Penicillin and amoxicillin are the first-line antibiotics used to treat strep throat. Both have been the standard treatment for decades because Group A Streptococcus, the bacterium responsible, has never developed resistance to them. A typical course lasts 10 days, and most people start feeling better within one to two days of the first dose.
Why Penicillin and Amoxicillin Are First Choice
These two antibiotics work by disrupting the construction of bacterial cell walls. Without intact walls, the bacteria can’t survive or reproduce. Group A Strep remains reliably susceptible to both drugs, which is unusual in an era when antibiotic resistance is a growing concern with many other infections.
Amoxicillin is often preferred for children because it comes in a chewable tablet and a flavored liquid suspension that are easier to take than penicillin. It also works well as a once-daily dose, which simplifies the routine for parents. For adolescents and adults, penicillin V taken twice daily is equally effective. Both options require a full 10-day course to completely clear the infection and reduce the risk of complications like rheumatic fever, a serious inflammatory condition that can damage the heart.
What to Expect After Starting Treatment
Most people notice improvement within one to two days of their first dose. Fever typically breaks first, followed by gradual relief of throat pain and swelling. You’re generally no longer contagious after just 12 hours on the antibiotic, which is why schools and daycares allow kids to return after that initial 12-hour window, provided they feel well enough.
If you don’t have a fever, you can usually resume normal activities 24 hours after taking your first dose. If you’re not improving at all after one to two days, contact your provider. That could signal the wrong diagnosis, a different strain, or an issue with how the medication is being absorbed.
Why You Need the Full 10 Days
Feeling better after two or three days doesn’t mean the infection is gone. Stopping early leaves surviving bacteria in your throat, which can reignite the infection or lead to complications. Rheumatic fever, peritonsillar abscess, and kidney inflammation are all potential consequences of undertreated strep. Completing the full course is one of the most effective things you can do to prevent these outcomes.
For people who are unlikely to finish a 10-day oral course, there’s a one-time injectable option: a single shot of benzathine penicillin G given in the office. It delivers the antibiotic in a slow-release form so no pills are needed afterward. This is sometimes used for children or in situations where follow-through with daily medication is a concern.
Options if You’re Allergic to Penicillin
About 10% of people report a penicillin allergy, and the alternative depends on the type of reaction you’ve had. If your allergy caused a rash but not a severe reaction like throat swelling or anaphylaxis, a first-generation cephalosporin such as cephalexin or cefadroxil is typically recommended. These drugs are structurally related to penicillin but are safe for most people with mild penicillin allergies. The course is also 10 days.
If you’ve had a severe or immediate allergic reaction to penicillin (hives within minutes, difficulty breathing, swelling of the face or throat), cephalosporins are off the table. In that case, a macrolide antibiotic like erythromycin is the standard alternative. Macrolides work through a completely different mechanism, targeting the bacteria’s ability to produce proteins rather than disrupting cell walls. The downside is that some strains of Group A Strep have developed resistance to macrolides, so they’re reserved for people who truly can’t take penicillin-type drugs.
Strep Throat Without Antibiotics
Strep throat will often resolve on its own within about a week, which raises the question of whether antibiotics are strictly necessary. The answer is yes, for several reasons. Antibiotics cut the duration of symptoms by one to two days, reduce the window of contagiousness from weeks down to 12 hours, and most importantly, dramatically lower the risk of rheumatic fever. Before antibiotics were widely used, rheumatic fever was a common and devastating consequence of strep infections, causing permanent heart valve damage in children and young adults.
Over-the-counter pain relievers like ibuprofen or acetaminophen can help manage throat pain and fever while the antibiotic takes effect, but they don’t replace antibiotic treatment. Warm salt water gargles, cold fluids, and throat lozenges can also ease discomfort during the first day or two before the medication kicks in.