Most upper respiratory infections are caused by viruses, which means antibiotics won’t help. When an upper respiratory infection is bacterial, amoxicillin or amoxicillin-clavulanate is typically the first choice, depending on whether the infection is in the throat, sinuses, or ears. The specific antibiotic, dose, and duration all depend on exactly where the infection is and what’s causing it.
Understanding when antibiotics are actually needed, and which ones work best for each situation, can help you have a more productive conversation with your doctor and avoid unnecessary prescriptions that contribute to resistance.
Most Upper Respiratory Infections Don’t Need Antibiotics
The common cold, acute bronchitis, and most sore throats are viral. When you have a runny nose and cough together, that combination is highly suggestive of a regular cold. Cold symptoms typically last 7 to 10 days, though a cough can linger for several weeks. No antibiotic will shorten that timeline.
Antibiotics are appropriate in a narrow set of situations: strep throat confirmed by a rapid test or culture, sinus symptoms lasting longer than 10 days without improvement, sinus symptoms that get worse after initially getting better (the “double worsening” pattern), and severe cases of ear infections. Outside of these scenarios, taking an antibiotic for an upper respiratory infection does more harm than good.
Strep Throat: Penicillin or Amoxicillin
Group A strep is the main bacterial cause of sore throats, and it’s the one your doctor tests for with a rapid swab. The CDC recommends penicillin or amoxicillin as the first-line treatment. Amoxicillin is more commonly prescribed in practice, partly because it comes in chewable and liquid forms that are easier for children and partly because many people tolerate the taste better.
The standard course is 10 days. Adults typically take 500 mg of amoxicillin twice daily or 250 mg of penicillin V four times daily. For children, the dose is weight-based. Most people start feeling noticeably better within 2 to 3 days of starting treatment, but finishing the full course matters for strep specifically because incomplete treatment raises the risk of complications like rheumatic fever.
Bacterial Sinusitis: Amoxicillin-Clavulanate
Sinus infections often start as viral colds that create swelling and mucus buildup, which can then set the stage for bacteria to grow. The peak window for a secondary bacterial sinus infection overlaps with the tail end of a cold, which is why doctors use the 10-day rule: if your sinus symptoms haven’t improved at all after 10 days, or if they worsened after initially getting better, a bacterial infection is more likely.
The Infectious Diseases Society of America recommends amoxicillin-clavulanate rather than plain amoxicillin for bacterial sinusitis. The clavulanate component helps overcome resistance from certain bacteria that can break down regular amoxicillin. For uncomplicated cases in adults, a 5 to 7 day course is the current guideline. Children are typically treated for 10 to 14 days.
One practical note: amoxicillin-clavulanate causes diarrhea in roughly 10% of people who take it, about five times the rate seen with plain amoxicillin. Taking it with food can help reduce stomach upset.
Ear Infections
Acute ear infections (otitis media) most commonly develop 2 to 5 days after an upper respiratory infection, when viral swelling blocks the drainage tube connecting the middle ear to the throat. Not all ear infections require antibiotics. Mild cases in older children often resolve on their own with pain management alone. When antibiotics are prescribed, amoxicillin is the standard first choice, with amoxicillin-clavulanate reserved for cases that don’t respond to initial treatment.
If You’re Allergic to Penicillin
About 10% of people report a penicillin allergy, though the actual rate of true allergy is much lower. If you’ve been told you’re allergic, your doctor has several alternatives. For strep throat, options include certain cephalosporins (the cross-reactivity risk with penicillin is only about 2%, lower than previously thought), clindamycin, or macrolides like azithromycin. For bacterial sinusitis, doxycycline is a common alternative.
Azithromycin (the well-known “Z-Pack”) deserves a specific mention because it’s one of the most commonly requested antibiotics for respiratory infections. While it remains an option for penicillin-allergic patients, resistance is a growing concern. Resistance rates among common respiratory bacteria have climbed significantly in recent years, with some pathogens showing resistance in over 40% of tested samples. This is one reason guidelines now favor penicillin-based antibiotics as the default choice when there’s no allergy.
How Quickly Antibiotics Work
When antibiotics are appropriately prescribed for a bacterial upper respiratory infection, most people feel meaningfully better within 2 to 3 days. That rapid improvement is actually one of the signals doctors look for to confirm the infection was bacterial in the first place.
Emerging evidence suggests that for many respiratory infections, shorter antibiotic courses of 3 to 5 days are just as effective as the traditional 7 to 10 day prescriptions, with fewer side effects. In practice, about one-third of patients already stop taking their antibiotics once they feel better. While guidelines are shifting toward shorter courses for sinusitis and some other infections, strep throat still requires the full 10 days. Your doctor can tell you the right duration for your specific diagnosis.
Why the “Just in Case” Antibiotic Backfires
Taking antibiotics for a viral infection won’t speed your recovery, but it will expose you to side effects and contribute to antibiotic resistance. Diarrhea, nausea, and yeast infections are common. More importantly, unnecessary antibiotic use drives resistance at both the individual and community level, making these drugs less effective when you or someone else truly needs them.
If your doctor doesn’t prescribe an antibiotic for your upper respiratory infection, that’s not a dismissal. It’s a sign they’ve assessed your symptoms and determined the infection is most likely viral. The better path in that case is managing symptoms with rest, fluids, pain relievers, and decongestants while your immune system does its job. If symptoms worsen after initially improving, or if you develop a high fever, that’s the point where a return visit makes sense to check for a secondary bacterial infection.