ATC Code J01DB01
Formula C16H17N3O4S
Molar Mass (g·mol−1) 347.39
Physical State solid
Melting Point (°C) 326.8
PKS Value 2.53
CAS Number 15686-71-2
PUB Number 27447
Drugbank ID DB00567
Solubility schlecht löslich in Wasser


Cephalexin is a first-generation cephalosporin antibiotic. Structurally, it belongs to the group of betalactams. Cephalexin is used to treat a number of susceptible bacterial infections by inhibiting cell wall synthesis.

Indications for the antibiotic include:

  • Respiratory tract infections
  • Middle ear infections
  • Infections of the skin and skin structures
  • Bone infections
  • infections of the urogenital tract

Cefalexin was developed in 1967 and was approved by the FDA on January 4, 1971. It is on the World Health Organization's list of essential medicines.



Cefalexin is a beta-lactam antibiotic of the cephalosporin family. It acts bactericidal by inhibiting the synthesis of the peptidoglycan layer of the bacterial cell wall. Since cefalexin is structurally very similar to the bacterial amino acid D-alanyl-D-alanine, it can irreversibly bind to the active site of PBP (penicillin-binding protein), which is responsible for the re-synthesis of the cell wall components of the pathogens. This leads to the formation of "runners" in the wall of the bacteria, causing them to become unstable and the bacteria to perish. Cefalexin is most effective against Gram-positive cocci and has moderate activity against some Gram-negative Bacillus species.


Good absorption in the upper gastrointestinal tract with nearly 100% oral bioavailability. Cephalexin is 10-15% bound to serum proteins in the blood. Cephalexin is not metabolized in the body and 90% is excreted unchanged in the urine. The elimination half-life of cefalexin is approximately 30 to 60 minutes in humans with normal renal function.

Drug Interactions

  • As with other β-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid
  • It is not recommended to take cephalexin with dofetilide, live cholera vaccine, warfarin, and cholesyramine.
  • Alcohol consumption decreases the absorption rate of cefalexin.
  • Cefalexin may lead to increased plasma concentrations of metformin in the body
  • Histamine H2 receptor antagonists such as cimetidine and ranitidine may decrease the effectiveness of cefalexin
  • Zinc and zinc supplements also interact with cefalexin and may decrease the concentration of cefalexin in the


Side effects

The most common adverse effects of cefalexin are:

  • Nausea
  • Vomiting
  • Diarrhea
  • Hypersensitivity reactions

Symptoms of overdose include blood in the urine, diarrhea, nausea, upper abdominal pain, and vomiting. Overdose is generally treated by supportive care, as diuresis, dialysis, hemodialysis, and hemoperfusion with charcoal have not been well studied in this case.

There is no hazard associated with administration to pregnant women. There is no evidence that cefalexin may cause harm to the infant during lactation.

Markus Falkenstätter

Markus Falkenstätter

Markus Falkenstätter ist Autor zu pharmazeutischen Themen in der Medizin-Redaktion von Medikamio. Er befindet sich im letzten Semester seines Pharmaziestudiums an der Universität Wien und liebt das wissenschaftliche Arbeiten im Bereich der Naturwissenschaften.

Mag. pharm Stefanie Lehenauer

Mag. pharm Stefanie Lehenauer

Stefanie Lehenauer ist seit 2020 freie Autorin bei Medikamio und studierte Pharmazie an der Universität Wien. Sie arbeitet als Apothekerin in Wien und ihre Leidenschaft sind pflanzliche Arzneimittel und deren Wirkung.

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