Cephalexin Classification
Cephalexin is a first-generation cephalosporin antibiotic. 1
Structural and Chemical Properties
- Cephalexin is a semisynthetic cephalosporin with a beta-lactam ring structure that is related to other cephalosporin antibiotics 1
- The drug contains a D-phenylglycyl group at the 7-amino position and an unsubstituted methyl group at the 3-position, which defines its first-generation classification 1
- It shares the beta-lactam ring structure with penicillins, which accounts for potential cross-reactivity in penicillin-allergic patients 2
Clinical Context and Usage
- As a first-generation oral cephalosporin, cephalexin is recommended for empirical treatment of mild skin and soft tissue infections caused by gram-positive cocci 2
- Multiple guidelines classify cephalexin alongside other first-generation cephalosporins for prophylaxis and treatment of infections, distinguishing it from second-generation (cefuroxime) and third-generation (ceftriaxone, cefotaxime) cephalosporins 2
Important Cross-Reactivity Considerations
- Patients with confirmed penicillin allergies have approximately 16.45% risk of cross-reactivity with cephalexin due to shared beta-lactam ring and R1 side chain structures 3
- Cephalexin should not be used in patients with history of anaphylaxis, angioedema, or urticaria following penicillin or ampicillin exposure 2, 3
- The cross-reactivity occurs primarily through R1 side chain similarity, with cephalexin sharing identical R1 side chains with ampicillin, amoxicillin, cefadroxil, and cefaclor 2