Penicillin and amoxicillin are the first-line antibiotics for bacterial tonsillitis, typically prescribed for 10 days. But antibiotics only work when bacteria are the cause, and most cases of tonsillitis are actually viral, meaning no antibiotic will help. Understanding which type you have, and which medication fits your situation, makes a real difference in how quickly you recover.
Not All Tonsillitis Needs Antibiotics
Tonsillitis simply means your tonsils are inflamed, and viruses cause the majority of cases. When a virus is responsible, antibiotics won’t shorten your illness or reduce your symptoms. The infection that does call for antibiotics is group A streptococcus, the bacterium behind strep throat. This is the specific diagnosis your doctor is looking for before writing a prescription.
Doctors use a set of clinical signs called the Centor criteria to decide whether testing is worthwhile. The four signs are: fever above 100.4°F, swollen and tender lymph nodes at the front of your neck, white or yellow patches (exudate) on your tonsils, and the absence of a cough. If you have zero or one of these, strep is unlikely and you probably won’t be tested at all. A score of two or higher typically leads to a rapid strep test, and a score of four sometimes warrants treatment even before test results come back. Adults over 44 score one point lower on this scale because strep becomes less common with age.
Penicillin and Amoxicillin: The Standard Treatment
When a strep test comes back positive, penicillin or amoxicillin is the recommended treatment. The CDC identifies both as the antibiotics of choice for group A strep. Neither one has developed resistance problems with this particular bacterium, which is why they’ve remained the top options for decades.
Amoxicillin is often preferred in practice, especially for children, because it tastes better in liquid form and can be taken less frequently. Adults can take it twice daily, and children’s doses are calculated by weight. There is also an extended-release tablet form taken once a day with food. Penicillin V works just as well but requires more frequent dosing for adults, up to four times daily.
Regardless of which one you’re prescribed, the standard course is 10 days. You’ll likely start feeling noticeably better within two to three days, but finishing the entire course matters. Stopping early allows surviving bacteria to linger, raising the risk of the infection coming back or causing complications.
Options If You’re Allergic to Penicillin
A penicillin allergy changes the picture. Your doctor will choose from a few alternative classes of antibiotics depending on the type and severity of your allergy.
- Cephalosporins are often the next choice if your allergy is mild (a rash, for example, rather than throat swelling or difficulty breathing). First-generation cephalosporins like cephalexin have a small cross-reactivity rate with penicillin, ranging from 1% to 8%. Third-generation cephalosporins have even lower cross-reactivity, under 1%. Your doctor will weigh the severity of your past reaction before choosing this route.
- Macrolides such as azithromycin are sometimes prescribed when penicillin and cephalosporins are both off the table. However, resistance is a growing problem. Among invasive group A strep samples tested in 2023, 27% were resistant to macrolides. That means roughly one in four strep strains won’t respond to azithromycin at all, which is why it’s considered a backup rather than a go-to.
- Clindamycin is another alternative, but it faces a similar resistance issue. In the same 2023 data, 26% of group A strep isolates were clindamycin resistant. Because of these numbers, the CDC recommends using clindamycin or macrolides only when the specific strain has been confirmed as susceptible.
If you were told you’re allergic to penicillin as a child, it’s worth knowing that many people outgrow that allergy. Penicillin allergy testing is a simple skin test, and confirming you can tolerate penicillin opens the door to the most effective, least resistance-prone treatment.
Why the Full 10-Day Course Matters
Ten days feels like a long time to take medication when your throat stops hurting on day three. But the treatment duration isn’t just about symptom relief. It’s designed to fully eliminate the bacteria and prevent serious complications.
The most significant risk of untreated or undertreated strep is rheumatic fever, an inflammatory condition that can damage heart valves. Severe rheumatic heart disease can require surgery and can be fatal. This complication is uncommon in countries where antibiotics are readily available, largely because the 10-day course is so effective at preventing it. Peritonsillar abscess, a painful pocket of pus that forms near the tonsil, is another potential complication of strep that isn’t adequately treated.
What to Expect During Recovery
Once you start antibiotics, most people notice their throat pain and fever improving within the first two to three days. You’re generally considered no longer contagious after 24 hours on antibiotics, which is the typical threshold for returning to school or work. During those first couple of days, over-the-counter pain relievers, cold fluids, and throat lozenges can help bridge the gap while the antibiotic takes effect.
If you don’t feel any improvement after 48 to 72 hours on antibiotics, contact your doctor. This could mean the infection is viral after all (a false-positive strep test, while uncommon, does happen), or that your particular strain is resistant to the prescribed medication. In those cases, switching to a different antibiotic or reconsidering the diagnosis is the next step.
Recurring Tonsillitis and Long-Term Considerations
Some people deal with tonsillitis multiple times a year. If you’re getting several confirmed strep infections annually, your doctor may discuss whether a tonsillectomy makes sense. The general benchmark used by most specialists is seven episodes in one year, five per year for two consecutive years, or three per year for three consecutive years. Removing the tonsils doesn’t make you immune to throat infections, but it significantly reduces their frequency and severity in people who meet those thresholds.
For people who get occasional tonsillitis, each episode is treated independently with a fresh course of antibiotics. There’s no benefit to keeping leftover antibiotics on hand or starting them before getting tested, since taking antibiotics for a viral infection adds side effects without any payoff and contributes to the broader problem of antibiotic resistance.