Amoxicillin, with or without clavulanate, is the first-line antibiotic for bacterial sinus infections in both adults and children. But most sinus infections are viral, meaning antibiotics won’t help at all. Understanding when antibiotics are actually needed, and which ones work best, can save you from unnecessary side effects and help you recover faster when you do need treatment.
Most Sinus Infections Don’t Need Antibiotics
The majority of sinus infections start with a virus, and viral infections clear up on their own. Antibiotics only work against bacteria, so taking them for a viral sinus infection does nothing except expose you to side effects and contribute to antibiotic resistance.
A bacterial sinus infection is typically diagnosed based on how long your symptoms last and how they behave. According to guidelines from the American Academy of Otolaryngology, your doctor will suspect a bacterial cause if your symptoms haven’t improved after 10 days, or if your symptoms initially got better and then worsened again within 10 days. That second pattern, sometimes called “double worsening,” is a strong signal that bacteria have taken hold after an initial viral illness. If your congestion, facial pain, and thick nasal discharge are steadily improving before the 10-day mark, you’re likely dealing with a virus and won’t benefit from antibiotics.
Amoxicillin: The Go-To Choice
When a bacterial sinus infection is confirmed or strongly suspected, amoxicillin is the standard starting point. It’s effective against the most common bacteria behind sinus infections, it’s inexpensive, and it has a well-understood safety profile. Your doctor may prescribe it alone or combined with clavulanate, an ingredient that helps it work against bacteria that have developed basic resistance mechanisms. A typical course lasts 5 to 10 days for adults.
Your doctor is more likely to choose the amoxicillin-clavulanate combination if you’ve taken amoxicillin recently (within the past month), if your symptoms are severe, or if a previous round of plain amoxicillin didn’t work. For children, guidelines recommend a higher weight-based dose of amoxicillin because a significant percentage of the bacteria that cause childhood sinusitis have reduced sensitivity to standard doses. Kids are usually treated for 7 to 10 days, or up to 14 days for severe cases.
Options If You’re Allergic to Penicillin
Amoxicillin belongs to the penicillin family, so it’s off the table if you have a penicillin allergy. In that case, your doctor will typically turn to one of two alternatives:
- Trimethoprim-sulfamethoxazole (commonly known as Bactrim or Septra), taken twice daily for about 10 days.
- A macrolide antibiotic like azithromycin (the well-known “Z-pack”), taken for three days, or clarithromycin, taken for up to 14 days.
These alternatives come with an important caveat. Azithromycin resistance is rising globally. The World Health Organization places azithromycin in its “Watch” category, meaning it carries a higher risk of driving antibiotic resistance and should be used carefully. Surveillance data from international databases show increasing resistance among the very bacteria that cause sinus infections. This doesn’t mean a Z-pack won’t work for you, but it’s one reason doctors don’t use it as a first choice, and why they may check local resistance patterns before prescribing it.
Why Stronger Antibiotics Are Reserved for Last
You might wonder about more powerful antibiotics like levofloxacin or moxifloxacin, which belong to a class called fluoroquinolones. These drugs do kill sinus infection bacteria effectively, but they carry serious risks that make them inappropriate for routine use. The FDA has warned that fluoroquinolones can cause disabling and potentially permanent side effects involving tendons, muscles, joints, nerves, and the central nervous system. These effects can occur together and may not resolve after stopping the medication.
The FDA’s position is clear: for sinus infections, the serious risks of fluoroquinolones generally outweigh the benefits when other treatment options exist. They should be reserved for patients who truly have no alternative, such as someone with multiple drug allergies who has failed other treatments.
Common Side Effects of First-Line Treatment
Amoxicillin and amoxicillin-clavulanate are generally well tolerated, but they do cause side effects in some people. The most common are digestive: diarrhea, upset stomach, and vomiting. Vaginal yeast infections can also occur because the antibiotic disrupts normal bacterial balance. Taking the medication with food often helps reduce stomach-related side effects.
Less commonly, some people develop a rash. A mild rash doesn’t always mean you’re allergic, but hives, difficulty breathing, swelling of the face or throat, or skin that blisters or peels are signs of a serious reaction that needs immediate medical attention. Rarely, amoxicillin-clavulanate can affect the liver, causing yellowing of the skin or eyes, dark urine, or pain in the upper right abdomen. If you’ve had liver problems after taking this antibiotic before, your doctor will choose something else.
One practical note: amoxicillin-clavulanate may reduce the effectiveness of hormonal birth control, including pills, patches, rings, and injections. If this applies to you, use a backup contraceptive method during your course of treatment.
Treatments That Help Alongside Antibiotics
Antibiotics target the bacteria, but they don’t directly relieve the congestion, pressure, and thick drainage that make sinus infections miserable. Adding non-antibiotic treatments can make a real difference in how quickly you feel better.
Saline nasal irrigation is one of the most effective options. Rinsing your nasal passages with a saltwater solution physically flushes out mucus, bacteria, and inflammatory debris. Research shows it produces a large improvement in symptoms compared to no treatment, and higher-volume rinses (more than 100 milliliters per side, roughly what a squeeze bottle or neti pot delivers) work better than low-volume saline sprays. You can do this several times a day with no meaningful risks.
Corticosteroid nasal sprays reduce inflammation in the sinus passages and can help with congestion and drainage. They’re available over the counter and are especially useful if allergies are contributing to your symptoms. For people with nasal polyps, these sprays reduce both symptom severity and polyp size. Combining saline irrigation with a corticosteroid spray is considered a strong first-line approach for managing sinus symptoms, whether or not you’re also on antibiotics.
Over-the-counter nasal decongestant sprays can provide short-term relief from stuffiness, but they shouldn’t be used for more than about a week. Longer use can cause rebound congestion that’s worse than the original problem.