Jul 26, 2022

Generic name:  cephalexin  [ sef-a-LEX-in ]
Drug class:  First generation cephalosporins

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.


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.

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. 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.

Detailed Keflex dosage information

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.

What to avoid

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.

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.

Keflex side effects  (more detail)

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.

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