Cephalexin 500mg: Uses, Dosage and Side Effects

Did you ever read ancient stories of war when cities had great walls that prevented attackers from taking over the cities?

The walls were strong enough to withstand pressure. But over time, attackers built highly specialized weapons which were capable of taking down the city walls!

Cephalexin is just like one of such weapons, designed to target and take down walls of bacteria cells in your body, rendering them defenseless and vulnerable to destruction.

defenseless wall

Cephalexin belongs to a class of drugs known as cephalosporin. Cephalosporin is captured under the wide umbrella of antibiotics (drugs used to fight against bacteria in your body). Cephalexin belongs to the first class of cephalosporin to be discovered; hence, it is called a first-generation cephalosporin. Other first-generation cephalosporin antibiotics are Cefadroxil and Cephradine.

Cephalexin Appearance and Uses

cephalexin appearance

Cephalexin itself is a white shiny powder, but it is packaged in capsules or formulated into tablets so that it can be conveniently taken by mouth. The powder is also available for formulation into suspension.


Cephalexin is used in the treatment of infections caused by bacteria, such as respiratory tract infections, ear infections, skin infections, bone infections, and urinary tract infections.

Cephalexin is not active against viruses; therefore, it is not recommended for use in the treatment of infections of viral origin such as cold or flu.

How Cephalexin Fights Bacterial Infections


The bacteria that cause infection in the body have a strong cell wall that makes the cell rigid. Without the wall, the bacteria cell could expand and burst. Because bacterial cells multiply by diving themselves, they are constantly breaking down and rebuilding their cell wall.

Separate enzymes (biological substances that speed up biological reactions) are involved in the breakdown and rebuilding of the cell wall. Cephalexin inhibits the enzyme involved in building the cell wall without interfering with the breakdown process. This results in the rapid degradation of the cell wall.

Also, without the enzyme building up the cell wall, there would be an excess of ‘building materials’ which would trigger their break down as well. This way, the cell breaks down its own cell wall.

How Is Cephalexin Used?

soldier at war

In order to completely ‘defeat’ the army of bacteria causing infection, you would need to have a sufficient amount of cephalexin ‘soldiers’ in your body per time. If you have less, the bacteria cells would win and, worse still, build stronger defenses that cephalexin would not be able to defeat subsequently. When this happens, it is called antibiotic resistance.

If you have too many cephalexin soldiers, they could cause damage to normal cells of your body too, resulting in unwanted effects. In order to have the right amount of cephalexin in your body, you would have to use it exactly as prescribed by the doctor.

The dose prescribed by the doctor will be dependent on your age and weight, and the type of infection being treated. The usual dose of cephalexin ranges from 1 to 4 grams daily given in divided doses.

Divided doses mean that the drug is divided into equal amounts and taken at regular intervals within 24 hours. For instance, 2 grams in divided doses could mean 1 gram every 12 hours or 500mg every 6 hours. Typically, adults dose is 500mg every 12 hours.

In children, Cephalexin is safer prescribed in milligrams per kilogram of the body weight of the child. The recommended ratio is 25 – 50mg per kilogram of body weight, also given in divided doses. For a child weighing 10kg and prescribed 30mg of Cephalexin per body weight, he would have a total daily dose of 300mg which can then be divided into 100mg every 8 hours or 150mg every 12 hours.


The doctor may prescribe cephalexin to be used for about 7 to 14 days depending on the severity of the infection being treated.

Side Effects of Cephalexin

Cephalexin, like most other effective drugs, is not free from side effects. Let us consider some of the common side effects of Cephalexin.

1. Allergic Reactions

allergic reaction

Because of the pathway it follows in carrying out its function effectively, Cephalexin is likely to interfere with some other body functions to cause a series of allergic reactions such as

  • Rash
  • Swelling under the skin
  • Difficulty Breathing
  • Wheezing
  • Throat swelling
  • Itching

2.  Gastrointestinal Side Effects

abdominal upset

Cephalexin may also have gastrointestinal side effects. These side effects are aggravated when it is not taken with a meal or with milk. They include;

  • Diarrhea
  • Abdominal pain
  • Nausea and vomiting

3.  Oral Thrush

Not all bacteria cells in the body are harmful. Some bacteria contribute to the normal functions of the body. For instance, some bacteria prevent the growth of yeast. Cephalexin does not differentiate ‘good’ bacteria from ‘bad’ bacteria.

It can destroy the protective bacteria, allowing the growth of yeast. This causes thrush. Similarly, cephalexin can destroy good bacteria in the mouth, resulting in whitish patches on the tongue known as oral thrush.

4. Other Side Effects

Other side effects of Cephalexin include; a headache, dizziness, aches and pains, and fatigue (constant tiredness). It is advisable to let your doctor know the side effects you may be experiencing, so you can be appropriately monitored.

7 Dos and Don’ts of Cephalexin Therapy

Here are a few general rules to follow when taking cephalexin. These rules, if well adhered to, help make the course of therapy more bearable.

1. Do Not Use Cephalexin Without A Prescription


Cephalexin is a broad spectrum antibiotic, meaning it has an effect on a wide range of bacteria. It should not be used without a doctor’s prescription, following a proper diagnosis.

2. Do Take With Food or Milk


Do not take cephalexin on an empty stomach as it may cause stomach upsets and gastrointestinal inconveniences. It is safer to take with food, that is alongside your meal or take it with a cup of milk.

3. Do Not Skip Doses

drug doses

As earlier explained. you need the right number of soldiers fighting for you per time. If you have a 12 hourly dosage regimen, take the capsules at 12 hours’ interval to maintain the optimal amount of Cephalexin in your body. If you skip a dose, you reduce the amount of cephalexin in your body for a while, weakening its effect.

However, if you forget to take a dose, take it immediately you remember. But if the time you remember is close to the time of the next dose, skip the missed dose and take the next.

Do not use double doses at once or too close to each other. It could result in an overdose, which could aggravate side effects such as nausea, vomiting, stomach pain, diarrhea and blood in the urine.

4. Do Not Chew, Split or Crush

Cephalexin capsules, tablets, and powders are carefully formulated for optimal absorption through your digestive tract into your bloodstream. When you chew or crush them, you alter the formulation, which may affect their absorption.

However, when taken whole, they are delivered to the site where they are ‘activated’ to do what they were designed to do.

5. Do Shake Suspensions Well To Formulate Them.

shake suspensions well

Cephalexin does not easily dissolve in water, so it is formulated as a powder for suspension rather than a solution. If the powder is prescribed for you, ask for help to formulate appropriately into a suspension.

This step-by-step approach to mixing a suspension can guide you if you choose to do it on your own. Ensure that you shake well before every use to uniformly disperse the suspended particles.

6. Do Keep Suspensions Safely In The Refrigerator

keep suspensions refridgerated

After mixing the suspension, ensure it is kept in a refrigerator. Suspensions are relatively unstable and can be easily broken down. Keeping at fridge temperature would help maintain its stability for a while.

Suspensions usually do not last longer than 14 days, even when properly refrigerated. Hence, dispose of all formulated suspensions after 14 days of the formulation.

Do not freeze it. While keeping in cold temperature helps to extend its stability window, freezing would result in coagulation of the particles, which is undesirable.

7. Do Let Your Physician Know If You Are Using Cephalexin

talk to your physician

If you are taking cephalexin, don’t keep it away from clinical staff, including your doctor, and laboratory scientist. This is because cephalexin should not be used with certain medications, hence your doctor would not place you on such medications while you are on cephalexin.

Also, cephalexin can interfere with some blood tests and urine tests, so your laboratory scientist can properly interpret your test results when they are aware that you have been taking cephalexin.

Drugs That Interact With Cephalexin


Metformin is a medication used in the management of diabetes. When metformin and cephalexin are used concurrently, cephalexin prevents the removal of metformin from the body, resulting in increased metformin concentration in the bloodstream.

This may result in hypoglycemia (low glucose concentration in the bloodstream). It may be necessary to reduce the dose of metformin.


In contrast to the metformin-cephalexin interaction, probenecid increases the concentrations of cephalexin in the bloodstream. Sometimes, your doctor may deliberately prescribe both medications together if the infection is particularly difficult to treat.

Let Us Wrap This Up

It is essential to acknowledge the effectiveness of antibiotics in fighting infections. However, it is more expedient to emphasize the effect of antimicrobial resistance which follows unethical use of antibiotics.

Do not use an antibiotic like Cephalexin except prescribed by a doctor. Also, do not repeat an antibiotic without first consulting your physician.

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Grace Adejuwon, B.Pharm

Grace Adejuwon joined 25 Doctors in 2019. She has a bachelor's degree in Pharmacy from the Obafemi Awolowo University with many years experience in pharmaceutical care, logistics and pharmacy business management. She is also the lead pharmacist at Synapse Services Ltd, a community pharmacy. An ardent lover of nature, she delights in spending time within the pages of books. She uses her love for welding words together to educate people, especially about drugs.
Grace Adejuwon, B.Pharm

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