Roughly one in four outpatient antibiotic prescriptions in the United States is for amoxicillin or its reinforced cousin, amoxicillin-clavulanate. The amoxicillin clavulanate vs amoxicillin decision comes down to one question: does the suspected bacteria produce an enzyme called beta-lactamase that inactivates plain amoxicillin? If yes, clavulanate is added to shield the drug. For a broader look at infection care, see our medical conditions guide. Plain amoxicillin is narrower, cheaper, and better tolerated; amoxicillin-clavulanate (sold as Augmentin) treats tougher infections at the cost of more stomach upset.
Quick Comparison at a Glance
Amoxicillin is a single-ingredient aminopenicillin. Amoxicillin-clavulanate combines amoxicillin with potassium clavulanate, a beta-lactamase inhibitor that has almost no antibacterial activity on its own but protects amoxicillin from enzymatic destruction. According to the FDA Augmentin label, common adult formulations include 500/125 mg every 8 hours and 875/125 mg every 12 hours. Plain amoxicillin is typically dosed 500 mg every 8 hours or 875 mg every 12 hours for most infections.
How Each Antibiotic Works
Both drugs kill bacteria by binding penicillin-binding proteins and disrupting cell wall synthesis, leading to bacterial lysis. The problem is that many common pathogens, including many strains of Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus (methicillin-sensitive), and anaerobes like Bacteroides, produce beta-lactamases that snip amoxicillin’s beta-lactam ring before it can do damage.
Clavulanate acts as a suicide inhibitor: it binds irreversibly to these enzymes, sacrificing itself so amoxicillin can reach its target. The net result is a meaningful expansion of coverage without changing the core antibiotic.
Spectrum and Effectiveness
Amoxicillin alone covers streptococci (including S. pneumoniae and group A strep), Enterococcus faecalis, Listeria, non-beta-lactamase-producing H. influenzae, and H. pylori (as part of combination therapy). It remains first-line for strep throat, dental infections in penicillin-tolerant patients, and uncomplicated otitis media in young children.
Amoxicillin-clavulanate adds meaningful coverage of beta-lactamase-producing strains, methicillin-susceptible S. aureus, and oral/bowel anaerobes. The IDSA 2012 acute bacterial rhinosinusitis guideline recommends amoxicillin-clavulanate as first-line in adults, largely because of rising beta-lactamase resistance in respiratory pathogens. It is also preferred for human and animal bite wounds, moderate diabetic foot infections, and aspiration pneumonia.
Side Effects Compared
Both drugs share the penicillin class risks: rash, hives, anaphylaxis in truly allergic patients, and rare Stevens-Johnson reactions. Gastrointestinal upset is where they differ most. Plain amoxicillin causes diarrhea in roughly 5 to 10 percent of patients. Amoxicillin-clavulanate roughly doubles that rate; clavulanate itself stimulates gut motility and alters flora more aggressively.
Amoxicillin-clavulanate also carries a higher risk of cholestatic hepatitis, a rare but real injury that usually shows up weeks after finishing the course. The NIH LiverTox database classifies it as one of the more common causes of idiosyncratic drug-induced liver injury, at roughly 1 to 17 cases per 100,000 prescriptions. Both drugs can trigger C. difficile colitis.
Dosing and How to Take It
For plain amoxicillin, adult dosing ranges from 250 mg to 875 mg every 8 to 12 hours depending on infection severity. Pediatric dosing is weight-based at 25 to 45 mg/kg/day divided, or 80 to 90 mg/kg/day for high-dose acute otitis media per AAP guidance.
Amoxicillin-clavulanate adult dosing is 500/125 mg every 8 hours, 875/125 mg every 12 hours, or extended-release 2000/125 mg every 12 hours for sinusitis. A critical rule: never double up regular strength tablets to hit a higher amoxicillin dose, because the clavulanate component has ceiling tolerability and causes more diarrhea at higher amounts. Take both drugs with food to reduce stomach upset; absorption is adequate either way.
Which Is Better for Specific Infections
Strep throat, dental abscess in a non-allergic patient, and uncomplicated urinary tract infections caused by susceptible E. coli are straightforward amoxicillin territory. Skip the clavulanate; broader coverage adds side effects without benefit.
Adult bacterial sinusitis, otitis media that fails high-dose amoxicillin, animal bites, and community-acquired aspiration pneumonia call for amoxicillin-clavulanate. The clinical rule of thumb: if you expect beta-lactamase-producing bugs, anaerobes, or skin flora from a bite, reach for the combination.
Cost and Availability
Both are generic and inexpensive. According to GoodRx, a 10-day course of generic amoxicillin 500 mg runs $4 to $15 at most US pharmacies. Generic amoxicillin-clavulanate 875/125 mg for 10 days typically runs $15 to $30, though chain pharmacy discount programs often drop it under $20. Brand-name Augmentin is several times more expensive and has no clinical advantage. Both require a prescription in the United States.
Interactions and Warnings
Amoxicillin reduces the effectiveness of oral typhoid vaccine and can give false positive urine glucose results with older Clinitest tablets. Both drugs can prolong the effect of warfarin and raise INR; monitor closely during and after treatment. Probenecid slows renal excretion of amoxicillin and raises serum levels. Allopurinol increases rash risk, especially in patients with high uric acid.
Neither should be used in patients with a true history of anaphylaxis, angioedema, or Stevens-Johnson reaction to any penicillin. A childhood “amoxicillin rash” is often a nonallergic viral or idiopathic eruption, but delabeling should be done with clinician guidance. For related reading, see our tylenol vs ibuprofen guide and our NSAID vs acetaminophen comparison for managing infection-related pain and fever.
Frequently Asked Questions
Is amoxicillin-clavulanate stronger than amoxicillin?
It is broader, not necessarily stronger. The amoxicillin dose inside Augmentin is the same amoxicillin. Clavulanate just prevents certain bacteria from destroying it, which expands the list of bugs that can be treated. Against susceptible strep, they are identical.
Why does Augmentin cause more diarrhea than plain amoxicillin?
Clavulanate stimulates gut motility and disrupts normal gut flora more aggressively than amoxicillin alone. Clinical trials show diarrhea in roughly 15 to 25 percent of patients on Augmentin versus 5 to 10 percent on plain amoxicillin.
Can I substitute amoxicillin for Augmentin if I run out?
No. If your infection requires the clavulanate component, switching to plain amoxicillin may allow beta-lactamase-producing bacteria to survive and relapse. Call your prescriber for a refill.
Does food affect absorption?
Both drugs are absorbed well with or without food, but taking them with a meal or snack reduces nausea and diarrhea, especially with Augmentin. The FDA label specifically recommends taking Augmentin at the start of a meal.
The Bottom Line
In the amoxicillin clavulanate vs amoxicillin matchup, plain amoxicillin wins on tolerability, cost, and narrow-spectrum stewardship for strep throat, dental infections, and susceptible UTIs. Amoxicillin-clavulanate is the right tool when beta-lactamase-producing bugs, anaerobes, or skin-bite flora are in play, such as adult bacterial sinusitis, bite wounds, and aspiration pneumonia. Let your clinician match the drug to the suspected pathogen rather than assuming broader coverage is automatically better; unnecessary clavulanate means more diarrhea, higher cost, and more pressure toward antibiotic resistance.