Amoxicillin is the most commonly prescribed antibiotic for strep throat in both children and adults. It’s the top recommendation from the CDC and infectious disease specialists because it’s effective, affordable, well-tolerated, and available in liquid form for kids. The standard course lasts 10 days, and most people start feeling noticeably better within one to two days of the first dose.
First-Line Antibiotics
Amoxicillin and penicillin are the two primary antibiotics used to treat strep throat. Group A Streptococcus, the bacterium responsible for strep, has never developed resistance to either one, which is why they’ve remained the go-to options for decades.
Amoxicillin is typically preferred in practice because it tastes better in liquid form (important for children) and can be taken once or twice daily. Adults generally take up to 1,000 mg once a day or 500 mg twice a day for 10 days. Children receive a weight-based dose. Penicillin V, the oral tablet form, works just as well but is prescribed less often simply because of convenience and taste.
For people who have trouble finishing a 10-day oral course, or when a provider wants to guarantee the full dose is received, a single injection of long-acting penicillin (penicillin G benzathine) is an option. One shot in the office covers the entire treatment. This approach reduces the risk of rheumatic fever by roughly 80%, compared to about 70% with oral penicillin, likely because there’s no chance of missed doses.
Options if You’re Allergic to Penicillin
If you have a penicillin allergy, the alternatives depend on how severe your allergy is. People whose reaction was a mild rash (not involving throat swelling, hives, or difficulty breathing) can often safely take a first-generation cephalosporin like cephalexin. These are chemically related to penicillin but rarely trigger the same allergic response in people with non-severe allergies.
If your allergy involved a serious reaction, cephalosporins are avoided entirely. In that case, macrolide antibiotics are the standard alternatives. Azithromycin is the most commonly prescribed because it’s a shorter course (typically five days) and causes fewer stomach issues than older macrolides like erythromycin. Clarithromycin is another option in the same drug class. Clindamycin, a different type of antibiotic, is also effective and sometimes preferred when macrolide resistance is a concern.
One thing worth knowing: macrolide resistance in strep bacteria has been climbing. A national surveillance study found roughly 8.5% of Group A Strep samples were resistant to macrolides, and some regions report higher rates. Penicillin and amoxicillin have zero resistance, which is another reason they remain the first choice whenever possible.
Why the Full 10-Day Course Matters
Ten days feels like a long time to take an antibiotic, especially when your throat feels fine after two or three days. But the full course serves a purpose beyond killing the bacteria in your throat. It significantly lowers the risk of rheumatic fever, a serious inflammatory condition that can damage the heart valves. Prompt antibiotic treatment reduces that risk by 70 to 80%.
Stopping early also increases the chance of the infection coming back. Bacteria that survive a partial course can repopulate, leading to a relapse that requires another round of treatment. Completing the full prescription is the single most important thing you can do to avoid complications and prevent reinfection.
How Quickly Antibiotics Work
Most people notice improvement within one to two days of starting antibiotics. Fever typically breaks first, followed by a gradual easing of throat pain. If you don’t feel any better after 48 hours, contact your provider. That could mean the diagnosis needs to be reconsidered, or rarely, that the antibiotic isn’t working as expected.
You’re generally considered no longer contagious after about 12 to 24 hours on antibiotics. Most schools and workplaces follow the 24-hour rule: once you’ve been on antibiotics for a full day and your fever has resolved, you can return. Before that window, strep spreads easily through respiratory droplets, so staying home during that first day of treatment protects the people around you.
What to Expect During Treatment
Amoxicillin and penicillin are well-tolerated overall, but mild side effects are common. Nausea, diarrhea, and stomach discomfort happen in a small percentage of people. Taking the antibiotic with food usually helps. Skin rashes can also occur, though a rash during amoxicillin treatment doesn’t always mean you’re allergic. Some rashes are a non-allergic reaction, particularly in children. If you develop hives, facial swelling, or difficulty breathing, that’s a true allergic reaction and requires immediate medical attention.
Azithromycin and clarithromycin tend to cause more digestive side effects than amoxicillin. Erythromycin is the most likely to upset your stomach, which is why it’s rarely the first alternative chosen despite being listed in older guidelines. Clindamycin can occasionally disrupt gut bacteria more significantly, so it’s usually reserved for situations where other options aren’t suitable.