Amoxicillin clavulanate is a combination antibiotic that pairs amoxicillin (a penicillin-type antibiotic) with clavulanic acid, an ingredient that prevents certain bacteria from resisting the antibiotic. It’s sold under the brand name Augmentin and is one of the most commonly prescribed antibiotics for sinus infections, ear infections, urinary tract infections, and several other bacterial infections.
How the Two Ingredients Work Together
Amoxicillin on its own is effective against many types of bacteria, but some bacteria have learned to defend themselves. They produce enzymes called beta-lactamases that break down amoxicillin before it can do its job. This is where clavulanic acid comes in: it binds to those enzymes near their active site and blocks them, essentially disarming the bacteria’s defense system. With the enzymes neutralized, amoxicillin can work normally.
This combination exists specifically for infections caused by bacteria that produce these protective enzymes. If a bacterial infection is already susceptible to plain amoxicillin, the combination isn’t necessary and shouldn’t be used.
What It Treats
Amoxicillin clavulanate is FDA-approved for a specific set of infections caused by resistant bacteria:
- Sinus infections
- Ear infections (acute bacterial otitis media, especially common in children)
- Lower respiratory tract infections, including some forms of pneumonia and bronchitis
- Skin infections, including wound infections and cellulitis
- Urinary tract infections
The drug also has good activity against anaerobic bacteria, the type that thrive in low-oxygen environments like deep wound infections or abscesses. This broader coverage is one reason doctors reach for it over plain amoxicillin in certain situations, particularly bite wounds, dental infections, and complicated skin infections.
Available Forms and Dosing Ratios
Amoxicillin clavulanate comes in tablets, chewable tablets, and a liquid suspension. The tablets are available in different strengths, but they all contain more amoxicillin than clavulanic acid. The most common adult tablet is 875 mg of amoxicillin paired with 125 mg of clavulanic acid, a 7:1 ratio. This ratio matters because the amount of clavulanic acid is what drives most of the gastrointestinal side effects, so formulations are designed to keep it as low as effective.
The liquid suspension, commonly prescribed for children, comes in a similar 7:1 ratio (400 mg amoxicillin to 57 mg clavulanic acid per 5 mL). Different tablet strengths are not interchangeable. Two 500 mg tablets are not the same as one 1,000 mg tablet because they’d deliver double the clavulanic acid.
Common Side Effects
The most frequent side effect is diarrhea or loose stools, affecting roughly 9 to 15% of people depending on the dose and schedule. Nausea occurs in about 3% of users, vomiting in about 1%, and skin rashes in about 3%. Taking the medication at the start of a meal can help reduce stomach upset and improve absorption of the clavulanic acid component.
Higher doses tend to cause more GI problems. In clinical trials comparing dosing schedules, the twice-daily 875 mg regimen produced less severe diarrhea than the three-times-daily 500 mg regimen, even though the total daily amoxicillin was similar. The key difference was the total daily amount of clavulanic acid. If diarrhea becomes persistent or severe, it’s worth contacting your prescriber rather than just powering through the course.
Liver-Related Concerns
In rare cases, amoxicillin clavulanate can cause liver inflammation. This is an uncommon but well-documented reaction tied specifically to the clavulanic acid component, not the amoxicillin. Symptoms can include yellowing of the skin or eyes, dark urine, or unusual fatigue. Anyone who has previously experienced liver problems from this drug should not take it again, as re-exposure can trigger the same injury.
Who Should Avoid It
People with a known penicillin allergy should not take amoxicillin clavulanate, since amoxicillin belongs to the penicillin family. Anyone who has had a previous liver reaction to this specific combination should also avoid it permanently. If you’ve had allergic reactions to other antibiotics in the cephalosporin class, mention this to your prescriber, as there can be some cross-reactivity.
Storing the Liquid Form
If you or your child is prescribed the liquid suspension, it needs to be refrigerated after the pharmacist mixes it. The dry powder can be stored at room temperature, but once reconstituted, it must stay in the fridge and be discarded after 10 days. Shake the bottle well before each dose, and use the measuring syringe provided rather than a kitchen spoon for accuracy.