Amoxicillin is the first-line antibiotic for a bacterial sinus infection, typically prescribed as a 5 to 7 day course. It’s effective against the most common bacteria involved, affordable, and causes fewer side effects than stronger alternatives. But not every sinus infection needs antibiotics, and the specific prescription you get depends on your allergy history, symptom severity, and how long you’ve been sick.
Most Sinus Infections Don’t Need Antibiotics
The vast majority of sinus infections start as viral illnesses, essentially a cold that inflames your sinuses. Antibiotics do nothing against viruses, so taking one too early won’t help and can cause unnecessary side effects like diarrhea or yeast infections.
A sinus infection is considered potentially bacterial when symptoms last longer than 10 days without improving, or when symptoms start to get better and then suddenly worsen again (sometimes called “double worsening”). Severe symptoms can also point to a bacterial cause: a high fever above 102°F along with thick, discolored nasal discharge and intense facial pain lasting at least 3 to 4 consecutive days. If your symptoms don’t meet these thresholds, you’re likely dealing with a viral infection that will resolve on its own within 7 to 10 days.
Amoxicillin: The Standard First Choice
For adults with a confirmed or strongly suspected bacterial sinus infection, the standard prescription is amoxicillin 500 mg taken three times daily for 5 to 7 days. IDSA guidelines also support amoxicillin-clavulanate (which adds a compound that helps overcome certain resistant bacteria) at 875/125 mg twice daily for 7 days as a first-line option. Some clinicians prefer amoxicillin-clavulanate from the start because it covers a broader range of bacteria.
If you live in an area where antibiotic-resistant bacteria are common (more than 10% of local pneumococcal samples show resistance), your doctor may prescribe a high-dose version. This roughly doubles the amount of amoxicillin to about 2,000 mg twice daily while keeping the clavulanate portion the same. High-dose therapy is also more likely if you’ve used antibiotics within the past month, have a compromised immune system, or have a child in daycare.
Alternatives If You’re Allergic to Penicillin
Amoxicillin is a penicillin-type drug, so it’s off the table if you have a true penicillin allergy. The go-to alternative in that case is doxycycline, usually 100 mg twice daily. It works well against the bacteria most commonly responsible for sinus infections and doesn’t cross-react with penicillin.
If your penicillin allergy is mild (a rash rather than throat swelling or anaphylaxis), you can likely tolerate a cephalosporin safely. Third-generation cephalosporins like cefpodoxime or cefixime are reasonable options, sometimes combined with clindamycin for broader coverage. Most people with a documented penicillin allergy actually aren’t truly allergic when formally tested, so if you’ve been avoiding penicillins based on a childhood reaction, allergy testing may open up more treatment options for you.
Why Z-Paks Are No Longer Recommended
Azithromycin (the well-known Z-Pak) used to be widely prescribed for sinus infections. It’s convenient: just 5 days, once daily. But guidelines now specifically recommend against it as initial therapy. The reason is straightforward: the bacteria most commonly causing sinus infections, particularly Streptococcus pneumoniae, have developed high resistance rates to azithromycin and related antibiotics in the same class. Prescribing it means a meaningful chance the drug simply won’t work. Trimethoprim-sulfamethoxazole faces the same resistance problem and is also not recommended.
Fluoroquinolones Are a Last Resort
Respiratory fluoroquinolones (levofloxacin, moxifloxacin) are powerful antibiotics that work well against sinus infection bacteria. But the FDA has placed its strongest warning, a boxed warning, on this drug class, advising that the serious risks generally outweigh the benefits for sinus infections when other options exist. These risks include tendon damage (including rupture), nerve problems, muscle and joint pain, and central nervous system effects. Some of these side effects can be disabling and permanent.
Fluoroquinolones should be reserved for people who genuinely cannot take any of the first-line options. If you’re prescribed one and you haven’t tried amoxicillin, amoxicillin-clavulanate, doxycycline, or a cephalosporin first, it’s worth asking your doctor why.
How Long You’ll Take Them
Current guidelines from the CDC and IDSA recommend 5 to 7 days of antibiotic therapy for uncomplicated bacterial sinusitis in adults. This is shorter than the 10 to 14 day courses that were once standard. Research shows shorter courses are equally effective for straightforward cases and reduce antibiotic exposure.
You should start feeling noticeably better within 3 to 5 days. If your symptoms haven’t improved at all after 3 to 5 days of antibiotics, that’s a signal to contact your doctor. It may mean the bacteria are resistant to the antibiotic you’re taking, or that something else is going on entirely, like a structural blockage or a non-bacterial cause.
Children Get the Same Drug, Different Dosing
For children with bacterial sinusitis, the first-line treatment is also amoxicillin, but at a higher weight-based dose than what was traditionally used. Pediatric guidelines recommend 80 to 90 mg per kilogram of body weight per day, split into two doses, with a maximum of 2 grams per dose. The higher dose is standard for children because a significant percentage of the bacteria causing pediatric sinus infections show reduced sensitivity to lower concentrations of amoxicillin.
Nasal Steroid Sprays Can Help Alongside Antibiotics
Adding a nasal corticosteroid spray to your antibiotic treatment modestly improves your chances of symptom relief. A meta-analysis of clinical trials found that nasal steroids increased the rate of symptom resolution by about 8 to 12 percentage points compared to antibiotics alone, with the most consistent benefits for facial pain and congestion. The effect was clearer at the 21-day mark than at 14 days, suggesting the spray’s benefit builds over time.
Over-the-counter options like fluticasone or triamcinolone nasal sprays are widely available. These aren’t a substitute for antibiotics when you truly have a bacterial infection, but they can make you more comfortable while the antibiotic does its work. Saline nasal rinses, staying well hydrated, and using a humidifier also help thin mucus and relieve pressure while you recover.