Cephalexin (Keflex) | Side Effects, Dosage, Uses, & More
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Generic Name:

cephalexin, Oral capsule

All Brands

  • Keflex
SECTION 1 of 5

Highlights for cephalexin

Oral capsule
1

Cephalexin is used to treat certain infections caused by bacteria.

2

This drug comes as a capsule, tablet, or liquid suspension that you take by mouth.

3

The oral capsule, oral tablet, and oral suspension are all available as generic drugs. The oral capsule is also available as the brand-name drug Keflex.

IMPORTANT INFORMATION

Allergy to β-lactam medications

If you’re allergic to β-lactam medications, many of which are antibiotics, you shouldn’t take this drug. You could have a serious allergic reaction.

Antibiotic-associated diarrhea

The use of almost all antibiotics, including cephalexin, can cause a reaction that leads to diarrhea. In addition to diarrhea, this reaction can cause severe inflammation of your colon. Severe cases of this reaction can be fatal (cause death). Call your doctor if you have diarrhea while taking or after taking this drug.

What is cephalexin?

Cephalexin is a prescription drug. It’s available as an oral capsule, oral tablet, or oral suspension.

Cephalexin is available as a generic drug. Generic drugs usually cost less. In some cases, they may not be available in every strength or form as the brand-name version. The oral tablet of cephalexin is also available as the brand-name drug Keflex.

Why it's used

Cephalexin is used to treat certain infections caused by bacteria.

More Details

How it works

Cephalexin belongs to a class of drugs called cephalosporins (antibiotics).

More Details

Why it's used

Cephalexin is used to treat certain infections caused by bacteria. These infections include:

  • respiratory tract infections
  • otitis media (middle ear infections)
  • skin and skin structure infections
  • bone infections
  • genitourinary (urinary tract) infections
  • pharyngitis (sore throat)

This drug is also used for prevention of endocarditis (inflammation of the heart valve) caused by an infection. 

How it works

Cephalexin belongs to a class of drugs called cephalosporins (antibiotics). A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Cephalexin works by interfering with the formation of the bacteria’s cell walls. This ruptures the walls and kills the bacteria.

This drug should only be used to treat bacterial infections. You shouldn’t use it to treat viruses, such as the common cold.

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SECTION 2 of 5

cephalexin Side Effects

Oral capsule

More common side effects

The more common side effects of cephalexin include:

  • diarrhea

  • indigestion

  • irritation or inflammation of your stomach lining

  • stomach pain

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 9-1-1 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Allergic reactions. Symptoms can include:

    • hives
    • trouble breathing
    • swelling of your face, lips, tongue, or throat
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

Cephalexin doesn’t cause drowsiness.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
SECTION 3 of 5

cephalexin May Interact with Other Medications

Oral capsule

Cephalexin can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Medications that might interact with this drug

Interactions that increase your risk of side effects
  • Side effects from cephalexin: Taking cephalexin with certain medications raises your risk of side effects from cephalexin. This is because the amount of cephalexin in your body is increased. Examples of these drugs include:
    • Probenecid
  • Side effects from other drugs: Taking cephalexin with certain medications raises your risk of side effects from these drugs. Examples of these drugs include:
    • Metformin. Taking these drugs together may cause kidney problems. Your doctor may adjust your dose of metformin to reduce this risk.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Cephalexin warnings
kidney problem warning
People with kidney problems

If you have kidney problems or a history of kidney disease, you may not be able to clear this drug from your body. This may increase the levels of this drug in your body and cause more side effects. Your doctor may adjust your dose if you have kidney disease. Talk to your doctor about whether this drug is safe for you.

pregnancy warning
Pregnant women

Cephalexin is a pregnancy category B drug. That means two things:

  1. Studies of the drug in pregnant animals have not shown risk to the fetus.
  2. There aren’t enough studies in pregnant women to show the drug poses a risk to the fetus.

Tell your doctor if you’re pregnant or plan to become pregnant. Cephalexin should be given to a pregnant woman only if clearly needed.

breast feeding warning
Women who are breast-feeding

Cephalexin passes into breast milk and may cause side effects in a child who is breastfed.

Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

senior warning
For seniors

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of the drug stays in your body for a longer time. This raises your risk of side effects.

children's warning
For children

This drug hasn’t been studied in children younger than 1 year of age with respiratory tract, middle ear, skin and skin structure, bone, and urinary tract infections.

allergy warning
Allergies

Cephalexin can cause a severe allergic reaction. Symptoms can include:

  • hives
  • trouble breathing
  • swelling of your face, lips, tongue, or throat

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 9-1-1 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction to it before. Taking it again could be fatal (cause death).

SECTION 4 of 5

How to Take cephalexin (Dosage)

Oral capsule

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What are you taking this medication for?

Respiratory tract infection

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 1–14 years)

25–50 mg/kg of body weight per day taken in divided doses. Your doctor may double your dose for severe infections.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Otitis media (middle ear infection)

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 1–14 years)

75–100 mg/kg of body weight per day taken in 4 divided doses.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Skin and skin structure infection

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours or 500 mg taken every 12 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours or 500 mg taken every 12 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 1–14 years)

25–50 mg/kg of body weight per day taken in divided doses. Your doctor may double your dose for severe infections.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Bone infections

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 1–14 years)

25–50 mg/kg of body weight per day taken in divided doses. Your doctor may double your dose for severe infections.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Genitourinary (urinary tract) infection

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have uncomplicated cystitis, you may be given 500 mg every 12 hours. Your doctor may give you a larger dose if you have a severe infection.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours. If you have uncomplicated cystitis, you may be given 500 mg every 12 hours. Your doctor may give you a larger dose if you have a severe infection.

Child dosage (ages 1–14 years)

25–50 mg/kg of body weight per day taken in divided doses. Your doctor may double your dose for severe infections.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Pharyngitis (sore throat)

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours or 500 mg taken every 12 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 15–17 years)

1–4 grams per day taken in divided doses. The usual dose is 250 mg taken every 6 hours or 500 mg taken every 12 hours. If you have a severe infection, your doctor may give you a larger dose.

Child dosage (ages 1–14 years)

25–50 mg/kg of body weight per day taken in divided doses. Your doctor may double your dose for severe infections.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Endocarditis prevention

Generic: cephalexin

Form: Oral capsule
Strengths: 250 mg, 500 mg
Form: Oral tablet
Strengths: 250 mg, 500 mg
Form: Oral suspension
Strengths: 125 mg/5 mL and 250 mg/5 mL

Brand: Keflex

Form: Oral capsule
Strengths: 250 mg, 500 mg, 750 mg
Adult dosage (ages 18–64 years)

2 grams taken 30–60 minutes before your procedure

Child dosage (ages 15–17 years)

2 grams taken 30–60 minutes before your procedure

Child dosage (ages 1–14 years)

50 mg/kg of body weight taken 30–60 minutes before your procedure. The total child’s dose shouldn’t be higher than the adult dosage.

Child dosage (ages 0–1 years)

This medication hasn’t been studied in children younger than 1 year for this condition.

Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dose or a different dosing schedule. This can help keep levels of this drug from building up too much in your body.

Special considerations

People with kidney problems:

  • People with a creatinine clearance (CrCL) of 10–50 mL/min: 500 mg taken every 8–12 hours
  • People with a CrCL of less than 10 mL/min: 250–500 mg taken every 12–24 hours
  • People receiving hemodialysis: 250 mg taken every 12–24 hours after each dialysis session

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

Cephalexin comes with risks if you don’t take it as prescribed.

If you stop taking the drug or don’t take it at all

If you don’t take this drug, your infection may not improve, or it may get worse.

If you miss doses or don’t take the drug on schedule

Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

If you take too much

You could have dangerous levels of this drug in your body. Symptoms may include:

  • nausea
  • vomiting
  • stomach aches
  • diarrhea
  • blood in your urine

If you think you’ve taken too much of this drug, act right away. Call your doctor or local Poison Control Center, or go to the nearest emergency room.  

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

Your symptoms and your infection should go away if this drug is working.

Cephalexin is a short-term drug treatment.

Important considerations for taking cephalexin

Store this drug carefully.

  • Store the tablets at room temperature. Keep them between 68ºF and 77ºF (20ºC and 25ºC).
  • Store the capsules between 59°F and 86°F (15°C and 30°C).
  • If your pharmacist didn’t mix the suspension, store the medication between 68ºF and 77º F (20ºC and 25ºC).
  • After mixing, store the suspension the refrigerator. You can keep it in the refrigerator for up to 14 days.
  • Don’t store this medication in moist or damp areas, such as bathrooms.

A prescription for this medication is refillable.

You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag. 
  • Don’t worry about airport X-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Clinical monitoring

You and your doctor should monitor certain health issues. This can help make sure you stay safe while you take this drug. These issues include:

  • Kidney function. Your doctor may do blood tests to check how well your kidneys are working. If your kidneys aren’t working well, your doctor may lower your dose of this drug.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

SECTION 5 of 5

How Much Does cephalexin Cost?

Oral capsule

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Show Sources

Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on January 14, 2016

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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