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Cefalexin ball-and-stick.png
Systematic (IUPAC) name
(7R)-3-Methyl-7-(α- D -phenylglycylamino)-3-cephem-4-carboxylic acid monohydrate
Clinical data
Trade names Keflex
AHFS/Drugs.com monograph
MedlinePlus a682733
Licence data US FDA:link
Pregnancy cat. A (AU) B (US)
Legal status Prescription Only (S4) (AU) POM (UK) -only (US)
Routes Oral
Pharmacokinetic data
Bioavailability Well absorbed
Protein binding 15%
Metabolism 80% excreted unchanged in urine within 6 hours of administration
Half-life For an adult with normal renal function, the serum half-life is 0.5-1.2 hours[1]
Excretion Renal
CAS number 15686-71-2 YesY
ATC code J01DB01 QJ51DB01
PubChem CID 2666
DrugBank DB00567
ChemSpider 25541 YesY
UNII 5SFF1W6677 YesY
KEGG D00263 YesY
Chemical data
Formula C16H17N3O4S 
Mol. mass 347.39 g/mol
 YesY (what is this?)  (verify)

Cefalexin (INN, BAN) or cephalexin (USAN, AAN) /ˌsɛfəˈlɛksɨn/ is a first-generation cephalosporin antibiotic introduced in 1967 by Eli Lilly and Company.[2][3] It is an orally administered agent that has antimicrobial activity against gram positive bacteria including Staphylococcus Aureus and Streptococcus.[4] Cefalexin has a similar antimicrobial spectrum to other first generation cephalosporins, including the intravenous agents cefalotin and cefazolin. It was first marketed as Keflex (Lilly), and is marketed under several other trade names.[2]

As of 2008, cefalexin was the most popular cephalosporin antibiotic in the United States, with more than 25 million prescriptions of its generic versions alone, for US$255 million in sales (though less popular than two other antibiotics, amoxicillin and azithromycin, each with 50 million prescriptions per year).[5][6]

Medical uses[edit]

Cefalexin is used to treat a number of infections including:

Cefalexin does not treat MRSA, or methacillin resistant staphylococcus aureus.[9]

Cefalexin is a useful alternative to penicillins in patients with penicillin intolerance. For example, penicillin is the treatment of choice for respiratory tract infections caused by Streptococcus, but cefalexin may be used as an alternative in penicillin intolerant patients.[10] Caution must be exercised when administering cephalosporin antibiotics to penicillin sensitive patients, because cross sensitivity with beta-lactam antibiotics has been documented in up to 10% of patients with a documented penicillin allergy. [11]

Mechanism of action[edit]

Cefalexin is a beta-lactam antibiotic. It is bactericidal and acts by inhibiting synthesis of the bacterial cell wall. It is most active against gram-positive cocci, and has moderate activity against some gram-negative bacilli.[12]

Drug interactions[edit]

Like other beta-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid.[13]

Adverse effects[edit]

The most common adverse effects of cefalexin, like other oral cephalosporins, are gastrointestinal disturbances and hypersensitivity reactions. Gastrointestinal disturbances include nausea, vomiting, and diarrhea. Hypersensitivity reactions include skin rashes, urticaria, fever, and anaphylaxis.[14] Pseudomembranous colitis has been reported with use of cephalexin.[14]

Symptoms of an allergic reaction include rash, itching, swelling, trouble breathing, or red, blistered, swollen or peeling skin. Overall, allergies occur in less than 0.1% of patients, but they are seen in about 1% to 10% of patients with penicillin allergy.[15]


  1. ^ McEvoy, G.K. (ed.). American Hospital Formulary Service - Drug Information 95. Bethesda, MD: American Society of Hospital Pharmacists, Inc., 1995 (Plus Supplements 1995)., p. 166
  2. ^ a b Sweetman, Sean C., ed. (2009). "Antibacterials". Martindale: The complete drug reference (36th ed.). London: Pharmaceutical Press. pp. 218–9. ISBN 978-0-85369-840-1. 
  3. ^ Sneader, Walter (2005). "Cephalosporin analogues". Drug discovery: a history. New York: Wiley. p. 324. ISBN 0-471-89980-1. Retrieved 2009-06-26. 
  4. ^ "FDA Cephalexin Drug Insert Label". 
  5. ^ "2008 Top 200 generic drugs by total prescriptions"  PDF (332.8 KB). Drug Topics (May 26, 2009). Retrieved on July 24, 2009.
  6. ^ "2008 Top 200 generic drugs by retail dollars"  PDF (399.4 KB). Drug Topics (May 26, 2009). Retrieved on July 24, 2009.
  7. ^ "Cephalexin". The American Society of Health-System Pharmacists. Retrieved 3 April 2011. 
  8. ^ "FDA Cephalexin Drug Label Insert". 
  9. ^ a b "Lexicomp: Cefalexin". 
  10. ^ "Lexicomp: Antibacterials". 
  11. ^ "FDA Cephalexin drug label". Retrieved 18 April 2014. 
  12. ^ "Cefalexin". Lexicomp. Retrieved 17 April 2014. 
  13. ^ "Cefalexin". Lexicomp. Retrieved 17 April 2014. 
  14. ^ a b "Cefalexin". Lexicomp. Retrieved 18 April 2014. 
  15. ^ Haberfeld, H, ed. (2009). Austria-Codex (in German) (2009/2010 ed.). Vienna: Österreichischer Apothekerverlag. ISBN 3-85200-196-X. 

External links[edit]