Penicillin and amoxicillin are the first-line antibiotics for strep throat. The CDC recommends either one as the preferred treatment, and the standard course lasts 10 days. Group A Streptococcus has never developed resistance to penicillin, which is why it remains the go-to choice decades after it was first used.
Why Penicillin and Amoxicillin Are First Choice
Both penicillin and amoxicillin work by destroying the bacterial cell wall. They bind to enzymes the bacteria need to build and maintain that wall, ultimately killing the organism. Group A Strep remains fully susceptible to these drugs, making them the most reliable and cost-effective option.
Amoxicillin is often preferred for children because it tastes better in liquid form and can be given once or twice daily instead of multiple times a day. For adults and teens, penicillin V taken twice daily for 10 days is the classic prescription. The two drugs are equally effective.
The Single-Shot Alternative
If finishing a 10-day course of pills sounds unlikely (for yourself or your child), there’s a one-and-done option: a single injection of long-acting penicillin G given in the muscle. It delivers the full treatment in one visit. This is especially useful for kids or anyone with a history of not completing antibiotic courses. The downside is the injection itself, which can be painful at the site.
Options If You’re Allergic to Penicillin
A penicillin allergy changes the playbook, and the alternative depends on how severe your allergy is.
If your reaction to penicillin was mild (a rash, for example, not throat swelling or difficulty breathing), a first-generation cephalosporin like cephalexin is typically recommended. These are chemically related to penicillin but are generally safe for people with non-severe allergies. The course is still 10 days.
If your allergy is severe, meaning you’ve had anaphylaxis, significant swelling, or breathing problems, cephalosporins are off the table too. In that case, erythromycin is the traditional alternative. However, there’s an important caveat: resistance to this class of antibiotics (called macrolides) has climbed significantly. Among invasive Group A Strep samples tested in 2023, 27% were resistant to macrolides. That means roughly one in four strep infections may not respond to these drugs. Your provider may want to confirm that the specific strain you have is susceptible before relying on this option.
Why the Full 10 Days Matter
You’ll likely feel dramatically better within two to three days of starting antibiotics. The temptation to stop early is real, but the 10-day course exists for a reason. Cutting it short increases the risk of the infection returning and, more importantly, raises the chance of serious complications like rheumatic fever, which can damage heart valves. Rheumatic fever is rare precisely because most people complete their antibiotic treatment.
How Quickly You Stop Being Contagious
Once you take your first dose, the clock starts ticking on contagiousness. Most public health guidelines consider you no longer contagious within 12 hours of starting antibiotics. That’s the standard threshold for returning to school or work. Before that 12-hour mark, you can still spread the bacteria through coughing, sneezing, or sharing drinks.
Managing Pain While Antibiotics Work
Antibiotics kill the bacteria, but they don’t provide immediate pain relief. Over-the-counter pain relievers like ibuprofen or acetaminophen are the mainstay for sore throat discomfort while you wait for the antibiotic to take full effect.
There’s also growing evidence that a single dose of a corticosteroid can speed up pain relief. A clinical practice guideline published in The BMJ found that corticosteroids increase the chance of complete pain resolution at 24 and 48 hours and shorten the time until you start feeling better. This applies to both adults and children five and older, regardless of whether the sore throat is bacterial or viral. The recommendation is considered weak, though, meaning it’s worth discussing with your provider rather than expecting it as standard care. Not everyone benefits equally, and individual preferences vary.