What to Know About Keflex (Cephalexin)

A Cephalosporin Antibiotic Approved to Treat Bacterial Infections

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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.

Common Side Effects of Cephalexin

Verywell / Theresa Chiechi


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 talk to your medical provider about any allergies you have 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 blood clotting time.
  • Use caution if you have a liver or kidney disease.
  • Liquid cephalexin may interact with diabetes due to the sugar content. 
  • Discuss any history of intestinal problems with your healthcare provider.

Talk to your healthcare provider about all medications, supplements, and vitamins that you currently take.

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 healthcare provider to make sure you are taking the right dose for you. 

Standard pediatric dosages:

  • General dosing: 25-50 milligrams (mg)/killogram (kg) body weight/day
  • Otitis media infection: 75-100 mg/kg/day

Standard adult dosages:

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

How to Take and Store

Follow these guidelines:

  • May be taken with or without food. 
  • Shake liquid form prior to taking.
  • Liquid medication must be stored in a refrigerator. Throw away any unused medication after two weeks.
  • Tablets and capsules stored at room temperature. 
  • Take exactly as directed even if you are feeling better. 
  • Take a missed dose as soon as you can.
  • If it is close to the time for your next dose, skip the missed dose and go back to your normal schedule.
  • Do not take two doses at the same time and do not take 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:

  • Symptoms associated with potential liver problems including dark urine, fatigue, lack of appetite, nausea, abdominal pain, light-colored stools, vomiting, or yellow skin.
  • Bruising
  • Bleeding
  • Severe loss of strength and energy
  • Confusion
  • Sensing things that seem real but are not
  • Unable to pass urine
  • Change in amount of urine passed
  • Seizures
  • Severe dizziness
  • Severe headache
  • Severe joint pain
  • Stevens-Johnson syndrome
  • Clostridioides difficile

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 may cause false-positive results of 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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2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Food and Drug Administration. Cephalexin.

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