(cefalexin 125mg)

Drug Effects

Synonyms(It is also Known As)

Cefalexin Sodium, Cephalexin 1-hydrate, Cephalexin hydrate, Cephalexin monohydrate, Cephalexine

Chemical Formula


Iupac Name

(6R,7R)-7-{[(2R)-2-amino-2-phenylacetyl]amino}- 3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene- 2-carboxylic acid


Cefalexin or more commonly cephalexin is a first-generation cephalosporin antibiotic introduced in 1967 by Eli Lilly and Company. It is an orally administered agent with a similar antimicrobial spectrum to the intravenous agents cefalotin and cefazolin. It was first marketed as Keflex (Lilly), and is marketed under several other trade names.


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). Cefalexin is used to treat a number of infections including: otitis media, streptococcal pharyngitis, bone and joint infections, pneumonia, cellulitis, andurinary tract infections. It may be used to prevent bacterial endocarditis.

Adverse Effect

Pain at inj site; hypersensitivity; GI disturbances; eosinophilia, neutropenia, leucopenia, thrombocytopenia.


Potentially Fatal: Anaphylactic reactions; nephrotoxicity

Mechanism Action

Cefalexin binds to one or more of the penicillin-binding proteins (PBPs) which inhibits the final transpeptidation step of peptidoglycan synthesis in bacterial cell wall, thus inhibiting biosynthesis and arresting cell wall assembly resulting in bacterial cell death.


Caution should be exercised in patients with history of stomach or bowel problems (eg, inflammation), blood clotting problems, kidney or liver problems, any allergy, who are taking other medications, elderly, children, during pregnancy and breast feeding. 


It may cause dizziness, do not drive a car or operate machinery while taking this medication. 


It may reduce platelet counts, avoid injury or bruising.

Drug Interaction

Probenecid produces higher and prolonged serum levels.


Potentially Fatal: Increased nephrotoxicity with aminoglycosides and furosemide.

Pregnancy Category

Category B: Either animal-reproduction studies have not demonstrated a foetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the 1sttrimester (and there is no evidence of a risk in later trimesters).


Almost completely absorbed from the GI tract with peak plasma concentrations after 1 hr (oral); may be delayed if taken with food.


Widely distributed but does not penetrate the CSF; bile (therapeutic concentrations). Crosses the placenta and enters the breast milk (small amounts). Protein-binding: Up to 15%


Not metabolised.


Via the urine within 6 hr by glomerular filtration and renal tubular secretion (>80% as unchanged); via the bile. May be removed by haemodialysis and peritoneal dialysis


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