Introduction

Amoxicillin and penicillin are two of many antibiotics on the market today. They’re actually in the same family of antibiotics, called the penicillin family. This family contains antibiotics that come from a fungus called Penicillium. Other examples include the antibiotics ampicillin and nafcillin. Drugs in this family work in similar ways to treat infections, but there are small differences in the kinds of bacteria each drug fights and the side effects each drug causes.

So while amoxicillin and penicillin are different, they’re similar in many ways. As antibiotics, both can be used to treat infections caused by bacteria. They work by stopping the bacteria from multiplying. Neither amoxicillin nor penicillin will work to treat infections caused by viruses such as colds or flu. Read on to learn more about how these drugs compare.

Drug features

Amoxicillin and penicillin are very similar drugs. The following table lists their features side by side.

Generic name AmoxicillinPenicillin
What are the brand-name versions?Amoxil, Moxatagnot available
Is a generic version available?yesyes
What is this drug used to treat?bacterial infectionsbacterial infections
What forms does it come in?oral capsule, oral tablet, oral extended-release tablet, chewable tablet, oral suspension*oral tablet, oral solution*
What is the typical length of treatment?varies based on condition varies based on condition
*Suspensions and solutions should be stored in a refrigerator and disposed of after 14 days.

What they treat

Amoxicillin and penicillin are both used to treat bacterial infections. However, the conditions they’re used to treat vary. Your doctor may do a susceptibility test to find out which drug may be better for your type of infection. For this test, your doctor collects a sample of your body fluid, such as saliva or urine. They send the sample to a lab to find out which strain of bacteria is growing in your body. Then, they choose the drug that best treats the infection caused by that type of bacteria.

The chart below lists examples of the different types of infections that amoxicillin and penicillin can be used to treat.

Possible usesAmoxicillinPenicillin
mild to moderate upper respiratory tract infections*xx
mild skin infectionsxx
scarlet fever x
tooth infectionsx
urinary tract infectionsx
ulcersx
* including pneumonia, sinus infections, ear infections, or throat infections

Cost, availability, and insurance

Amoxicillin and penicillin are both available as generic drugs. Generic medications are copies of brand-name medications. They have the same features as brand-name versions, such as dosage, intended use, side effects, and route of administration. However, generic medications typically cost less than brand-name medications. Therefore, penicillin and the generic versions of amoxicillin are likely cheaper than the brand-name versions of amoxicillin.

Both amoxicillin and penicillin are typically covered by most health insurance plans without a prior authorization. Brand-name medications, on the other hand, may require a prior authorization.

Side effects

Both amoxicillin and penicillin can cause side effects. Call your doctor if you have any serious side effects when using these drugs.

The charts below list examples of possible side effects from amoxicillin and penicillin.

Common side effectsAmoxicillinPenicillin
mild skin rashXX
stomach upset XX
nausea X
vomitingXX
diarrheaXX
black, hairy tongueXX
Serious side effectsAmoxicillinPenicillin
allergic reaction*XX
bloody or watery diarrheaXX
unusual bleeding or bruisingX
seizuresX
yellowing of the eyes or skinX
*This can include skin rash, hives, and swelling of the mouth or tongue.

Drug interactions

Amoxicillin and penicillin also interact with similar medications. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

The table below lists examples of drugs that most often interact with amoxicillin and penicillin.

Drugs that may cause interactionsAmoxicillinPenicillin
methotrexate xx
allopurinolx
probenecidxx
warfarinxx
birth control pillsxx
mycophenolatexx
other antibioticsxx

Before starting amoxicillin or penicillin, tell your doctor about all medications, vitamins, or herbs you’re taking. This can help your doctor prevent possible interactions.

Precautions

Keep the following precautions in mind if your doctor prescribes amoxicillin or penicillin.

Conditions of concern

Certain medications can make certain health conditions or diseases worse. For example, if you have severe kidney disease, you should talk with your doctor before taking amoxicillin or penicillin. Also ask your doctor if you can use amoxicillin and penicillin safely if you have severe allergies or asthma. You’re at higher risk of side effects from these medications.

Allergies

If you know that you’re allergic to penicillin, you shouldn’t take penicillin or penicillin antibiotics such as amoxicillin. The reverse is also true: If you’re allergic to amoxicillin, you shouldn’t take penicillin or other penicillin antibiotics.

In addition, if you’re allergic to cephalosporin antibiotics, you’re at risk for an allergic reaction to penicillin antibiotics.

Symptoms of an allergic reaction to amoxicillin or penicillin can include:

  • trouble breathing
  • hives
  • rash
  • swelling of your lips or tongue

If you have any of these symptoms, stop taking the antibiotic and call your doctor right away. If your symptoms are severe, call 911 or go to the nearest emergency room.

Severe diarrhea

Antibiotics such as amoxicillin or penicillin can cause severe diarrhea. Sometimes the diarrhea is linked with an infection by a type of bacteria called Clostridium difficile (C. diff). Symptoms of C. diff infection can include:

  • watery diarrhea that is severe or lasts more than two days
  • cramping in your abdomen
  • dehydration (low fluid levels in your body), which typically doesn’t cause symptoms
  • inflammation of the colon, which typically doesn’t cause symptoms
  • weight loss

If you have these symptoms, call your doctor right away. If your symptoms are severe, go to the nearest emergency room.

Use with alcohol

You can drink alcohol while taking either amoxicillin or penicillin. There are no special precautions against using these drugs with alcohol. Still, there are other things to consider about drinking while treating an infection. For more information, read about combining antibiotics and alcohol.

Talk with your doctor

Amoxicillin and penicillin are very similar drugs with a few differences, such as:

  • the forms they come in
  • the conditions they treat
  • the more serious side effects they can cause

If you have a bacterial infection, your doctor will prescribe the best antibiotic to treat your type of infection. This may be amoxicillin, penicillin, or another drug.

If you have questions about these drugs, be sure to ask your doctor. Here are a few key points to remember if your doctor prescribes amoxicillin or penicillin for you

Remember

  • Be sure to take amoxicillin or penicillin exactly as your doctor prescribes until all of the medication is gone, even if you feel better. Stopping treatment with an antibiotic too early may cause the bacteria to come back and be even stronger.
  • Tell your doctor if you’re allergic to amoxicillin, penicillin, or cephalosporin antibiotics.
  • Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. Call your doctor right away if you take one of these drugs and have watery diarrhea that is severe or lasts more than two days.