The standard antibiotic for strep throat is amoxicillin or penicillin V. These two have been the go-to treatments for decades, and for good reason: no strain of group A strep has ever developed resistance to either one. Most doctors today lean toward amoxicillin, especially for children, because it tastes better in liquid form and can be taken just once or twice a day.
Why Amoxicillin and Penicillin Are First Choice
Amoxicillin and penicillin V remain the top recommendations from both the CDC and the Infectious Diseases Society of America. The bacteria that cause strep throat, group A Streptococcus, have never produced a single documented case of resistance to penicillin-type antibiotics. That’s remarkable given how common resistance has become with other bacteria and other drugs. It means these older, inexpensive antibiotics work just as reliably today as they did when they were first introduced.
Amoxicillin tends to be the practical favorite. It comes in immediate-release tablets, chewable tablets, and a liquid suspension that can be mixed into milk, juice, or formula for young children. For kids, the typical course is once daily for 10 days. Adults and adolescents usually take it twice daily. Penicillin V works equally well but requires more frequent dosing for adults (up to four times a day), which makes it harder to stick with.
The Full 10 Days Matter
The standard course for strep throat is 10 days, regardless of whether you’re taking amoxicillin or penicillin. Most people start feeling noticeably better within one to two days, and it’s tempting to stop early. But the full course is necessary to completely clear the bacteria from your throat and prevent complications.
The most serious complication that antibiotics help prevent is acute rheumatic fever, an inflammatory condition that can damage the heart valves. Rheumatic fever is uncommon in countries where strep is routinely treated, precisely because antibiotics are so effective at eliminating the infection before the immune system overreacts. Stopping your antibiotics early, even if you feel fine, increases the risk of the bacteria lingering and triggering this kind of immune response.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, your doctor will typically prescribe a cephalosporin-type antibiotic (as long as your allergy isn’t severe), or possibly azithromycin or clindamycin. However, these alternatives come with a significant caveat: resistance is a real concern.
A large global analysis of antibiotic resistance in Streptococcus species found that about 34% of group A strep strains showed resistance to azithromycin, the most commonly prescribed penicillin alternative. That means roughly one in three cases may not respond to it. Resistance to clindamycin was lower, around 10%, but still present. By contrast, penicillin and cephalosporin resistance remains at zero. This is a major reason why doctors avoid prescribing azithromycin as a first-line option when penicillin-based antibiotics are safe for the patient.
If you’ve been told you have a penicillin allergy, it’s worth knowing that many people who were labeled allergic as children can actually tolerate penicillin as adults. Allergy testing can clarify this and potentially open the door to the most effective treatment.
How Quickly You’ll Feel Better
Symptoms typically start improving within a day or two of your first dose. Fever usually breaks first, followed by a gradual easing of the sore throat and difficulty swallowing. You’re considered no longer contagious after 24 hours on antibiotics, as long as your fever has resolved. That’s the general threshold for returning to work, school, or daycare.
If you don’t notice any improvement after two to three days, that’s worth a follow-up. It could mean the diagnosis was actually a viral infection (which antibiotics won’t help), or in rarer cases, that the particular strain isn’t responding to the prescribed antibiotic.
Why Strep Needs an Antibiotic at All
Many sore throats are caused by viruses and resolve on their own. Strep throat is different. It’s a bacterial infection, and while your immune system can eventually fight it off without medication, leaving it untreated carries real risks. Beyond rheumatic fever, untreated strep can lead to kidney inflammation, abscesses around the tonsils, and spread of the infection to the bloodstream or surrounding tissue. Antibiotics dramatically shorten the illness, reduce the chance of passing it to others, and prevent these complications. A rapid strep test or throat culture confirms whether bacteria are actually present, so antibiotics are only prescribed when they’re genuinely needed.