Cefaclor
Also known as: Ceclor · Raniclor · cefaclorum · cefaklor · cefkloras · kefakloori · compound 99638
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Skin or soft tissue infections | 7 mg/kg PO q8h | PO | q8h | 21-30 days | 🌎 NA |
| Systemic, lower respiratory tract infections | 10-13 mg/kg PO q8h | PO | q8h | 14 days | 🌎 NA |
- Systemic, lower respiratory tract infections: Maximum daily dose is 1 gram.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Skin or soft tissue infections | 7 mg/kg PO q8h | PO | q8h | 21-30 days | 🌎 NA |
| Systemic, lower respiratory tract infections | 10-13 mg/kg PO q8h | PO | q8h | 14 days | 🌎 NA |
- Systemic, lower respiratory tract infections: Maximum daily dose is 1 gram.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Cefaclor is an oral second-generation cephalosporin antibiotic. It shares a similar overall spectrum of activity with first-generation cephalosporins (such as cephalexin) but offers enhanced activity against certain gram-negative bacteria, including strains of E. coli, Klebsiella pneumoniae, and Proteus mirabilis.
Clinical Pearl: While there is limited clinical experience with cefaclor in veterinary medicine, it serves as a potentially useful alternative when an oral cephalosporin is desired to treat bacterial infections that are resistant to first-generation cephalosporins but remain susceptible to cefaclor based on culture and sensitivity testing.
Mechanism of action
Cefaclor is a bactericidal beta-lactam antibiotic.
- It binds to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall.
- Binding → Inhibition of the third and final stage of bacterial cell wall synthesis (peptidoglycan cross-linking).
- Defective cell wall → Cell lysis mediated by bacterial cell wall autolytic enzymes (autolysins).
It possesses slightly better stability against certain beta-lactamases produced by gram-negative organisms compared to first-generation cephalosporins.
Safety & warnings
Contraindications
- Known hypersensitivity to cephalosporins
- Use with caution in patients with documented penicillin allergy (potential cross-reactivity)
- Severe renal impairment (requires dosage adjustment)
Adverse effects
- Nausea
- Diarrhea
- Hypersensitivity reactions (including anaphylaxis)
- Serum-sickness-like reactions
- Erythema multiforme (rare)
- Rash
- Transient increases in liver enzymes
- Transient increases in BUN and serum creatinine
Precautions
Use cautiously in patients with documented penicillin allergies due to the potential for cross-reactivity. Dosage adjustment is recommended in patients with severe renal impairment. Cephalosporins may cause false-positive urine glucose determinations when using the copper reduction method and falsely elevated serum or urine creatinine values when using the Jaffe reaction. May cause a false-positive direct Coombs' test.
Drug interactions
Reduces extent of absorption of extended-release cefaclor tablets
Reduced renal excretion of cefaclor
Rare reports of increased anticoagulant effect
Monitoring
- Clinical efficacy (resolution of infection)
- Renal function in patients with pre-existing renal insufficiency
Pharmacokinetics
Half-life
Absorption
In dogs, about 75% of an oral dose is absorbed, but an apparent first-pass effect reduces bioavailability to about 60%. Food delays, but does not appreciably alter the amount absorbed.
Distribution
Distributed to many tissues, but levels are lower in interstitial fluid than those found in serum. Crosses the placenta and enters breast milk.
Metabolism
Dogs appear to metabolize a greater percentage of cefaclor than do rats, mice, or humans.
Elimination
Very high levels are excreted into the urine unchanged. Bile levels are higher than those found in serum.
Overdose
Cefaclor appears quite safe in dogs.
- Chronic high doses: Dogs given daily PO doses of 200 mg/kg/day for 30 days developed soft stools, occasional emesis, and transient moderate decreases in hemoglobin.
- Massive chronic doses: One dog given 400 mg/kg/day for one year developed a reversible thrombocytopenia.
Available products
Formulations
- Capsules
- Chewable Tablets
- Extended-Release Tablets
- Powder for Oral Suspension
Human-labeled
- Cefaclor Oral Capsules: 250 mg & 500 mg
- Cefaclor Chewable Tablets: 125 mg, 187 mg, 250 mg, & 375 mg
- Cefaclor Extended-Release Oral Tablets: 375 mg & 500 mg
- Cefaclor Powder for Oral Suspension: 125 mg/5 mL, 187 mg/5 mL, 250 mg/5 mL, & 375 mg/5 mL
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules, tablets, and powder for suspension should be stored at room temperature (15-30°C). After reconstituting, the oral suspension should be stored in the refrigerator and discarded after 14 days.
Client information
Important: Give this medication exactly as directed by your veterinarian. Even if your pet appears completely well, continue treating for the full duration prescribed to prevent the infection from returning or becoming resistant.
- Administration: It is preferable to give this medication on an empty stomach. However, if your pet vomits or loses their appetite after taking it, you can give future doses with a small amount of food.
- Side Effects: Mild stomach upset (soft stool, occasional vomiting) can occur.
- When to Call the Vet: Contact your veterinarian immediately if your pet develops severe vomiting, severe diarrhea, or signs of an allergic reaction (such as facial swelling, hives, or severe itching).
- Storage: If you were given a liquid suspension, keep it in the refrigerator and throw away any unused portion after 14 days.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.