Cephalexin vs. Amoxicillin: Similarities and Differences

Medically reviewed by Lindsay Cook, PharmD

Cephalexin is an antibiotic that treats various bacterial infections such as pneumonia, other respiratory tract infections, and infections of the ears, urinary tract, skin, bone, and genitals. Cephalexin is a member of a class of drugs called cephalosporins.

Amoxicillin is an antibiotic that treats bacterial infections like pneumonia, bronchitis, and infections of the ears, throat, nose, skin, and urinary tract. Amoxicillin is a member of a class of drugs called penicillin antibiotics.

Antibiotics only treat bacterial infections and are not effective in treating viral infections like the cold or flu. Cephalexin and amoxicillin are both generic prescription antibiotics. They have various similarities and differences. This article will provide information about both antibiotics.

What Is Cephalexin and How Does It Work?

Cephalexin is classified as a cephalosporin antibiotic. It is a first-generation cephalosporin antibiotic, meaning that it was among the first cephalosporins developed. It is also part of a larger class known as beta-lactam antibiotics. Beta-lactam antibiotics include all cephalosporin drugs as well as all penicillin drugs, including amoxicillin.

Cephalexin works by preventing certain types of bacteria from building their cell walls. This causes the bacteria to die and prevents the infection from growing and spreading.

Cephalexin can be used to treat the following types of bacterial infections when the infection is known or thought to be susceptible to (can be treated by) cephalexin:

• Respiratory tract infections

• Middle ear infections

• Infections of the skin and skin structure (layers of the skin)

• Bone infections

• Genitourinary tract infections (infections of the urinary tract and reproductive or genital system)

Cephalexin is a generic medication and is available by prescription only. Cephalexin is available as an oral capsule, oral tablet, and oral suspension (liquid). Keflex is the brand name associated with cephalexin, but it is no longer available in the United States as a brand-name drug. Only generic cephalexin is available.

Cephalexin is only for treating certain types of bacterial infections. You will not find cephalexin as an ingredient in any other types of medication that are not antibiotics.

Cephalexin can be taken by adults and children over 1 year of age, although in some cases, healthcare providers will prescribe cephalexin off-label in infants. Off-label means taking a drug approved by the U.S. Food and Drug Administration (FDA) to treat a condition for which it didn't receive FDA approval.

Some other examples of off-label uses for cephalexin include:

• Diabetic foot ulcers

• Prevention of urinary tract infection

What Is Amoxicillin and How Does It Work?

Amoxicillin is classified as a penicillin antibiotic. Like cephalexin, amoxicillin is also part of the larger class of beta-lactam antibiotics. Amoxicillin works by preventing bacteria from building their cell wall. This causes the bacteria to die and prevents bacteria from growing and spreading.

Amoxicillin can treat the following types of bacterial infections when the infection is known or thought to be susceptible to amoxicillin treatment:

• Ear, nose, and throat infections

• Infections of the skin and skin structure

• Genitourinary tract infections

• Lower respiratory tract infections such as pneumonia or bronchitis

• H. pylori infection (in combination with lansoprazole, or lansoprazole plus clarithromycin); A bacteria that infects the stomach and can cause ulcers

Amoxicillin is a generic medication and is available by prescription only. Amoxicillin is available as an oral capsule, oral tablet, oral chewable tablet, and oral suspension (liquid). It is also known by the brand name of Amoxil, although most prescriptions for this medication are filled with generic amoxicillin.

Amoxicillin is taken by adults, children, and infants. Some examples of off-label uses for amoxicillin include:

• Treatment of pregnant people with chlamydia

• Lyme arthritis (inflammation of the joints associated with Lyme disease)

Amoxicillin can also be found as an ingredient in the antibiotic Augmentin.

Dosing Guidelines

General dosing guidelines for cephalexin and amoxicillin are as follows.

Cephalexin

For adults and adolescents 15 years of age and older, the cephalexin dosage is:

• 250 milligrams (mg) by mouth every six hours for seven to 14 days; or

• 500 mg by mouth every 12 hours for seven to 14 days

• Higher doses may be required for more severe infections

For children over 1 year of age, the dosage will depend on the type and severity of infection as well as the child's weight.

Amoxicillin

Amoxicillin dosing is as follows:

• For mild to moderate infections of the ear, nose, throat, skin, skin structure, or genitourinary tract, the adult dosage is 500 mg by mouth every 12 hours or 250 mg by mouth every eight hours. The length of treatment will vary but is often 10 days or longer.

• For severe infections of the ear, nose, throat, skin, skin structure, or genitourinary tract, the adult dosage is 875 mg by mouth every 12 hours or 500 mg by mouth every eight hours. The length of treatment will vary but is often 10 days or longer.

• For adults with lower respiratory tract infections, the dosage is 875 mg by mouth every 12 hours or 500 mg by mouth every eight hours. The length of treatment will vary but is often 10 days or longer.

• For children, the dosage will depend on the type and severity of the infection and the child's weight.

Onset to Action

Cephalexin starts working quickly, reaching its highest levels in the body within one hour. A dose of cephalexin lasts for about six to eight hours in the body.

Amoxicillin also starts working quickly, reaching its highest levels in the body within an hour or two. A dose of amoxicillin lasts in the body for about five to eight hours.

Regardless of which antibiotic you take, you may start to feel better relatively quickly, possibly within a day or two. However, this does not mean you can stop taking the medicine.

You must finish a course of antibiotics to ensure the infection clears and to prevent bacteria from becoming resistant. If bacteria become resistant to an antibiotic, the antibiotic will not work the next time you need it.

Side Effects

Each medication may have side effects.

Cephalexin

Common side effects of cephalexin include:

• Stomach problems like nausea, vomiting, diarrhea, stomach pain, and heartburn

• Rectal or genital itching

• Dizziness

• Feeling overwhelmingly tired

• Agitation

• Confusion

• Headache

• Joint pain

Amoxicillin

Common side effects of amoxicillin include:

• Stomach problems like nausea, vomiting, and diarrhea

• Altered taste

• Headache

Serious Side Effects

Call your healthcare provider right away if you experience serious side effects. Call 911 if your symptoms feel life-threatening or you think you have a medical emergency. Serious side effects of cephalexin and amoxicillin can include the following:

• Anaphylaxis (serious allergic reaction): Get emergency medical help if you have urticaria (hives), difficulty breathing, or swelling of the face, lips, tongue, or throat.

• Life-threatening skin reaction: Get emergency medical help if you have a fever, a sore throat, burning eyes, skin pain, a red or purple rash, or blistering/peeling skin.

• Antibiotic-associated diarrhea: In some cases, diarrhea may occur during or after treatment, even several months after you finish taking an antibiotic. This type of diarrhea can be life-threatening, so notify your healthcare provider right away if you have watery or bloody stools and stomach pain.

Report Side Effects

Cephalexin or amoxicillin may cause other side effects. Call your healthcare provider if you have any unusual problems while taking your medication. If you experience a serious side effect, you or your provider may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Safely Taking Cephalexin vs. Amoxicillin

Here are some tips for safely taking cephalexin or amoxicillin:

• Before taking your medication, read the medication label and the patient information leaflet that comes with your prescription. Ask your healthcare provider or pharmacist if you have any questions.

• Take your medication exactly as directed by your healthcare provider for the full course of treatment unless you have a serious reaction or your provider advises you to stop taking your medicine.

• When taking the liquid formulation, shake the bottle well before measuring. Measure with a medication measuring device. Kitchen or other household measuring devices are not as accurate and should not be used to measure medicine. You can ask the pharmacist for an oral syringe or dosing cup. Your pharmacist will also tell you how to store your liquid medicine.

• Either medication can be taken with or without food. You can take it with food if your stomach is upset from the medicine.
  

• If you miss a dose of either medication, the directions are the same for either cephalexin or amoxicillin. Take the missed dose when you remember. But if it's almost time for the next dose, skip the missed dose. Continue taking your medication at the regular times. Taking extra medication or doubling up on doses is unnecessary to make up for a missed dose.

• Tell your healthcare provider if you are pregnant, planning to become pregnant, or breastfeeding/chestfeeding.

Potential for Interaction

Before taking cephalexin or amoxicillin, tell your healthcare provider about all of the medicines you take, including:

• Prescription medications

• Over-the-counter medicines

• Vitamins

• Supplements

While taking cephalexin or amoxicillin, do not start any new medications without approval from your healthcare provider.

Some examples of drug interactions with cephalexin include:

• Metformin, a generic prescription medication taken for type 2 diabetes; this drug is also found as an ingredient in various combination medications that contain more than one ingredient, such as Janumet (sitagliptin/metformin) or Invokamet (canagliflozin/metformin)

• Probenecid, a prescription medication taken to treat gout (probenecid should not be taken with cephalexin)

Some examples of drug interactions with amoxicillin include:

• Probenecid (in some cases, healthcare providers prescribe probenecid along with amoxicillin to increase the effect of amoxicillin, taking advantage of the drug interaction)

• Jantoven (warfarin), a prescription blood thinner

• Zyloprim (allopurinol), a prescription medication used to prevent gout
  

This is not a full list of drug interactions. Other drug interactions may occur with cephalexin or amoxicillin. Consult your healthcare provider for more information about drug interactions and how they may affect you.

Which One Is Better for Me?

The best medication for you can only be determined by your healthcare provider. There are many factors to consider, such as what bacteria is causing the infection, your symptoms and diagnosis, other medical conditions you have, other medications you take, allergies to medications, and other individual factors.

For example, you should not take cephalexin if you are allergic to cephalexin or any other cephalosporin medication, such as Omnicef (cefdinir) or Ceftin (cefuroxime). You should not take amoxicillin if you are allergic to amoxicillin or penicillins, such as penicillin or Augmentin (amoxicillin and clavulanic acid).

Because cephalexin and amoxicillin both fall under the broad category of beta-lactam antibiotics, if you are allergic to one, there is a chance you may be allergic to the other. However, in many cases, people who are allergic to penicillin or amoxicillin can safely take cephalexin. You can ask your healthcare provider for personalized medical advice regarding allergies to medications.

Additionally, you should tell your healthcare provider about any medical conditions (especially any problems with your stomach, kidneys, or liver) you have, as well as your medical history and family history. Also, tell your healthcare provider if you are pregnant, planning to become pregnant, or breastfeeding/chestfeeding.

Your healthcare provider can examine you, order necessary tests, and prescribe the appropriate antibiotic for you.

Preventing Bacterial Infections

Various types of bacteria cause bacterial infections. Some common examples of bacteria include Staphylococcus, Streptococcus, and E. coli. Here are some general tips on preventing infections:

• Wash your hands thoroughly and often, especially after blowing your nose, using the restroom, or coming in contact with someone who is ill.

• When you sneeze or cough, cover your mouth and nose with a tissue, then throw it out and wash your hands. If you don't have a tissue, cough or sneeze into your elbow—not your hands.

• If you have a cut on your skin, clean it and place a bandage on it. If you have a serious cut, see a healthcare provider.

• Avoid picking at scabs and squeezing pimples.

• Do not share cups or eating utensils.

• Avoid coming into contact with used tissues or similar items.

Summary

Cephalexin and amoxicillin are antibiotics that treat various bacterial infections in adults and children. They are available in various formulations such as pills and liquids that are taken by mouth. Antibiotics like cephalexin and amoxicillin are taken to treat bacterial infections and are not effective against viral infections such as the cold or flu.

Cephalexin and amoxicillin have some things in common but some differences as well. Consult your healthcare provider for more information about these medications.

Frequently Asked Questions

How do I store cephalexin or amoxicillin?

Cephalexin or amoxicillin tablets or capsules can be stored at room temperature, away from direct light, heat, and moisture.

Cephalexin liquid is stored in the refrigerator. Amoxicillin liquid is generally stored in the refrigerator, but other forms of it can be stored at room temperature. If you or your child is prescribed the liquid formulation, ask your pharmacist about specific storage requirements.

Keep all medications out of sight and out of reach of children and pets.

How do cephalexin and amoxicillin differ from azithromycin?

Cephalexin and amoxicillin fall into the category of beta-lactam antibiotics. Azithromycin, often referred to by the brand name Zithromax, is in a class of antibiotics known as macrolide antibiotics.

Azithromycin, which is usually taken once a day, can treat various bacterial infections such as bronchitis, pneumonia, sexually transmitted infections (STI), and infections of the skin, throat, ears, lungs, sinuses, and reproductive organs.

Read the original article on Verywell Health.