Antibiotics used to treat strep throat if allergic to penicillin

Key takeaways:

• Penicillin and amoxicillin are antibiotics that treat a variety of bacterial infections, including strep throat.

• Penicillin is an older antibiotic, and it doesn’t fight as many types of bacteria as amoxicillin. But they’re both possible first-choice options for treating strep throat. 

• Both medications are generally well-tolerated. But they have the potential to cause allergic reactions, some of which can be serious.

Penicillin and amoxicillin are two common antibiotics. For good reason, too. They’re relatively affordable, they treat many different bacterial infections, and they can help you start feeling better pretty quickly. 

If you’ve ever had a case of strep throat — a bacterial infection that can cause uncomfortable symptoms like a sore throat and fever — you may have been given penicillin or amoxicillin to provide relief. But since they’re both considered first-choice treatments for strep throat, how do you know if one is a better choice for you?

Here, we’ll compare penicillin vs. amoxicillin for strep throat. We’ll also walk though when one might be a better option for you or a loved one. 

What is penicillin?

Penicillin is a prescription antibiotic medication. It belongs to a group of conveniently-named antibiotics called penicillin antibiotics. It was also the first antibiotic to ever be discovered. 

Penicillin is available in an oral form (penicillin V) and an injectable form (penicillin G). Penicillin V is more common than penicillin G, and it’s available in the following forms:

• Oral tablets: 250 mg, 500 mg

• Oral solution: 125 mg per 5 mL, 250 mg per 5 mL 

What is penicillin used to treat?

Penicillin treats many types of bacterial infections. This includes ear, nose, and throat infections (including strep throat), lower respiratory tract infections, and skin infections. 

The types of infections listed above can be caused by a variety of bacterial species. And penicillin doesn’t work against all of them. It also doesn’t cover as many types of bacteria as amoxicillin, which we’ll discuss next. This is because many bacterial species have developed resistance to penicillin.

What is amoxicillin?

Amoxicillin is another prescription-only antibiotic medication. It’s also a type of penicillin antibiotic, but it’s only available as an oral medication. It’s available in the following forms:

• Capsules: 250 mg, 500 mg

• Tablets: 500 mg, 875 mg

• Chewable tablets: 125 mg, 250 mg

• Oral suspension: 125 mg per 5 mL, 200 mg per 5 mL, 250 mg per 5 mL, and 400 mg per 5 mL

What is amoxicillin used to treat?

Amoxicillin is used to treat bacterial infections. It’s a helpful option for certain types of infections, including:

• Ear, nose, and throat infections (including strep throat)

• Lower respiratory infections

• Skin infections

• Helicobacter pylori (H. pylori) infection

In some cases, amoxicillin may be used off-label for other infections too, like Lyme disease, actinomycosis (infection commonly affecting the face or neck), and endocarditis (infection of the heart valve).

Amoxicillin is also available as a combination product called amoxicillin/clavulanate (Augmentin). Together, this combination can make your treatment more successful in certain situations.

How do penicillin antibiotics work for strep throat?

Penicillin antibiotics work by stopping bacterial growth, which helps kill the bacteria that are causing your infection. By doing this, they help improve your symptoms and make you less contagious.

But how do they do this? Most bacteria have a cell wall, which keeps them intact. It also protects them from outside invaders. Penicillin antibiotics interfere with bacterial cells’ ability to make their cell walls. 

In a way, think of this like getting rid of the outside walls of a building. A building can’t stand without its walls or other supporting elements. 

How are penicillin and amoxicillin dosed and given?

The way penicillin and amoxicillin are dosed depends on the type of infection that’s being treated. Your medical history, age, and preferences also play a role. You should also take them exactly as prescribed by your healthcare provider. 

Penicillin dosing for strep throat

A typical oral penicillin dose involves taking 125 mg, 250 mg, or 500 mg by mouth every 6 to 8 hours. The specific dose depends on the infection that’s being treated and the severity of your infection.

When it comes to treating strep throat, adolescents and adults often take 500 mg by mouth 2 times daily or 250 mg 4 times daily for 10 days. Children often take 250 mg by mouth 2 to 3 times daily for 10 days. 

Amoxicillin dosing for strep throat

A typical amoxicillin dose for adults consists of taking 250 mg to 875 mg by mouth every 8 to 12 hours. But children’s dosing is a bit different — it’s based on body weight.

For strep throat specifically, amoxicillin dosing is also based on body weight. It’s common to receive 50 mg of amoxicillin per kg of body weight (mg/kg) daily (or 25 mg/kg 2 times daily) for 10 days. Based on these numbers, your healthcare provider can calculate your ideal dose. 

How effective are penicillin and amoxicillin for treating strep throat?

Penicillin and amoxicillin are both effective options for treating strep throat. With either option, you may start to feel better within 2 days. They’re thought to be equally effective to one another. 

Both amoxicillin and penicillin have a few possible benefits for strep throat, including:

• Reducing the severity of your symptoms

• Shortening the amount of time your symptoms last

• Preventing the spread of strep throat to others

• Preventing other serious conditions, like rheumatic fever

But in order to truly be effective, antibiotics like these should be taken for their fully prescribed duration — even if you feel completely symptom-free after a few days. Stopping your antibiotic too soon can make your treatment less effective. It may also lead to antibiotic resistance.

What are the known side effects of penicillin and amoxicillin?

Penicillin and amoxicillin can both cause side effects, and many of them are related to your gastrointestinal tract. Below are the most common side effects associated with each. 

Especially with children or anyone needing a liquid formulation, taste can play a role in product selection. For example, your healthcare provider may recommend amoxicillin over penicillin since it may be more palatable.

What are the serious side effects of penicillin and amoxicillin?

Allergic reactions, including potentially severe ones, are possible. 

If you’re allergic to a penicillin antibiotic, your healthcare provider may avoid giving you other penicillin antibiotics. Examples of these include dicloxacillin, ampicillin, and oxacillin. However, know that many penicillin allergies aren’t true allergies. If you think you’ve had a reaction in the past to penicillin, let your healthcare provider know. They can help you determine if you're allergic to penicillin or not. 

However, if a penicillin allergy is severe, your healthcare provider may also avoid giving certain medications from another group of antibiotics — cephalosporins. These are chemically similar to penicillin antibiotics, and they may cause a similar reaction. 

Another rare but serious side effect is Stevens-Johnson syndrome (SJS). SJS is a rare skin condition that can cause rashes, blisters, and skin peeling. It’s considered a medical emergency.

Both medications can also cause a Clostridium difficile (C. diff) infection. This is an infection that causes symptoms like infectious diarrhea, cramps, and fever. It’s highly contagious and can cause severe complications.  

What interactions do penicillin and amoxicillin have?

Penicillin and amoxicillin both have interactions to watch for. 

For instance, these medications can interact with amoxicillin if they’re taken together:

• Allopurinol

• Anticoagulants

• Probenecid

Penicillin also has many drug interactions to watch for, some of which are different from amoxicillin’s interactions. This includes certain sulfa medications and certain diuretics. It’s important to make sure your health care provider is aware of all medications and supplements you are taking.

How much do penicillin and amoxicillin cost?

Penicillin and amoxicillin are both widely available as generic products. They’re also relatively affordable. 

Without insurance, the average retail price of 20 tablets of penicillin — about 10 days worth of medication — is about $20. With a free GoodRx coupon, you may be able to get it for as low as $4 at certain pharmacies. Similarly, the average retail price of 20 capsules of amoxicillin — about 10 days worth of medication — is about $11. With a free GoodRx coupon, you may be able to get it for as low as $3 at certain pharmacies.

Can you take penicillin and amoxicillin together for strep throat?

No. Amoxicillin and penicillin work the same way to stop the growth and spread of bacteria. There’s no added benefit in taking them together to fight strep throat.

The bottom line

Penicillin and amoxicillin are used for many of the same bacterial infections, but they have some key differences. Amoxicillin covers more bacterial species than penicillin, so it may work better in some situations. However, they’re both first-choice options to consider for strep throat. If you’re allergic to either one, your healthcare provider may choose a different medication altogether.

Bogas, G., et al. (2020). Penicillin and cephalosporin cross-reactivity: Role of side chain and synthetic cefadroxil epitopes. Clinical and Translational Allergy. 

Centers for Disease Control and Prevention. (n.d.). Is it really a penicillin allergy?

Centers for Disease Control and Prevention. (2018). Pharyngitis (strep throat).

Centers for Disease Control and Prevention. (2018). Rheumatic fever: All you need to know.

Centers for Disease Control and Prevention. (2022). Strep throat: All you need to know.

Choby, B. A. (2009). Diagnosis and treatment of streptococcal pharyngitis. American Family Physician. 

Dykhuizen, D. (2005). Species numbers in bacteria. Proceedings of the California Academy of Sciences. 

Gee, S. C., et al. (2007). Palatability of liquid anti-infectives: Clinician and student perceptions and practice outcomes. The Journal of Pediatric Pharmacology and Therapeutics. 

Kohanski, M. A., et al. (2010). How antibiotics kill bacteria: From targets to networks. Nature Reviews Microbiology.

PD-Rx Pharmaceuticals, Inc. (2022). Penicillin [package insert].

Proficient Rx LP. (2022). Amoxicillin [package insert].

Ren, J., et al. (2020). Antibiotic-induced black hairy tongue: Two case reports and a review of the literature. Journal of International Medical Research. 

Sharma, S., et al. (2022). Actinomycosis. StatPearls.

Yip, D. W., et al. (2021). Penicillin. StatPearls.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

Was this page helpful?

Subscribe and save.Get prescription saving tips and more from GoodRx Health. Enter your email to sign up.

By signing up, I agree to GoodRx's Terms and Privacy Policy, and to receive marketing messages from GoodRx.

Which antibiotic is best for strep throat?

What do you take for strep throat if allergic to amoxicillin?

What antibiotics treat tonsillitis if allergic to penicillin?

Is azithromycin good for strep throat?