The first-line antibiotic for a bacterial sinus infection is amoxicillin-clavulanate, a combination of amoxicillin plus an ingredient that helps it work against resistant bacteria. Most sinus infections are viral, though, and don’t need antibiotics at all. The type of antibiotic your doctor prescribes depends on your allergy history, how severe your symptoms are, and whether you’ve taken antibiotics recently.
When a Sinus Infection Actually Needs Antibiotics
Most sinus infections start as viral illnesses and clear up on their own within 7 to 10 days. Antibiotics won’t help with a viral infection. Three specific patterns suggest the infection has become bacterial and may benefit from antibiotic treatment:
- Persistent symptoms: Congestion, facial pressure, and nasal discharge lasting 10 days or longer without any improvement.
- Severe onset: A fever of 102°F or higher along with thick nasal discharge and facial pain lasting 3 to 4 days.
- Double worsening: Symptoms that start to improve after 4 to 7 days, then suddenly get worse again.
If your symptoms don’t fit any of these patterns, you likely have a viral infection. Over-the-counter decongestants, saline rinses, and pain relievers are the standard approach while you wait it out.
Amoxicillin-Clavulanate as First Choice
Infectious disease guidelines recommend amoxicillin-clavulanate over plain amoxicillin for bacterial sinus infections. The added ingredient (clavulanate) blocks a defense mechanism that some bacteria use to inactivate amoxicillin, making the combination effective against a wider range of sinus pathogens. It’s also preferred over stronger antibiotics like fluoroquinolones because it carries fewer risks of serious side effects.
A higher dose version is recommended in certain situations: if you live in an area with high rates of drug-resistant bacteria, have used antibiotics in the past month, were recently hospitalized, are immunocompromised, or are younger than 2 or older than 65. Children in daycare also fall into this higher-dose category because of their increased exposure to resistant bacteria.
The most common side effect is diarrhea, which affects roughly 9 to 15% of people taking the drug. Nausea occurs in about 3% of cases. Taking it with food can reduce stomach upset. Probiotics or yogurt during your course may also help, though the evidence on that is mixed.
How Long You’ll Take Them
Adults typically take antibiotics for 5 to 7 days for an uncomplicated bacterial sinus infection. Some guidelines extend this to 10 days depending on the severity. Children are generally treated for 10 to 14 days because shorter courses haven’t been as well studied in younger patients. Your doctor may adjust the length based on how quickly your symptoms improve, but finishing the full prescribed course matters for preventing resistance.
Alternatives if You’re Allergic to Penicillin
Amoxicillin-clavulanate is a penicillin-type drug, so it’s off the table if you have a penicillin allergy. The alternative depends on how severe your allergy is.
If your reaction to penicillin was mild (a rash, for example) and you can tolerate related drugs called cephalosporins, you have two main options. Doxycycline is one, taken twice daily. A third-generation cephalosporin is the other, sometimes combined with a second antibiotic to cover a broader range of bacteria.
If your penicillin allergy is severe, meaning you’ve had throat swelling, difficulty breathing, or anaphylaxis, you should avoid all penicillin-related drugs including cephalosporins. In that case, doxycycline is the go-to choice. It works well against the bacteria most commonly responsible for sinus infections and doesn’t share any structural similarity with penicillin.
Fluoroquinolones like levofloxacin or moxifloxacin are reserved as a last resort for people who can’t take any of the above options. These antibiotics carry risks of tendon damage, nerve problems, and other serious side effects that generally outweigh their benefits for a standard sinus infection.
Why Your Doctor Won’t Prescribe Azithromycin
Azithromycin (the popular “Z-Pack”) was once commonly prescribed for sinus infections, but guidelines now recommend against it. The reason is resistance. The bacteria that cause most sinus infections, particularly Streptococcus pneumoniae, have developed widespread resistance to this class of drugs. In some regions, over 95% of these bacteria are resistant to macrolide antibiotics like azithromycin and erythromycin. Prescribing them for sinusitis means a high chance the antibiotic simply won’t work, while still exposing you to side effects and contributing to further resistance.
Antibiotics for Children With Sinus Infections
Children get the same first-line drug as adults: amoxicillin-clavulanate. The dose is calculated by weight. A standard dose runs 40 to 45 mg per kilogram of body weight per day, while the high-dose version bumps that up to 90 mg per kilogram per day. High-dose treatment is more common in children under 2 and those in daycare settings, where exposure to resistant bacteria is more likely.
A meta-analysis published by the American Academy of Pediatrics confirmed that antibiotics provide a meaningful benefit over placebo for children with confirmed bacterial sinusitis. The treatment course for children runs 10 to 14 days, longer than the adult recommendation, and the liquid suspension form makes dosing easier for younger kids. Doxycycline is generally avoided in children under 8 because it can cause permanent tooth discoloration, so allergy alternatives in younger children require closer coordination with a pediatrician.
What to Expect During Treatment
Most people notice improvement within 48 to 72 hours of starting antibiotics. If your symptoms haven’t improved at all after 3 to 5 days, your doctor may switch you to a different antibiotic or reconsider whether the infection is truly bacterial. Congestion and post-nasal drip can linger for a week or two even after the infection clears, so some residual symptoms are normal.
Saline nasal rinses, staying hydrated, and using a humidifier can all help manage symptoms while the antibiotic does its work. Nasal steroid sprays can reduce swelling in the sinus passages and speed drainage, making them a useful add-on to antibiotic therapy for more stubborn cases.