The first-line antibiotic for a bacterial sinus infection is amoxicillin, with or without clavulanate (sold as Augmentin). A typical course lasts 5 to 10 days. But here’s the important part: most sinus infections are viral, meaning antibiotics won’t help at all. The antibiotic question only matters once you and your doctor have established that bacteria are actually involved.
Most Sinus Infections Don’t Need Antibiotics
Roughly 90% of sinus infections start with a virus, the same kind that causes the common cold. Viral sinusitis causes the same miserable symptoms: congestion, facial pressure, thick nasal discharge, headache. These infections resolve on their own within 7 to 10 days. Taking an antibiotic for a viral sinus infection does nothing to speed recovery and only increases your risk of side effects like diarrhea, yeast infections, and antibiotic resistance.
The distinction between viral and bacterial sinusitis matters because the symptoms overlap almost entirely. You can’t tell the difference just by looking at the color of your mucus. Green or yellow discharge happens with both viral and bacterial infections.
When Antibiotics Are Actually Warranted
Doctors use specific clinical criteria to determine whether a sinus infection has become bacterial. The American Academy of Otolaryngology recognizes two main patterns:
- The 10-day rule. Symptoms like purulent nasal drainage, nasal obstruction, or facial pain/pressure persist for at least 10 days with no improvement. A viral infection would typically be getting better by this point.
- Double sickening. You start to feel better after the initial illness, then your symptoms suddenly worsen again. This pattern suggests a secondary bacterial infection has taken hold.
European guidelines add a few more indicators: one-sided facial pain, one-sided discolored nasal discharge, and fever above 100.4°F. The presence of three or more of these signs raises suspicion of bacterial involvement. If your symptoms don’t fit either pattern, watchful waiting is the recommended approach, even if you feel terrible.
First-Line Antibiotic: Amoxicillin-Clavulanate
When antibiotics are warranted, amoxicillin with or without clavulanate is the standard first choice. The clavulanate component helps the antibiotic work against bacteria that have developed a common resistance mechanism. Treatment typically runs 5 to 10 days, with your doctor choosing the duration based on symptom severity and how quickly you respond.
If the standard dose doesn’t work, a high-dose version of amoxicillin-clavulanate is the next step before switching antibiotic classes entirely. This higher dose is particularly useful in areas with high rates of resistant bacteria or when the initial course didn’t resolve symptoms.
The three bacteria most commonly responsible for sinus infections are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Amoxicillin-clavulanate covers all three effectively, which is why it remains the go-to choice.
If You’re Allergic to Penicillin
Amoxicillin is a penicillin-type antibiotic, so if you have a penicillin allergy, you’ll need an alternative. The options depend on the type of allergic reaction you’ve had.
Doxycycline is a common alternative for adults. The usual approach is a higher dose on the first day (200 mg), followed by 100 mg once daily for the remaining days of a roughly 5-day course. Doxycycline is not recommended for children under 12.
Levofloxacin, a fluoroquinolone antibiotic, is another option for patients with penicillin allergies. However, fluoroquinolones carry an FDA boxed warning for increased risk of tendon rupture and tendinitis. This risk is higher in people over 60, those taking corticosteroids, and organ transplant recipients. Because of these serious side effects, fluoroquinolones are generally reserved for situations where safer alternatives aren’t available or haven’t worked.
Why Your Doctor Won’t Prescribe Azithromycin
Many people expect a Z-pack (azithromycin) for sinus infections because it used to be commonly prescribed. It’s convenient, just a few days of pills, and it’s generally well tolerated. But it’s no longer recommended for bacterial sinusitis because of resistance.
Streptococcus pneumoniae, one of the primary bacteria behind sinus infections, has developed widespread resistance to macrolide antibiotics like azithromycin and clarithromycin. Resistance rates in some regions exceed 95%. Prescribing azithromycin for a bacterial sinus infection now carries a significant chance of simply not working, while still exposing you to side effects and contributing to further resistance. If your doctor offers azithromycin for a sinus infection, it’s worth asking about amoxicillin-clavulanate instead.
Antibiotics for Children
Children get sinus infections frequently, and the same rule applies: most are viral. When antibiotics are needed, amoxicillin is also first-line for kids, dosed by body weight. High-dose amoxicillin for children runs around 80 to 90 mg per kilogram of body weight per day, split into two doses, with a maximum of 2 grams per dose.
For children with penicillin allergies, alternatives include cephalosporin-type antibiotics like cefdinir or cefuroxime, as long as the child hasn’t had a severe anaphylactic reaction to penicillin (since these antibiotic classes are chemically related). Doxycycline can be used in children 12 and older. Your pediatrician will choose based on your child’s age, weight, allergy history, and local resistance patterns.
What to Do While You Wait or Recover
Whether your sinus infection is viral or you’re taking antibiotics for a bacterial one, symptom management makes a real difference. Saline nasal irrigation (using a neti pot or squeeze bottle) helps flush out mucus and reduce congestion. Over-the-counter decongestants can provide short-term relief, though nasal spray decongestants shouldn’t be used for more than three days to avoid rebound congestion.
Nasal corticosteroid sprays like fluticasone, available over the counter, can reduce inflammation in the sinus passages. They work best when used consistently rather than as needed. Pain from sinus pressure responds well to standard pain relievers like ibuprofen or acetaminophen. Staying hydrated and using a humidifier can also help thin mucus and keep your nasal passages from drying out.
If you’re on antibiotics and your symptoms haven’t improved after 3 to 5 days, contact your doctor. You may need a different antibiotic, a higher dose, or further evaluation to rule out complications like a sinus abscess or spread of infection.