The standard antibiotic for strep throat is penicillin or amoxicillin, taken for 10 days. These have been the go-to treatment for decades because Group A Streptococcus, the bacterium that causes strep throat, has never developed resistance to penicillin. If you have a penicillin allergy, your doctor will choose from a short list of alternatives depending on the type of allergy you have.
First-Line Antibiotics for Children and Adults
The recommended antibiotic differs slightly by age. For children, amoxicillin is preferred because it tastes better in liquid form and can be given once a day. The CDC recommends a weight-based dose taken once daily for 10 days, up to a maximum of 1,000 mg. For teenagers and adults, penicillin V is the standard choice, taken either twice or four times daily for the same 10-day course.
Both drugs work the same way and are equally effective. The reason amoxicillin gets the nod for kids is purely practical: children are more likely to finish a course of medicine that doesn’t taste terrible and only needs to be taken once a day. For adults who can swallow pills without issue, penicillin V is inexpensive and widely available.
A full 10 days matters even though you’ll feel better much sooner. Stopping early leaves surviving bacteria in your throat, which raises the risk of the infection returning and of a serious complication called rheumatic fever, a condition that can damage heart valves. During epidemics studied over the past half-century, up to 3% of untreated strep infections led to rheumatic fever. Completing the antibiotic course prevents this in most cases.
Options If You’re Allergic to Penicillin
Not all penicillin allergies are the same, and what you’re prescribed depends on how severe your reaction was. If your allergy caused a rash but not a serious reaction like throat swelling or difficulty breathing, a first-generation cephalosporin is typically recommended. These are chemically related to penicillin but are generally safe for people whose allergy is mild.
If you’ve had a severe, immediate-type reaction to penicillin (hives, swelling, anaphylaxis), cephalosporins are off the table. In that case, your doctor will prescribe a macrolide antibiotic. Azithromycin and clarithromycin are the two most commonly used because erythromycin, the older macrolide, tends to cause significant stomach upset that makes people quit the course early.
Growing Resistance to Macrolides
There is one important caveat with macrolide antibiotics. Unlike penicillin, Group A Strep can develop resistance to them. Surveillance data from Australia shows erythromycin resistance in strep isolates was below 4% for a decade, then climbed to 9.5% by 2021 before falling back to about 6% in 2023. Clindamycin resistance follows a similar pattern, hitting 11% in 2022 before dropping to 6%. These numbers fluctuate as different bacterial strains circulate through the population.
This doesn’t mean macrolides won’t work for you, but it does explain why they aren’t first-line for everyone. Penicillin and amoxicillin remain effective essentially 100% of the time, which is why doctors reserve macrolides for patients who truly can’t take penicillin-type drugs.
How Quickly Antibiotics Work
Most people start feeling noticeably better within one to two days of starting treatment. Fever tends to break first, followed by a gradual reduction in throat pain. You become non-contagious faster than you might expect: within 12 hours of your first dose, you’re no longer spreading the bacteria to others. That 12-hour mark is the standard threshold schools and workplaces use for return.
If your symptoms haven’t improved at all after two to three days on antibiotics, contact your doctor. This could mean the diagnosis needs to be reconsidered, or in rare cases, that the prescribed antibiotic isn’t working.
Why a Test Comes Before a Prescription
Strep throat can look identical to a viral sore throat, and antibiotics do nothing for viruses. That’s why doctors confirm the diagnosis with a rapid strep test or throat culture before prescribing anything. The rapid test gives results in minutes. If it comes back negative but your symptoms are suspicious, a throat culture (which takes one to two days) can catch infections the rapid test missed.
Doctors also use a clinical scoring system to decide who needs testing in the first place. It assigns points based on factors like fever, swollen tonsils with white patches, swollen lymph nodes in the neck, absence of cough, and age. A high score doesn’t confirm strep, but it identifies people who are most likely to benefit from testing. A low score, especially in someone with a cough and runny nose, points toward a virus and usually means no test is needed.
What Happens If Strep Goes Untreated
Most strep throat infections will eventually resolve on their own, but leaving them untreated carries real risks. The most concerning is rheumatic fever, which can develop one to five weeks after the infection. Rheumatic fever causes inflammation in the heart, joints, and nervous system, and the heart damage it causes can be permanent. Antibiotics nearly eliminate this risk.
Other potential complications include peritonsillar abscess, where a pocket of pus forms near the tonsils, and post-streptococcal kidney inflammation. These are uncommon but serious enough that treatment is strongly recommended for anyone with a confirmed positive test, even if their symptoms feel manageable.