Oxacillin Sodium — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	10-20 mg/kg	q8h	Duration: 5-7 days or as clinically indicated Notes: Administer on an empty stomach (1 hour before or 2 hours after feeding) for optimal absorption.
Dog	IV/IM	10-20 mg/kg	q6-8h	Duration: 5-7 days or as clinically indicated Notes: IV administration should be slow (over 5-10 minutes).
Cat	PO	10-20 mg/kg	q8h	Duration: 5-7 days or as clinically indicated Notes: Administer on an empty stomach.
Cat	IV/IM	10-20 mg/kg	q6-8h	Duration: 5-7 days or as clinically indicated Notes: IV administration should be slow.
Horse	IV	10-20 mg/kg	q6h	Duration: 5-7 days or as clinically indicated Notes: Administer slowly IV; oral absorption is poor in horses.
Cattle	IM	10-20 mg/kg	q12h	Duration: 5-7 days or as clinically indicated Notes: Extra-label use; observe withdrawal times.
Small Ruminants	IM	10-20 mg/kg	q12h	Duration: 5-7 days or as clinically indicated Notes: Extra-label use; observe withdrawal times.
Rabbit	PO	10-15 mg/kg	q8-12h	Duration: 5-7 days or as clinically indicated Notes: Extra-label use; monitor for gastrointestinal upset.
Bird/Poultry	PO/IM	10-20 mg/kg	q8-12h	Duration: 5-7 days or as clinically indicated Notes: Extra-label use; limited data.

Clinical Indications & Species Uses

General Indications

Treatment of infections caused by penicillinase-producing staphylococci, including skin, soft tissue, respiratory, bone, and joint infections.

Dog (Canine)

Treatment of infections caused by penicillinase-producing staphylococci, including pyoderma, wound infections, abscesses, osteomyelitis, and respiratory tract infections.

Cat (Feline)

Treatment of staphylococcal infections, including skin infections, wound infections, and abscesses.

Horse (Equine)

Treatment of staphylococcal infections, including respiratory infections, wound infections, and septic arthritis.

Small Ruminants (Sheep / Goat)

Treatment of staphylococcal infections, including mastitis and skin infections (extra-label use).

Rabbit & Small Mammals

Treatment of staphylococcal infections, including abscesses and respiratory infections (extra-label use).

Pharmacology & Mechanism of Action

Drug Class: Penicillinase-resistant penicillin | Pharmacological Group: Beta-lactam antibiotic

Mechanism of Action: Oxacillin is a semisynthetic penicillin that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby interfering with the transpeptidation reaction in peptidoglycan cross-linking. This leads to cell wall weakening, lysis, and death, primarily in actively dividing bacteria. Its resistance to staphylococcal beta-lactamases (penicillinases) makes it effective against penicillinase-producing staphylococci.

Pharmacodynamics: Oxacillin is bactericidal and time-dependent. Its efficacy correlates with the duration of time that serum concentrations exceed the minimum inhibitory concentration (MIC) for the pathogen. It is active against gram-positive bacteria, including Staphylococcus aureus (including penicillinase-producing strains), Streptococcus spp., and some anaerobes. It is not effective against methicillin-resistant staphylococci (MRSA) or gram-negative organisms.

⚡ Pharmacokinetics Summary

Absorption: Oxacillin is acid-stable and well absorbed after oral administration in monogastric animals, but absorption is variable and food can reduce it. In ruminants, oral absorption is poor due to ruminal degradation. Parenteral administration (IM/IV) provides reliable absorption.

Distribution: Oxacillin is widely distributed in body fluids and tissues, but penetration into the central nervous system is poor unless the meninges are inflamed. It crosses the placenta and is excreted in milk. Protein binding is high (approximately 90-95% in dogs and cats).

Metabolism: Oxacillin undergoes minimal hepatic metabolism. It is primarily eliminated unchanged by the kidneys via tubular secretion and glomerular filtration. Some biliary excretion occurs.

Excretion: Renal excretion is the primary route, with about 70-80% of the drug excreted unchanged in urine. Biliary excretion accounts for a minor portion. In animals with renal impairment, dosage adjustment may be necessary.

Half-Life: Dog: 0.5-1 hour; Cat: 0.5-1 hour; Horse: 0.5-1 hour; Cattle: 0.5-1 hour (approximate).

Bioavailability: Oral bioavailability is variable (30-50% in dogs and cats) and is reduced by food. IM injection provides near-complete absorption.

Protein Binding: Approximately 90-95% in dogs and cats; lower in other species (e.g., 80% in horses).

Available Formulations & Strengths

Oral Capsule 250 mg, 500 mg (PO)

Oral Tablet 250 mg, 500 mg (PO)

Oral Solution (reconstituted) 250 mg/5 mL (PO)

Injectable Solution (as sodium salt) 250 mg/vial, 500 mg/vial, 1 g/vial, 2 g/vial (IV/IM)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to penicillins or cephalosporins
History of allergic reactions to beta-lactam antibiotics
Use in rabbits, guinea pigs, hamsters, and other small rodents (oral administration may cause fatal enteritis due to disruption of normal gut flora)

Warnings & Clinical Precautions:

Use with caution in animals with renal impairment; dosage adjustment may be required.
Use with caution in animals with a history of gastrointestinal disease (especially colitis).
Parenteral administration may cause tissue irritation at injection site.
In food animals, observe withdrawal times to avoid drug residues.
Prolonged use may result in overgrowth of non-susceptible organisms (superinfection).
Use in horses: oral administration is unreliable; use parenteral route.
In ruminants, oral administration is ineffective due to ruminal degradation.

Adverse Effects & Reactions

Common:

Gastrointestinal upset (nausea, vomiting, diarrhea) after oral administration
Injection site pain or inflammation

Serious / Severe:

Anaphylaxis (rare but potentially fatal)
Severe allergic reactions
Acute interstitial nephritis
Clostridial enterocolitis in horses and rabbits

Rare:

Hepatotoxicity
Blood dyscrasias (neutropenia, thrombocytopenia)
Neurological signs (seizures) with high doses or renal impairment

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Probenecid	Decreases renal tubular secretion of oxacillin, increasing serum concentrations and prolonging half-life.	Moderate
Aminoglycosides (e.g., gentamicin)	Synergistic bactericidal effect against some gram-positive bacteria; however, do not mix in the same syringe or solution as they may inactivate each other.	Mild
Tetracyclines and chloramphenicol	May antagonize the bactericidal effect of penicillins; avoid concurrent use.	Moderate
Methotrexate	Penicillins may reduce renal clearance of methotrexate, increasing its toxicity.	Moderate
Oral contraceptives (in humans, but relevant in research)	May reduce efficacy of oral contraceptives; not typically relevant in veterinary medicine.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Gastrointestinal signs (vomiting, diarrhea)
Neurological signs (tremors, seizures) especially with high doses or renal impairment
Allergic reactions (urticaria, angioedema, anaphylaxis)

Emergency Treatment Protocol: Discontinue the drug. Provide symptomatic and supportive care. For anaphylaxis, administer epinephrine, corticosteroids, and antihistamines as needed. For seizures, use diazepam or barbiturates. In severe cases, consider hemodialysis (though not commonly performed in veterinary patients).

Food Animal Withdrawal Times

🥩 Meat: 5 days🥛 Milk: 3 days

Withdrawal times are not officially established for oxacillin in food animals; these are suggested based on similar penicillins. Consult regulatory authorities and use extra-label with caution. For cattle, milk withdrawal is typically 3 days and meat withdrawal 5 days when used at label doses. For poultry, egg withdrawal is not established; avoid use in layers.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C) for oral formulations; injectable solutions should be stored at 2-8°C after reconstitution and used within 7 days.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from moisture and light. Reconstituted oral solutions should be refrigerated and used within 14 days. Injectable solutions should be used promptly after reconstitution; discard unused portions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Oxacillin is approved for use in dogs and cats in the US for certain indications. It is not approved for food animals; use in food animals is extra-label.

Extra-Label (Off-Label) Use: In the US, extra-label use in food animals is permitted under AMDUCA with a valid veterinary-client-patient relationship, provided that withdrawal times are extended and residues are avoided. In the EU, similar rules apply under Regulation (EC) 470/2009. Use in minor species may be extra-label.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Oxacillin is a valuable antibiotic for treating penicillinase-producing staphylococcal infections in companion animals. It is not effective against MRSA. Due to its short half-life, frequent dosing is required. Oral absorption is variable, so parenteral administration is preferred for severe infections. In food animals, its use is limited by withdrawal times and lack of approval. Always perform culture and sensitivity testing when possible. Monitor for adverse effects, especially in animals with renal impairment. For rabbits and rodents, avoid oral administration due to risk of enteritis.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)