cephalexin
Keflex (cephalexin) is a first-generation cephalosporin antibiotic that kills bacteria by dismantling their cell walls. It is used for susceptible infections of the respiratory tract, middle ear, skin, bones and urinary tract.
This page is based on the FDA label for cephalexin, cross-checked with MedlinePlus and the National Cancer Institute dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
A bacterium lives inside a pressurised suit, its cell wall, and must keep patching the suit as it grows. Cephalexin hides the patching tools, so every new seam stays open. Pressure builds inside, the suit tears along the unsealed seams, and the bacterium bursts.
In simple terms
Bacteria need a strong outer wall to keep their shape and survive. Cephalexin belongs to the cephalosporin family of antibiotics and blocks the enzymes, called penicillin-binding proteins, that stitch the wall together. Without those final stitches the wall stays fragile, breaks open and the bacterium dies. Because human cells have no such wall, the medicine affects bacteria much more than our own tissues.
In depth
Cephalexin is an orally absorbed beta-lactam of the first-generation cephalosporin class. Its beta-lactam ring acylates the active-site serine of penicillin-binding proteins in the bacterial inner membrane, inhibiting the transpeptidation of peptidoglycan strands. Wall assembly stalls, autolytic enzymes degrade existing mesh and osmotic lysis follows. It is bactericidal against susceptible staphylococci, streptococci and common urinary pathogens.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
How cephalexin, a first-generation cephalosporin, works
- A bacterium lives inside a pressurised suit, its cell wall, and must keep patching the suit as it grows.
- Cephalexin hides the patching tools, so every new seam stays open. Pressure builds inside, the suit tears along the unsealed seams, and the bacterium bursts.
- Cephalexin is an orally absorbed beta-lactam of the first-generation cephalosporin class.
- Its beta-lactam ring acylates the active-site serine of penicillin-binding proteins in the bacterial inner membrane, inhibiting the transpeptidation of peptidoglycan strands.
Target: Penicillin-binding proteins (PBPs)
Bacterial enzymes that cross-link the cell wall mesh; blocking them leaves the wall weak and leaky so the bacterium cannot survive.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- Respiratory tract infections caused by susceptible bacteria
- Otitis media
- Skin and skin structure infections
- Bone infections
- Genitourinary tract infections, including acute prostatitis
Official sources
The statements on this page trace back to these records.
- U.S. Food and Drug Administration: cephalexin prescribing information
U.S. Food and Drug Administration
- MedlinePlus: cephalexin
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: cephalexin
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.