Penicillin and amoxicillin are the go-to antibiotics for strep throat. They’ve been the standard treatment for decades, and Group A Streptococcus bacteria have never developed resistance to them. Most people start feeling noticeably better within a day or two of their first dose.
Why Penicillin and Amoxicillin Are First Choice
The CDC lists penicillin or amoxicillin as the antibiotic of choice for strep throat. Both are effective, affordable, and have a long safety track record. The reason doctors haven’t moved on to newer antibiotics is simple: strep bacteria remain fully susceptible to penicillin, so there’s no need for anything stronger.
Amoxicillin is often preferred for children because it comes in a chewable tablet and a liquid suspension that tastes better than penicillin. It also has the advantage of once-daily dosing (compared to penicillin, which needs to be taken multiple times a day), making it easier for parents to stay on schedule. Adults are typically prescribed penicillin V, taken twice daily at 500 mg or four times daily at 250 mg.
For people who are unlikely to finish a full course of oral antibiotics, there’s a one-shot option. A single injection of penicillin G cures strep throat without any follow-up doses. It’s given based on weight: a lower dose for children under about 60 pounds, and a full dose for everyone else.
The Full 10-Day Course Matters
Regardless of which antibiotic you’re prescribed, the standard course for strep throat is 10 days. This is longer than many people expect, especially since symptoms improve so quickly. But the full course isn’t just about making you feel better. It’s about fully clearing the bacteria and preventing complications.
The most serious complication strep throat can cause is rheumatic fever, an inflammatory condition that can damage the heart valves. Antibiotics are highly effective at preventing it, even when treatment doesn’t start right away. Research from the American Heart Association shows that penicillin prevents rheumatic fever even when started as late as nine days after symptoms begin. That said, starting sooner means you feel better sooner and stop spreading the infection faster.
Stopping antibiotics early because you feel fine is one of the most common mistakes. Your throat may feel normal by day three or four, but the bacteria can still be present. Finishing the course ensures the infection is truly gone.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, the alternative depends on how severe your allergy is. For people whose reaction was mild (a rash, for example), a first-generation cephalosporin is typically recommended. These antibiotics are chemically related to penicillin but are generally safe for people with non-severe allergies.
For people with a severe penicillin allergy, such as throat swelling or anaphylaxis, the usual alternatives are macrolide antibiotics like azithromycin or clarithromycin. Erythromycin is also an option, though it tends to cause more stomach upset, so most doctors prescribe one of the newer macrolides instead.
One thing worth knowing: macrolide antibiotics face some resistance from strep bacteria. Canadian surveillance data from 2018 to 2022 found that roughly 9 to 15 percent of Group A Strep samples were resistant to erythromycin (and resistance to erythromycin generally applies to azithromycin and clarithromycin as well). Penicillin resistance, by contrast, is essentially zero. So if you’ve been told you’re allergic to penicillin but were never formally tested, it may be worth discussing allergy testing with your doctor, since many people who were labeled penicillin-allergic in childhood can actually tolerate it safely.
How Quickly You’ll Feel Better
Most people notice improvement within one to two days of starting antibiotics. Fever usually breaks first, followed by a gradual reduction in throat pain. By day three, many people feel close to normal, though mild soreness can linger.
You stop being contagious surprisingly fast. Within 12 hours of your first antibiotic dose, you’re no longer considered infectious. That’s the standard used by schools and workplaces: children and adults can return after being on antibiotics for at least 12 hours, as long as they feel well enough.
What Happens Without Antibiotics
Strep throat will eventually resolve on its own in most cases, usually within about a week. But going without antibiotics carries real risks. Beyond rheumatic fever, untreated strep can lead to kidney inflammation, abscesses around the tonsils, and spread of the infection to the bloodstream or surrounding tissue. You also remain contagious for much longer without treatment.
Antibiotics shorten the duration of symptoms, reduce the risk of complications, and protect the people around you. For a condition where the first-line treatment is inexpensive, well-tolerated, and highly effective, there’s little reason to skip it.