Amoxicillin is the first-line antibiotic prescribed for bacterial sinus infections in both adults and children. For cases where standard amoxicillin may not be enough, doctors often prescribe amoxicillin-clavulanate, which pairs amoxicillin with a second ingredient that helps it work against a broader range of bacteria. Most uncomplicated cases call for 5 to 7 days of treatment.
That said, not every sinus infection needs antibiotics. Most are caused by viruses, and antibiotics won’t help with those. Understanding when antibiotics are actually warranted, which ones are used, and how quickly they work can save you a frustrating round of ineffective treatment.
When a Sinus Infection Actually Needs Antibiotics
The majority of sinus infections start as viral illnesses and clear up on their own within a week or so. Antibiotics only help when the infection is bacterial, and doctors use three specific patterns to make that call:
- Persistent symptoms: Nasal discharge or daytime cough lasting more than 10 days with no improvement.
- Severe symptoms: A fever of 102°F (39°C) or higher along with thick, discolored nasal discharge or facial pain lasting 3 to 4 days.
- Double sickening: Symptoms that seem to get better after 5 to 6 days of a cold, then suddenly worsen again with new or returning fever, cough, or nasal discharge.
If your symptoms don’t match any of these three patterns, you’re likely dealing with a viral infection. Over-the-counter decongestants, saline rinses, and pain relievers are the standard approach while it runs its course.
The Standard First-Line Antibiotic
Amoxicillin is the go-to choice because it’s effective against the bacteria most commonly responsible for sinus infections, it’s inexpensive, and it has a relatively mild side-effect profile. When there’s concern about resistant bacteria, perhaps because you’ve used antibiotics recently or your symptoms are more severe, amoxicillin-clavulanate is the preferred upgrade. The clavulanate component disables a defense mechanism some bacteria use to resist amoxicillin.
For uncomplicated bacterial sinusitis, current guidelines from the Infectious Diseases Society of America recommend a 5 to 7 day course. Longer courses of 10 to 14 days were once standard but are no longer considered necessary for straightforward cases. Your doctor may still prescribe a longer course if your infection is severe or if you have underlying health conditions.
Options if You’re Allergic to Penicillin
Since amoxicillin belongs to the penicillin family, people with a penicillin allergy need a different approach. The two most common alternatives are trimethoprim-sulfamethoxazole (often called by the brand name Bactrim) and macrolide antibiotics like azithromycin or clarithromycin. Azithromycin is popular for its convenience: the typical course is just three days.
For people who haven’t improved on initial treatment, who have moderate disease, or who’ve recently taken other antibiotics, fluoroquinolones like levofloxacin or moxifloxacin are sometimes prescribed. These are powerful, broad-spectrum antibiotics, but they carry a higher risk of side effects, so doctors generally reserve them for situations where simpler options have failed or aren’t appropriate.
Antibiotics for Children
Children with bacterial sinus infections follow the same basic playbook. Amoxicillin or amoxicillin-clavulanate are the first-line choices, with dosing based on the child’s weight. Pediatric guidelines from the American Academy of Pediatrics align with adult recommendations on this point. If your child has a penicillin allergy, the pediatrician will select an alternative based on the child’s age and the severity of the infection.
How Quickly Antibiotics Work
Don’t expect to feel better immediately. It typically takes a few days for antibiotics to noticeably reduce symptoms. You might still have congestion, pressure, and fatigue for the first two or three days of treatment even though the medication is already fighting the infection.
If you see no improvement after 7 days on antibiotics, that’s a signal to follow up with your doctor. The bacteria causing your infection may be resistant to the antibiotic you’re taking, and a switch to a different class may be needed. In some cases, doctors add a second antibiotic that targets a different set of bacteria.
Chronic Sinus Infections Are Treated Differently
Chronic sinusitis, where symptoms persist for 12 weeks or longer, doesn’t follow the same antibiotic rules as an acute infection. No antibiotic has formal FDA approval for chronic sinusitis, though they’re still widely prescribed. In the U.S., the most commonly used classes are penicillin-type antibiotics (about 33% of prescriptions), macrolides (26%), and fluoroquinolones (19%).
When a chronic sinus infection flares up acutely, doctors typically treat it as a short-term bacterial episode. One common approach is a two-week course of amoxicillin-clavulanate. Macrolide antibiotics are also used in some chronic cases, not just for their bacteria-fighting ability but because they have anti-inflammatory properties that may help reduce swelling in the sinuses over time. The treatment plan for chronic sinusitis is more individualized and often involves nasal steroids, saline irrigation, or other therapies alongside or instead of antibiotics.