Amoxicillin is the standard first-line antibiotic for acute bacterial sinusitis in both adults and children. In many cases, it’s prescribed with clavulanate (a combination that broadens its effectiveness against resistant bacteria). A typical course lasts 5 to 7 days for uncomplicated cases, though some providers prescribe up to 10 days depending on severity.
That said, most sinus infections are viral and don’t need antibiotics at all. The key is knowing when bacteria are likely involved, which antibiotics work best, and what happens if the first choice doesn’t clear things up.
When Sinusitis Actually Needs Antibiotics
The majority of sinus infections start as viral illnesses and resolve on their own within 7 to 10 days. Antibiotics won’t help with a viral infection, and prescribing them unnecessarily contributes to antibiotic resistance. Three patterns suggest a bacterial infection is at play and antibiotics may be warranted:
- Persistent symptoms: Nasal congestion, facial pain or pressure, and discolored nasal discharge lasting 10 days or more without improvement.
- Severe onset: High fever (102°F or higher) along with facial pain and purulent nasal discharge lasting at least 3 to 4 consecutive days.
- Double worsening: Symptoms that initially seem to improve, then suddenly get worse again after 5 to 6 days, with new fever, increased congestion, or worsening headache.
If your symptoms don’t fit any of these patterns, supportive care with nasal saline rinses, decongestants, and pain relievers is the recommended approach.
First-Line Antibiotics for Adults
When antibiotics are appropriate, amoxicillin with or without clavulanate is the go-to choice. Standard amoxicillin works well for straightforward cases. Adding clavulanate is recommended for people at higher risk of harboring resistant bacteria, including those who have used antibiotics in the past month, have chronic health conditions, or live in areas with high rates of drug-resistant infections.
The typical treatment course is 5 to 7 days for uncomplicated acute bacterial sinusitis, per Infectious Diseases Society of America guidelines. Some providers extend this to 10 days based on symptom severity or how slowly symptoms are improving. You should notice meaningful improvement within 48 to 72 hours of starting treatment. If you don’t, that’s a signal to contact your provider rather than wait out the full course.
Options If You’re Allergic to Penicillin
Penicillin allergy is one of the most commonly reported drug allergies, and it changes the treatment approach significantly. Doxycycline is the preferred alternative for adults, typically taken twice daily.
If you’ve been told you’re allergic to penicillin but can still tolerate a related class of drugs called cephalosporins (which is common, since true cross-reactivity is rare), your provider may prescribe a third-generation cephalosporin like cefixime or cefpodoxime instead. These are sometimes combined with clindamycin for broader coverage.
Respiratory fluoroquinolones like levofloxacin and moxifloxacin are reserved as a last resort. While effective against sinus infections, they carry a risk of serious side effects including tendon damage, nerve problems, and mood changes. For most people with sinusitis, the risks of fluoroquinolones outweigh the benefits when other options are available.
Why Azithromycin Isn’t Recommended Anymore
If you’ve been prescribed a Z-pack (azithromycin) for a sinus infection in the past, you’re not alone. It used to be a popular choice. Current guidelines, however, no longer recommend macrolide antibiotics like azithromycin or clarithromycin as reliable options for bacterial sinusitis. The reason is resistance: one of the primary bacteria behind sinus infections, Streptococcus pneumoniae, has developed widespread resistance to this entire drug class. Most strains that resist older macrolides also resist the newer versions, making the whole group unreliable for sinusitis treatment.
Trimethoprim-sulfamethoxazole (commonly known as Bactrim) was also previously listed as an alternative but has fallen out of favor in updated guidelines for similar resistance concerns.
What Happens When the First Antibiotic Doesn’t Work
If your symptoms haven’t improved after 72 hours on amoxicillin, or if they briefly improve and then come back within six weeks, your provider will typically step up to a broader-spectrum antibiotic. The most common second-line option is high-dose amoxicillin-clavulanate. In areas with known antibiotic resistance, the amoxicillin component may be dosed at 80 to 90 mg per kilogram of body weight per day, which is roughly double the standard dose.
If that combination still isn’t working, or if you can’t take penicillin-based drugs, a respiratory fluoroquinolone like levofloxacin or moxifloxacin becomes a reasonable next step. At this point, the benefit of clearing a stubborn infection tips the balance in favor of these stronger drugs.
Antibiotics for Children With Sinusitis
The first-line treatment for children mirrors what’s used in adults: amoxicillin or amoxicillin-clavulanate. The American Academy of Pediatrics recommends the same criteria for distinguishing bacterial from viral infections in kids, though children tend to get sinus infections more frequently because their immune systems are still developing and their sinuses are smaller and drain less efficiently.
High-dose amoxicillin (80 to 90 mg per kilogram per day) is particularly important in pediatric cases in communities where resistant bacteria are common. For children with penicillin allergies, the alternatives are more limited than in adults since doxycycline is generally avoided in young children, and fluoroquinolones carry additional concerns in pediatric patients. Your child’s provider will weigh these factors on a case-by-case basis.
Chronic Sinusitis Is Treated Differently
Chronic sinusitis, defined as symptoms persisting for 12 weeks or longer, is a fundamentally different condition from an acute bacterial infection. Current guidelines from the American Academy of Otolaryngology explicitly recommend against routinely prescribing antibiotics for chronic sinusitis without an active flare-up. Antibiotics are also not required as a prerequisite before sinus imaging or surgery.
Chronic sinusitis often involves inflammation rather than active infection, which is why treatment focuses on nasal corticosteroid sprays, saline irrigation, and sometimes surgery to improve drainage. When a flare-up does occur on top of chronic sinusitis, a short course of antibiotics similar to the acute sinusitis approach may be appropriate. But the long-term management of chronic sinusitis relies on controlling inflammation, not repeated rounds of antibiotics.