Keflex (cephalexin) is a cephalosporin antibiotic. It works by fighting bacteria in your body. Keflex is used to treat many different types of infections caused by bacteria. Keflex may also be used for purposes not listed in this medication guide.

Side Effects

More common side effects



tired feeling


joint pain

Less common side effects

blistering, peeling, or red skin rash

bruising or bleeding


convulsions (seizures)

dark urine

decreased urination


halos around lights

yellowing of the skin or eyes

Rare side effects



bloody stools

blurred vision

chest pain or discomfort


Keflex can cause serious side effects. Stop taking Keflex and call your doctor at once if you have:

severe stomach pain, diarrhea that is watery or bloody;

kidney problems–little or no urination, blood in your urine, swelling, rapid weight gain;


signs of a severe allergic reaction: hives, fever, swollen glands, joint pain, general ill feeling, unusual bruising or bleeding, severe fatigue, nausea, vomiting, rapid breathing, skin rash, itching.

Keflex can pass into breast milk and may harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

Do not give Keflex to a child without medical advice.


The recommended dose for most types of bacterial infections is 250 mg every 6 hours, or 500 mg every 12 hours. Keflex may be taken with or without food.

To treat a bladder infection, the recommended adult dose is 3 grams (mg) in a single dose. Keflex should be taken at evenly spaced intervals.

How does Keflex work?

Keflex belongs to a class of drugs called cephalosporin antibiotics. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions. Keflex works by killing bacteria that cause infections.