Amoxicillin is the first-line antibiotic for bacterial sinus infections in adults, typically prescribed as a 5 to 10 day course. But most sinus infections are viral, not bacterial, which means antibiotics won’t help the majority of people dealing with sinus misery. Understanding when antibiotics actually make sense, and which ones work best in different situations, can save you from taking a drug you don’t need.
Most Sinus Infections Don’t Need Antibiotics
Roughly 90% of sinus infections start with a virus, the same kind that causes the common cold. These infections clear up on their own, and no antibiotic will speed that process along. The CDC recommends a “watchful waiting” approach for mild symptoms: your provider may suggest waiting 2 to 3 days before starting antibiotics, giving your immune system a chance to handle the infection. Some providers write a prescription but ask you to hold off on filling it unless symptoms persist or worsen.
A bacterial sinus infection is suspected when symptoms last at least 10 days without improvement, or when you experience “double sickening,” where you start to feel better, then get noticeably worse again within 10 days. Other signs pointing toward a bacterial cause include thick, discolored nasal discharge (especially on one side), severe facial pain concentrated on one side, and fever above 100.4°F.
Amoxicillin: The Standard First Choice
When antibiotics are warranted, amoxicillin at 500 mg three times daily is the go-to for adults. It’s effective against the three bacteria responsible for most sinus infections: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. It’s also inexpensive, widely available, and generally well tolerated.
For patients at low risk of antibiotic resistance who respond well to treatment, a 5 to 7 day course is sufficient. Longer courses of 7 to 10 days are typically reserved for people with a higher risk of resistant bacteria or those whose initial treatment didn’t work. Shorter courses have been associated with similar outcomes and fewer side effects compared to longer ones, so there’s no benefit to taking antibiotics longer than necessary.
When a Stronger Option Is Needed
Amoxicillin-clavulanate (commonly sold as Augmentin) combines amoxicillin with an ingredient that disables a defense mechanism some bacteria use to resist the drug. Two of the three main sinus infection bacteria can produce enzymes called beta-lactamases that break down amoxicillin before it works. Moraxella catarrhalis does this universally, and Haemophilus influenzae does so in up to 65% of cases, depending on the region.
Your provider may start with amoxicillin-clavulanate instead of plain amoxicillin if you have severe symptoms, if you’ve used antibiotics recently (which raises the chance of resistant bacteria), if you live in an area with high resistance rates, or if a first round of amoxicillin didn’t clear the infection. The broader coverage does come with a trade-off: more gastrointestinal side effects, particularly diarrhea.
Antibiotics for Children
Children with uncomplicated bacterial sinus infections are also treated with amoxicillin-based antibiotics. When resistance isn’t a concern, amoxicillin-clavulanate at a standard dose (based on the child’s weight) is the current consensus first-line treatment. For children with severe symptoms or a higher risk of resistant bacteria, a high-dose formulation is preferred.
The same diagnostic rules apply to kids: symptoms that hang on for 10 or more days without getting better, or a clear worsening after initial improvement, suggest a bacterial cause worth treating.
Options if You’re Allergic to Penicillin
Amoxicillin belongs to the penicillin family, so people with penicillin allergies need alternatives. For mild allergies (a rash but no breathing problems or swelling), certain cephalosporin antibiotics like cefuroxime, cefpodoxime, or cefdinir are appropriate substitutes. These are chemically related to penicillin but are tolerated by most people with mild penicillin allergies.
For serious penicillin allergies involving anaphylaxis or severe reactions, providers may prescribe clarithromycin or azithromycin (commonly known as a Z-Pack). However, these medications have a significant limitation: nearly 40% of Streptococcus pneumoniae samples in the U.S. are resistant to them. Resistance rates in respiratory samples specifically are even higher, reaching 47%. In some regions, like the South Atlantic states, resistance in respiratory samples exceeds 60%. This means a Z-Pack has a meaningful chance of simply not working against one of the most common sinus infection bacteria.
Why Z-Packs Are Popular but Often Ineffective
Azithromycin is one of the most commonly prescribed antibiotics for sinus infections despite not being a recommended first-line treatment. Its appeal is obvious: it’s taken once daily for just three to five days, and it’s easy on the stomach. But the high resistance rates make it a poor choice when better options are available. Guidelines reserve it for patients who truly cannot tolerate penicillins or cephalosporins.
Resistance rates vary by geography but remain above 25% in every U.S. region, with the highest overall rate (54%) in the West North Central states. Even in the regions with the lowest resistance, at least one in four pneumococcal isolates will shrug off the drug entirely.
Fluoroquinolones: A Last Resort
Fluoroquinolone antibiotics like levofloxacin are effective against sinus infection bacteria, but the FDA has placed a boxed warning on the entire drug class, its strongest safety alert. These drugs carry risks of serious, sometimes permanent side effects involving tendons, muscles, joints, nerves, and the central nervous system. The FDA’s position is that for uncomplicated bacterial sinus infections, the risks generally outweigh the benefits when other treatment options exist. They should only be considered when all other alternatives have failed or aren’t tolerable.
Symptom Relief While You Recover
Whether your sinus infection is viral or bacterial, and whether you’re on antibiotics or not, symptom management makes a real difference. Saline nasal rinses help clear mucus and reduce congestion. Over-the-counter pain relievers address facial pressure and headache. Nasal steroid sprays can reduce inflammation in the sinus passages. Staying well hydrated thins mucus and supports recovery.
If you are prescribed antibiotics, don’t expect immediate relief. Most people notice improvement within 2 to 3 days of starting treatment. If symptoms haven’t improved after 3 to 5 days on antibiotics, contact your provider, as this may signal a resistant organism or an alternate diagnosis that needs a different approach.