Amoxicillin is the standard first-line antibiotic for a bacterial sinus infection in both adults and children, typically prescribed for 5 to 10 days. Your doctor may prescribe amoxicillin-clavulanate instead if you’re at higher risk for a resistant infection. Most sinus infections are viral and don’t need antibiotics at all, but when bacteria are the cause and symptoms are severe or persistent, these are the go-to options.
Why Most Sinus Infections Don’t Need Antibiotics
The majority of sinus infections start as viral illnesses, and antibiotics do nothing against viruses. Symptoms like congestion, facial pressure, and thick nasal discharge can look identical whether the cause is viral or bacterial. Doctors typically wait to see if symptoms last beyond 10 days, get significantly worse after initial improvement, or start unusually severe (high fever with facial pain for 3 or more consecutive days) before diagnosing a bacterial infection and considering antibiotics.
First-Line Treatment: Amoxicillin
Plain amoxicillin remains the recommended starting antibiotic for uncomplicated bacterial sinusitis. It’s effective against the most common bacteria involved, it’s inexpensive, and it has a relatively mild side effect profile. A course of 5 to 10 days is standard for adults.
When there’s a higher chance the bacteria are resistant to plain amoxicillin, doctors prescribe amoxicillin-clavulanate instead. The clavulanate component blocks a defense mechanism some bacteria use to neutralize amoxicillin. You’re more likely to get this version if you’ve taken antibiotics recently, have a compromised immune system, or live in an area with high antibiotic resistance. Interestingly, studies comparing the two haven’t found a major difference in cure rates (around 65 to 80 percent for both), but the added coverage matters in specific situations.
The most common side effects of amoxicillin-clavulanate are digestive: diarrhea, upset stomach, and vomiting. The clavulanate component is usually responsible for the gut symptoms. Taking it with food helps. Serious reactions like skin rashes, difficulty breathing, or signs of liver problems (yellowing skin, dark urine) are rare but require immediate medical attention.
Options if You’re Allergic to Penicillin
If you have a penicillin allergy, the two primary alternatives are doxycycline and respiratory fluoroquinolones (such as levofloxacin or moxifloxacin). For mild infections, doxycycline is generally preferred. It’s effective against the common sinus pathogens and carries fewer safety concerns than fluoroquinolones.
Fluoroquinolones are reserved for situations where other options won’t work. In 2016, the FDA added its strongest safety warning to fluoroquinolones, stating that the risks generally outweigh the benefits for acute bacterial sinusitis when alternative treatments are available. These drugs can cause disabling side effects involving tendons, muscles, joints, nerves, and the central nervous system, and some of these effects can be permanent. For a routine sinus infection, the risk isn’t worth it unless you truly have no other option.
Why Azithromycin Isn’t Recommended
A Z-pack (azithromycin) is what many people expect to receive for a sinus infection, but guidelines no longer recommend it as a reliable choice. The reason is resistance. Roughly 35 percent of the most common sinus bacteria, Streptococcus pneumoniae, are resistant to azithromycin and related antibiotics. That means about one in three bacterial sinus infections won’t respond to it at all. Many strains carry high-level resistance, making the drug essentially useless against them. Despite its convenient dosing schedule, it’s simply not effective often enough to be a good first pick.
Treatment for Children
Children follow the same basic approach: amoxicillin is first-line. The standard dose for uncomplicated cases is 45 mg/kg per day, split into two doses. In communities where resistant bacteria are more common (above 10 percent prevalence), or when a child is under 2, attends daycare, or has recently taken antibiotics, doctors use a high-dose version at 80 to 90 mg/kg per day, often with clavulanate added.
The ideal duration of treatment in children hasn’t been nailed down precisely. Recommendations have ranged from 10 to 28 days. One practical approach many pediatricians use is to continue antibiotics for 7 days after a child’s symptoms resolve, which typically results in a minimum 10-day course while avoiding unnecessarily long treatment for kids who improve quickly.
When a Second-Line Antibiotic Is Needed
If you don’t improve after 3 to 5 days on amoxicillin, your doctor will typically switch to amoxicillin-clavulanate if you weren’t already on it, or move to doxycycline or a fluoroquinolone. True treatment failure, where symptoms plateau or worsen despite a full course of the right antibiotic, sometimes requires imaging or a referral to an ENT specialist to rule out complications like an abscess or a fungal infection.
Chronic sinusitis, where symptoms persist for 12 weeks or longer, is a different situation entirely. It’s often driven by inflammation, structural issues, or nasal polyps rather than an active bacterial infection, and antibiotics alone rarely solve it. Treatment for chronic cases usually involves nasal corticosteroid sprays, saline rinses, and sometimes surgery rather than repeated rounds of antibiotics.
What to Expect During Treatment
Once you start an appropriate antibiotic for bacterial sinusitis, you should notice improvement within 3 to 5 days. Symptoms don’t vanish overnight, but the facial pressure, fever, and thick discolored discharge should gradually ease. If nothing changes or things get worse during that window, contact your prescriber rather than waiting out the full course.
While on antibiotics, saline nasal rinses and over-the-counter pain relievers can help manage symptoms. Finishing the full prescribed course matters even after you feel better, because stopping early can leave enough bacteria alive to cause a relapse or contribute to resistance.