Amoxicillin is the go-to antibiotic for strep throat in both children and adults. It’s effective, well-tolerated, affordable, and available in liquid form for kids. For people with a penicillin allergy, several alternatives work well, including certain cephalosporins and macrolide antibiotics.
Why Amoxicillin Is the First Choice
Amoxicillin tops the list because Group A Streptococcus, the bacterium behind strep throat, has never developed resistance to it. That’s unusual in an era of growing antibiotic resistance, and it makes amoxicillin a reliable pick every time. The standard course is 10 days, taken either once or twice daily. For children, the dose is based on body weight, with a maximum of 1,000 mg per day.
Penicillin itself also works and is considered equally effective, but amoxicillin tastes better in liquid form and can be dosed once a day, which makes it the more practical option for families with young children.
A single injection of penicillin is another route. It’s sometimes used when there’s concern a patient won’t complete the full 10-day oral course. One shot and it’s done.
Options If You’re Allergic to Penicillin
If you have a penicillin allergy, the alternatives depend on the type of reaction you’ve had. People whose allergy causes a rash but not breathing problems or facial swelling can typically take a first-generation cephalosporin like cephalexin or cefadroxil. These are in a related drug family but are considered safe when the allergy isn’t severe. The course is also 10 days.
For people with a more serious penicillin allergy (hives, throat swelling, anaphylaxis), cephalosporins are off the table. In that case, macrolide antibiotics are the go-to. Azithromycin is the most commonly prescribed because it only requires five days of treatment and reaches high concentrations in throat tissue. Clarithromycin is another macrolide option, taken for 10 days.
There’s one caveat with macrolides: resistance is growing. Canadian surveillance data from 2018 to 2022 found that roughly 9 to 15 percent of invasive Group A Strep samples were resistant to erythromycin, which signals broader macrolide resistance. That means azithromycin won’t work for a small but meaningful percentage of strep cases. If you’re prescribed a macrolide and your symptoms aren’t improving after two days, it’s worth following up.
Why the Full 10 Days Matters
Most people start feeling noticeably better within one to two days of their first dose. By that point, fever typically drops and throat pain eases up. It’s tempting to stop taking the antibiotic once you feel fine, but the 10-day course exists for a specific reason: preventing rheumatic fever.
Rheumatic fever is a rare but serious inflammatory condition that can damage the heart valves. It develops when the immune system overreacts to a strep infection that wasn’t fully cleared. Completing the full antibiotic course is the primary way to prevent it. This is one situation where “I feel better” and “I’m actually better” are not the same thing. Take every dose, even when your throat feels completely normal by day three.
How Quickly You Stop Being Contagious
Once you start antibiotics, you’re generally no longer contagious within 12 hours. Schools and daycares use this same 12-hour window as their readmission benchmark. So if you take your first dose in the evening, you’re typically cleared to return to work or school the next morning, assuming you feel up to it.
Without antibiotics, strep remains contagious for two to three weeks, even as symptoms fade on their own. The infection can resolve without treatment in many cases, but the contagious window is much longer and the risk of complications is higher.
Getting Tested Before Treatment
Strep throat symptoms overlap heavily with viral sore throats: pain when swallowing, swollen tonsils, fever, sometimes a headache. The difference matters because antibiotics do nothing for a virus. A rapid strep test takes about five minutes and gives a reliable answer. If it comes back negative but symptoms are highly suspicious, a throat culture can catch cases the rapid test misses, with results usually back in one to two days.
Testing first prevents unnecessary antibiotic use, which contributes to resistance and exposes you to potential side effects (nausea, diarrhea, rash) for no benefit. If your provider prescribes antibiotics for a sore throat without testing, it’s reasonable to ask why.
What to Expect During Treatment
The most common side effects of amoxicillin are mild: stomach upset, diarrhea, and occasionally a rash. Taking it with food helps reduce nausea. For children on the liquid form, refrigerating it can improve the taste.
If your symptoms haven’t improved at all after 48 hours on antibiotics, something else may be going on. The strain could be resistant to the prescribed drug (more likely with macrolides than amoxicillin), or the diagnosis might need a second look. Persistent high fever, worsening throat pain, or difficulty opening your mouth could signal a complication like a peritonsillar abscess, which needs prompt attention beyond standard antibiotics.