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Keflex

Generic name: cephalexin

Last updated August 27, 2026 0 views Reviewed by Philip Thornton, DipPharm
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What is Keflex?

Keflex is a cephalosporin (SEF a low spor in) antibiotic. It works by fighting bacteria in your body.

Keflex is used to treat infections caused by bacteria, including upper respiratory infections, ear infections, skin infections, urinary tract infections and bone infections.

Keflex is used to treat infections in adults and children who are at least 1 year old.

How should I take Keflex?

Take Keflex exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Do not use Keflex to treat any condition that has not been checked by your doctor.

Use this medicine for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. Cephalexin will not treat a viral infection such as the flu or a common cold.

Do not share Keflex with another person, even if they have the same symptoms you have.

This medicine can affect the results of certain medical tests, including urine glucose (sugar) tests. Tell any doctor who treats you that you are using this medicine.

Store the tablets and capsules at room temperature away from moisture, heat, and light.

Warnings

You should not use Keflex if you are allergic to cephalexin or to similar antibiotics, such as Ceftin, Cefzil, Omnicef, and others. Tell your doctor if you are allergic to any drugs, especially penicillins or other antibiotics.

Tell your doctor if you have kidney disease, liver disease, a stomach or intestinal disorder such as colitis, or diabetes.

Take this medication for the entire length of time prescribed by your doctor. Your symptoms may get better before the infection is completely treated. Keflex will not treat a viral infection such as the common cold or flu.

Before taking this medicine

To make sure Keflex is safe for you, tell your doctor if you have ever had

  • an allergy to any drug (especially penicillin);
  • liver or kidney disease; or
  • intestinal problems, such as colitis.

Tell your doctor if you are pregnant or breast-feeding.

Keflex side effects

Get emergency medical help if you have signs of an allergic reaction to Keflex (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Call your doctor at once if you have:

  • severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
  • unusual tiredness, feeling light-headed or short of breath;
  • easy bruising, unusual bleeding, purple or red spots under your skin;
  • a seizure;
  • pale skin, cold hands and feet;
  • yellowed skin, dark colored urine;
  • fever, weakness; or
  • pain in your side or lower back, painful urination.

Common Keflex side effects may include:

  • diarrhea;
  • nausea, vomiting;
  • indigestion, stomach pain; or
  • vaginal itching or discharge.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include nausea, vomiting, stomach pain, diarrhea, and blood in your urine.

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or bloody, call your doctor before using anti-diarrhea medicine.

What other drugs will affect Keflex?

Tell your doctor about all your other medicines, especially:

  • metformin; or
  • probenecid.

This list is not complete. Other drugs may interact with cephalexin, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Common questions about Keflex

What are the best antibiotics for a tooth infection?
There are several antibiotics that kill the common mouth bacteria that cause tooth infections. The best (first-line) antibiotics for tooth infection include: Amoxicillin, Penicillin, Cephalexin, Clindamycin, Azithromycin. Amoxicillin is often the first choice because it is widely effective and has the fewest gastrointestinal side effects. Continue reading
Can cephalexin treat a UTI and how fast does it work?
Cephalexin can treat many uncomplicated urinary tract infections (UTIs) when the bacteria are susceptible to it, but most guidelines do not list it as a first‑line antibiotic for otherwise healthy adults. Most people with an uncomplicated lower UTI who receive an effective antibiotic start to notice symptom relief within about 24–48 hours, although full resolution can take several days. Continue reading
What are the best antibiotics for boils?
There is no single best antibiotic for a boil, and many boils do not need one at all. Draining the boil is the main treatment. When an antibiotic is added, the usual choices are cephalexin, dicloxacillin, trimethoprim-sulfamethoxazole (Bactrim), doxycycline, or clindamycin. Your provider picks one based on whether MRSA is likely, how sick you are, where the boil is, and your allergies. Continue reading
What is the Best Antibiotic for Strep Throat?
Penicillin and amoxicillin are the first-choice antibiotics for strep throat. According to the CDC, Group A Streptococcus (the bacteria that cause Strep throat) has never shown resistance to penicillin, making it the gold standard treatment. Continue reading
Is Cephalexin safe for dogs? Uses, dosage, side effects?
Cephalexin is safe to use in dogs when under the supervision of a veterinarian. It is commonly prescribed for bacterial infections. Side effects are usually mild, and giving it with food might help prevent some stomach side effects. Continue reading
Can Cephalexin treat an abscess in the mouth or gum infection?
Cephalexin can help treat some mouth or gum abscesses because it kills many of the bacteria that cause dental infections. However, it is not the first‑line antibiotic and never replaces proper dental procedures such as drainage or root‑canal treatment. It should only be used under the direction of a dentist or physician, especially because inappropriate use can promote antibiotic resistance and may fail against certain resistant oral bacteria. Continue reading
If people are allergic to amoxicillin can they take cephalexin?
Cephalexin is not a penicillin and does not contain penicillin or amoxicillin, but people with certain kinds of serious penicillin allergies may still have a small chance of reacting to it because the drugs are related. The actual risk depends on the type and severity of the past reaction and should be discussed with a health professional. Continue reading
Does cephalexin cause yeast infections?
Yes. Cephalexin, like other broad‑spectrum antibiotics, can increase the risk of vaginal yeast infections in some people by disrupting normal protective bacteria in the vagina and allowing Candida yeast to overgrow. Continue reading
Can you take cephalexin for a spider bite?
Cephalexin is not routinely needed for a spider bite and is usually only prescribed if the bite site becomes secondarily infected with bacteria, such as cellulitis (a spreading skin infection). Do not start cephalexin (or any antibiotic) for a spider bite without specific advice from a healthcare professional. Continue reading

Related medicines

Before you take this medicine: the information on this page is general and may not cover your personal circumstances. Read the label supplied with your medicine and ask a pharmacist or doctor if you are unsure, especially if you are pregnant, breastfeeding, taking other medicines or managing a long-term condition.
General medicine information Consumer-friendly language Source: Drugs.com

Content is provided for education and is not medical advice. See our medical disclaimer. Source page medically reviewed by Philip Thornton, DipPharm on August 27, 2026.