Penicillin and amoxicillin are the recommended first-line antibiotics for strep throat. Both have been the standard treatment for decades because Group A Streptococcus, the bacterium that causes strep, has never developed resistance to them. Most people start feeling better within one to two days of their first dose, and they’re typically no longer contagious after 24 hours on treatment.
Penicillin and Amoxicillin: The First Choice
The CDC recommends penicillin or amoxicillin as the go-to treatment for strep throat in both children and adults. Between the two, amoxicillin is often preferred for kids because it tastes better in liquid form and can be given once a day. For adults, penicillin V taken twice daily at 500 mg is a common option.
The standard course for both medications is 10 days. That duration matters. Even though symptoms improve quickly, stopping early gives the bacteria a chance to survive and raises the risk of complications like rheumatic fever, a serious inflammatory condition that can damage the heart. Finishing the full course is one of the primary ways to prevent it.
For people who have trouble remembering a daily pill for 10 days, there’s a one-shot alternative: a single injection of penicillin G given at the doctor’s office. One visit, no pills to remember, and the treatment is complete.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, the alternatives depend on what kind of reaction you’ve had. People whose allergy causes a rash but not a severe reaction (like throat swelling or difficulty breathing) can typically take a first-generation cephalosporin such as cephalexin. These are chemically related to penicillin but different enough that most people with mild penicillin allergies tolerate them without problems. The usual adult course is 500 mg twice daily for 10 days.
If your allergy is more severe, involving hives, swelling, or anaphylaxis, cephalosporins are off the table too. In that case, the options shift to a completely different class of antibiotics called macrolides. Azithromycin is the most commonly prescribed, largely because it has a shorter, simpler course: one higher dose on the first day followed by four more days at a lower dose, for five days total. Clarithromycin is another macrolide option. Erythromycin is also effective but tends to cause more stomach upset, so it’s prescribed less often in practice.
One thing to know about macrolides: unlike penicillin, they can run into resistance. Resistance rates for Group A Strep to macrolides fluctuate over time and by region, sometimes reaching above 10%. Penicillin and amoxicillin don’t have this problem, which is a key reason they remain the top choice whenever possible.
Treatment for Children
Children with strep throat are treated with the same antibiotics as adults, just at weight-based doses. Amoxicillin is the most popular choice for kids because it comes in a flavored liquid suspension and can be dosed once daily (based on the child’s weight, up to a maximum of 1,000 mg). That once-a-day schedule makes it far easier for parents to stay on track compared to giving penicillin two or three times a day.
Penicillin V is also an option for children, typically at 250 mg given two to three times daily for 10 days. For kids who resist taking oral medication altogether, the single penicillin injection is available, with a lower dose for children under about 60 pounds.
Children who are feeling well and fever-free can usually return to school or daycare after they’ve been on their antibiotic for at least 24 hours.
Why the Full 10 Days Matters
Most people feel dramatically better after just a day or two on antibiotics, which creates a strong temptation to stop taking them. But the 10-day course exists for a specific reason: it takes that long to fully eliminate the bacteria from your throat. Cutting it short increases the chance of the infection coming back and, more importantly, raises the risk of rheumatic fever. Rheumatic fever can develop weeks after an inadequately treated strep infection and cause lasting damage to heart valves.
Rheumatic fever is also more likely to recur once someone has had it. People with a history of it need ongoing antibiotic prophylaxis, essentially low-dose preventive antibiotics, to protect against future strep infections triggering another episode. Completing that initial 10-day course is the simplest way to avoid ever reaching that point.
What to Expect During Recovery
Antibiotics don’t bring instant relief, but they work fast. Most people notice their fever dropping and throat pain easing within the first one to two days. During that initial window, over-the-counter pain relievers, warm liquids, and cold foods like popsicles can help manage discomfort.
You’re generally considered no longer contagious after 24 hours on antibiotics. Before that point, strep spreads easily through respiratory droplets, so staying home from work or school for at least that first day protects the people around you. If your fever persists beyond two to three days of treatment, or your symptoms worsen instead of improve, that’s worth a follow-up call to your doctor. It could signal a complication like a peritonsillar abscess, or in rare cases, a need to switch antibiotics.
Confirming the Diagnosis First
Antibiotics only help if you actually have strep. Most sore throats are caused by viruses, which antibiotics can’t treat. Your doctor will confirm the diagnosis with a rapid strep test (results in minutes) or a throat culture (results in one to two days) before prescribing anything. Taking antibiotics for a viral sore throat won’t speed your recovery and contributes to antibiotic resistance, so this step is worth the brief wait.