Penicillin and amoxicillin are the first-choice antibiotics for strep throat. Both are taken for 10 days, and most people start feeling better within two to three days of their first dose. If you’re allergic to penicillin, a few alternative antibiotics work well, though the options narrow depending on the type of allergy you have.
Penicillin and Amoxicillin: The Standard Treatment
Group A strep bacteria have never developed resistance to penicillin, which is why it remains the top recommendation after decades of use. Amoxicillin, a close relative of penicillin, is equally effective and often preferred for children because it tastes better in liquid form and can be given once a day.
For adults and teens, penicillin V is typically prescribed as 500 mg twice daily for 10 days. Children take a lower dose, usually 250 mg two or three times daily for the same duration. Amoxicillin simplifies things further: children can take a single daily dose (based on weight, up to 1,000 mg), and adults follow a similar schedule. Both drugs are inexpensive and widely available.
The full 10 days matters even though you’ll feel better much sooner. Stopping early leaves bacteria alive and increases the chance of the infection returning or, in rare cases, triggering complications like rheumatic fever.
The One-Shot Option
If finishing a 10-day course of pills is likely to be a problem, there’s an injectable alternative. A single shot of long-acting penicillin G benzathine, given in a doctor’s office, treats the infection completely with no follow-up doses needed. It’s the same antibiotic delivered in a form that releases slowly over days. The injection is given into a muscle, usually the thigh or buttock, and the dosing is based on body weight. This option is especially useful for young children or anyone who has trouble sticking with daily medications.
Alternatives for Penicillin Allergies
About 10% of people report a penicillin allergy, so alternatives come up often. The right substitute depends on how severe your allergy is.
If your reaction to penicillin was mild (a rash, for example, rather than throat swelling or difficulty breathing), a first-generation cephalosporin like cephalexin is generally safe. Cephalosporins are structurally related to penicillin, but true cross-reactivity is uncommon. Your prescriber will assess whether this is appropriate based on your allergy history.
For more serious penicillin allergies, the usual alternatives are macrolide antibiotics (like azithromycin) or clindamycin. These belong to entirely different drug families and carry no cross-reactivity risk. However, there’s a catch: strep bacteria are increasingly resistant to macrolides. Surveillance data from Europe show macrolide resistance rates climbing to around 9% in some years, and similar trends have appeared elsewhere. That means azithromycin won’t work for roughly 1 in 10 strep infections, a failure rate high enough that some clinicians prefer clindamycin when penicillin is off the table.
How Quickly Antibiotics Work
You can expect fever to break and throat pain to start improving within the first 24 to 48 hours of treatment. By day three, most people feel significantly better. You stop being contagious even faster: within about 12 hours of your first dose. That’s the benchmark schools and daycares use to decide when a child can return.
Despite the quick symptom relief, the bacteria take longer to fully clear. That’s the reason behind the 10-day course. Cutting it short while you feel fine is the most common mistake people make with strep treatment.
Why Antibiotics Are Prescribed at All
Strep throat will usually resolve on its own, so you might wonder why antibiotics are standard. The primary reason is preventing rheumatic fever, a serious inflammatory condition that can damage the heart. During historical epidemics, up to 3% of untreated strep infections led to rheumatic fever. The rate is lower now in typical community settings, but the stakes are high enough that treatment is strongly recommended. Appropriate antibiotic therapy prevents rheumatic fever in most cases.
Antibiotics also reduce the risk of the infection spreading to nearby tissue, which can lead to a peritonsillar abscess (an intensely painful pocket of pus behind the tonsil). And by shortening the contagious window from a week or more down to about 12 hours, treatment helps protect the people around you.
Getting the Right Diagnosis First
Antibiotics should only be prescribed after a positive rapid strep test or throat culture. Most sore throats are caused by viruses, and antibiotics do nothing for those. Clinical guidelines recommend using a scoring system based on your symptoms (fever, swollen lymph nodes, absence of cough, visible pus on the tonsils) to decide who should be tested. A low score suggests a viral cause, and testing may not be needed.
There are exceptions. If you live with someone who has a confirmed strep infection, have a history of rheumatic fever, or show signs of a more serious complication like scarlet fever, testing is warranted even if your symptoms are mild. Children under three are also handled differently because strep infections in that age group often don’t produce the classic sore throat presentation, making standard scoring systems unreliable.
What Happens if You Skip Treatment
Most untreated strep infections resolve within a week, but the risks linger. Rheumatic fever typically develops two to four weeks after the initial infection, and about a third of rheumatic fever cases follow strep infections that were never symptomatic enough for the person to seek care. You can’t always prevent what you don’t know about, but when strep is diagnosed, treating it is straightforward and eliminates most of the downstream risk.
Post-streptococcal kidney inflammation is another possible complication, though antibiotics haven’t been conclusively shown to prevent it. The kidneys typically recover fully regardless, but the condition can cause alarming symptoms like dark urine and facial swelling in the weeks following a strep infection.