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Amoxicillin vs. Penicillin: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on January 15, 2024
Amoxicillin is a broad-spectrum antibiotic and a derivative of penicillin, effective against a wider range of bacteria compared to penicillin, which is the first discovered antibiotic and effective against a narrower spectrum of bacteria.

Key Differences

Amoxicillin, a broader-spectrum antibiotic, is effective against more types of bacteria, including some that are resistant to penicillin, while penicillin is primarily effective against Gram-positive bacteria.
Amoxicillin is often prescribed for ear infections, pneumonia, and urinary tract infections, owing to its broad effectiveness, unlike penicillin, which is commonly used for strep throat and syphilis.
The structure of amoxicillin allows it to be more readily absorbed in the digestive tract, thus it can be taken orally, whereas penicillin is less stable in the stomach and often requires injection.
Amoxicillin has a lower chance of causing allergic reactions compared to penicillin, which is known for higher rates of allergies in some individuals.
Resistance development can be more prevalent with amoxicillin due to its broad use, while penicillin, being more specific, has a slightly lower risk of resistance development.

Comparison Chart

Spectrum of Activity

Broad-spectrum, effective against a wider range of bacteria
Narrower spectrum, mainly effective against Gram-positive bacteria

Common Uses

Ear infections, pneumonia, UTIs
Strep throat, syphilis


Oral absorption is effective
Often requires injection

Allergic Reactions

Generally lower incidence
Higher incidence of allergies


Higher risk due to broad use
Lower risk due to specific use

Amoxicillin and Penicillin Definitions


Amoxicillin is effective orally.
Amoxicillin can be conveniently taken as a pill.


It is effective against Gram-positive bacteria.
Penicillin is commonly used to treat strep throat.


Amoxicillin is part of the penicillin antibiotic family.
Amoxicillin shares some characteristics with other penicillin-based drugs.


Penicillin is the first-discovered antibiotic.
Penicillin revolutionized medicine in the 1940s.


Amoxicillin is a broad-spectrum antibiotic.
Amoxicillin is often prescribed for bacterial ear infections.


It has a narrower spectrum compared to amoxicillin.
Penicillin is not effective against certain bacteria that amoxicillin can treat.


It is a derivative of penicillin.
Amoxicillin was developed to overcome some bacteria resistant to penicillin.


Penicillin is often administered through injection.
Injectable penicillin is used for syphilis treatment.


It's used to treat various bacterial infections.
Doctors prescribe amoxicillin for certain types of pneumonia.


Penicillin can cause allergic reactions in some people.
Patients with penicillin allergies are often given alternative antibiotics.


A semisynthetic penicillin, C16H19N3O5S, having an antibacterial spectrum of action similar to that of ampicillin.


An antibiotic drug obtained from molds especially of the genus Penicillium or produced synthetically, available in various preparations and usually used to treat infections caused by gram-positive bacteria.


(pharmaceutical drug) A moderate-spectrum, bacteriolytic beta-lactam antibiotic C16H19N3O5S closely related to ampicillin and with similar properties, but more readily absorbed when taken orally. It is used to treat bacterial infections caused by susceptible microorganisms.


Any of a group of broad-spectrum antibiotic drugs, synthetic or semisynthetic, that are derived from penicillin.


An antibiotic; a semisynthetic oral penicillin (trade names Amoxil and Larotid and Polymox and Trimox and Augmentin) used to treat bacterial infections


(pharmaceutical drug) Any of a group of narrow-spectrum antibiotics obtained from Penicillium molds or synthesized, that have a beta-lactam structure and are active against gram-positive bacteria and used in the treatment of various infections and diseases.


(mycology) A blue mold of the genus Penicillium that produces penicillin.


Any of a variety of substances having a structure containing a beta-lactam ring fused to a thiirane ring, to which a carboxyl group is attached, but most commonly interpreted as benzyl penicillin. They are notable as powerful antibacterial agents of relatively low toxicity which have found extensive use in medicine for treating bacterial infections. They are categorized as one of the classes of beta-lactam antibiotic. They are produced naturally by some fungi and bacteria, and industrial production processes almost invariably start from some form of the penicillin nucleus produced by fermentation of microorganisms. The fermentation products are then chemically modified to produce derivatives of enhanced potency, safety, or antibacterial spectrum. The first penicillin to see extensive use clinically (during World War II) was penicillin G, also called benzypenicillin, and commonly simply "penicillin".


Any of various antibiotics obtained from penicillium molds (or produced synthetically) and used in the treatment of various infections and diseases


What is amoxicillin?

Amoxicillin is an antibiotic used to treat a variety of bacterial infections.

What infections does amoxicillin treat?

It treats infections like ear infections, pneumonia, and urinary tract infections.

Can amoxicillin cause allergic reactions?

Yes, especially in individuals allergic to penicillin.

Is amoxicillin the same as penicillin?

No, but it belongs to the same class of antibiotics as penicillin.

Can penicillin cause side effects?

Yes, including allergic reactions, nausea, and diarrhea.

Can amoxicillin be taken with alcohol?

Alcohol may increase side effects but doesn't affect the medication's efficacy.

Is amoxicillin safe for pregnant women?

Generally, yes, but it should be taken under medical advice.

Is penicillin effective against all infections?

No, it's mainly effective against specific types of bacterial infections.

How long does it take for amoxicillin to work?

Symptoms usually improve within a few days of starting treatment.

Can amoxicillin treat viral infections?

No, it's only effective against bacterial infections.

What are the common side effects of amoxicillin?

They include nausea, vomiting, and diarrhea.

How long should a penicillin course last?

Typically, it's taken for 7-14 days, depending on the infection.

How is amoxicillin administered?

It's available in capsules, liquid form, and injectable.

What is penicillin?

Penicillin is an antibiotic used to treat bacterial infections, first discovered in 1928.

Is penicillin used in modern medicine?

Yes, it remains a commonly used antibiotic.

What should I do if I'm allergic to penicillin?

Seek alternative antibiotics and inform healthcare providers of the allergy.

How does penicillin work?

It works by inhibiting the growth of bacteria.

Can penicillin treat skin infections?

Yes, it's often prescribed for certain skin infections.

Is penicillin overused?

There's concern about overuse leading to antibiotic resistance.

Can children take penicillin?

Yes, but the dosage is adjusted based on age and weight.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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