The recommended first-line antibiotic for a bacterial sinus infection in adults is amoxicillin-clavulanate, a stronger version of plain amoxicillin that covers a wider range of bacteria. For adults who can’t take penicillin-type drugs, doxycycline is the go-to alternative. But before choosing any antibiotic, the bigger question is whether you actually need one, since most sinus infections are viral and clear up on their own.
Most Sinus Infections Don’t Need Antibiotics
The vast majority of sinus infections start as viral illnesses. They cause the same miserable symptoms (congestion, facial pressure, thick mucus) but won’t respond to antibiotics at all. Clinical guidelines identify bacterial sinusitis based on specific patterns: symptoms lasting at least 10 days without improvement, or a “double sickening” pattern where you start to feel better and then get noticeably worse again within 10 days.
Other signs pointing toward a bacterial cause include one-sided facial pain, fever above 100.4°F, and thick discolored discharge coming primarily from one side. If your symptoms don’t fit these patterns, an antibiotic is unlikely to help and may cause unnecessary side effects like diarrhea or yeast infections.
Amoxicillin-Clavulanate as First Choice
Guidelines from the Infectious Diseases Society of America recommend amoxicillin-clavulanate over plain amoxicillin for adults with confirmed or strongly suspected bacterial sinusitis. The clavulanate component blocks a defense mechanism that some bacteria use to resist amoxicillin, making the combination effective against a broader set of bugs that commonly infect the sinuses.
For adults over 40 kg (about 88 pounds), the typical dose is 875/125 mg taken every 12 hours. When a higher dose is needed, particularly for coverage of resistant strains of a common sinus-infecting bacterium, the dose goes up to 2,000 mg of amoxicillin with 125 mg of clavulanate every 12 hours. Your prescriber will decide which tier based on local resistance patterns and your risk factors. Treatment for adults typically lasts five to seven days, which is shorter than many people expect.
Alternatives if You’re Allergic to Penicillin
If you have a penicillin allergy, doxycycline at 100 mg twice daily is a well-supported option. It’s highly active against respiratory bacteria and works through a completely different mechanism than penicillin-type drugs, so cross-reactivity isn’t a concern.
Most people who believe they have a penicillin allergy can actually tolerate cephalosporins safely, a related but distinct drug class. If your doctor determines that’s the case for you, a third-generation cephalosporin like cefpodoxime or cefixime is another reasonable choice, sometimes combined with clindamycin for broader coverage.
Respiratory fluoroquinolones like levofloxacin or moxifloxacin are effective but generally reserved for people who truly can’t take any of the options above. These carry a higher risk of serious side effects (tendon problems, nerve damage) and are considered second-line for that reason.
Antibiotics for Children With Sinus Infections
In children, amoxicillin or amoxicillin-clavulanate remains first-line, but the recommendation leans more firmly toward amoxicillin-clavulanate than it does in adults. Dosing is weight-based, typically 45 mg per kg of body weight given twice daily. Treatment courses run longer than in adults, usually 10 to 14 days.
Children with penicillin allergies have fewer options. Levofloxacin is one choice, dosed by both weight and age. Kids under five take it twice daily, while those five and older take it once daily. Another approach pairs clindamycin with an oral cephalosporin like cefdinir, though this only works if the child’s allergy allows cephalosporin use.
What to Expect During Treatment
You should notice some improvement within three to five days of starting antibiotics. If symptoms haven’t budged by 72 hours, or if they worsen, that’s a signal to contact your prescriber. The antibiotic may need to change because the bacteria involved could be resistant to the first choice.
Finishing the full prescribed course matters even after you start feeling better. Stopping early can leave surviving bacteria behind, increasing the chance of relapse or resistance. Side effects from amoxicillin-clavulanate are usually limited to digestive issues. Taking it with food reduces stomach upset significantly.
Chronic Sinusitis Is a Different Situation
If sinus symptoms persist for 12 weeks or longer, you’re dealing with chronic rhinosinusitis, which is a fundamentally different condition. Antibiotics play a smaller role here. When they are used for acute flare-ups of chronic sinusitis, courses can run up to three weeks, much longer than for a standard acute infection. Research has shown that even in acute cases, antibiotic and placebo groups often reach the same level of improvement by day 10, which underscores how much of sinus recovery happens through the body’s own healing.
Chronic sinusitis management typically centers on nasal saline rinses, steroid nasal sprays, and identifying underlying contributors like allergies or structural problems rather than repeated antibiotic courses.