Cephalosporin

Cefalexin

A first-generation oral cephalosporin for skin, urinary, throat, ear and bone infections, mostly those caused by streptococci and staphylococci.

Also called cephalexin (US name).

Drug card

Class: Cephalosporin
How it works: Binding penicillin-binding proteins so the bacterial wall is never cross-linked
Used for: Skin and soft tissue infections
Urinary tract infections, including prostatitis
Strep throat, if penicillin allergy is not immediate-type
Middle ear infections (otitis media)
Known for: Allergic rash, hives and swelling
Its name: cef- means a cephalosporin

Study it as a flashcard, and it comes back before you forget it.

Mechanism of action

How does cefalexin work?

Cefalexin is a first-generation cephalosporin taken by mouth. It acts best on Gram-positive cocci such as Streptococcus pyogenes and methicillin-susceptible Staphylococcus aureus, with narrower Gram-negative cover (E. coli, Proteus mirabilis, Klebsiella). MRSA, most enterococci and Pseudomonas resist it.

Like other cephalosporins: Cephalosporins are beta-lactams first derived from Acremonium (Cephalosporium) fungi. Like penicillins, they bind and inactivate penicillin-binding proteins, so peptidoglycan is not cross-linked and the bacterial cell wall weakens and lyses. They withstand many beta-lactamases; from first to third generation, Gram-negative activity rises and Gram-positive activity falls.

Uses

What is cefalexin used for?

Skin and soft tissue infections
Urinary tract infections, including prostatitis
Strep throat, if penicillin allergy is not immediate-type
Middle ear infections (otitis media)
Bone infections
Chest infections, including pneumonia

Side effects

Side effects of cefalexin

Allergic rash, hives and swellingKnown forSerious
Diarrhea
Nausea and vomiting
Stomach pain and indigestion
AnaphylaxisSerious
C. difficile colitisSerious
Genital itching, thrush and vaginitis
Hemolytic anemiaSerious
Seizures if doses are not cut in kidney failureSerious
Transient hepatitis and cholestatic jaundiceSerious
Interstitial nephritis (reversible)Serious
Dizziness and headache

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

Penicillin allergy: up to 1 in 10 may cross-react; avoid it after an immediate-type penicillin reaction.
Metformin: cefalexin raises metformin levels, so watch for low blood glucose and adjust metformin.
Kidney impairment: the dose is lowered to avoid seizures.
Zinc supplements lower cefalexin levels, so the two are taken at least 3 hours apart.

Good to know: WHO lists it as a first-choice Access antibiotic for skin and soft tissue infections. It does not treat MRSA.

Remember it

A way to remember it

Climb the generations, gain the Gram-negatives: from first to third generation, Gram-negative reach grows while Gram-positive reach shrinks.

First-generation cefalexin suits streptococcal and staphylococcal skin infections. Second-generation cefuroxime adds beta-lactamase-producing H. influenzae. Third-generation ceftriaxone and cefixime reach gonococci, E. coli and Klebsiella, and cefixime misses most staphylococci.

Written for biofideX

Its name

cef- means cephalosporin
Cefalexin, cefuroxime, ceftriaxone and cefixime share it. Older US names keep the spelling ceph- (cephalexin).
Every drug name stem

Its class

Cephalosporins

Other cephalosporins with a card:

Easily mixed up with penicillins and carbapenems.

All about cephalosporins

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

Practice it

Antibiotics: the cell wall

Cefalexin is one of 12 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

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