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Amoxicillin vs. penicillin: Differences, similarities, and which is better for you

Drug overview & main differences | Conditions treated | Efficacy | Insurance coverage and cost comparison | Side effects | Drug interactions | Warnings | FAQ

If you’ve ever been sick with a bacterial infection, you may have been prescribed an antibiotic like amoxicillin or penicillin. As penicillin-type antibiotics, these drugs are two of the most common antibiotics prescribed. Both amoxicillin and penicillin treat similar bacterial infections of the respiratory tract, genitourinary tract, ear, nose, and throat.

Amoxicillin and penicillin are generic antibiotics that belong to a larger class of antibiotics called beta-lactams. These drugs work by blocking the bacteria’s ability to build and maintain their protective structure known as the cell wall. Without the cell wall, the bacteria can’t survive.

Despite their similar nature, amoxicillin and penicillin can kill different types of bacteria. Because of this, they can be used in different ways.

What are the main differences between amoxicillin and penicillin?


Amoxicillin is a newer version of penicillin that covers more types of bacteria. Amoxicillin was created by modifying the original chemical structure of penicillin to make it more potent.

Both amoxicillin and penicillin cover Streptococcal bacteria. However, Amoxicillin is considered a broad-range antibiotic that covers a wider variety of bacteria compared to penicillin. Amoxicillin is sometimes combined with a beta-lactamase inhibitor, such as clavulanic acid, to make it even more potent.


Because penicillin became one of the most commonly used antibiotics in the world, many bacterial species have gained resistance against it. However, it is still useful for certain bacterial infections.

Penicillin is a narrow-range antibiotic that covers gram-positive bacteria and some gram-negative bacteria. Penicillin can be given as an injection (penicillin G) as well as an oral tablet or liquid suspension (penicillin V).

Main differences between amoxicillin and penicillin
Amoxicillin Penicillin
Drug class Antibiotic
Brand/generic status Brand and generic versions available Brand and generic versions available
What is the brand name? Moxatag, Amoxil Pfizerpen (penicillin G)
What form(s) does the drug come in? Oral tablet
Oral tablet, chewable
Oral capsule
Oral powder for suspension
Oral tablet
Oral powder for suspension
IV powder for injection
What is the standard dosage? 500 mg every 12 hours or 250 mg every 8 hours.

Dosing depends on the infection being treated.

125 to 250 mg every 6 to 8 hours

Dosing depends on the infection being treated.

How long is the typical treatment? 7–10 days

Duration depends on the infection being treated.

2–10 days

Duration depends on the infection being treated.

Who typically uses the medication? Adults, children, and infants aged 3 months and older Adults and children aged 12 years and older

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Conditions treated by amoxicillin and penicillin

Amoxicillin and penicillin can treat many different bacterial infections including lower respiratory tract infections and dental infections. Amoxicillin and penicillin are commonly prescribed to treat middle ear infections, otherwise known as otitis media. Both antibiotics can also treat certain infections of the urinary tract and skin.

Amoxicillin is FDA-approved to treat bacterial infections such as gonorrhea. It can also treat H. pylori infections and throat infections like pharyngitis and tonsillitis. For respiratory tract infections like community-acquired pneumonia (caused by streptococcus pneumonia), amoxicillin is an option in areas with low antibiotic resistance.

Penicillin is often used to treat bacterial endocarditis, scarlet fever, and dental infections. Skin infections caused by Staphylococcus aureus can also be treated with penicillin, although the penicillin G form is preferred.

Can amoxicillin and penicillin treat viral infections?

It’s important to note that antibiotics including amoxicillin and penicillin are not effective against viral infections such as COVID-19. These types of infections are caused by viruses and do not respond to antibiotics. However, viral infections can weaken the immune system and lead to bacterial infections, which may warrant antibiotic treatment.

Condition Amoxicillin Penicillin
Ear, nose, and throat infections Yes Yes
Lower respiratory tract infections Yes Yes
Dental infections Yes Yes
Genitourinary tract infections Yes Yes
Skin and soft tissue infections Yes Yes
Scarlet Fever Yes Yes
Bacterial endocarditis Yes Yes
Infections caused by E. coli, Salmonella, H. influenzae, Shigella Yes No

Is amoxicillin or penicillin more effective?

Although both antibiotics are effective for treating bacterial infections, their effectiveness depends on the bacteria causing the infection. Amoxicillin is able to get rid of a broader range of bacteria compared to penicillin. Although both antibiotics are effective against streptococci, amoxicillin is more effective against E. coli and H. influenzae, among others.

According to a 2018 systematic review, amoxicillin is better for treating community-acquired pneumonia compared to penicillin. However, results showed that penicillin may be better for respiratory tract infections in general due to its narrow coverage. There was no significant difference between the two antibiotics when treating otitis media.

One of the primary goals of fighting bacterial infections is to prevent resistance. Bacterial resistance can lead to stronger infections which can be harder to treat. This is why knowing what bacteria is causing the infection is important. Talk with your healthcare provider to find the best treatment option that works for you.

Coverage and cost comparison of amoxicillin vs. penicillin

Amoxicillin is a commonly prescribed antibiotic that is almost always covered by Medicare and insurance plans. The typical average cost of amoxicillin is around $24. However, a SingleCare discount card can lower this cost to around $5. Amoxicillin is usually purchased as a generic tablet, capsule, or oral liquid.

Like amoxicillin, penicillin is also widely available and covered by most insurance plans. If you are picking up penicillin from the pharmacy, it will most likely be the penicillin V or penicillin VK form. The average cost of penicillin V is $40. However, with a SingleCare discount card, this cost can be lowered to around $9. The cost will depend on which pharmacy you use and whether you get the pill or liquid form.

  Amoxicillin Penicillin
Typically covered by insurance? Yes Yes
Typically covered by Medicare? Yes Yes
Standard dosage 500 mg tablets 250 mg tablets
Typical Medicare copay $0–$10 $0–$18
SingleCare cost $5+ $8.80+

Common side effects of amoxicillin vs. penicillin

Amoxicillin and penicillin have similar side effects. The most common side effects of these antibiotics are diarrhea, nausea, and vomiting.

One difference between amoxicillin and penicillin is that amoxicillin is more likely to produce a skin rash. This rash can range in severity from mild to severe. However, it usually goes away within a few days. Talk to your doctor if you or your child develops a rash.

  Amoxicillin Penicillin
Side Effect Applicable? Frequency Applicable? Frequency
Diarrhea Yes >1% Yes *not reported
Nausea Yes >1% Yes *
Vomiting Yes >1% Yes *
Rash Yes >1% No

This may not be a complete list. Consult your doctor or pharmacist for possible side effects.
Source: DailyMed (Amoxicillin), DailyMed (Penicillin)

Drug interactions of amoxicillin vs. penicillin

Amoxicillin and penicillin can interact with several other medications. Penicillin-type antibiotics may interact with methotrexate, a drug often used to treat rheumatoid arthritis. Taking amoxicillin or amoxicillin can affect how the body processes methotrexate, which may lead to toxicity.

Antigout medications like probenecid and allopurinol can lead to increased blood levels of amoxicillin or penicillin. This interaction may lead to increased side effects.

The effectiveness of amoxicillin and penicillin may be reduced when they’re taken with birth control pills or other antibiotics.

Combining amoxicillin or penicillin with warfarin may affect how warfarin is processed in the body. This may result in an increased risk of bleeding.

Drug Drug Class Amoxicillin Penicillin
Methotrexate Antimetabolite Yes Yes


Antigout Yes Yes
Ethinyl estradiol
Oral contraceptives Yes Yes
Warfarin Anticoagulant Yes Yes
Antibiotics Yes Yes

This may not be a complete list of all possible drug interactions. Consult a doctor with all the medications you may be taking.

Warnings of amoxicillin and penicillin

Serious hypersensitivity and allergic reactions have been reported with amoxicillin and penicillin. Allergic reactions may lead to anaphylaxis or anaphylactic shock. If you experience difficulty breathing, severe rash, and severe nausea, seek medical attention immediately.

If you are prescribed a course of amoxicillin or penicillin treatment, it’s important to finish all of the antibiotics even if you’re feeling better. If you don’t finish treatment, the bacteria may have a chance to mutate and develop resistance to the antibiotic. This can lead to a more severe infection that would require further treatment.

Talk to your doctor if you experience or have a history of the following:

  • Diarrhea after taking antibiotics
  • Allergies to antibiotics
  • Liver or kidney problems

Frequently asked questions about amoxicillin vs. penicillin

What is amoxicillin?

Amoxicillin is an antibiotic known by its brand names Amoxil and Moxatag. As a penicillin-type antibiotic, amoxicillin can treat respiratory tract infections, genitourinary tract infections, and ear, throat, and nose infections. Amoxicillin comes in tablet, capsule, and liquid forms.

What is penicillin?

Penicillin is a commonly used antibiotic that is used to treat a number of bacterial infections. It is often used to treat infections caused by Streptococcus and other gram-positive bacteria. Penicillin is available as penicillin G (injection) and penicillin V (oral).

Are amoxicillin and penicillin the same?

Amoxicillin and penicillin are not the same drug. Amoxicillin is a newer, modified version of penicillin that covers a broader range of bacteria.

Is amoxicillin or penicillin better?

Amoxicillin or penicillin may be more effective depending on the bacterial infection being treated. Amoxicillin can cover infections caused by other types of bacteria such as E. coli, Salmonella, and H. influenzae. Penicillin may be better to target specific types of bacteria in order to prevent antibiotic resistance.

Can I use amoxicillin or penicillin while pregnant?

Both amoxicillin and penicillin are in Pregnancy Category B. This means that they are generally safe for use during pregnancy. Still, it’s important to consult your doctor or healthcare provider to ensure you’re getting the best treatment while pregnant.

Can I use amoxicillin or penicillin with alcohol?

Drinking alcohol in moderation will not affect how well amoxicillin or penicillin works. There is no known interaction between alcohol and these antibiotics. However, alcohol may affect your body and immune system as a whole which can delay how fast you recover from the infection.

Can you take amoxicillin if you are allergic to penicillin?

No. Amoxicillin should not be taken if you have a true allergy to penicillin. This is because the chemical structure of amoxicillin is very similar to that of penicillin. If you’ve experienced an allergic reaction to penicillin in the past, your doctor may prescribe an antibiotic from a different class.

Can you outgrow penicillin allergy?

Yes. It is possible to outgrow a penicillin allergy over time. One review from the Journal of the American Medical Association found that 80% of people with a penicillin allergy become tolerant after 10 years. Penicillin allergies are also sometimes misreported during childhood. Depending on your past experience with penicillin, your healthcare provider may recommend trying penicillin again if necessary.

Which antibiotics to avoid with penicillin allergy?

If you have a penicillin allergy, you should avoid taking other penicillin-type antibiotics. Other antibiotics that are similar to penicillin include amoxicillin, ampicillin, and cephalosporins such as Keflex. Talk to your doctor about your treatment options if you are allergic to penicillin.