Amoxicillin is the go-to antibiotic for a bacterial sinus infection, and it has been for years. It’s effective against the most common bacteria involved, it’s inexpensive, and it causes relatively few side effects. In some cases, your provider may prescribe amoxicillin-clavulanate instead, which adds a second ingredient that helps the antibiotic work against resistant bacteria. Both are considered first-line treatments for adults and children.
That said, most sinus infections are viral and don’t need antibiotics at all. Understanding when antibiotics actually help, which ones are best, and what to expect during treatment can save you time, side effects, and a prescription that won’t do anything.
Most Sinus Infections Don’t Need Antibiotics
The vast majority of sinus infections start with a virus, like the common cold. Viral sinusitis causes the same miserable symptoms (congestion, facial pressure, thick nasal discharge) but clears up on its own within 7 to 10 days. Antibiotics do nothing against viruses, so taking them during a typical sinus infection just exposes you to side effects without any benefit.
A bacterial sinus infection is suspected when one of three patterns shows up:
- Persistent symptoms: Congestion, discharge, or facial pain 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 for at least three consecutive days at the start of illness.
- Double-sickening: Symptoms that started improving after five or six days, then suddenly get worse again, with a new fever, increased headache, or worsening discharge.
If your symptoms fit one of these patterns, antibiotics are reasonable. If you’re on day four of a sinus infection and feeling lousy but not dramatically worse, you’re almost certainly dealing with a virus.
First-Line Antibiotics for Adults
When antibiotics are warranted, amoxicillin with or without clavulanate is the standard first choice. The American Academy of Family Physicians recommends it as first-line therapy for 5 to 10 days.
Plain amoxicillin works well for straightforward cases. Amoxicillin-clavulanate (often sold as Augmentin) is the stronger option your provider may choose if you’ve recently used antibiotics, if your symptoms are severe, or if there’s concern about resistant bacteria in your area. The clavulanate component disables a defense mechanism that certain bacteria use to resist amoxicillin.
Both are taken by mouth, typically twice or three times a day depending on the formulation. Side effects are generally mild: stomach upset, diarrhea, and occasionally a rash. The clavulanate version is more likely to cause digestive issues because of its effect on gut bacteria.
Options if You’re Allergic to Penicillin
Amoxicillin belongs to the penicillin family, so if you have a penicillin allergy, your provider needs a different approach. The alternatives depend on whether your allergy is mild (a rash years ago) or severe (throat swelling, anaphylaxis).
For mild penicillin allergies, certain cephalosporin antibiotics are often safe to use. Cefdinir, cefuroxime, and cefpodoxime are all options that cover the same bacteria. These are structurally related to penicillin, but the cross-reactivity rate is very low, so most people with a mild penicillin allergy tolerate them without problems.
For true severe allergies, doxycycline is a common alternative. It belongs to a completely different antibiotic class and has no cross-reactivity with penicillin. Trimethoprim-sulfamethoxazole (Bactrim) has also been used, though resistance among sinus bacteria has increased in recent years.
Antibiotics That Are No Longer Recommended
Azithromycin (the well-known Z-pack) used to be one of the most commonly prescribed antibiotics for sinus infections. It’s convenient: just three days of pills. But current guidelines no longer recommend it as a go-to option. The two bacteria most often responsible for bacterial sinusitis have developed high rates of resistance to azithromycin and other macrolide antibiotics, meaning the drug frequently fails to clear the infection.
The same resistance problem applies to clarithromycin, another macrolide. Trimethoprim-sulfamethoxazole has also seen rising resistance rates. These drugs may still be prescribed for patients with severe penicillin allergies who have limited options, but they’re no longer considered reliable first choices. If you’ve been prescribed a Z-pack for a sinus infection and it didn’t work, resistance is a likely explanation.
How Long Treatment Lasts
For adults with uncomplicated bacterial sinusitis, a course of 5 to 10 days is standard. Shorter courses (5 to 7 days) are increasingly favored for mild to moderate cases because they cause fewer side effects and contribute less to antibiotic resistance, while still clearing the infection effectively.
Longer courses of 10 to 14 days may be appropriate if your symptoms are severe, if you have a weakened immune system, or if an initial round of antibiotics didn’t work. Children with severe disease or treatment failure are also typically treated for 10 to 14 days.
You should start feeling noticeably better within three to five days of starting antibiotics. If your symptoms haven’t improved at all by day five, that’s worth a follow-up call to your provider. It may mean the bacteria are resistant to the antibiotic you’re taking, and a switch is needed.
What to Do While You Wait
Whether or not you end up on antibiotics, symptom management makes a real difference. Saline nasal irrigation (using a neti pot or squeeze bottle) physically flushes out mucus and bacteria, and it’s one of the most consistently helpful interventions for sinus infections of any type. Over-the-counter nasal steroid sprays reduce inflammation in the sinus passages and can speed drainage.
Pain relievers like ibuprofen or acetaminophen help with facial pressure and headache. Decongestant sprays (oxymetazoline) can provide short-term relief, but using them for more than three consecutive days can cause rebound congestion that makes things worse. Staying well-hydrated and using a humidifier can also thin mucus and ease discomfort.
If you’re in the first 10 days of symptoms and they’re gradually improving, these measures alone are usually enough. Antibiotics become the right tool when the pattern clearly points to a bacterial cause, and in those cases, amoxicillin or amoxicillin-clavulanate remains the best starting point.