Plain amoxicillin on its own is not a recommended treatment for impetigo. The reason comes down to resistance: the bacteria most commonly responsible for impetigo can break down amoxicillin before it works. However, amoxicillin combined with clavulanic acid (sold as Augmentin) is a standard oral treatment and works well against the infection.
Why Plain Amoxicillin Falls Short
Impetigo is caused primarily by Staphylococcus aureus, sometimes alongside Group A Streptococcus. The problem is that over 95% of S. aureus strains in the U.S. produce an enzyme called beta-lactamase, which chews up amoxicillin’s active structure before it can kill the bacteria. That makes plain amoxicillin ineffective in the vast majority of impetigo cases.
Even when strep bacteria are involved, clinical guidelines advise against using amoxicillin or other penicillins that are vulnerable to beta-lactamase. Since lab cultures often aren’t done before treatment starts, and both staph and strep frequently coexist in the same sores, prescribing plain amoxicillin means risking treatment failure.
How Amoxicillin-Clavulanate Works
Clavulanic acid has almost no bacteria-killing ability on its own, but it acts as a shield for amoxicillin. It binds to the beta-lactamase enzyme and deactivates it, so amoxicillin can do its job of destroying the bacterial cell wall. This combination covers both staph and strep reliably, which is why it’s listed alongside cephalexin and dicloxacillin as a first-line oral antibiotic for impetigo.
For adults, the typical course is one 500 mg tablet every 12 hours. For children three months and older with mild to moderate skin infections, dosing is weight-based. The standard course lasts five days, though it can be extended if sores haven’t improved by then.
When You Actually Need Oral Antibiotics
Not every case of impetigo requires a pill. Localized, non-bullous impetigo (the more common type, with honey-colored crusts) is best treated with a topical antibiotic like mupirocin, applied directly to the sores for five to seven days. Soaking crusts in warm water before applying the ointment can help relieve itching, though removing crusts isn’t strictly necessary.
Oral antibiotics like amoxicillin-clavulanate become necessary when:
- There are more than five lesions or they cover a wide area
- The infection is bullous impetigo (large, fluid-filled blisters rather than small crusted sores)
- There are signs of deeper infection, such as swollen lymph nodes, fever, or involvement of tissue beneath the skin
- Multiple people are affected in a household, childcare setting, or sports team
Other Oral Options Besides Amoxicillin-Clavulanate
Cephalexin (Keflex) is probably the most commonly prescribed oral antibiotic for impetigo. Like amoxicillin-clavulanate, it resists beta-lactamase and covers both staph and strep. Dicloxacillin is another option. All three belong to the beta-lactam family but are designed to withstand the enzyme that renders plain amoxicillin useless.
If a culture confirms the infection is caused purely by streptococcus with no staph involvement, oral penicillin alone can work. But this scenario is uncommon enough that most providers start with broader coverage.
What to Expect During Treatment
Once you start antibiotics, you’re generally no longer contagious after 48 hours. Children should stay home from school or daycare for those first two days. Sores typically begin drying out and shrinking within the first few days of treatment, and most cases resolve fully within one to two weeks.
If lesions clear up but new ones appear shortly after, that usually means the bacteria were reintroduced, often from scratching insect bites or touching the original sores. Keeping fingernails short, washing hands frequently, and avoiding shared towels or clothing all reduce the chance of spreading or re-seeding the infection. If sores haven’t improved after five days of antibiotics, the course may need to be extended or the antibiotic switched based on culture results.
The Strep Complication Worth Knowing About
When impetigo is caused by certain strains of Group A Streptococcus, there’s a small risk of a kidney condition called post-streptococcal glomerulonephritis. It typically shows up one to two weeks after the skin infection and can cause dark or cola-colored urine, swelling in the face or ankles, and reduced urine output. Prompt antibiotic treatment of impetigo helps reduce the spread of strep but hasn’t been definitively proven to prevent this complication in the individual patient. Still, treating the infection quickly limits how much the bacteria can multiply and spread to others, which lowers community-level risk.