Keflex: 7 things you should know - Drugs.com (2024)

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 31, 2023.

1. How it works

  • Keflex is a brand (trade) name for cephalexin which is an antibiotic that may be used to treat infections caused by susceptible bacteria.
  • Keflex (cephalexin) works by binding to and blocking the activity of enzymes responsible for making peptidoglycan, an important component of the bacterial cell wall. Keflex is bactericidal (which means it kills bacteria) and it works in a similar way to penicillins. Cephalexin is called a broad-spectrum antibiotic because it is effective against a wide range of bacteria.
  • Keflex belongs to the class of antibiotics known as cephalosporins. Keflex is a first-generation cephalosporin and is mainly effective against gram-positive bacteria.

2. Upsides

  • Keflex treats a wide range of infections caused by susceptible strains of bacteria that may occur in the respiratory tract, ear, genitourinary area, bone, or skin.
  • Keflex has excellent activity against gram-positive staphylococci and streptococci bacteria, including susceptible isolates of Staphylococcus aureus, Streptococcus pneumoniae, S. pyrogens, Haemophilus influenzae, Klebsiella pneumoniae, Moraxella catarrhalis, and Proteus mirabilis.
  • The usual dosage of Keflex is 250mg every 6 hours but a dose of 500mg every 12 hours may also be administered. Larger dosages may be administered for more severe infections. Treatment is usually given for 7 to 14 days.
  • May be given with or without food.
  • Has few drug interactions.
  • Keflex is available as a generic under the name cephalexin.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Diarrhea, dyspepsia, abdominal pain, and nausea, have been reported. May alter some laboratory tests. Seizures have been reported rarely.
  • Approximately 10% of people who are allergic to penicillin are also allergic to cephalosporins. Tell your doctor if you have ever had an allergy to antibiotics.
  • Positive direct Coombs' tests have been reported during treatment with cephalosporin antibacterials, such as Keflex.
  • The dosage of Keflex requires adjusting for people with moderate-to-severe kidney disease.
  • Severe diarrhea, caused by the overgrowth of a bacteria called Clostridium difficile, is a potential side effect of almost all antibacterial agents, including Keflex. Symptoms include persistent, watery, and sometimes bloody diarrhea.
  • Should only be used to treat infections caused by susceptible strains of bacteria. Where possible culture and susceptibility information should be considered when selecting or modifying antibacterial therapy.
  • May increase the time it takes for blood to clot. People with liver or kidney disease, who are malnourished, receiving a long course of therapy, or already on anticoagulants are more at risk.
  • May interact with some drugs including metformin, probenecid, and some urine glucose tests.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Keflex is a cephalosporin-type antibiotic that may be used in the treatment of gram-positive cocci infections. However, it should be used with caution in people with a penicillin allergy.

5. Tips

  • Can be taken with or without food.
  • Take exactly as directed and for the duration intended. Do not finish the course earlier than prescribed, even if you feel better because this encourages the growth of resistant bacteria. Do not take Keflex for any other infection other than the one you have been prescribed it for. Keflex will not treat viral infections such as the flu.
  • Seek medical advice if chronic diarrhea develops during or following a course of Keflex.
  • Talk to your doctor if you develop any worrying side effects after taking Keflex such as abdominal pain, excessive bruising or bleeding, or a rash.

6. Response and effectiveness

  • Peak concentrations of Keflex are reached one hour after dosing; however, it may take up to 48 hours before infection-related symptoms start to abate. Keep taking Keflex for the total duration prescribed, even if you feel better.

7. Interactions

Medicines that interact with Keflex may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Keflex. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Keflex include:

  • anticoagulants (blood thinners), such as warfarin (may prolong bleeding time)
  • chloramphenicol
  • estradiol or other estrogens
  • metformin
  • other antibiotics, such as chloramphenicol, sulfonamides, macrolides, and tetracycline
  • probenecid
  • probiotics, such as Lactobacillus
  • sodium picosulfate
  • vaccinations, such as BCG, cholera, or typhoid vaccine (may diminish the effectiveness)
  • vitamins, such as fat-soluble vitamins A, D, E, or K, folate, iron, or zinc (may decrease blood concentrations of Keflex).

Note that this list is not all-inclusive and includes only common medications that may interact with Keflex. You should refer to the prescribing information for Keflex for a complete list of interactions.

More about Keflex (cephalexin)

  • Check interactions
  • Compare alternatives
  • Reviews (90)
  • Drug images
  • Side effects
  • Dosage information
  • During pregnancy
  • Support group
  • Drug class: first generation cephalosporins
  • Breastfeeding

Patient resources

  • Keflex drug information
  • Keflex (Cephalexin Capsules and Tablets)
  • Keflex (Cephalexin Suspension)

Other brands

Biocef

Professional resources

  • Keflex prescribing information
  • Cephalexin (AHFS Monograph)

Related treatment guides

  • Bladder Infection
  • Bacterial Infection
  • Acne
  • Bacterial Endocarditis Prevention

References

  • Keflex (cephalexin) [Package Insert]. Revised 04/2023. Pragma Pharmaceuticals, LLC https://www.drugs.com/pro/keflex.html

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Keflex only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2024 Drugs.com. Revision date: August 31, 2023.

Medical Disclaimer

Keflex: 7 things you should know - Drugs.com (2024)

FAQs

What do I need to know about Keflex? ›

Take this medication by mouth as directed by your doctor, usually every 6 to 12 hours with or without food. If you are using the suspension, shake the bottle well before each dose. Measure the dose carefully using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose.

Is 7 days of Keflex enough? ›

Dosage for Keflex

The usual dose of oral KEFLEX is 250 mg every 6 hours, but a dose of 500 mg every 12 hours may be administered. Treatment is administered for 7 to 14 days. For more severe infections larger doses of oral KEFLEX may be needed, up to 4 grams daily in two to four equally divided doses.

What should you not take with Keflex? ›

Tell your doctor or pharmacist before starting to take cefalexin if you take any of these medicines:
  • probenecid, a medicine used to treat gout.
  • metformin, a medicine used to treat diabetes.
  • medicines that make you pee more (diuretics) including furosemide.
  • other antibiotics.

Is 500mg of Keflex 3 times a day too much? ›

Dosage. Cefalexin comes as tablets, capsules and a liquid that you swallow. Your dose of cefalexin will depend on why you're taking it but for most infections, adults usually take 500mg, 2 or 3 times a day. Your dose may be higher if you have a severe infection and be lower for children.

What should you not eat or drink with cephalexin? ›

Are there any foods and drink I should avoid? No, you can eat and drink normally while taking cefalexin.

What is the most common side effect of Keflex? ›

The most common cephalexin (Keflex) side effects are diarrhea, nausea, and stomach pain. Headache, fatigue, and dizziness are also possible. Cephalexin can raise the risk of vaginal irritation and infection while you're taking it. Most cephalexin side effects are mild and can be managed at home.

Why do I feel weird after taking cephalexin? ›

Antibiotic-associated diarrhea warning: 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).

Can I stop Keflex after 7 days? ›

Keep using this medicine for the full treatment time, even if you feel better after the first few doses. Your infection may not clear up if you stop using the medicine too soon.

Is Keflex a very strong antibiotic? ›

Is cephalexin a strong antibiotic? Cephalexin treats many type of infections and covers many different organisms (bugs). It can fight against a wider range of bacteria than penicillin and amoxicillin, but this doesn't necessarily mean that cephalexin is the best choice for all infections.

Why can't you lie down after taking cephalexin? ›

Can I lie down after taking cephalexin? After taking the antibiotic, you should avoid lying down since it may increase the time it takes for the medication to pass through your oesophagus and into your stomach, potentially irritating your oesophagus.

What foods to avoid with Keflex? ›

What Not to Eat while Taking Antibiotics
  • Foods high in acidity. Highly acidic foods repel absorption of drugs in our body. ...
  • Allergens and sugars. Gluten, dairy, and sugar are common allergens which suppress the ability of our white blood cells to destroy bacteria. ...
  • Dairy products. ...
  • Foods high in fiber. ...
  • Alcohol.
Jan 12, 2018

What vitamins should I avoid while taking cephalexin? ›

Cephalexin and multivitamin with minerals should not be taken orally at the same time. Products that contain zinc may interfere with the absorption of cephalexin into the bloodstream and reduce its effectiveness. You should take multivitamin with minerals at least three hours after taking cephalexin.

Is Keflex stronger than Amoxicillin? ›

Is cephalexin or amoxicillin stronger? When dosed appropriately, both antibiotics are effective against their covered organisms. The organism coverage of cephalexin makes it effective in some conditions that amoxicillin is not, including mastitis and bone and joint infections.

Can Keflex be left out of the fridge? ›

If you store the suspension out of the refrigerator, it will not keep well. Do not use any suspension that is left in the bottle after 14 days. Do not store cephalexin or any other medicine in the bathroom or near a sink.

What are the rules for taking cephalexin? ›

How to use Cephalexin. Take this medication by mouth as directed by your doctor, usually every 6 to 12 hours with or without food. If you are using the suspension, shake the bottle well before each dose. Measure the dose carefully using a special measuring device/spoon.

How quickly does Keflex start working? ›

Response and effectiveness

Peak concentrations of Keflex are reached one hour after dosing; however, it may take up to 48 hours before infection-related symptoms start to abate. Keep taking Keflex for the total duration prescribed, even if you feel better.

What are the guidelines for Keflex? ›

Adults and children 15 years of age and older—1000 to 4000 milligrams (mg) per day, taken in divided doses. Children 1 year of age and older—Dose is based on body weight and must be determined by your doctor. The dose is usually 25 to 100 milligrams (mg) per kilogram (kg) per day, taken in divided doses.

References

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