1 What is cephalexin?

Brand: Keflex, Panixine, Zartan, Biocef

Generic: Cephalexin

Cephalexin is a prescription antibiotic that belongs in the cephalosporin family. It is one of the first cephalosporin drugs developed and marketed; it was approved for use by the Food and Drug Administration or FDA in 1971.

Scientists continuously work to improve the structure of cephalosporins. Doing this allows the drug to become effective against a wider range of bacteria. With each development, a new batch of cephalosporins are developed and classified as another generation. Cephalexin belongs to the first generation of cephalosporins. 

It comes as a tablet form, capsule form and a liquid formulation called suspension. Cephalexin is available in various strengths: 250-mg and 500-mg for tablets and capsules; 125-mg / 5-mL and 250-mg / 5-mL for suspension, and 125-, 500-, and 750-mg for hydrochloride formulations.

It is available as generic medication, which is often preferred for its more economical price. However, cephalexin also has branded counterparts, marketed by various manufacturers. Popular brands of cephalexin include Keflex, Panixine, Zartan, and Biocef. If you prefer generic medicine, make sure to inform your doctor in case he prescribed a branded one.

Cephalexin is a prescription drug. This means that you need a prescription from a doctor before you can buy this drug at your local pharmacy. Misuse of antibiotics results to reduced effectiveness and even causes the development of antibiotic-resistant strains of bacteria. In turn, these are very difficult and expensive to treat because the antibiotics that are readily available will not be effective against these bacterial infections.

2 Cephalexin uses

As the name “antibiotic” suggests, it is anti bacteria. It is used to treat infections caused by various types of bacteria. Cephalexin, and other cephalosporins, are called broad-spectrum antibiotics because they are effective against a wide range of bacteria.

Cephalexin works by binding to the bacteria and blocking the activity of the enzymes responsible in producing peptidoglycan. This is an important component of the bacterial cell wall, which is vital to the survival of the bacteria. By interfering with the bacteria’s ability to make cell walls, cephalexin makes bacteria susceptible to external factors that will kill them.

It is important to note that this drug is not effective and should not be used against viral infections like the common cold and flu. Misuse of antibiotics results in reduced effectiveness and even antibiotic-resistant strains of bacteria. Be sure to consult your doctor and get a prescription. In the age of internet where there is lots of information available online, it is good to remember that self-diagnosing and self-medicating is especially dangerous when using antibiotics.

Aside from bacterial infections, cephalexin is also sometimes given to patients who have allergies to penicillin. This is done when said patients have to undergo dental or upper respiratory tract procedures. This is a precautionary measure taken by medical practitioners to prevent heart valve infections from developing.

3 What does cephalexin treat?

Cephalexin is used to treat bacterial infections like pneumonia and other respiratory infections, as well as skin, middle ear, and bone infections. Doctors also commonly prescribe cephalexin for UTI. However, you should avoid using cephalexin for sinus infection.


Here is a more comprehensive list of diseases that cephalexin is used to treat.

  • Strep throat
  • Tonsillitis
  • Infection of the middle ear caused by Streptococcus
  • Infection of the middle ear by H. Influenzae Bacteria
  • Infection of the middle ear caused by Moraxella Catarrhalis
  • Infection of the middle ear caused by Staphylococcus
  • Bacterial pneumonia caused by Streptococcus
  • Urinary tract infection caused by Klebsiella Bacteria
  • Urinary tract infection due to E. Coli Bacteria
  • Skin infection due to Streptococcus Pyogenes Bacteria
  • Skin infection due to Staphylococcus Aureus Bacteria
  • Infection of the urinary tract caused by Proteus Bacteria
  • Infection of a joint
  • Bone infection due to Streptococcus Bacteria
  • Bone infection caused by Staphylococcus Aureus Bacteria
  • Infection of the prostate gland caused by E. Coli
  • Infection of the prostate gland caused by Klebsiella
  • Infection of the prostate gland caused by Proteus

Aside from treating infections, cephalexin can also be used to prevent bacterial infections and complications. This happens to prevent endocarditis in patients with artificial heart valves when they have to undergo dental procedures. This is also done to prevent urinary tract infections and foot infections in diabetics.


4 Cephalexin side effects

Medication is important to help our bodies overcome many diseases and infections. However, despite their necessary effects, taking medications sometimes comes with negative and uncomfortable side effects.

The most common side effect associated with cephalexin is diarrhea. If the condition becomes watery, bloody or too severe that it interferes with your normal day-to-day activities, contact your doctor as soon as possible.

Here are common side effects experienced by people taking cephalexin:

  • Acidic or sour stomach
  • Upset stomach
  • Burning feeling in the chest or stomach or heartburn
  • Belching, indigestion
  • Irregular heartbeat
  • Dryness of the mouth
  • Anxiety, restlessness or nervousness
  • Shaking
  • Feeling irritable
  • Trouble sleeping
  • Seeing, hearing or feeling things that are not there
  • Itching in the vagina or genital area
  • White or brownish vaginal discharge
  • Pain during sexual intercourse
  • Muscle pain or stiffness
  • Pain, swelling or redness in the joints
  • Difficulty moving

There are also some side effects that may seem minor but are really symptoms of bigger conditions or negative effects. If you experience one or more of the side effects in the succeeding list, seek immediate medical attention or consult your doctor immediately.

  • Abdominal or stomach pain or tenderness
  • Bloating
  • Nausea or vomiting
  • Loss of appetite
  • Unusual weight loss
  • Clay-colored, light-colored, or black and tarry stools
  • Blood in the stool
  • General swelling of the body
  • Blistering, peeling or loosening of the skin
  • Red skin lesions, often with a purple spot in the center
  • Sores, ulcers or white spots on the lips or in the mouth
  • Puffiness or swelling of the eyelids or around the eyes, face, lips or tongue
  • Swollen or painful glands
  • Unpleasant breath odor
  • Increased thirst
  • Sore throat
  • Difficulty breathing or swallowing
  • Coughing up blood
  • Chest pain or tightness
  • Nosebleeds
  • Red, irritated eyes
  • Yellowing of the skin or eyes
  • Chills or fever
  • General exhaustion and weakness
  • Headache
  • Increased pulse rate
  • Paleness of the skin
  • Back pain
  • Joint, leg or general muscle pain
  • Painful or difficult urination
  • Dark urine or blood in the urine
  • Heavier menstrual flow or vaginal bleeding
  • Prolonged bleeding from wounds and cuts
  • Unusual bleeding or bruising
  • Paralysis

Despite this intimidating and extensive list, cephalexin is considered to be generally well-tolerated. There is a low incidence of side effects reported. Do not allow the fear of side effects to be the reason for you to avoid medications that will help heal your body.

Also, if you encounter any suspicious or abnormal symptoms that are not listed above, do not be afraid to consult your doctor anyway.

5 Cephalexin dosage

Cephalexin is taken orally, with or without food, every 6 or 12 hours for 7 to 14 days, depending on the patient’s condition. Patients must be extra mindful and responsible in taking their antibiotics. As much as possible, medication should be taken at the same time every day.

It is important that the prescription is followed and the medicine is taken until the last day indicated, even if the patient feels better or if he or she thinks to be completely healed. Otherwise, the infection may not be completely treated and removed from the body. This could develop bacteria that are resistant to antibiotics, which are then very difficult to treat.

This type of drug should be used exactly as prescribed by the doctor. If there is anything that a patient is unsure of, he or she must ask questions and clarify everything with his or her doctor or pharmacist.

Listed below are the common dosages prescribed:

  • Dosage for adults, to treat bacterial infection: 250- to 500-mg orally every six hours, for 7 to 21 days, depending on the severity and nature of the infection
  • Dosage for adults, to treat upper respiratory tract infection: 250- to 500-mg orally every six hours, for 7 to 10 days
  • Dosage for adults, to treat skin or soft tissue infections: 250-mg orally every six hours or 500-mg orally every 12 hours
  • Dosage for adults, to treat pharyngitis: 250-mg orally every six hours or 500-mg orally every 12 hours
  • Dosage for adults, to treat cystitis: 250-mg orally every six hours or 500-mg orally every 12 hours for 7 to 14 days
  • Dosage for adults, to treat otitis media: 500-mg orally every six hours, for 10 to 14 days
  • Dosage for adults, to treat osteomyelitis: 500-mg orally every six hours, for 4 to 6 weeks, depending on the severity and nature of the infection
  • Dosage for adults, to treat prostatitis or pyelonephritis: 500-mg orally every six hours for 14 days
  • Dosage for kids, to treat skin and soft tissue infections: 12.5- to 25-mg/kg orally every 12 hours
  • Dosage for kids, to treat otitis media: 12.5- to 25-mg/kg every six hours
  • Dosage for kids aged 1 year and up, to treat pharyngitis: 12.5- to 25-mg/kg orally every 12 hours

If the medication is effective, the patient should feel some improvement in his condition a few days after the first dosage.

The patient should carefully observe his condition. If he does not feel any improvement or if his symptoms become worse, he should immediately return to his doctor for consultation.

Cephalexin may trigger allergic reactions in some people. Upon taking the first dosage, observe your body for allergic reactions like swelling in the face, redness or itching. If you are allergic to certain medications, penicillin or other cephalosporin antibiotics, including but not limited to cefaclor, cefazolin, cefditoren, cefotetan, cefoxitin, ceftibuten, cefuroxime, cefepime, ceftibuten, ceftriaxone, and cefotaxime, you are more likely to be allergic to cephalexin as well. If you suspect an allergic reaction, inform your doctor immediately.

In case you miss a dose, take it as soon as you remember. However, if by the time you remember taking your medication, the next dose is already too close, then skip the missed dose and take the next one as scheduled. Return to your regular schedule afterwards and do not take extra medicine to prevent over dosage. Inform your doctor about the dose you missed as this might affect the treatment plan.

If, on the other hand, you overdose, seek emergency medical attention immediately. Watch out for these symptoms: vomiting, nausea, stomach pain, diarrhea, and blood in the urine.

6 Cephalexin drug interactions

A total of 44 drugs are reported to react with cephalexin.

Cephalexin, when taken with certain drugs, can have adverse effects. Always keep a list of all of your past and current medications and medical conditions to keep your doctor informed. This list should include prescription and non-prescription medication, nutritional supplements, herbal products, and vitamins. Your doctor will have to adjust what medicine to prescribe, and at what dosage, depending on your situation.

Here is a list of drugs and supplements that you should take note of when taking cephalexin.

Cephalexin and birth control pills do not go well together either. Cephalosporin drugs like cephalexin can possibly reduce the efficacy of combined oral contraceptives for progesterone and estrogen. Cephalexin impairs bacterial flora in the gastrointestinal tract and this may affect estrogen levels that are recycled in the large intestine. The antibiotic may render your contraceptives useless, or at the very least, less effective. Your doctor will adjust your dosage of contraceptives to make sure that you are safe.

It is also best not to mix cephalexin and alcohol. There are no significant interactions observed between cephalexin and alcohol, when alcohol consumption is done in moderation. However, alcohol speeds up the body’s excretory system. This means that antibiotics are excreted out, in the form of urine, faster when you drink alcohol. This decreases its efficacy because it is immediately flushed out of your system. Antibiotics also pass through the liver as they are excreted from the body. Drinking alcohol while taking cephalexin may overload and cause strain on your liver. For people with only mild infections, this may not be an issue. However, it is always best to discuss details like this with your physician so that he or she may provide you with sound advice that is appropriate for your condition.

Aside from drugs, cephalexin may also affect your body differently if you have certain medical conditions like kidney or liver problems, stomach or bowel movement issues, and blood clotting problems.

Taking cephalexin particularly endangers patients that experience the conditions listed below.

  • Colitis. Some patients develop pseudomembranous colitis, up to two months after treatment with cephalexin has ended. The condition ranges from mild to life-threatening. For patients with a history of gastrointestinal diseases, and particularly colitis, the drug should be given cautiously. Colitis is characterized by severe and persistent diarrhea, as well as severe abdominal cramps.
  • Renal dysfunction. Because antibiotics like cephalexin are eliminated through the kidney, people with renal dysfunction may worsen their condition if they also take cephalexin. The doctor will have to adjust the dosage, balancing the severity of the infection against the degree of renal impairment.
  • Liver disease. Cephalexin is associated with cases of hepatitis. Patients with existing liver disease will be at higher risk. Your doctor will have to monitor your condition closely to ensure that the treatment of your infection will not adversely affect your liver condition.
  • Dialysis. The procedure hemodialysis removes antibiotics like cephalexin from the patient’s system. So if a person takes cephalexin before his dialysis procedure, the antibiotic will simply be washed away and not take effect. For this reason, doses will be scheduled by the physician after dialysis, or another option is to do supplemental doses instead.
  • Seizures. In some patients, taking cephalexin has been observed to trigger seizures. This happens particularly in patients with renal impairment and for which dosage was not reduced. Your physician will closely monitor your condition so he can adjust your treatment as necessary.

7 Cephalexin vs. amoxicillin

Cephalexin and amoxicillin are both prescription antibiotics. Cephalexin belongs in the first-generation cephalosporin family. This type of drugs is effective against a wide range of bacterial infections. On the other hand, amoxicillin is a penicillin, the oldest type of antibiotics. Their structures are similar. They both treat bacterial infections by blocking the bacteria’s ability to create protective cell walls.

Both are also available in tablet and liquid suspension forms.

Being an old drug, amoxicillin is a reliable and more affordable option, however more strains of bacteria are resistant to it than amoxicillin.

Amoxicillin is associated with fewer side effect incidences than cephalexin. However, if you are taking any medication that results to blood thinning, cephalexin may not be an option. It also thins the blood and using both medications will increase your risk of bleeding too much.

We cannot say that one is stronger than the other or that one is more effective. In the end, you always have to consult with your doctor before taking medicine. Only a medical professional can competently decide which medication will work best for your specific condition at the lowest risk possible.

8 How long does it take for cephalexin to work?

The patient should feel some improvement in his or her condition a few days after the first dosage.

Depending on the severity and nature of the infection, the symptoms, like fever, might disappear after the first few days. But it is important to remember that even if the patient feels completely well, this medication should be taken exactly as the doctor prescribed, for its entire duration. Also, make sure to schedule a check-up with your doctor after the last day of medication. This ensures that the treatment worked completely and no trace of the bacteria was left. Incorrect usage of antibiotics may lead to the development of antibiotic-resistant strains of bacteria, which become so much harder and more expensive to treat.

9 Cephalexin during pregnancy

Taking cephalexin while you are pregnant may cause harm to your baby. The medication crosses the human placenta and may adversely affect your baby, leading to congenital defects. The antibiotic cephalexin has been used by women in various stages of their pregnancies without causing negative and permanent effects on their babies. However, the drug should still be taken with great care and only under the supervision and direction of a medical professional. The drug is only prescribed to treat diseases in pregnant women when the need for it has been clearly established. This is done so as not to expose the pregnant woman and her unborn child to unnecessary risks.

For new mothers, taking cephalexin and breastfeeding may not be a good idea. Studies show that the medication can be transferred to human milk, although in small amounts. Make sure to inform your doctor that you are breastfeeding so he or she can give you the appropriate medical advice. While the trace amounts excreted into the mother’s milk is unlikely to cause harm to a nursing infant, there are antibiotics more suitable for breastfeeding women. Other cephalosporins are recommended by the American Academy of Pediatrics as more compatible with breastfeeding.

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