Amoxicillin is the first-line antibiotic for bacterial sinus infections in both adults and children. It’s effective against the most common bacteria responsible for sinusitis, it’s inexpensive, and it has relatively few side effects. Your doctor may prescribe it alone or combined with clavulanate (a compound that helps it work against resistant bacteria), typically for 5 to 10 days.
That said, most sinus infections are viral and don’t need antibiotics at all. The antibiotic question only matters once your infection meets specific criteria suggesting bacteria are involved.
When a Sinus Infection Actually Needs Antibiotics
Roughly 90% of sinus infections start as viral illnesses, and antibiotics won’t help with those. Clinical guidelines from the Infectious Diseases Society of America identify three patterns that signal a bacterial infection worth treating:
- Persistent symptoms: Congestion, facial pressure, and nasal discharge lasting 10 or more days with no improvement.
- Severe onset: High fever (102°F or higher) along with purulent nasal discharge or facial pain for at least three consecutive days at the start of the illness.
- Double-sickening: Symptoms that initially improve over five to six days, then suddenly worsen again with returning fever, increased headache, or heavier nasal discharge.
If your sinus infection fits one of these patterns, antibiotic treatment is recommended at the time of diagnosis. If you’re still in the first week with mild to moderate symptoms that are gradually improving, you’re likely dealing with a virus that will resolve on its own.
First-Line Antibiotic: Amoxicillin
Amoxicillin, with or without clavulanate, is the standard starting point for adults. Your doctor will choose between the two based on local resistance patterns and your risk factors. The clavulanate version is generally preferred if you’ve taken amoxicillin recently, if your symptoms are more severe, or if you live in an area where resistant bacteria are more common.
For children, guidelines recommend high-dose amoxicillin because a significant percentage of the bacteria that cause pediatric sinusitis have some degree of resistance to standard doses. If a child has already taken amoxicillin in the past month or isn’t improving on it, the combination with clavulanate is the next step.
A typical course lasts 5 to 10 days. Shorter courses work for many uncomplicated cases, while longer courses are reserved for infections that are slower to respond.
Alternatives if You Have a Penicillin Allergy
If you’re allergic to penicillin, doxycycline is the most straightforward alternative. It covers the same bacteria and is taken twice daily (or once daily at a higher dose).
Most people who believe they’re allergic to penicillin can actually tolerate cephalosporins, a related class of antibiotics. If that applies to you, third-generation cephalosporins like cefixime or cefpodoxime are solid options. Your doctor can help determine whether your allergy history makes cephalosporins safe to try. For severe penicillin allergies where cephalosporins are also off the table, doxycycline remains the go-to choice.
What Happens When the First Antibiotic Doesn’t Work
If your symptoms haven’t improved within 48 to 72 hours of starting an antibiotic, or they persist beyond 10 to 14 days of treatment, second-line options come into play. This doesn’t necessarily mean the infection is dangerous. It usually means the specific bacteria involved are resistant to the first drug, or the antibiotic isn’t reaching the infection effectively.
Second-line choices typically include amoxicillin-clavulanate (if you started on plain amoxicillin), second- or third-generation cephalosporins, or macrolide antibiotics. If your infection has a dental origin or your nasal discharge has a foul smell, anaerobic bacteria are likely involved, which requires different coverage.
Common Side Effects to Expect
Amoxicillin and amoxicillin-clavulanate are generally well tolerated, but digestive side effects are common. Diarrhea, upset stomach, and nausea are the most frequent complaints. The clavulanate component tends to cause more stomach issues than plain amoxicillin, so taking it with food helps. Vaginal yeast infections are also possible, since antibiotics disrupt normal bacterial balance.
Serious reactions are uncommon but worth knowing about. A rash, difficulty breathing, or facial swelling could signal an allergic reaction that needs immediate attention. Liver problems are a rare but known risk, particularly with amoxicillin-clavulanate. Signs to watch for include yellowing of the skin or eyes, dark urine, or unusual fatigue. If you’ve had liver issues with this drug before, your doctor will choose a different antibiotic entirely.
Symptom Relief While Antibiotics Work
Antibiotics target the bacteria, but they won’t immediately relieve the pressure, congestion, and pain that make sinus infections miserable. Most people start feeling better within two to three days, but full resolution can take the entire course. In the meantime, a few strategies can make the wait more bearable.
Saline nasal irrigation (using a neti pot or squeeze bottle) physically flushes mucus and reduces congestion without medication. Over-the-counter nasal steroid sprays reduce inflammation in the sinus passages. Decongestant sprays work faster but should be limited to three days to avoid rebound congestion. Warm compresses over the sinuses, staying well hydrated, and sleeping with your head slightly elevated all help with drainage and comfort.