Amoxicillin-clavulanate is the top recommended antibiotic for a bacterial sinus infection in adults. It has an efficacy rate above 90% against the bacteria most commonly responsible for sinusitis. But here’s the important catch: most sinus infections are viral, not bacterial, and antibiotics won’t help a viral infection at all. Knowing the difference matters before any prescription enters the picture.
Most Sinus Infections Don’t Need Antibiotics
The vast majority of sinus infections start as viral illnesses, essentially a cold that settles into your sinuses. These typically improve on their own within 7 to 10 days. Prescribing antibiotics for a viral sinus infection doesn’t speed recovery and contributes to antibiotic resistance, which is a growing problem. One of the bacteria that causes sinus infections, Streptococcus pneumoniae, already shows resistance to common antibiotics like macrolides in over 40% of non-invasive samples tested in the U.S.
A bacterial sinus infection is diagnosed based on specific patterns, not just how miserable you feel. Clinicians look for one of three scenarios:
- Persistent symptoms lasting 10 days or more without improvement
- Severe onset with a fever of 102°F or higher, along with thick discolored nasal discharge or facial pain, for at least three consecutive days
- Double worsening, where symptoms start to get better after five or six days and then suddenly get worse again (new fever, increased headache, or worsening discharge)
If your symptoms don’t fit any of these three patterns, your infection is almost certainly viral, and an antibiotic won’t help.
First-Line Antibiotic for Adults
When a bacterial sinus infection is confirmed, amoxicillin-clavulanate is the standard first choice. It combines a penicillin-type antibiotic with an ingredient that overcomes one of the main ways bacteria resist it. The typical course for adults runs 7 to 10 days, and it’s usually taken twice daily. Your prescriber may choose a standard or high-dose version depending on how severe your symptoms are and local resistance patterns in your area.
Plain amoxicillin (without the clavulanate) is sometimes still prescribed, particularly for children, but the combination version is generally preferred for adults because it covers a broader range of bacteria, including strains that have developed resistance to amoxicillin alone.
The most common side effect is digestive upset, particularly diarrhea. Taking it with food helps. Even if you feel significantly better after a few days, finishing the full course is important. Stopping early can allow surviving bacteria to rebound, potentially creating a harder-to-treat infection.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, doxycycline is the go-to alternative. The typical adult dose is 100 mg twice daily. It’s effective against the same bacteria that cause sinus infections and avoids the penicillin family entirely.
Most people who report a penicillin allergy can actually tolerate a related class of antibiotics called cephalosporins safely. If your allergic reaction was mild (a rash years ago, for example), your doctor may offer a third-generation cephalosporin instead. These are sometimes combined with another antibiotic to broaden coverage.
Fluoroquinolones like levofloxacin and moxifloxacin also have efficacy rates above 90% for bacterial sinusitis, but they carry a risk of serious side effects including tendon damage, nerve problems, and mood changes. Because of this, they’re reserved for situations where no other option works. They are not a casual backup choice.
Antibiotics for Children
For kids, high-dose amoxicillin is the first-line treatment, dosed by weight at 80 to 90 mg per kilogram per day, split into two doses. The high-dose approach is recommended because more than 10% of the Streptococcus pneumoniae bacteria found in children show reduced susceptibility to standard-dose amoxicillin.
If a child has already taken amoxicillin in the past month, or if symptoms don’t improve after starting it, the next step is high-dose amoxicillin-clavulanate. For children with penicillin allergies, options include cephalosporins like cefdinir or cefpodoxime, or doxycycline dosed by weight.
Supportive Care Alongside Antibiotics
Antibiotics target the bacteria, but they don’t directly relieve the pressure, congestion, and pain that make sinus infections so uncomfortable. A few simple additions can make a noticeable difference while the antibiotic does its work.
Saline nasal spray or a neti pot rinse physically flushes mucus and irritants out of your nasal passages. Using saline several times a day keeps things moving and reduces that heavy, clogged feeling. If you use a neti pot, always use distilled or previously boiled water to avoid introducing new organisms into your sinuses.
Nasal corticosteroid sprays (like fluticasone or budesonide, available over the counter) reduce the swelling inside your nasal passages that traps mucus in the first place. They work best when used consistently rather than as a one-time measure. These sprays are safe to use alongside antibiotics and can shorten the time it takes to feel noticeably better.
What to Expect During Treatment
Most people start feeling improvement within 48 to 72 hours of starting the right antibiotic. If you don’t notice any change after three to five days, that’s a signal to contact your prescriber. It could mean the bacteria involved are resistant to the chosen antibiotic, or the diagnosis may need revisiting.
Recurrent sinus infections, four or more episodes per year, sometimes point to an underlying issue like nasal polyps, a deviated septum, or an immune system problem. In those cases, treatment shifts from managing individual infections to figuring out why they keep happening, which may involve imaging or a referral to an ear, nose, and throat specialist.