Amoxicillin is the first-line antibiotic for bacterial sinus infections in both adults and children. In many cases, it’s prescribed in combination with clavulanate (a compound that helps it work against resistant bacteria). Most uncomplicated cases call for a 5 to 7 day course, though your doctor may adjust this based on how quickly your symptoms improve.
Not every sinus infection needs antibiotics, though. The majority are caused by viruses, and antibiotics won’t help those. Understanding when antibiotics are actually warranted, which ones work best, and what to expect from treatment can save you unnecessary side effects and help you recover faster.
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 only help when the infection is bacterial, and there are three clinical patterns that signal a bacterial cause:
- Persistent symptoms: Congestion, facial pressure, and nasal discharge lasting 10 days or longer without improvement.
- Severe onset: A fever of 102°F or higher along with thick nasal discharge and facial pain lasting 3 to 4 consecutive 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’re almost certainly dealing with a viral infection. Over-the-counter decongestants, saline rinses, and pain relievers are the appropriate treatment in that case. The three bacteria most commonly responsible when infection is bacterial are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
First-Line Antibiotics for Adults
Amoxicillin, either alone or combined with clavulanate, is the standard starting point. The clavulanate version is preferred when there’s concern about antibiotic-resistant bacteria, which is more likely if you’ve taken antibiotics recently, live in an area with high resistance rates, or have had repeated sinus infections. Treatment typically lasts 5 to 7 days for uncomplicated cases.
One antibiotic you might expect to see on this list is azithromycin (the well-known Z-pack). Despite its popularity, current guidelines do not recommend it as a first-line or preferred alternative for sinus infections. Resistance rates among the bacteria that cause sinusitis have made it unreliable. If your doctor prescribes a Z-pack for a sinus infection, it’s worth asking whether a more effective option might be appropriate.
Alternatives if You’re Allergic to Penicillin
Since amoxicillin is a penicillin-type drug, a significant number of people need a different option. Doxycycline is the most straightforward substitute and works well against the common sinus infection bacteria. It’s taken twice daily (or once daily at a higher dose) and is suitable for adults who can’t take any penicillin-family drugs.
If you’ve had a mild or delayed allergic reaction to penicillin (one that appeared more than 72 hours after taking it), certain cephalosporin antibiotics like cefpodoxime or cefixime are generally safe to use. These are sometimes combined with clindamycin for broader coverage. Even people with more serious penicillin allergies can often tolerate these cephalosporins, though this should be discussed carefully with your prescriber.
Fluoroquinolones like levofloxacin are effective against sinus infection bacteria but come with serious caveats. The FDA has placed its strongest warning (a Boxed Warning) on these drugs, noting that their risks generally outweigh the benefits for sinus infections when other treatment options exist. These risks include potentially permanent damage to tendons, muscles, joints, and nerves. Fluoroquinolones should only be considered when no other antibiotic is an option.
Antibiotics for Children
Children follow the same first-line approach as adults: amoxicillin, with or without clavulanate. The dose is weight-based, and the specific amount depends on the child’s age, severity of illness, and risk factors for resistant bacteria.
For mild to moderate cases in children 2 and older who don’t attend daycare and haven’t recently taken antibiotics, a standard dose is typical. Children under 2, those in daycare, those who’ve had recent antibiotics, or those with moderate to severe symptoms get a higher dose formulation to cover resistant strains of bacteria more effectively.
For children with penicillin allergies, the alternatives include cefdinir, cefuroxime, or cefpodoxime. In young children under 2 who have a serious penicillin allergy and moderate or severe sinusitis, doctors may combine clindamycin with cefixime to ensure coverage against both resistant pneumococcal bacteria and H. influenzae. Levofloxacin is a last-resort option in pediatric cases as well.
What to Expect During Treatment
You should notice some improvement within 3 to 5 days of starting antibiotics. If your symptoms haven’t budged at all in that window, contact your doctor. This could mean the bacteria causing your infection are resistant to the antibiotic you’re taking, and a switch may be needed. A second antibiotic course is most justified when resistant bacteria are suspected, which is more common in people who’ve used antibiotics recently.
The most common side effects of amoxicillin-clavulanate are digestive: diarrhea, upset stomach, and occasional vomiting. Taking it with food helps reduce stomach issues. Vaginal yeast infections are also common since the antibiotic disrupts normal bacterial balance. These side effects are usually mild and resolve once you finish the course.
Watch for signs of a more serious reaction, including a rash or hives, difficulty breathing or swallowing, swelling of the face or throat, severe or bloody diarrhea, or yellowing of the skin or eyes. These warrant immediate medical attention.
Why Finishing the Full Course Matters
Even if you feel better after two or three days, stopping antibiotics early can leave surviving bacteria behind. Those survivors are the ones most likely to be partially resistant, and they can repopulate and cause a harder-to-treat infection. The 5 to 7 day course recommended for uncomplicated sinusitis is already shorter than what was standard a decade ago, so completing it is a relatively small commitment that significantly reduces the chance of relapse or resistance.