Penicillin and amoxicillin are the first-line antibiotics for strep throat. They’ve been the go-to treatment for decades because group A strep bacteria have never developed resistance to them, they’re inexpensive, and they work reliably. Most courses last 10 days, and you should start feeling noticeably better within a day or two of your first dose.
First-Line Treatments: Penicillin and Amoxicillin
Penicillin V (the oral tablet form) and amoxicillin are considered equally effective and are recommended as the primary treatment for confirmed strep throat in both adults and children. Amoxicillin tends to be the more common prescription in practice, partly because it comes in a chewable tablet and liquid form that tastes better for kids, and partly because it can be taken with or without food.
A standard course runs 10 days. That length isn’t arbitrary. Shorter courses don’t fully clear the bacteria from your throat, which increases the chance of relapse or complications. Even though you’ll likely feel much better after 24 to 48 hours, finishing the full course matters. Stopping early is one of the most common reasons strep comes back.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, your options depend on the type of reaction you’ve had. For people whose allergy caused a rash but not a severe reaction like throat swelling or anaphylaxis, cephalosporins are a solid alternative. Cephalexin (taken twice daily for 10 days) and cefadroxil (once daily for 10 days) are both recommended. These are chemically related to penicillin but distant enough that most people with mild penicillin allergies tolerate them without issues.
If your penicillin allergy is severe, meaning it caused hives, swelling, difficulty breathing, or anaphylaxis, cephalosporins are off the table too. In that case, the alternatives include:
- Azithromycin: A 5-day course, with a higher dose on the first day followed by four days at a lower dose. This is the shortest treatment option available.
- Clarithromycin: Taken twice daily for 10 days.
- Clindamycin: Taken three times daily for 10 days.
There’s a catch with all three of these alternatives. Resistance is a real and growing problem. Among invasive group A strep samples tested in 2023, 27% were resistant to macrolides like azithromycin, and 26% were resistant to clindamycin. Resistance rates vary by region, so what works in one area may not work as well in another. This is a key reason these antibiotics aren’t used as first-line treatments for anyone who can tolerate penicillin.
Why a Z-Pack Isn’t the Best Choice
Azithromycin (commonly known as a “Z-Pack”) is one of the most frequently prescribed antibiotics in the U.S. for all sorts of infections, and many people expect to receive it for strep throat. It’s appealing because it’s only five days and taken once a day. But that convenience comes with a tradeoff: roughly one in four strep infections may not respond to it due to bacterial resistance.
If your doctor prescribes azithromycin for strep and your symptoms aren’t improving after two to three days, the antibiotic may not be working. Penicillin and amoxicillin don’t carry this risk because group A strep has remained universally sensitive to them.
How Quickly Antibiotics Work
Most people notice real improvement within one to two days of starting antibiotics. The sore throat eases, fever drops, and swallowing becomes less painful. You stop being contagious even faster. Within 12 hours of your first dose, you’re generally no longer able to spread the infection to others. That’s the threshold most schools and workplaces use for return.
Full symptom resolution can take several more days, though. Swollen lymph nodes in the neck often linger for a week or more even after the bacteria are cleared. That’s normal and doesn’t mean the antibiotic failed.
Why Treatment Matters
Strep throat can technically resolve on its own, but leaving it untreated creates real risks. The most serious is rheumatic fever, an inflammatory condition that can damage heart valves permanently. Severe cases of rheumatic heart disease require surgery and can be fatal. Antibiotics prevent this complication almost entirely.
Untreated strep can also lead to a kidney inflammation called post-streptococcal glomerulonephritis, peritonsillar abscess (a painful collection of pus behind the tonsils), and spread of the infection into the bloodstream. These complications are uncommon with proper antibiotic treatment, which is why getting tested and treated when you have classic strep symptoms, like sudden sore throat, fever, swollen tonsils with white patches, and no cough, is worth the effort.
Confirming It’s Actually Strep
Antibiotics only help if the sore throat is actually caused by bacteria. Most sore throats are viral, and antibiotics do nothing for those. A rapid strep test takes about 5 to 10 minutes in a clinic and is the standard way to confirm the diagnosis before starting treatment. If the rapid test is negative but strep is still strongly suspected (especially in children), a throat culture may be sent to a lab for a more definitive answer.
Symptoms that point toward strep rather than a virus include sudden onset of throat pain, pain when swallowing, fever, red and swollen tonsils (sometimes with white patches), and tiny red spots on the roof of the mouth. A cough, runny nose, hoarseness, and conjunctivitis tend to signal a viral infection instead. Getting tested before taking antibiotics protects you from unnecessary side effects and helps reduce antibiotic resistance at the population level.