Keflex Side Effects, Important Info, How to Use & More

Keflex belongs to the category of drugs called cephalosporin antibiotics. It is an antibiotic used to fight bacterial infections. It works by hindering the growth of the cell wall of gram-positive and some gram-negative bacteria.

It is used to treat many bacterial infections such as upper respiratory infections, skin infections, UTI (urinary tract infections) and ear infections. It is also used in treating specific types of strep throat, bacterial endocarditis, and pneumonia.


This medication does not work for viral infections such as flu, common cold, etc. Unnecessary and more prolonged use of medicine can lead to decreased effectiveness. Similarly, administering the drug for less than a prescribed period of time may lead to bacteria becoming immune to it.


Side Effects:

Common side effects:

Some mild side effects might include:

  • Throat swelling
  • Wheezing
  • Mild nausea, vomiting, diarrhea
  • Rash
  • Itching
  • Joint pain
  • Vaginal itching or discharge.
  • Swelling under the skin
  • Dizziness, tired feeling
  • Difficulty breathing

Serious side effects:

Report immediately to the doctor if you experience any of the rare but severe side effects including:

  • Confusion, agitation
  • Pale or yellowed skin, dark colored urine, fever, confusion or weakness
  • Diarrhea that is watery or bloody
  • Hallucinations (seeing things that are not there)
  • Easy bruising or bleeding, unusual weakness
  • Urinating infrequently or not at all.
  • Seizure(convulsions)
  • Fever
  • A sore throat
  • Headaches
  • severe blistering, peeling, and red skin rashes all over the body.

Use of this medicine for prolonged periods of time can lead to a yeast infection or oral thrush. It may also rarely be the cause of severe intestinal conditions, resulting from resistant bacteria, such as Clostridium difficile.

It is advised to immediately tell your doctor if you observe mucus/ blood in your stool, cramping or constant stomach pain and persistent diarrhea.


How to use:

Take medicine as advised by your doctor usually at an increment of 6 to 12 hours with or without food. For best results and maximum effectiveness take the medication around the same time every day.

The dose may vary from one individual to the other based on their age, medical history and response to the medicine. Among children, weight is also a factor taken into account.

In case of suspension fluid, make sure you shake the bottle well before pouring it into a spoon. For more accuracy, use a measuring spoon instead of a household one to prevent under or overdosing on the medicine.

Continue taking the medication for the prescribed period of time even if the symptoms of infection seemed to have disappeared before it. Ceasing to take medicine before time could lead to the infection returning with more force.



In case you miss a dose, take it as soon as you remember. However, if by the time you remember it is time for the next dose then skip the previous one and take the next dose. If you overdose on the drug immediately report to the emergency or poison centers. Symptoms of overdosing include:

  • Blood in urine
  • Nausea
  • Vomiting
  • Stomach ache
  • Diarrhea

Store Keflex at room temperature, away from light, heat, and moisture.



Before taking medicine, make sure you tell your doctor about any allergies of yours especially ones related to penicillin or other cephalosporin’s. It is advised to also tell your doctor about your complete medical history relating to the kidney, intestinal or stomach diseases.

Furthermore, Keflex may also render live bacterial vaccines such as typhoid ineffective. Thus, you should not take vaccines for immunization unless your doctor asks you to.


The liquid form of Keflex contains sugar and can raise the blood glucose levels of diabetics. Additionally, for diabetics to be taking this medicine in addition to metformin may experience hyperglycemia, and thus, they should only administer this antibiotic upon their doctor’s advice.

Using antibiotics may also make birth control ineffective.