Penicillin and amoxicillin are the two antibiotics recommended as first-choice treatments for strep throat. Both are highly effective against the bacteria that cause the infection, and the strep bacterium has never developed resistance to either one. Most people start feeling better within one to two days of their first dose.
First-Choice Antibiotics
The CDC recommends penicillin or amoxicillin as the go-to treatment for strep throat. Both kill the same bacterium (Group A Streptococcus), and the choice between them often comes down to convenience. Amoxicillin can be taken once or twice daily, while penicillin V typically requires two to four doses per day depending on your age. Amoxicillin also comes in a chewable tablet and liquid suspension that taste better, making it the more common pick for children.
Both antibiotics are taken for a full 10 days. This is important: even though you’ll likely feel significantly better after 48 hours, stopping early increases the risk of the infection coming back and raises the chance of complications like rheumatic fever, a serious inflammatory condition that can damage the heart. Finishing the full course is one of the most effective ways to prevent that outcome.
For people who are unlikely to complete a 10-day oral course, there’s a one-shot option. A single injection of benzathine penicillin G treats the infection in one visit, eliminating any concern about missed doses.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, your alternatives depend on the type of reaction you’ve had. Allergies fall into two broad categories, and each opens up different treatment paths.
If your allergy caused a rash but not breathing problems or swelling (a non-immediate reaction), first-generation cephalosporins are a safe and effective substitute. These are closely related to penicillin but are well tolerated by most people with mild penicillin allergies.
If your allergy involved a severe or immediate reaction like throat swelling or anaphylaxis, cephalosporins are off the table. In that case, your doctor will turn to a different class of antibiotic entirely. Clindamycin is one option. Macrolide antibiotics like azithromycin (the well-known “Z-Pack”) and clarithromycin are also FDA-approved for strep throat, though guidelines don’t recommend them as first-line choices. Erythromycin, an older macrolide, is another alternative, though it tends to cause more stomach upset than the newer options.
Why Macrolides Aren’t First Choice
Azithromycin and clarithromycin work against strep, but there’s a growing resistance problem. Canadian surveillance data from 2018 to 2022 found that roughly 9 to 15 percent of strep samples tested resistant to erythromycin, the macrolide class marker. That means if you take a macrolide, there’s about a 1-in-10 chance it simply won’t work. Penicillin and amoxicillin, by contrast, have a resistance rate of essentially zero. The strep bacterium has remained fully susceptible to penicillin for decades, which is unusual and is exactly why it remains the top recommendation.
How Quickly Antibiotics Work
Most people notice real improvement within one to two days of starting treatment. Fever typically breaks first, followed by a gradual easing of throat pain. If you don’t feel any better after 48 hours on antibiotics, contact your doctor. That could mean the diagnosis needs a second look or the chosen antibiotic isn’t working.
You also become much less contagious very quickly. Within 12 hours of your first dose, you’re generally no longer spreading the bacteria. Schools and daycares typically require children to have completed at least 12 hours of antibiotic treatment before returning.
Why Treatment Matters Beyond Symptom Relief
Strep throat will often resolve on its own in terms of sore throat and fever. The reason antibiotics are strongly recommended isn’t just to speed up recovery. It’s to prevent complications that can emerge days or weeks later. Rheumatic fever is the most serious of these. It triggers inflammation in the heart, joints, and nervous system, and it can cause permanent heart valve damage. Antibiotics dramatically reduce this risk when taken promptly after diagnosis.
Other potential complications include peritonsillar abscess (a painful pocket of pus behind the tonsil) and post-streptococcal kidney inflammation. These are uncommon, but antibiotic treatment makes them rarer still. The 10-day course isn’t just about killing the bacteria in your throat. It’s about fully clearing the infection so your immune system doesn’t mount the kind of misdirected inflammatory response that leads to these problems.