Penicillin and amoxicillin are the recommended antibiotics for strep throat. Group A Streptococcus, the bacterium behind strep, has never developed resistance to penicillin, making it a reliable first choice decades after it was introduced. Most people start feeling better within a day or two of their first dose.
First-Line Antibiotics: Penicillin and Amoxicillin
The CDC recommends penicillin or amoxicillin as the primary treatment for strep throat. Both are equally effective at clearing the infection and preventing complications. Amoxicillin is often preferred for children because it tastes better in liquid form and can be taken once daily, while penicillin typically requires multiple doses throughout the day.
For adolescents and adults, penicillin V is taken as 500 mg twice daily for 10 days. Amoxicillin dosing for children is based on body weight, up to a maximum of 1,000 mg per day. Both courses last a full 10 days, and finishing the entire prescription matters even after symptoms disappear. Stopping early increases the chance the infection returns.
For people who have trouble taking pills reliably, or for young children who may resist a 10-day course, a single injection of a long-acting form of penicillin is an option. Children under about 60 pounds receive a lower dose, while older children and adults receive a higher one. One shot and the treatment is complete.
If You’re Allergic to Penicillin
About 10% of people report a penicillin allergy, and the alternative depends on how severe that allergy is. If your reaction was mild (a rash, for example, but not throat swelling or difficulty breathing), a first-generation cephalosporin is typically the next choice. These are chemically related to penicillin but are considered safe for people whose allergic reactions were not severe.
If you’ve had a serious allergic reaction to penicillin, the options shift to a different class of antibiotics entirely. Azithromycin, clarithromycin, erythromycin, and clindamycin are all alternatives. Azithromycin has the advantage of a shorter course, usually 3 to 5 days, because the drug stays active in your body longer than other antibiotics. All the other alternatives still require a 10-day course.
There’s an important caveat with these backup options. Macrolide antibiotics like azithromycin and clarithromycin face growing resistance from strep bacteria in some regions. Studies from certain areas have found resistance rates to macrolides above 70%, meaning the drug simply doesn’t work against those strains. Resistance patterns vary by geography, so your prescriber’s choice may depend partly on what’s circulating in your area. Penicillin and amoxicillin don’t have this problem.
How Strep Is Diagnosed Before Prescribing
Not every sore throat is strep, and antibiotics won’t help viral infections. Clinicians use a set of four signs to estimate the likelihood of strep: fever of 100.4°F (38°C) or higher, no cough, swollen lymph nodes at the front of your neck, and white patches or swelling on the tonsils. Each sign present adds one point on a scoring system. A score of 3 or higher suggests strep is likely enough to warrant a rapid strep test or throat culture before starting treatment.
Rapid strep tests give results in minutes and are quite accurate when positive. A negative rapid test is sometimes followed up with a throat culture, which takes a day or two but catches cases the rapid test misses. Antibiotics are prescribed once testing confirms strep, not based on symptoms alone.
What to Expect After Starting Treatment
Most people notice their fever dropping and throat pain easing within the first one to two days on antibiotics. You become much less contagious quickly: within 12 hours of your first dose, you’re generally no longer able to spread strep to others. That 12-hour mark is also the standard threshold for returning to school or work.
Even though you’ll feel better fast, the bacteria aren’t fully eliminated in those first couple of days. The full 10-day course (or 3 to 5 days for azithromycin) is designed to wipe out the infection completely. Incomplete treatment is one of the main reasons strep comes back, sometimes within weeks.
Why Treating Strep Matters Beyond the Sore Throat
Strep throat is uncomfortable but manageable. The real reason antibiotics are important is what untreated strep can lead to. Rheumatic fever, a condition where the immune system attacks the heart valves, is a rare but serious complication of untreated strep. Antibiotics prevent rheumatic fever even when started up to 9 days after symptoms begin, according to research from the American Heart Association. That’s a generous window, but there’s no reason to wait.
Other potential complications include peritonsillar abscess (a painful collection of pus near the tonsils) and post-streptococcal kidney inflammation. These are uncommon with proper treatment. The 10-day antibiotic course was specifically designed to prevent these outcomes, not just to resolve the sore throat.