What Is Cephalexin (Keflex)?
Cephalexin, an antibiotic in the cephalosporin family, is used to treat infections caused by bacteria.
Cephalexin is prescribed to treat respiratory tract, middle ear, skin, bone, and urinary tract infections (UTI).
It's also used to prevent infections caused by streptococcal bacteria, including prevention of rheumatic fever. Cephalexin isn't recommended for sinus infections.
Cephalexin is sometimes called a first-generation cephalosporin because it was one of the first cephalosporins developed and marketed.
It was approved by the Food and Drug Administration in 1971 and was first sold by Eli Lilly and Company under the brand name Keflex; today Keflex is made and sold by Shionogi Inc.
It's also available as a generic medication in tablet or liquid form (called suspension).
Cephalexin and other cephalosporin antibiotics are broad-spectrum antibiotics, meaning they're used to treat a wide range of infections caused by many different bacteria.
Cephalexin kills susceptible bacteria by interfering with the bacteria’s ability to make cell walls, which are necessary for the bacteria cells to survive.
Cephalexin should only be used when there's strong evidence to support its use. Overusing broad-spectrum antibiotics can lead to serious infections from drug-resistant bacteria ("superbugs").
Treating colds or flu symptoms with broad-spectrum antibiotics can lead to antibiotic resistance and more severe infections that are harder to treat.
If you're allergic to penicillin, there's about a 10 percent chance that you will also be allergic to cephalexin.
You could be at higher risk for side effects from cephalexin if you have a history of liver, kidney, or colon disease, so tell your doctor about any of these conditions as well.
Like other antibiotics, cephalexin may cause an overgrowth of bacteria called Clostridium difficile in your colon. Toxins produced by C. difficile can cause diarrhea and a condition called pseudomembranous colitis.
Being on other antibiotics may also increase your risk for pseudomembranous colitis, so tell your doctor about any recent antibiotic use.
Cephalexin and Pregnancy
Cephalexin should be used only if clearly needed during pregnancy, and with caution during breastfeeding.
Tell your doctor if you are or may become pregnant or if you are breastfeeding.
Cephalexin for Dogs
Veterinarians often prescribe cephalexin to dogs with bacterial infections including skin, bone, urinary tract, respiratory, and other infections.
The drug can be given with food and is usually well-tolerated by dogs, but some may have side effects including nausea or vomiting.
Cephalexin should be avoided in animals that have had an allergic reaction to penicillins or other cephalosporin antibiotics.
Cephalexin Coupons and Prices
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Cephalexin Side Effects
Symptoms of an allergic reaction to cephalexin may include:
- Swelling under the skin
- Throat swelling
- Difficulty breathing
Digestive system side effects may include:
- Abdominal pain
- Nausea and vomiting
Other possible side effects of cephalexin include vaginal discharge, headache, dizziness, aches and pains, confusion, mouth sores, and fatigue. Let your doctor know about any side effects you experience.
Stop taking cephalexin and call your doctor immediately if you experience:
- Severe skin rash or swelling
- Any trouble breathing or swallowing
- Sudden bruising or bleeding
Always tell your doctor about any medications you are taking, including other prescription drugs, over-the-counter (OTC) drugs, vitamins, dietary supplements, and herbal remedies.
Certain drugs are known to interact with cephalexin and may cause problems:
Cephalexin may increase blood levels of the type 2 diabetes drug metformin. This could increase your risk for side effects.
Cephalexin may build up in the blood when combined with the medication probenecid (Benemid, Probalan), which is used to treat gout.
In some cases, probenecid may be used along with antibiotics to increase antibiotic strength.
Using antibiotics may make birth control pills ineffective. A second form of contraception is recommended while you're on antibiotics.
The dose of cephalexin prescribed will depend on the type of infection and whether the person taking it is a child or an adult.
Here are general guidelines for cephalexin dosage:
- The usual adult dose ranges from 1 to 4 grams a day, given in divided doses.
- Typical adult doses of cephalexin are 250 mg every 6 hours, or 500 mg every 12 hours.
- The usual dose for a child is 25 to 50 milligrams (mg) per kilogram of weight, given in divided doses.
- Keflex capsules come in 250, 333, 500, and 750 mg options.
Doses may be doubled for more severe infections.
Depending on the type of infection, treatment may last from 7 to 14 days.
If very large doses of cephalexin are needed, another type of cephalosporin that can be given by injection or an intravenous infusion may be used.
Here are some general rules for taking cephalexin:
- Take it with food or milk to prevent an upset stomach.
- Always take it as directed and for as long as directed. Skipping doses or not finishing your cephalexin prescription can lead to a more dangerous and resistant infection.
- Do not chew, split, or crush cephalexin capsules. Take them whole with a full glass of water, and with food or milk.
- Store capsules in a safe, dry place and at room temperature.
- Keep cephalexin suspension in the refrigerator. Don't freeze it. Unused suspension should be thrown away after 14 days.
- If you are using cephalexin suspension, make sure to shake the liquid well before each dose.
- Cephalexin use may interfere with some laboratory tests. These include blood tests and some urine testing done for diabetes. Always let your caregiver know you are taking cephalexin before you are tested.
An overdose of cephalexin can occur.
Symptoms of an overdose include nausea, vomiting, stomach pain, diarrhea, and blood in the urine.
If you think you've taken an overdose, or if someone else may have overdosed on cephalexin, call a poison control center at 800-222-1222 or call 911.
Missed Dose of Cephalexin
If you miss a dose, do not double your dose.
If you are close to your dose time, take your normal dose.
If you are well past your dose time, wait to take a dose until the next scheduled time.
By Chris Iliades, MD | Medically Reviewed by Niya Jones, MD, MPH
Latest Update: 2014-03-17
Copyright © 2014 Everyday Health Media, LLC
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