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Cephalexin (Keflex)



Cephalexin is an antibiotic that is sometimes used as an alternative to penicillin due to similarities in activity and structure. It is used to treat a variety of infections including infections of the skin, ear, urinary tract, and bone. It is active in killing gram positive bacteria, and has some activity against gram negative bacteria.




How to Use


Take this medication by mouth with water. It can be taken with or without food.


Take this medication exactly as prescribed. There should be at least 4-6 hours between doses.


Be sure to complete your entire course of this medication. Do not stop taking it because you are feeling better, unless directed by a doctor.


If you miss a dose, take it as soon as you can. If it is already almost time for your next dose, take only that next dose. Do not double up on any dose.



Important Information


Notify your doctor if your symptoms do not begin to improve after a few days of taking this medicine.


Notify your doctor if you have severe diarrhea, or diarrhea that lasts for more than 2 days. Do not self treat yourself for diarrhea.


This medicine can result in a false positive sugar urine test.



Side effects that should be immediately reported to your healthcare provider


Allergic reaction(hives, itching, swelling of the face or mouth), trouble breathing, difficulty or pain passing urine, severe diarrhea, yellowing of the skin or eyes,  red, blistering, loosening or peeling skin, seizures.



Other Side Effects


Heartburn, nausea, vomiting, muscle or joint pain, headache, genital irritation.



Be sure that your prescribing doctor is aware if you have any of the the following conditions before taking this medication


Kidney disease, stomach or intestinal conditions such as colitis, history of allergic reactions, pregnancy or breastfeeding.



Adult Dose


Impetigo, Skin Infections, Osteomyelitis, Ear Infections, Urinary Tract Infections, and Respiratory Infections


250 mg by mouth every 6 hours.




500 mg by mouth every 12 hours for around 7-14 days.



Severe Infections


As much as 4 grams per day in 2-4 divided doses for around 7-14 days.




1. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis 2014;59:e10-52.


2. Cephalexin capsule, tablet, suspension [package insert]. North Wales, PA: Teva Pharmaceuticals USA; 2015.


3. Keflex® oral capsules, cephalexin oral capsules[package insert]. Florham Park, NJ: Shionogi Inc. (per FDA); 2015.


4. Tipper DJ. Mode of action of beta-lactam antibiotics. Pharmacol Ther 1985;27:1-35.

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