Cephalexin – Properties, Uses, and Dosage


Cephalexin is a semisynthetic first-generation cephalosporin antibiotic having methyl and beta-(2R)-2-amino-2-phenylacetamido groups at the 3- and 7- of the cephem skeleton, respectively. It is effective against both Gram-negative and Gram-positive organisms, and is used for treatment of infections of the skin, respiratory tract and urinary tract. It has a role as an antibacterial drug. It is a cephalosporin, a semisynthetic derivative and a beta-lactam antibiotic allergen. It is a conjugate acid of a cephalexin(1).

Properties and Characteristics of Cephalexin

Drug class Antibiotic
Brand Names Keflex
Synonyms Cefalexin, Cefalexina, Céfalexine, Cefalexinum
Molecular Formula C16H17N3O4S
Molecular Weight 347.4 g/mol
IUPAC Name (6R,7R)-7-[[(2R)-2-amino-2-phenylacetyl]amino]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid
Structural formula of main components
Pure active ingredient Cephalexin
Appearance White to off-white, crystalline powder
Melting point 326.8°C
Solubility Slightly soluble in water; practically insoluble in alcohol, chloroform, ether
Excretion Excreted in the urine
Storage Should be stored in tight containers at a temperature less than 40 °C, preferably between 15-30 °C.
Available Forms Capsule, Tablet, Syrup, Suspension,
Prescription Doctors prescription is required

Uses of Cephalexin

Cephalexin is used to treat infections caused by bacteria that are susceptible to the effects of cephalexin. Common infections that cephalexin is used for include:

  • Middle ear infections (otitis media)
  • Tonsillitis
  • Throat infections
  • Laryngitis
  • Bronchitis
  • Pneumonia
  • Urinary tract (UTIs)
  • Skin
  • Bone infections

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible:

  • Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
  • Redness, blistering, peeling, or loosening of the skin, including inside the mouth
  • Severe diarrhea, fever
  • Unusual vaginal discharge, itching, or odor

Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):

  • Diarrhea
  • Headache
  • Nausea

This list may not describe all possible side effects. Call your doctor for medical advice about side effects.

Mechanism of action

Cephalexin is a first-generation cephalosporin antibiotic. Cephalosporins contain a beta lactam and dihydrothiazide.7 Unlike penicillins, cephalosprins are more resistant to the action of beta lactamase. Cephalexin inhibits bacterial cell wall synthesis, leading breakdown and eventually cell death.

Drug Interactions

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

  • Dofetilide

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Cholera Vaccine, Live
  • Methotrexate
  • Probenecid
  • Warfarin

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Cholestyramine

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Colitis (inflammation in gut), history of or
  • Diarrhea, severe, history of or
  • Seizures, history of—Use with caution. May make these conditions worse.
  • Kidney disease or
  • Liver disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.

Typical dosing for Cephalexin

The dose is the same for the cephalexin capsules, tablets, and liquid suspension.

  • Adults and children 15 years of age or older: The typical dose is 250 mg by mouth every 6 hours. An alternative dose is 500 mg by mouth every 12 hours. You’ll typically need to take cephalexin for 7 to 14 days. For more severe infections, you might need a higher dose (up to 4 grams total per day).
  • Children age 1 to up to 15 years: The dose is based on your child’s body weight. The recommended total daily dose is 25 mg/kg to 50 mg/kg of body weight by mouth. This total dose is divided into smaller doses throughout the day, as directed by your child’s provider. Your child will typically need to take cephalexin for 7 to 14 days. For more severe infections, such as an ear infection, your child might need a higher dose of up to 100 mg/kg per day.

Your dose might differ if you have kidney problems.


Symptoms of oral overdose may include nausea, vomiting, epigastric distress, diarrhea, and hematuria. In the event of an overdose, institute general supportive measures.

Forced diuresis, peritoneal dialysis, hemodialysis, or charcoal hemoperfusion have not been established as beneficial for an overdose of cephalexin.

Cephalexin warnings

This drug comes with several warnings.

Allergy warning

Cephalexin can cause a severe allergic reaction. Symptoms can include:

  • Hives
  • Trouble breathing
  • Swelling of your face, lips, tongue, or throat

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 911 or go to the nearest emergency room.

Do not take this drug again if you’ve ever had an allergic reaction to it before. Taking it again could be fatal (cause death).

Warnings for certain groups

For people with kidney problems: If you have kidney problems or a history of kidney disease, you may not be able to clear this drug from your body. This may increase the levels of this drug in your body and cause more side effects. Your doctor may adjust your dose if you have kidney disease. Talk with your doctor about whether this drug is safe for you.

For pregnant people: You can take cefalexin at any stage during pregnancy. There’s no evidence that it causes harm to the baby. It’s important to treat infection during pregnancy as there’s a risk that it could make you unwell if left untreated.

For people who are nursing: It’s OK for you to take cefalexin while breastfeeding. Only tiny amounts of cefalexin get into breast milk, so it does not normally cause any side effects in your baby. However, it has caused diarrhoea in a few infants. It’s important to treat an infection while you’re breastfeeding as there’s a risk that it could make you unwell if left untreated.

Talk to your health visitor, midwife, doctor or pharmacist as soon as possible if you have any concerns, including if your baby:

  • Is not feeding as well as usual
  • Has sickness or diarrhoea
  • Has oral thrush (a fungal infection in their mouth) or a skin rash

Cefelaxin and fertility: There’s no evidence to suggest that cefalexin affects fertility in men or women.

For seniors: The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of the drug stays in your body for a longer time. This raises your risk of side effects.

For children: This drug hasn’t been studied in children younger than 1 year of age with respiratory tract, middle ear, skin and skin structure, bone, and urinary tract infections.

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