Amoxicillin-clavulanate is the recommended first-line antibiotic for bacterial sinus infections in both adults and children. But here’s the important caveat: most sinus infections are viral, meaning antibiotics won’t help at all. Only about 2 to 10 percent of sinus infections are actually bacterial, so knowing whether you truly need an antibiotic matters just as much as knowing which one to take.
Most Sinus Infections Don’t Need Antibiotics
Sinus infections overwhelmingly start as viral illnesses, essentially a cold that inflames the sinus passages. These resolve on their own within 7 to 10 days. Three specific patterns suggest your sinus infection has become bacterial and may benefit from antibiotics:
- Persistent symptoms: Nasal congestion, facial pressure, or discharge lasting 10 days or more without any improvement.
- Severe onset: A fever of 102°F or higher along with thick nasal discharge or facial pain lasting 3 to 4 consecutive days.
- “Double sickening”: Symptoms that start to improve after 4 to 7 days and then suddenly get worse again.
If your symptoms don’t match any of these patterns, you almost certainly have a viral infection. Taking antibiotics for a viral sinus infection won’t speed your recovery and contributes to antibiotic resistance.
The First-Line Choice: Amoxicillin-Clavulanate
For adults with a confirmed or strongly suspected bacterial sinus infection, a 5 to 10 day course of amoxicillin is the standard starting treatment. If there’s concern about a resistant strain of bacteria, high-dose amoxicillin-clavulanate (amoxicillin combined with a compound that helps it work against resistant bacteria) is preferred. This combination covers the three main bacteria responsible for sinus infections more reliably than plain amoxicillin alone, which is why many clinicians now default to the combination version.
For children, the same drug is first-line. Kids with severe or worsening symptoms are typically started on antibiotics right away. For children whose symptoms have simply persisted beyond 10 days without getting worse, it’s acceptable to either start antibiotics immediately or wait and observe for 72 hours, beginning treatment only if there’s no improvement in that window.
Why the Z-Pack Isn’t Recommended
Azithromycin (the “Z-Pack”) is one of the most commonly requested antibiotics for sinus infections, but infectious disease guidelines specifically recommend against it. The reason is straightforward: the main bacterium behind most sinus infections, Streptococcus pneumoniae, has developed high rates of resistance to azithromycin and similar drugs in its class. Trimethoprim-sulfamethoxazole (commonly known as Bactrim) has the same problem. Both are considered unreliable choices, and prescribing them increases the chance of treatment failure.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, doxycycline is the most commonly recommended alternative. It’s taken twice daily and covers the relevant bacteria well. If you can tolerate cephalosporins (a related but distinct class of antibiotics that many people with penicillin allergies can safely take), a third-generation cephalosporin like cefpodoxime or cefixime is another option, sometimes paired with clindamycin for broader coverage.
It’s worth noting that many people who believe they have a penicillin allergy actually don’t. If your “allergy” is based on a childhood reaction you barely remember, or a side effect like an upset stomach, your doctor may want to explore whether amoxicillin-clavulanate is actually safe for you. True penicillin allergy with a serious reaction (hives, throat swelling, anaphylaxis) is a different situation entirely.
Why Fluoroquinolones Are a Last Resort
Antibiotics like levofloxacin and moxifloxacin (fluoroquinolones) work well against sinus bacteria, but they carry a boxed warning from the FDA, the most serious safety alert a drug can have. These medications are associated with potentially permanent side effects involving the tendons, muscles, joints, nerves, and central nervous system. The FDA has stated plainly that the risks of fluoroquinolones generally outweigh the benefits for sinus infections when other treatment options exist. They should only be considered if you cannot take any of the alternatives listed above.
What Else Helps During Treatment
Antibiotics alone aren’t the whole picture. Two additional treatments have solid evidence behind them:
Saline nasal irrigation, using a neti pot or squeeze bottle with sterile saline, helps flush mucus and bacteria from the sinuses. Guidelines recommend it as a useful add-on to antibiotics. You can use either regular saline or a slightly saltier hypertonic solution. Many people find this provides noticeable relief within a day or two.
Nasal corticosteroid sprays (like fluticasone, available over the counter) are recommended alongside antibiotics, especially if you have a history of allergies. They reduce the swelling that traps mucus in your sinuses, helping them drain more effectively.
Perhaps surprisingly, oral decongestants like pseudoephedrine and antihistamines like diphenhydramine are not recommended as add-on treatments for bacterial sinusitis. While they might provide temporary symptom relief, they haven’t been shown to improve recovery and can cause side effects like drowsiness, elevated heart rate, or rebound congestion.
How Long Treatment Takes
A standard course runs 5 to 10 days for most adults. You should notice meaningful improvement within 3 to 5 days of starting antibiotics. If your symptoms haven’t improved at all after 3 to 5 days of treatment, that’s a sign the antibiotic may not be working, either because the bacteria are resistant to it or because the infection wasn’t bacterial in the first place. At that point, your doctor may switch to a different antibiotic or reconsider the diagnosis. Completing the full prescribed course, even once you feel better, helps ensure the infection is fully cleared and reduces the chance of resistance developing.