The best antibiotic for a bacterial sinus infection is amoxicillin-clavulanate, often sold under the brand name Augmentin. It’s the recommended first-line treatment for adults based on guidelines from the Infectious Diseases Society of America. But here’s the important caveat: most sinus infections are viral, meaning antibiotics won’t help at all. Knowing when you actually need an antibiotic matters just as much as knowing which one to take.
Most Sinus Infections Don’t Need Antibiotics
The majority of sinus infections are caused by viruses, not bacteria. They feel miserable, but they resolve on their own within 7 to 10 days. During that time, over-the-counter pain relievers, saline nasal rinses, and decongestants can help manage symptoms.
A sinus infection is likely bacterial, and worth treating with antibiotics, in three specific scenarios: your symptoms persist for 10 days or longer without any improvement; you develop a fever of 102°F or higher along with nasal discharge and facial pain lasting 3 to 4 days; or your symptoms start to improve after 4 to 7 days and then suddenly get worse again. That last pattern, sometimes called “double worsening,” is a strong signal that bacteria have taken hold of what started as a viral infection.
Why Amoxicillin-Clavulanate Is First Choice
Amoxicillin alone used to be the go-to antibiotic for sinus infections, but resistance patterns have shifted. One of the main bacteria responsible for sinus infections, Streptococcus pneumoniae, has become harder to treat. Roughly 2 in 5 pneumococcal infections now involve strains that are resistant to at least one antibiotic, according to CDC data. The CDC classifies antibiotic-resistant S. pneumoniae as a serious threat.
Amoxicillin-clavulanate addresses this problem. The clavulanate component blocks a defense mechanism that some bacteria use to neutralize amoxicillin, making the antibiotic effective against a broader range of resistant strains. This is why current guidelines favor it over plain amoxicillin for both adults and children.
The standard adult dose is 875 mg of the amoxicillin component with 125 mg of clavulanate, taken twice daily. In cases where resistance is a greater concern (for example, if you’ve recently taken antibiotics or live in an area with high resistance rates), your doctor may prescribe a high-dose version: 2,000 mg of amoxicillin with 125 mg of clavulanate, twice daily. For adults, the typical course lasts 5 to 7 days. Children usually need a longer course of 10 to 14 days.
Alternatives If You’re Allergic to Penicillin
Amoxicillin-clavulanate is a penicillin-type antibiotic, so it’s off the table if you have a penicillin allergy. In that case, doxycycline is the most commonly recommended alternative, taken at 100 mg twice daily.
If your allergy is mild enough that you can still tolerate cephalosporins (a related but different class of antibiotics), there are additional options. Third-generation cephalosporins like cefixime or cefpodoxime can work, sometimes combined with another antibiotic for broader coverage. Your prescriber can help determine whether cephalosporins are safe for you based on the type of allergic reaction you’ve had in the past.
Fluoroquinolones like levofloxacin or moxifloxacin are reserved as a last resort. While effective against sinus pathogens, these drugs carry a risk of serious side effects, including tendon damage, nerve problems, and mood changes. For a straightforward sinus infection, those risks generally outweigh the benefits when other options are available.
Managing Side Effects
The most common side effects of amoxicillin-clavulanate are digestive: diarrhea, upset stomach, and occasionally vomiting. The clavulanate component is the usual culprit. Taking the medication with a meal or snack significantly reduces the chance of stomach upset.
Mild diarrhea during treatment is normal and usually manageable. However, watery or bloody stools, stomach cramps, or fever during or even weeks after finishing the course can signal a more serious gut infection and need medical attention. Vaginal yeast infections are also a common side effect, since the antibiotic disrupts the normal balance of bacteria throughout the body.
What Affects Your Antibiotic Choice
While amoxicillin-clavulanate is the standard recommendation, several factors can change what’s best for you specifically. People who have recently taken antibiotics are more likely to harbor resistant bacteria, which may call for a high-dose regimen or a different drug class entirely. Certain chronic conditions, a history of recurrent sinus infections, or prior antibiotic failures also influence the decision.
Geography plays a role too. Resistance patterns vary by region, and clinicians in areas with high rates of resistant bacteria may adjust their prescribing accordingly. If you’ve been prescribed an antibiotic for a sinus infection and your symptoms haven’t improved after 3 to 5 days on treatment, the original antibiotic may not be covering the bacteria involved, and a switch may be warranted.
One thing that doesn’t help: asking for a stronger or broader-spectrum antibiotic “just in case.” Unnecessary antibiotic use is one of the main drivers of resistance. Narrow, targeted therapy that matches the likely bacteria is both more effective for you and better for public health in the long run.