Pseudomembranous colitis and Clostridium difficile have been reported with use of cefalexin.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. Interactions
Like other β-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid. Alcohol consumption reduces the rate at which it is absorbed. Cefalexin also interacts with metformin, an antidiabetic drug, and this can lead to higher concentrations of metformin in the body. Histamine H2 receptor antagonists like cimetidine and ranitidine may reduce the efficacy of cefalexin by delaying its absorption and altering its antimicrobial pharmacodynamics. Pharmacology
Mechanism of action
Cefalexin is a beta-lactam antibiotic of the cephalosporin family. It is bactericidal and acts by inhibiting synthesis of the peptidoglycan layer of the bacterial cell wall. 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. It is most active against gram-positive cocci, and has moderate activity against some gram-negative bacilli. 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. Pharmacokinetics
Cefalexin is rapidly and almost completely absorbed from the gastrointestinal tract with oral administration.
It is on the World Health Organizations List of Essential Medicines. In 2019, it was the 83rd most commonly prescribed medication in the United States, with more than 9 million prescriptions. In Canada, it was the fifth most common antibiotic used in 2013. In Australia, it is one of the top 15 most prescribed medications. Medical uses
Cefalexin can treat a number of bacterial infections including otitis media, streptococcal pharyngitis, bone and joint infections, pneumonia, cellulitis, and urinary tract infections. It may be used to prevent bacterial endocarditis. It can also be used for the prevention of recurrent urinary-tract infections.Cefalexin does not treat methicillin-resistant Staphylococcus aureus infections.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. 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. Pregnancy and breastfeeding
It is category A in Australia meaning that no evidence of harm has been found after being taken by many pregnant women. Use during breast feeding is generally safe. 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, the latter being the most common. Hypersensitivity reactions include skin rashes, urticaria, fever, and anaphylaxis.