Amoxicillin and penicillin are the best antibiotics for strep throat. They are the recommended first-line treatments because the bacteria that cause strep throat have never developed resistance to them, they’re inexpensive, and they work reliably. Most people start feeling better within one to two days of the first dose.
Why Amoxicillin and Penicillin Are First Choice
Strep throat is caused by Group A Streptococcus bacteria, and these bacteria remain fully susceptible to penicillin and amoxicillin. That’s notable because resistance is a growing problem with other antibiotics. Around 1 in 3 invasive Group A strep infections now show resistance to erythromycin and clindamycin, which makes those alternatives less dependable.
Amoxicillin is often preferred in practice, especially for children, because it tastes better in liquid form and can be taken just once or twice a day. Penicillin V works equally well but typically requires more frequent doses for adults (twice daily at 500 mg, or four times daily at 250 mg). Both require a full 10-day course. That length isn’t just about clearing the infection from your throat. It’s specifically designed to prevent rheumatic fever, a serious inflammatory condition that can damage the heart valves. About one-third of rheumatic fever cases follow strep infections where the person either didn’t seek treatment or didn’t complete a full course.
What to Expect After Starting Treatment
You should notice your fever dropping and throat pain easing within a day or two of your first dose. You also become much less contagious quickly: within 12 hours of starting antibiotics, you’re generally no longer spreading the bacteria. Schools and daycares use that 12-hour mark as the standard for when kids can return.
Even though you’ll feel better fast, finishing the full 10 days matters. Stopping early can leave enough bacteria behind to trigger complications, including rheumatic fever and kidney inflammation, or simply cause the infection to come back.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, your options depend on what type of reaction you’ve had. For people whose allergy causes a rash but not a severe, immediate reaction (like throat swelling or anaphylaxis), first-generation cephalosporins such as cephalexin or cefadroxil are effective alternatives. These are chemically related to penicillin but are generally safe for people with milder allergies.
For people with a severe, immediate-type penicillin allergy, macrolide antibiotics like azithromycin or clarithromycin are the usual go-to. However, these come with a caveat: resistance among Group A strep bacteria to this class of drugs has been climbing. Erythromycin, an older macrolide, is the guideline-recommended option for penicillin-allergic patients, though it’s known for causing stomach upset, which is why many doctors prescribe azithromycin or clarithromycin instead. All of these alternatives still require completion of the prescribed course, though the exact duration varies by drug.
Why a Test Comes Before the Prescription
A sore throat alone isn’t enough to warrant antibiotics. Most sore throats are caused by viruses, and antibiotics do nothing for viral infections. Before prescribing, your doctor will use a rapid strep test (a quick throat swab with results in minutes) or a throat culture to confirm the bacteria are actually present. This step protects you from taking antibiotics you don’t need, which reduces your risk of side effects and helps slow the broader problem of antibiotic resistance.
If your rapid test is negative but your doctor still suspects strep, especially in children, a throat culture may be sent to a lab. That takes a day or two for results but catches cases the rapid test misses.
One-Shot Alternative
For people who are unlikely to complete a 10-day pill regimen, there’s an injectable option: a single intramuscular shot of benzathine penicillin G. One dose covers the full treatment. It’s sometimes used for children, teens, or anyone with a history of not finishing oral courses. The trade-off is the injection itself, which can be painful at the site, but it eliminates the compliance issue entirely.