Cloxacillin
Cloxacillin sodium; Cloxacillin benzathine
Also known as: Orbenin-DC · Dry-Clox · Dariclox · Boviclox · Opticlox · BRL-1621 · sodium cloxacillin · chlorphenylmethyl isoxazolyl penicillin sodium · methylchlorophenyl isoxazolyl penicillin sodium · cloxacilina sodica · cloxacillinum natricum · P25 · Cloxacillin benzathine
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 |
|---|---|---|---|---|---|
| Susceptible infections | 20-40 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Staph. pyoderma, diskospondylitis, osteoarthritis or skin infections | 10-15 mg/kg PO q6h for 14-84 days | PO | q6h | 14-84 days | 🌎 NA |
| Systemic infections, bacteremia | 10-40 mg/kg PO q6-8h for 7-14 days | PO | q6-8h | 7-14 days | 🌎 NA |
| Ocular infections | Apply 1/10 of a tube (0.3 g) | topical | q24h | — | 🌍 EU |
- Susceptible infections: Oral dosage forms are no longer available commercially in the USA
- Ocular infections: Specifically for beta-lactamase-producing Staphylococcus
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections | 20-40 mg/kg PO or IM q6-8h | PO/IM | q6-8h | — | 🌎 NA |
| Staph. pyoderma, diskospondylitis, osteoarthritis or skin infections | 10-15 mg/kg PO q6h for 14-84 days | PO | q6h | 14-84 days | 🌎 NA |
| Systemic infections, bacteremia | 10-40 mg/kg PO q6-8h for 7-14 days | PO | q6-8h | 7-14 days | 🌎 NA |
| Ocular infections | Apply 1/10 of a tube (0.3 g) | topical | q24h | — | 🌍 EU |
- Ocular infections: Specifically for beta-lactamase-producing Staphylococcus
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Mastitis (treatment or prophylaxis) caused by susceptible organisms - Lactating cow | After milking out and disinfecting teat, instill contents of syringe; massage. | Intramammary | q12h | 3 total doses | 🌎 NA |
| Mastitis (treatment or prophylaxis) caused by susceptible organisms - Dry (non-lactating) cows | After last milking (or early in the dry period), instill contents of syringe and massage into each quarter. | Intramammary | Once | — | 🌎 NA |
- Mastitis (treatment or prophylaxis) caused by susceptible organisms - Lactating cow: Using lactating cow formula (Dari-Clox)
- Mastitis (treatment or prophylaxis) caused by susceptible organisms - Dry (non-lactating) cows: Using dry cow formula (benzathine)
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
- Class: Narrow-spectrum, penicillinase-resistant penicillin (isoxazolyl-penicillin).
- Spectrum: Highly effective against penicillinase-producing gram-positive cocci, particularly Staphylococcus species.
- Limitations: Inactive against Rickettsia, mycobacteria, fungi, Mycoplasma, and viruses. Methicillin-resistant staphylococci (MRSA/MRSP) are inherently resistant.
- Availability: In the USA, only intramammary infusion products are currently marketed for veterinary use (dairy cattle). Oral formulations are no longer commercially available in the US, though they may be compounded or available internationally.
Mechanism of action
Cloxacillin is a bactericidal beta-lactam antibiotic.
Binds to Penicillin-Binding Proteins (PBPs) → inhibits peptidoglycan cross-linking → disrupts bacterial cell wall synthesis → cell lysis and death.
Mechanistic Pearl: The bulky isoxazolyl side chain sterically hinders staphylococcal beta-lactamases, preventing the enzymatic hydrolysis of the beta-lactam ring that normally inactivates natural penicillins.
Safety & warnings
Contraindications
- Known hypersensitivity to penicillins or cephalosporins
Adverse effects
- Hypersensitivity reactions (rashes, fever, anaphylaxis)
- Eosinophilia
- Neutropenia
- Agranulocytosis
- Thrombocytopenia
- Leukopenia
- Anemias
- Lymphadenopathy
- Local irritation (ophthalmic)
Precautions
Warning: Contraindicated in patients with a history of hypersensitivity to penicillins.
- Cross-Reactivity: Use cautiously in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., cephalosporins, cefamycins, carbapenems). In humans, 1-15% of cephalosporin-allergic patients cross-react with penicillins.
- Pregnancy: FDA Category B (human); Papich Class A (veterinary). Generally considered safe, but use only when potential benefits outweigh risks. Crosses the placenta but no documented teratogenic problems.
Monitoring
- Clinical efficacy (resolution of infection/mastitis)
- Signs of hypersensitivity or toxicity
- Resolution of clinical signs of ocular infection
- Signs of local irritation or hypersensitivity
Pharmacokinetics
Absorption
Minimal systemic absorption expected from topical ophthalmic application.
Distribution
Distributes well into local ocular tissues.
Metabolism
Hepatic (for systemically absorbed fraction).
Elimination
Renal (for systemically absorbed fraction).
Overdose
Overdosage of intramammary infusions is unlikely to pose much systemic risk to the patient.
Note: Excessive dosing may prolong required withdrawal times for milk and meat in food-producing animals.
Available products
Formulations
- Intramammary infusion (peanut-oil gel or vegetable oils)
- Oral capsules/suspension (historically/internationally)
- Ophthalmic suspension 16.7%
Veterinary
- Cloxacillin Benzathine 500 mg intramammary syringe (Orbenin-DC, Dry-Clox, Boviclox)
- Cloxacillin Sodium 200 mg intramammary syringe (Dariclox)
- Opticlox ophthalmic suspension
- Orbenin ophthalmic suspension
Human-labeled
- None (Oral dosage forms no longer marketed in USA)
Regulatory status
POM-V
POM-V
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unless otherwise instructed by the manufacturer, cloxacillin benzathine or cloxacillin sodium mastitis syringes should be stored at temperatures less than 25°C in tight containers.
Client information
Important: If using oral compounded formulations for pets, complete the entire prescription even if the pet feels better.
- Food Animals: Adhere strictly to withdrawal times. Dry cow products (benzathine) require a 28-30 day slaughter withdrawal. Lactating cow products (sodium) require a 48-hour milk withdrawal and 10-day slaughter withdrawal.
- Allergic Reactions: Watch for signs of allergy such as hives, facial swelling, or difficulty breathing. Contact your veterinarian immediately if these occur.
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.