Cefaclor
Beta-lactams
Beta-lactams
Oral second-generation cephalosporin for otitis, pharyngitis, urinary and skin infections; known for serum sickness-like reactions in children.
Quick facts
- Group
- Beta-lactams
- Target
- Penicillin-binding proteins (bacterial transpeptidases)
- Used for
- Otitis media · Lower respiratory tract infections · S
- Key effects
- Diarrhoea and other gut symptoms · Morbilliform rash
- Monitor
- Rash · INR in people on oral anticoagulants
- ATC
- J01DC04
No doses: the clinician sets them by the current guideline.
Mechanism of action
No structure of cefaclor bound to a PBP is published; the figure shows cefalotin, a cephalosporin with the same beta-lactam core, acylating the Streptomyces R61 DD-peptidase, the classic PBP model.
Cefaclor acylates the penicillin-binding proteins and blocks peptidoglycan cross-linking; the wall weakens and the bacterium lyses. Compared with the first generation it gains some activity against H. influenzae and other gram-negatives, but beta-lactamase-negative, ampicillin-resistant H. influenzae is considered resistant.
- Well absorbed by mouth
- Acylates the PBPs of the bacterial wall
- Peptidoglycan cross-linking stops
- The bacterium lyses (bactericidal)
Indications
- Otitis media Acute otitis media →
- Lower respiratory tract infections, including pneumonia Community-acquired pneumonia →
- S. pyogenes pharyngitis and tonsillitis (penicillin is usually the first choice) Streptococcal pharyngitis →
- Urinary tract infections, including cystitis and pyelonephritis Urinary tract infection (acute cystitis) →
- Skin and soft-tissue infections
Adverse effects
Common
- Diarrhoea and other gut symptoms
- Morbilliform rash, itching and hives
- Eosinophilia
- Genital itching or vaginitis
Contraindications
- Allergy to cephalosporins
Key interactions
- Warfarin and other oral anticoagulants
- Increased anticoagulant effect and longer prothrombin time are reported.
- Probenecid
- Reduces its renal excretion.
- Copper-reduction urine glucose tests
- False positives.
What is monitored
- Rash, joint pain or fever a few days after starting (above all in children)
- INR in people on oral anticoagulants
- Diarrhoea during and after treatment
Administration and safety
- Capsules and suspension, with or without food
- The extended-release tablet is swallowed whole, close to a meal
- The suspension is shaken and measured with an oral syringe
Pregnancy and breastfeeding
Animal studies showed no fetal harm and adequate human studies are lacking; it is used only when clearly needed.
Nursing care
- Ask about penicillin and cephalosporin allergy and about reactions to a previous cefaclor course
- Teach carers to recognise a rash with joint pain
- Warn that it may lower the effect of hormonal contraceptives
- Ask the patient to report watery or bloody diarrhoea
Pharmacokinetics
- Absorption
- Well absorbed by mouth; food delays and lowers the peak but not the total amount absorbed.
- Elimination
- Renal: 60% to 85% leaves unchanged in the urine within 8 hours.
- Half-life
- Short, 0.6 to 0.9 hours; a little longer in kidney failure.
Test yourself
Think of the answer, then tap the question to see it.
A child on a second course of cefaclor develops rash, fever and joint pain a few days in. What reaction is this?
A serum sickness-like reaction, more frequent with cefaclor in children and with repeat courses; it settles when the drug is stopped.
Which cephalosporin generation does cefaclor belong to?
The second: somewhat more active against H. influenzae and gram-negatives than the first.
How is cefaclor eliminated, and how long is its half-life?
Mostly unchanged in the urine; its half-life is short, under an hour with normal kidneys.
Connections
← Back to the class: Beta-lactams
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CEFACLOR capsule (DailyMed (U.S. National Library of Medicine), 2026); Cefaclor: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); CEPHALOTHIN COMPLEXED WITH DD-PEPTIDASE (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.