Amox-clav is a combination antibiotic that pairs amoxicillin (a penicillin-type antibiotic) with clavulanate, an ingredient that prevents certain bacteria from resisting the antibiotic. You may see it on your prescription label as amoxicillin-clavulanate, or by its brand name Augmentin. It’s one of the most commonly prescribed antibiotics for ear infections, sinus infections, respiratory infections, urinary tract infections, skin infections, and bite wounds.
The reason this combination exists is straightforward: some bacteria have learned to fight off amoxicillin on their own, and clavulanate stops that defense mechanism in its tracks.
How It Works
Amoxicillin kills bacteria by breaking apart their cell walls. But many bacteria produce enzymes that can chew up amoxicillin before it gets the chance to work. These enzymes, called beta-lactamases, are one of the main ways bacteria become resistant to antibiotics.
Clavulanate solves this problem. It binds to those bacterial enzymes near their active site, blocking them from disabling the amoxicillin. Clavulanate doesn’t kill bacteria on its own. It simply clears the way for amoxicillin to do its job. Think of it as a bodyguard that neutralizes the bacteria’s weapon so the antibiotic can get through.
Why Not Just Use Regular Amoxicillin?
Amoxicillin alone works well against many common infections, but it has blind spots. Adding clavulanate expands its reach considerably. The combination covers bacteria that plain amoxicillin cannot touch, including staph bacteria (MSSA), a wider range of bacteria found in the gut and urinary tract, and the anaerobic bacteria commonly involved in human and animal bite wounds. Overall, amox-clav provides better coverage against both the types of bacteria that need oxygen to survive and those that don’t.
Your doctor will typically choose amox-clav over plain amoxicillin when the infection is more severe, when the bacteria involved are likely to be resistant, or when the infection site (like a bite wound) tends to harbor tougher organisms.
What It Treats
Amox-clav is FDA-approved for several types of bacterial infections:
- Sinus infections caused by resistant bacteria
- Ear infections (acute otitis media), especially common in children
- Lower respiratory tract infections like bronchitis or pneumonia
- Skin infections, including those from staph, E. coli, and related bacteria
- Urinary tract infections caused by resistant strains of E. coli and similar organisms
Doctors also frequently prescribe it off-label for bite wounds, dental infections, and certain diabetic foot infections.
Common Tablet Strengths
When you see “amox-clav 875/125” on your prescription, the first number is the amoxicillin dose and the second is the clavulanate dose. The three standard tablet strengths are 250/125, 500/125, and 875/125. Notice that the clavulanate stays at 125 mg across all three. That’s intentional: you need only a fixed amount of clavulanate to block the bacterial enzymes, while the amoxicillin dose scales up for more serious infections.
For mild to moderate infections, the typical adult dose is 500/125 every 12 hours or 250/125 every 8 hours. More severe infections or respiratory infections usually call for 875/125 every 12 hours or 500/125 every 8 hours. Children are dosed based on body weight, and kids weighing 40 kg (about 88 pounds) or more follow the adult schedule.
Taking It With Food Matters
Amox-clav works best when you take it at the start of a meal. This isn’t just about reducing stomach upset. Studies tracking how the drug absorbs show that taking it on an empty stomach significantly reduces how much amoxicillin gets into your bloodstream. The drug empties from the stomach too quickly when there’s no food, and amoxicillin absorbs poorly from the deeper parts of the intestine.
On the flip side, taking it well after finishing a meal reduces how much clavulanate you absorb, because the tablet gets trapped in the upper stomach too long. The sweet spot is right at the beginning of eating, which gives both ingredients the best chance of absorbing properly.
Side Effects
The most common side effect is diarrhea, which happens more often with amox-clav than with amoxicillin alone. The clavulanate component is the main culprit. It disrupts gut bacteria more aggressively, and many people notice loose stools within the first few days of treatment. Taking the medication with food helps reduce this.
Nausea, vomiting, and stomach pain are also common. Some people, particularly women, develop yeast infections because the antibiotic disrupts the normal balance of microorganisms in the body. Skin rashes occur in a small percentage of users. Most of these side effects are mild and resolve once you finish the course.
Liver Effects
A less common but more serious concern is liver irritation. The risk is low for most people, but it increases with prolonged or repeated courses of the drug and in adults over 65. When both of those factors are present, the risk of liver injury rises to roughly 1 in 1,000 users. Women and older adults are more susceptible to developing jaundice (yellowing of the skin or eyes) from this medication. If you notice dark urine, pale stools, or yellowing skin while taking amox-clav, that warrants prompt medical attention.
Penicillin Allergy and Amox-Clav
Since amoxicillin is a penicillin, people with a true penicillin allergy should not take amox-clav. However, the allergy picture is more nuanced than many people realize. Up to 80% of beta-lactam allergy cases involve amoxicillin-clavulanate, but recent research has revealed that clavulanate itself can be the trigger in over a third of confirmed allergic reactions. Clavulanate generates its own allergic markers that are distinct from penicillin and amoxicillin, meaning some people who react to amox-clav may actually tolerate plain amoxicillin just fine.
If you’ve had a reaction to amox-clav in the past, allergy testing can help determine whether the culprit was the amoxicillin, the clavulanate, or both. This distinction matters because it affects which antibiotics are safe for you in the future.