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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, Cepol, Ceporexine, Ceporex[1]
AHFS/Drugs.com monograph
MedlinePlus a682733
Licence data US FDA:link
Legal status
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[2]
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 
Molecular mass 347.39 g/mol
Physical data
Melting point 326.8 °C (620.2 °F)
 YesY (what is this?)  (verify)

Cefalexin (INN, BAN) or cephalexin (USAN, AAN) /ˌsɛfəˈlɛksɨn/ is an antibiotic useful for the treatment of a number of bacterial infections. It is taken by mouth and is active against gram-positive bacteria and some gram-negative bacteria.[3] It is in the class of first-generation cephalosporins and has similar activity to other beta-lactam antibiotics, within this group, including the intravenous agent cefazolin.[4]

Cefalexin can treat a number of bacterial infections, including: those of the middle ear, bone and joint, skin, and urinary tract. It may also be used for pneumonia, strep throat, and to prevent bacterial endocarditis. Cefalexin is not effective against methicillin-resistant Staphylococcus aureus (MRSA). Cefalexin can be used in those who have mild or moderate allergies to penicillin, but is not recommended in those with severe allergies. Like other antibiotics, cefalexin cannot treat viral infections, such as the common cold or acute bronchitis.[3]

Possible side effects include: allergies, stomach and intestinal upset, and Clostridium difficile diarrhea.[3] To date no evidence of harm has been found when used during pregnancy[3][5] or breast feeding.[6] It can be used in children and those over 65 years of age. Those with kidney problems may require a decrease in dose.[3]

In 2012, cefalexin was one of the top 100 most prescribed medications in the United States.[7] In Australia, it is one of the top 15 most prescribed medications.[8] It was developed in 1967[9] and first marketed in 1969 and 1970 by a number of companies, including Glaxo Wellcome and Eli Lilly and Company under the names Keflex and Ceporex, among others.[1][10] It is available as a generic drug under several other trade names and is not very expensive.[3][11] It is on the World Health Organization's List of Essential Medicines, a list of the most important medications needed in a health system.[12]

Medical uses[edit]

A course of cefalexin capsules, commonly prescribed for infections

Cefalexin is used to treat a number of infections including: otitis media, streptococcal pharyngitis, bone and joint infections, pneumonia, cellulitis, and urinary tract infections.[3] It may be used to prevent bacterial endocarditis.[3] It can also be used for the prevention of recurrent urinary-tract infections.[13]

Cefalexin does not treat methicillin-resistant Staphylococcus aureus infections.[13]

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.[14] 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.[15]

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.[16] Pseudomembranous colitis has been reported with use of cefalexin.[16]

Symptoms of an allergic reaction include rash, itching, swelling, trouble breathing, or red, blistered, swollen, or peeling skin. Overall, cefalexin allergy occurs in less than 0.1% of patients, but it is seen in 1% to 10% of patients with a penicillin allergy.[17]

Pregnancy and breastfeeding[edit]

It is pregnancy category B in the United States and category A in Australia, meaning that no evidence of harm has been found after being taken by many pregnant women.[3][5] Use during breast feeding is generally safe.[6]


Like other β-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid.[18] Alcohol consumption does not have a negative interaction with cefalexin,[19] but reduces the rate at which it is absorbed.[20]

Mechanism of action[edit]

Cefalexin is a beta-lactam antibiotic of the cephalosporin family.[21] It is bactericidal and acts by inhibiting synthesis of the peptidoglycan layer of the bacterial cell wall.[22] As cefalexin closely resembles d-alanyl-d-alanine, an amino acid ending on the peptidoglycan layer of the cell wall, it is able to irreversibly bind to the active site of PBP, which is essential for the synthesis of the cell wall.[23] It is most active against gram-positive cocci, and has moderate activity against some gram-negative bacilli.[24] However, some bacterial cells have the enzyme ß-lactamase, which allows the cell to be immune to cefalexin.[25]

Brand names[edit]

Other common names for cefalexin include Cefadal, Derantel, Mecilex, Medoxine, Xahl, and Tokiolexin. [26]


  1. ^ a b McPherson, Edwin M. (2007). Pharmaceutical Manufacturing Encyclopedia. (3rd ed.). Burlington: Elsevier. p. 915. ISBN 9780815518563. 
  2. ^ 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
  3. ^ a b c d e f g h i "Cephalexin". The American Society of Health-System Pharmacists. Retrieved Apr 21, 2014. 
  4. ^ Brunton, Laurence L. (2011). "53, Penicillins, Cephalosporins, and Other β-Lactam Antibiotics". Goodman & Gilman's pharmacological basis of therapeutics. (12th ed.). New York: McGraw-Hill. ISBN 978-0071624428. 
  5. ^ a b "Prescribing medicines in pregnancy database". Australian Government. 3 March 2014. Retrieved 22 April 2014. 
  6. ^ a b Wendy Jones (2013). Breastfeeding and Medication. Routledge. p. 227. ISBN 9781136178153. 
  7. ^ Bartholow, Michael. "Top 200 Drugs of 2012". Pharmacy Times. Retrieved 22 April 2014. 
  8. ^ Australia's Health 2012: The Thirteenth Biennial Health Report of the Australian Institute of Health and Welfare. Australian Institute of Health and Welfare. 2012. p. 408. ISBN 9781742493053. 
  9. ^ [compiled; Hey], edited by Edmund (2007). Neonatal formulary 5 drug use in pregnancy and the first year of life (5th ed.). Blackwell. p. 67. ISBN 9780470750353. 
  10. ^ Ravina, Enrique (2011). The evolution of drug discovery : from traditional medicines to modern drugs (1. Aufl. ed.). Weinheim: Wiley-VCH. p. 267. ISBN 9783527326693. 
  11. ^ Hanlon, Geoffrey; Hodges, Norman (2012). Essential Microbiology for Pharmacy and Pharmaceutical Science. Hoboken: Wiley. p. 140. ISBN 9781118432433. 
  12. ^ "WHO Model List of EssentialMedicines". World Health Organization. October 2013. p. 6. Retrieved 22 April 2014. 
  13. ^ a b "Lexicomp: Cefalexin". 
  14. ^ "Lexicomp: Antibacterials". 
  15. ^ "FDA Cephalexin drug label". Retrieved 18 April 2014. 
  16. ^ a b "Cefalexin". Lexicomp. Retrieved 18 April 2014. 
  17. ^ Haberfeld, H, ed. (2009). Austria-Codex (in German) (2009/2010 ed.). Vienna: Österreichischer Apothekerverlag. ISBN 3-85200-196-X. 
  18. ^ "Cefalexin". Lexicomp. Retrieved 17 April 2014. 
  19. ^ "Cefalexin (Cefalexin 250mg capsules)". NHS Choices. 
  20. ^ Barrio Lera JP, Alvarez AI, Prieto JG (June 1991). "Effects of ethanol on the pharmacokinetics of cephalexin and cefadroxil in the rat". J Pharm Sci 80 (6): 511–6. PMID 1941538. 
  21. ^ "Cephalosporin". Encyclopaedia Britannica, Inc. 2005. p. 35. 
  22. ^ Fisher, J. F.; Meroueh, S. O.; Mobashery, S. (2005). ""Bacterial Resistance to ß-Lactam Antibiotics: Compelling Opportunism, Compelling Opportunity"". Chemical Reviews 105 (2): 395-424. 
  23. ^ Fisher, J. F.; Meroueh, S. O.; Mobashery, S. (2005). ""Bacterial Resistance to ß-Lactam Antibiotics: Compelling Opportunism, Compelling Opportunity"". Chemical Reviews 105 (2): 395-424. 
  24. ^ "Cefalexin". Lexicomp. Retrieved 17 April 2014. 
  25. ^ Drawz, S. M.; Bonomo, R. A. (2010). "Three Decades of ß-Lactamase Inhibitors". Clinical Microbiology Reviews 23 (1): 160-201. 
  26. ^ https://scifinder.cas.org

External links[edit]