What to Know About Keflex (Cephalexin)

A Cephalosporin Antibiotic Approved to Treat Bacterial Infections

Keflex (cephalexin) is a first generation cephalosporin antibiotic used to treat confirmed and suspected bacterial infections in the respiratory tract, skin, bone, and genitourinary tract. This specific antibiotic is best used to treat gram-positive bacterial infections. It is available as a capsule, tablet, and suspension (liquid) to take by mouth.

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Cephalexin is most commonly used for the treatment of bacterial infections for acute otitis media, respiratory tract infections, skin and skin structure infections, bone infections and genitourinary infections. Specific bacterial infections include the following:

Acute otitis media:

  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Moraxella catarrhalis

Respiratory tract infections: 

  • Staphylococcus aureus
  • Streptococcus pyogenes

Skin and skin structure infections:

  • Staphylococcus aureus
  • Streptococcus pyogenes

Bone infections:

  • Staphylococcus aureus
  • Proteus mirabilis

Genitourinary tract:

Cephalexin is also used for prophylaxis treatment for endocarditis and the treatment of tunnel infections or exit site infections in patients with peritoneal dialysis catheters.

Before Taking

It’s important to discuss with your medical provider all allergies to medications prior to taking a cephalosporin including penicillin allergies. Do not use this medicine if you are allergic to cephalexin or to other cephalosporin antibiotics. Other precautions and contraindications include:

  • Cephalexin interacts with numerous medications such as warfarin, metformin, probenecid, other antibiotics, and certain vitamins.
  • May increase clotting time.
  • Use caution if diagnosed with a liver or kidney disease.
  • Liquid cephalexin may interact with diabetes due to the sugar content. 
  • Discuss with a medical provider if you have a history of intestinal problems.

Talk to your doctor about all medications, supplements, and vitamins that you currently take. While some drugs pose minor interaction risks, others may outright contraindicate use or prompt careful consideration as to whether the pros of treatment outweigh the cons in your case.

Other Cephalosporins

Keflex (cephalexin) is a first-generation cephalosporin. Others include cephradine, cefadroxil, and cefazolin. Second-generation cephalosporins are more active against gram-negative bacteria. They include cefoxitin, cefotetan, cefuroxime, and cefprozil. Third-generation cephalosporins include ceftazidime and Rocephin (ceftriaxone).


All listed dosages are according to the drug manufacturer. Check your prescription and talk to your doctor to make sure you are taking the right dose for you. 

Standard pediatric dosages:

  • General dosing: 25-50 mg/kg/day
  • Otitis media infection: 75-100 mg/kg/day

Standard adult dosages:

  • General dosing: 250 mg every 6 hours. Maximum of 4000 mg/day
  • Infections such as strep throat, skin infections, cystitis: 500 mg every 12 hours

How to Take and Store

Follow these guidelines:

  • May be given with or without food. 
  • Shake liquid form prior to administration.
  • Liquid medication must be stored in a refrigerator. Throw away any part not used after two weeks.
  • Tablets and capsules stored at room temperature. 
  • Take exactly as directed even if feeling better. 
  • Take a missed dose as soon as you think about it.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
  • Do not take two doses at the same time or extra doses.
  • Do not change the dosage of the medication without consultation from a medical provider. 

Side Effects

As with all medications, there are possible side effects you may experience while taking Cephalexin. Common and less severe side effects include:

Even though these may be rare, Cephalexin does have side effects that require immediate medical attention as they can be life-threatening:

It is also important to take note that individuals can have a severe allergic reaction, otherwise known as anaphylaxis, as a result of taking cephalexin. Individuals suffering from an allergic reaction to cephalexin may experience the following symptoms: hives, difficulty breathing including wheezing, swelling of face lips, tongue, and/or throat.

Warnings and Interactions

Be aware of these:

  • Prolonged use may cause an overgrowth of nonsusceptible organisms.
  • Cephalexin crosses the placenta and should be used with caution in people who are pregnant. Do not take if pregnant, planning on getting pregnant, or breastfeeding.
  • Have your blood sugar checked regularly if taking this medication for a long time.
  • Cephalexin may interact with some laboratory results including urine glucose tests.
  • Do not stop taking the medication until all doses have been taken or instructed to by a healthcare provider.
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Article Sources
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  1. Food and Drug Administration. Cephalexin.

  2. U.S. National Library of Medicine. Cephalexin. Updated June 15, 2016.