Penicillin and amoxicillin are the top choices for treating strep throat. Neither one is newer or stronger than the other in this case. Group A Streptococcus, the bacterium behind strep throat, has never developed resistance to penicillin, making these two antibiotics consistently effective after decades of use.
Why Amoxicillin and Penicillin Are First Choice
Both antibiotics work the same way, destroying the cell wall of the strep bacterium. Amoxicillin is prescribed more often in practice, especially for children, because it tastes better in liquid form and can be taken once or twice a day instead of multiple times. The standard course for both is 10 days.
For adults, penicillin V is typically prescribed at 500 mg twice daily. Amoxicillin dosing for children is weight-based, up to a maximum of 1,000 mg per day. A single injection of penicillin G is another option, which eliminates the need to remember pills for 10 days. This is sometimes used when there’s concern a patient may not finish a full oral course.
How Quickly Symptoms Improve
Most people start feeling noticeably better within one to two days of the first dose. Fever usually drops first, followed by a gradual easing of throat pain. If you see no improvement after 48 hours on antibiotics, contact your prescriber. That timeline matters because it can signal a different infection, a resistant strain, or a need to re-evaluate the diagnosis.
You stop being contagious roughly 12 hours after taking the first dose. That’s the threshold schools and workplaces generally use for return. Before antibiotics, strep can remain contagious for two to three weeks even as symptoms fade on their own.
Options If You’re Allergic to Penicillin
A true penicillin allergy (hives, swelling, difficulty breathing) rules out both penicillin and amoxicillin. In that case, alternatives include a first-generation cephalosporin like cephalexin, though this is only safe if your allergy was mild, since cephalosporins share some structural similarity with penicillin. For more severe penicillin allergies, clarithromycin or erythromycin are commonly used instead.
Azithromycin (the popular “Z-pack”) was once a go-to alternative, but resistance has changed the picture. According to CDC surveillance data, around 1 in 3 invasive group A strep infections are now caused by bacteria resistant to both erythromycin and clindamycin, antibiotics in the same family as azithromycin. That doesn’t mean these drugs never work, but it does mean your provider may choose a different option or confirm the strain’s sensitivity before prescribing one.
Why the Full 10 Days Matter
Strep throat often feels completely resolved by day three or four. The temptation to stop taking the antibiotic early is real, but the remaining days of treatment serve a purpose beyond symptom relief. A full course clears the bacterium from your throat, which reduces the risk of complications and prevents you from becoming a carrier who can still spread strep to others without feeling sick.
The most serious complication antibiotics help prevent is acute rheumatic fever, an inflammatory condition that can damage heart valves. Rheumatic fever typically develops one to five weeks after an untreated or inadequately treated strep infection. It’s uncommon in the U.S. today largely because antibiotics are prescribed so routinely. Completing the full course also helps prevent peritonsillar abscess, a painful pocket of pus that can form near the tonsils and sometimes requires drainage.
Strep vs. a Viral Sore Throat
Antibiotics only work against strep throat, not viral sore throats, which account for the majority of sore throats in adults. The key distinguishing features of strep are sudden onset of severe throat pain, fever above 101°F (38.3°C), swollen and tender lymph nodes in the front of the neck, and white patches or streaks on the tonsils. Cough, runny nose, and hoarseness point more toward a virus.
A rapid strep test or throat culture confirms the diagnosis. Rapid tests return results in minutes and are highly accurate when positive. A negative rapid test in a child is often followed up with a throat culture, which takes one to two days but catches cases the rapid test misses. For adults, a negative rapid test is usually considered reliable enough on its own because the risk of rheumatic fever is much lower.
What to Do While Waiting for the Antibiotic to Work
Over-the-counter pain relievers like ibuprofen or acetaminophen help manage throat pain and fever in the first couple of days before the antibiotic fully kicks in. Cold drinks, ice pops, and soft foods are easier to tolerate than anything rough or acidic. Warm salt water gargles (about half a teaspoon of salt in a cup of warm water) can temporarily soothe throat irritation, though they don’t treat the infection itself.
Staying hydrated matters more than most people realize during strep throat. Painful swallowing often leads to drinking less, which can make fatigue and headaches worse. Small, frequent sips of water or broth are easier to manage than large glasses.