Amoxicillin, with or without clavulanate, is the first-line antibiotic for bacterial sinus infections in both adults and children. But most sinus infections are viral, which means antibiotics won’t help at all. The key question isn’t just which antibiotic to take, but whether you actually need one.
Most Sinus Infections Don’t Need Antibiotics
Around 90% of sinus infections start with a virus. They cause the same miserable symptoms as bacterial infections: congestion, facial pressure, thick nasal discharge, headache. But antibiotics do nothing against viruses, and these infections typically clear on their own within 7 to 10 days.
Your doctor may recommend a “watchful waiting” approach, giving your immune system 2 to 3 days to fight off the infection before considering antibiotics. Some providers write a prescription but ask you to wait before filling it, only using it if symptoms don’t improve. This strategy avoids unnecessary antibiotic use, which contributes to resistance and exposes you to side effects for no benefit.
When a Sinus Infection Is Bacterial
Bacterial sinusitis is diagnosed based on three specific patterns, any one of which suggests bacteria rather than a virus:
- Persistent symptoms: Congestion, facial pain, or nasal discharge lasting 10 days or more with no improvement.
- Severe onset: A high fever (102°F or higher) along with purulent nasal discharge or facial pain lasting at least 3 days from the start of illness.
- Double worsening: Symptoms that initially start to improve after 5 to 6 days, then suddenly get worse again with renewed fever, headache, or increased nasal discharge.
If your symptoms follow one of these patterns, your doctor will likely prescribe an antibiotic. There’s no routine lab test or imaging scan needed for an uncomplicated case. The diagnosis is clinical, based on your symptom timeline.
Amoxicillin Is the Standard Choice
Both the American Academy of Otolaryngology and the Infectious Diseases Society of America recommend amoxicillin with or without clavulanate as the go-to antibiotic for acute bacterial sinusitis. Clavulanate is an add-on ingredient that helps amoxicillin work against bacteria that have developed basic resistance. Your doctor may choose the combination version if you’ve recently taken antibiotics, if your symptoms are severe, or if you live in an area with higher rates of resistant bacteria.
The typical course runs 5 to 10 days for adults. Children follow the same first-line recommendation. Your doctor will determine the exact duration based on how severe your symptoms are and how quickly they respond to treatment.
If You’re Allergic to Penicillin
Amoxicillin belongs to the penicillin family, so it’s off the table if you have a penicillin allergy. The most commonly recommended alternative is doxycycline, which works well against the bacteria that cause sinus infections. Respiratory fluoroquinolones (like levofloxacin) are another option, though doctors generally reserve these for situations where other choices aren’t suitable, since they carry a higher risk of side effects.
One antibiotic you might expect to see on this list is azithromycin (the popular “Z-pack”). It’s no longer recommended for bacterial sinusitis. The bacteria most commonly responsible for sinus infections, particularly Streptococcus pneumoniae, have developed significant resistance to azithromycin and related drugs. Bacteria resistant to older versions of these medications are also resistant to the newer ones, making the entire class unreliable for this purpose.
What to Expect During Treatment
Once you start antibiotics, you should notice improvement within 2 to 3 days. Congestion and facial pressure typically begin to ease, and fever (if present) should resolve. If you don’t feel any better after 3 days on antibiotics, contact your doctor. This could mean the bacteria are resistant to the antibiotic you’re taking, or the diagnosis may need to be reconsidered.
Finish the full course even if you feel better partway through. Stopping early increases the chance that surviving bacteria regroup and cause a relapse.
Common Side Effects of Amoxicillin
Amoxicillin is generally well tolerated, but gastrointestinal symptoms are common. Nausea, vomiting, and diarrhea are the most frequent complaints. The clavulanate version tends to cause more stomach upset than plain amoxicillin, so taking it with food can help.
Less common but more serious reactions include skin rash, hives, or signs of an allergic reaction like swelling of the face, throat, or tongue, or difficulty breathing. Severe watery or bloody diarrhea can occur during treatment or even up to two months afterward, which signals a secondary gut infection that needs medical attention. If you notice any of these, stop taking the medication and seek care.
Symptom Relief While You Wait
Whether you’re on antibiotics or riding out a viral infection, supportive care makes a real difference in how you feel day to day. Saline nasal rinses (using a neti pot or squeeze bottle) help flush out thick mucus and reduce congestion without medication. Over-the-counter pain relievers manage facial pressure and headache effectively. Nasal steroid sprays can reduce the swelling inside your nasal passages that blocks drainage.
Decongestant sprays work quickly but shouldn’t be used for more than 3 days, since they cause rebound congestion that makes things worse. Oral decongestants are an option for longer use but raise blood pressure, so they’re not appropriate for everyone. Staying well hydrated and using a humidifier, especially at night, keeps mucus thinner and easier to clear.