Cephalexin and Amoxicillin: Similarities and Differences

By Terez Malka, MD
Medically reviewed checkmarkMedically reviewed
January 21, 2022

Cephalexin and amoxicillin are common beta-lactam antibiotics. Both are broad-spectrum antibiotics, meaning they work against a wide range of bacteria.

They are often used to treat similar types of bacterial infections, but they are not the same.

One thing that is the same: Neither of these antibiotics is used for treating viral infections like colds, the flu, or COVID-19, since antibiotics do not treat viruses.

However, they may be given to address secondary infections in some patients.

In this article, I’ll explain more about what these two medications are—and their similarities and differences.

I’ll talk about the dosages, side effects, and uses of each, as well as other drugs that may interact with cephalexin and amoxicillin.

What is Cephalexin?

Cephalexin is a cephalosporin antibiotic sold under the brand name Keflex.

It’s a first-generation cephalosporin; there are now five generations of this type of antibiotic.

Later generations of cephalosporins are continuing to be developed to treat different kinds of bacteria and address the problem of antibiotic resistance.

Cephalexin is used to treat many common bacterial infections.

It works by disrupting bacterial cell wall growth, which stops them from replicating.

This prevents the infection from continuing.

Cephalexin may be prescribed as a tablet, capsule, or suspension liquid. It may be used in children or adults.

Have questions about an antibiotic prescription? Chat with a doctor today for just $35
Chat Now

What is Amoxicillin?

Amoxicillin is an antibiotic in the class of penicillin-like drugs that is sold under brand names including Amoxil and Moxatag.

Amoxicillin is very effective for many bacterial infections, but others may be resistant to it.

It is one of the most commonly prescribed of all medications: More than 50 million prescriptions for amoxicillin are filled in the United States each year. 

Amoxicillin works by preventing bacterial growth by destroying the protective cellular exterior.

It is available as a tablet, chewable tablet, capsule, or suspension liquid. It may be given to children and adults.

Usage

Both amoxicillin and cephalexin are used for many common types of bacterial infections.

ConditionCephalexinAmoxicillin
Respiratory tract infectionsYesYes
SinusitisYesYes
Ear, nose, and throat infectionsYesYes
Urinary tract infectionsYesYes, but only when paired with clavulanate potassium
Skin and soft tissue infectionsYesYes, typically paired with clavulanate potassium
Oral infectionsYesYes
Lyme diseaseNoYes
Stomach ulcers caused by H. pylori bacteriaNoYes
Anthrax exposureNoYes
Endocarditis preventionYesYes

Your healthcare provider may use either of these medications for other purposes.

If you have a bacterial infection, your doctor will choose the antibiotic that is most effective for your medical history, your current infection, allergies, or other health-related factors.

Dosage

Because cephalexin and amoxicillin are different drugs, their dosages are not the same—and they aren’t comparable to each other.

Your doctor will prescribe an effective dosage for you based on your infection severity and type.

Both will typically start to work on your infection within a few days.

Even if you start feeling better, you should not stop taking your prescription until it is complete to avoid the development of bacterial resistance, and to make sure your infection fully clears.

Stopping your antibiotics too soon could also result in a recurrence of your infection.

Cephalexin

Dosages for cephalexin vary based on the type of infection being treated.

Prescriptions for cephalexin are typically for 7-14 days.

  • Typical dosage for adults: 1-4 grams daily, divided between 2-4 doses
  • Typical dosage for children: 25-50 mg per kilogram of body weight daily, divided between 2-4 doses

Amoxicillin

Dosages for amoxicillin will depend on the type of infection you are being treated for.

Prescriptions for amoxicillin may range from 7-10 days.

  • Typical dosage for adults: 750-1750 mg daily, divided between 2-3 doses
  • Typical dosage for children: 20-90 mg per kilogram of body weight daily, divided between 2-3 doses

Your doctor will prescribe the appropriate dose and duration to effectively treat your infection.

A dose too low or treatment too short may not completely clear your infection.

Side Effects

Both cephalexin and amoxicillin can cause side effects.

While most are mild, some may be severe or lead to allergic reactions that require emergency medical treatment.

Keep your doctor informed of how you are feeling when you are taking any type of drug.

Common, Mild Side Effects — Cephalexin vs. Amoxicillin

Side effectCephalexinAmoxicillin
DiarrheaYesYes
Abdominal painYesLess likely
IndigestionYesLess likely
VomitingYesYes
NauseaYes Yes
HeadacheYesYes
FatigueYesLess likely
Vaginal discharge or itchinessYesYes
Increased creatinine levelsYesYes
Changes in tasteLess likelyYes

Less Common, More Serious Side Effects — Cephalexin vs. Amoxicillin

Side effectCephalexinAmoxicillin
AnaphylaxisPossiblePossible
HivesPossiblePossible
Trouble breathingPossiblePossible
Swelling of the face, lips, tongue, eyes, or throatPossiblePossible
Trouble swallowingPossiblePossible
Skin blistersPossiblePossible
Severe diarrhea or bloody stoolsPossiblePossible
Severe stomach crampsPossiblePossible

Drug Interactions

Most medications can interact with other drugs.

It’s important to understand how all of your medications can affect each other to avoid serious side effects or decreased effectiveness.

Your pharmacist will go over potential interactions.

Make sure your healthcare provider knows everything you take, including OTC medications, dietary supplements, and herbs.

Drug Interactions — Cephalexin vs. Amoxicillin

Drug Interacts with:CephalexinAmoxicillin
MetforminYesNo
Blood thinnersYesYes
FurosemidePossiblyNo
ProbenecidYesYes
AllopurinolNoYes
Other antibioticsYesYes
Oral contraceptivesNoNo

If you have kidney or liver diseases, talk to your healthcare provider about whether amoxicillin or cephalexin are safe for you to use.

Have questions about an antibiotic prescription? Chat with a doctor today for just $35
Chat Now

When to See a Doctor

If you have any symptoms of a bacterial infection, including fever, burning during urination, bleeding gums, or if you are otherwise feeling unwell, check in with your healthcare provider for personalized medical advice.

If your symptoms are caused by a bacterial infection, you will most likely need antibiotics to recover.

If bacterial illnesses go untreated, they can result in more serious infections.

How K Health Can Help

It’s not always easy to get in at your doctor’s office, or maybe you don’t even have a primary care provider. Did you know you can get affordable primary care with the K Health app?

Download K to check your symptoms, explore conditions and treatments, and if needed text with a doctor in minutes. K Health’s AI-powered app is HIPAA compliant and based on 20 years of clinical data.

Frequently Asked Questions

What is the strongest antibiotic for bacterial infections?
There is no single strongest antibiotic. The effectiveness of a particular antibiotic against bacterial infection is determined by the type of bacteria that is causing the illness, as well as factors like severity of the infection and the patient’s medical history, including drug allergies. Cephalexin and amoxicillin can both be effective for many of the same uses, such as urinary tract infections, respiratory infections, and infections of the teeth or gums.
Which antibiotic is best to take when pregnant or breastfeeding?
Both cephalexin and amoxicillin are considered to be safe during pregnancy and breastfeeding when needed. Your doctor and your baby’s doctor can help you decide what treatment is right for you and safe for your baby.
Which antibiotic can be taken with alcohol?
Certain antibiotics should never be mixed with alcohol due to serious potential consequences. Amoxicillin and cephalexin do not have severe interactions with alcohol, but your doctor may still recommend avoiding alcohol while you are being treated since alcohol can impact your immune system and how effective your medication may be.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Terez Malka, MD

Dr. Terez Malka is a board-certified pediatrician and emergency medicine physician.