Cefalexin

Cefalexin, also spelled cephalexin, is an antibiotic that can treat a number of bacterial infections.[4] It kills gram-positive and some gram-negative bacteria by disrupting the growth of the bacterial cell wall.[4] Cefalexin is a beta-lactam antibiotic within the class of first-generation cephalosporins.[4] It works similarly to other agents within this class, including intravenous cefazolin, but can be taken by mouth.[5]

Cefalexin
Clinical data
Pronunciation/ˌsɛfəˈlɛksɪn/
Trade namesKeflex, Ceporex, others[1]
Other namescephalexin (BAN UK), cephalexin (USAN US)
AHFS/Drugs.comMonograph
MedlinePlusa682733
License data
Pregnancy
category
  • AU: A [2]
  • US: B (No risk in non-human studies) [2]
    Routes of
    administration    		by mouth
    ATC code
    Legal status
    Legal status
    • AU: S4 (Prescription only)
    • UK: POM (Prescription only)
    • US: ℞-only
    Pharmacokinetic data
    BioavailabilityWell absorbed
    Protein binding15%
    Metabolism80% excreted unchanged in urine within 6 hours of administration
    Elimination half-lifeFor an adult with normal renal function, the serum half-life is 0.6–1.2 hours[3]
    ExcretionRenal
    Identifiers
    CAS Number
    PubChem CID
    IUPHAR/BPS
    DrugBank
    ChemSpider
    UNII
    KEGG
    ChEBI
    ChEMBL
    CompTox Dashboard (EPA)
    ECHA InfoCard100.036.142
    Chemical and physical data
    FormulaC16H17N3O4S
    Molar mass347.39 g/mol g·mol−1
    3D model (JSmol)
    Melting point326.8 °C (620.2 °F)
      (verify)

    Cefalexin can treat certain bacterial infections, including those of the middle ear, bone and joint, skin, and urinary tract.[4] It may also be used for certain types of pneumonia, strep throat, and to prevent bacterial endocarditis.[4] Cefalexin is not effective against infections caused by methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus, or Pseudomonas.[4] Like other antibiotics, cefalexin cannot treat viral infections, such as the flu, common cold or acute bronchitis.[4] Cefalexin can be used in those who have mild or moderate allergies to penicillin.[4] However, it is not recommended in those with severe penicillin allergies.[4]

    Common side effects include stomach upset and diarrhea.[4] Allergic reactions or infections with Clostridium difficile, a cause of diarrhea, are also possible.[4] Use during pregnancy or breast feeding does not appear to be harmful to the baby.[4][6][7] It can be used in children and those over 65 years of age.[4] Those with kidney problems may require a decrease in dose.[4]

    Cefalexin was developed in 1967.[8][9][10] It was first marketed in 1969 and 1970 under the names Keflex and Ceporex, among others.[1][11] Generic drug versions are available under other trade names and are inexpensive.[4][12] It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.[13] In 2017, it was the 102nd most commonly prescribed medication in the United States, with more than seven million prescriptions.[14][15] In Canada, it was the fifth most common antibiotic used in 2013.[16] In Australia, it is one of the top 15 most prescribed medications.[17]

    Medical uses
    A course of cefalexin capsules, commonly prescribed for infections

    Cefalexin can treat a number of bacterial infections including otitis media, streptococcal pharyngitis, bone and joint infections, pneumonia, cellulitis, and urinary tract infections.[4] It may be used to prevent bacterial endocarditis.[4] It can also be used for the prevention of recurrent urinary-tract infections.[4]

    Cefalexin does not treat methicillin-resistant Staphylococcus aureus infections.[4]

    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.[4] 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.[18]

    Pregnancy and breastfeeding

    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.[4][6] Use during breast feeding is generally safe.[7]

    Adverse effects

    The most common adverse effects of cefalexin, like other oral cephalosporins, are gastrointestinal (stomach area) disturbances and hypersensitivity reactions. Gastrointestinal disturbances include nausea, vomiting, and diarrhea, diarrhea being most common.[19] Hypersensitivity reactions include skin rashes, urticaria, fever, and anaphylaxis.[4] Pseudomembranous colitis and Clostridium difficile have been reported with use of cefalexin.[4]

    Signs and 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.[20]

    Interactions

    Like other β-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid.[4] Alcohol consumption reduces the rate at which it is absorbed.[21] Cefalexin also interacts with metformin, an antidiabetic drug,[4] and this can lead to higher concentrations of metformin in the body.[4][22] Histamine H2 receptor antagonists like cimetidine and ranitidine may reduce the efficacy of cefalexin by delaying its absorption and altering its antimicrobial pharmacodynamics.[23]

    Pharmacology

    Mechanism of action

    Cefalexin is a beta-lactam antibiotic of the cephalosporin family.[24] It is bactericidal and acts by inhibiting synthesis of the peptidoglycan layer of the bacterial cell wall.[25] 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.[25] It is most active against gram-positive cocci, and has moderate activity against some gram-negative bacilli.[4] However, some bacterial cells have the enzyme β-lactamase, which hydrolyzes the beta-lactam ring, rendering the drug inactive. This contributes to antibacterial resistance towards cefalexin.[26]

    Pharmacokinetics

    Like most other cephalosporins, cefalexin is not metabolized or otherwise inactivated in the body.[23][27] The biological half-life of cefalexin is approximately 30 to 60 minutes.[27]

    Society and culture

    It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.[13] The World Health Organization classifies cefalexin as highly important for human medicine.[28]

    Names

    Cefalexin is the International Nonproprietary Name (INN) and Australian Approved Name (AAN), while cephalexin is the British Approved Name (BAN) and United States Adopted Name (USAN). Brand names for cefalexin include Keflex, Acfex, Cephalex, Ceporex, L-Xahl, Medoxine, Ospexin, and Torlasporin.[29]

    Cost

    Cefalexin is relatively inexpensive.[30] A seven-day course of cefalexin costs a consumer about CA$25 in Canada in 2014.[31] The wholesale cost of this amount is about CA$4.76 as of 2019.[32] In the United States this amount costs a consumer about US$20.96 as of 2019.[33] In Australia a course of treatment costs from A$12 to A$26.77 as of 2019.[34] In the United Kingdom the costs to the consumer is generally £9.[35] The wholesale price in the developing world is about US$2.18 as of 2015.[36]

    References
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    3. 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
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    10. US patent 3507861, Robert B Morin & Billy G Jackson, "Certain 3-methyl-cephalosporin compounds", published 1970-04-21, issued 1970-04-21, assigned to Eli Lilly and Co
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    • "Cephalexin". Drug Information Portal. U.S. National Library of Medicine.
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