic jaundice and hepatitis – co-amoxiclav carries a higher risk of this serious liver reaction than most other antibiotics; symptoms include jaundice, dark urine, pale stools, and fatigue; this can occur during treatment or up to several weeks after completing the course
- Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis – rare but severe blistering skin reactions
- C. difficile-associated diarrhoea – persistent watery or bloody diarrhoea, abdominal cramping, fever
- Interstitial nephritis – rare inflammation of the kidneys presenting with reduced urine output, swelling, or fever
- Haemolytic anaemia – rare destruction of red blood cells; pallor, fatigue, breathlessness
Co-amoxiclav contains amoxicillin, a penicillin antibiotic. Do not take co-amoxiclav if you have a known allergy to penicillin or any beta-lactam antibiotic. Always disclose all drug allergies to your clinician before starting treatment.
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 kidney clearance of methotrexate, potentially raising it to toxic blood levels. This combination requires close monitoring of methotrexate levels and kidney function if concurrent use cannot be avoided.
Co-amoxiclav significantly enhances the anticoagulant effect of warfarin, raising the risk of serious bleeding. INR must be monitored closely – ideally within a few days of starting co-amoxiclav – in patients taking warfarin. Dose adjustment of warfarin may be necessary.
As with other antibiotics, co-amoxiclav may theoretically reduce the efficacy of hormonal contraceptives. Use an additional contraceptive method during treatment and for 7 days after completing the course.
Probenecid reduces the kidney excretion of amoxicillin (the amoxicillin component of co-amoxiclav), leading to higher and more sustained blood levels. This may occasionally be used intentionally by clinicians but should only occur under medical supervision.
Concurrent use of allopurinol with amoxicillin-containing antibiotics significantly increases the likelihood of a skin rash. Inform your clinician if you take allopurinol for gout.
Antibiotics may reduce the effectiveness of live bacterial vaccines. Avoid vaccination with these products during an antibiotic course unless clinically essential.
Co-amoxiclav may reduce blood levels of mycophenolate, potentially reducing immunosuppressive efficacy in transplant patients. Monitoring is advisable in patients on this medication.
Important Warnings
Co-amoxiclav is associated with a significantly higher risk of cholestatic hepatitis than most other antibiotics. This serious liver reaction can occur during treatment or up to 6–8 weeks after completing the course. Risk factors include older age, male sex, and prolonged courses. Seek immediate medical attention if you develop jaundice (yellowing of the skin or eyes), dark urine, pale stools, or persistent fatigue during or after taking co-amoxiclav. Co-amoxiclav should be avoided in patients with a history of cholestatic jaundice or hepatic impairment related to previous co-amoxiclav use.
Anaphylaxis is a rare but potentially fatal reaction to penicillin antibiotics. Symptoms include sudden hives, facial or throat swelling, difficulty breathing, rapid heart rate, and collapse. If these occur, stop taking co-amoxiclav immediately and call 999.
Co-amoxiclav is one of the antibiotics most commonly associated with Clostridioides difficile infection. The clavulanic acid component significantly disrupts gut flora, making CDAD more likely than with many other antibiotics. If you develop persistent, watery, or bloody diarrhoea during or after treatment, contact a clinician promptly. Do not self-treat with anti-diarrhoeal medications.
Diarrhoea and nausea are notably more common with co-amoxiclav than with amoxicillin alone, due to the effects of clavulanic acid on gut motility and flora. Always take co-amoxiclav with food at the start of a meal to minimise these effects. If diarrhoea is severe or persistent, contact your clinician.
Patients with significantly reduced kidney function may require dose adjustment or an alternative antibiotic. The amoxicillin component is primarily excreted by the kidneys and can accumulate to toxic levels in renal impairment. Always disclose any history of kidney disease before starting co-amoxiclav.
Co-amoxiclav is generally used during pregnancy only when clearly necessary. There is some data suggesting a possible association between co-amoxiclav use in premature labour and a risk of necrotising enterocolitis in the newborn, and it is therefore not recommended as the first-line antibiotic during pregnancy unless specifically indicated. Amoxicillin alone is often preferred. It passes into breast milk in small amounts. Always inform your clinician if you are pregnant or breastfeeding.
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
Yes. A licensed clinician can assess your symptoms via a telehealth consultation and prescribe co-amoxiclav if it is clinically appropriate. Prescriptions are typically sent to your preferred pharmacy the same day, often within minutes of your consultation.
No. Because hyoscine butylbromide does not cross the blood-brain barrier, it does not cause sedation or drowsiness. This makes it safe to take when driving or operating machinery, unlike some other medications used for pain or nausea.
Amoxicillin is a broad-spectrum penicillin antibiotic, while co-amoxiclav contains amoxicillin plus clavulanic acid. Clavulanic acid protects the amoxicillin from being destroyed by beta-lactamase enzymes produced by resistant bacteria, significantly broadening the range of infections that can be treated. Co-amoxiclav is used when the infection is caused by, or likely to involve, organisms resistant to amoxicillin alone.
The clavulanic acid component of co-amoxiclav has a direct effect on gut motility and significantly disrupts the balance of the intestinal microbiome, making diarrhoea and other gastrointestinal side effects more common than with amoxicillin alone. Taking co-amoxiclav with food at the start of a meal helps reduce these effects.
Yes. Augmentin is the most well-known brand name for co-amoxiclav. The generic term co-amoxiclav and the brand name Augmentin refer to the same combination antibiotic containing amoxicillin and clavulanic acid.
Yes. Animal and human bites are a key indication for co-amoxiclav, as bite wound infections typically involve a mixed flora of bacteria including anaerobes and organisms that produce beta-lactamases. Co-amoxiclav's broad spectrum including anaerobic coverage makes it the antibiotic of choice for bite wound prophylaxis and treatment in UK guidelines.
There is no known dangerous interaction between alcohol and co-amoxiclav. However, alcohol can impair the immune system and slow recovery from infection, and may worsen the gastrointestinal side effects of co-amoxiclav. It is advisable to avoid or minimise alcohol consumption during treatment.
Co-amoxiclav is used in pregnancy in specific circumstances, but it is not the first-line antibiotic choice during pregnancy due to concerns about a potential risk of necrotising enterocolitis in premature newborns when used in the context of pre-term labour. For most common infections during pregnancy, amoxicillin alone is preferred. Always inform your clinician if you are pregnant before starting any antibiotic
Take the missed dose as soon as you remember, with food. If it is almost time for your next scheduled dose, skip the missed one and continue as normal. Never take a double dose to compensate for a missed one.
Yes. Co-amoxiclav is suitable for children and is available in paediatric oral suspension formulations. Doses are calculated based on the child's weight and age. Your clinician will prescribe the appropriate formulation and dose.
Co-amoxiclav and flucloxacillin are both used for skin and soft tissue infections but have different spectrums. Flucloxacillin is specifically targeted at penicillinase-producing Staphylococcus aureus and is the preferred choice for uncomplicated staphylococcal skin infections. Co-amoxiclav has a broader spectrum covering a wider range of organisms including anaerobes and Gram-negative bacteria, making it more appropriate for bite wounds, diabetic foot infections, and mixed-flora infections.