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. Pseudomembranous colitis and Clostridium difficile have been reported with use of cefalexin. Less common and more serious side effects include bruising of the skin and yellowing of the skin or eye whites. 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. It is also not recommended to take cephalexin with dofetilide, live Cholera vaccine, warfarin, and cholesyramine. 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. Zinc and zinc supplements also interact with cefalexin and may reduce the amount of cefalexin in the body. 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. Absorption is slightly