Dicloxacillin Sodium

Antibiotic Penicillinase-resistant penicillin

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 11-15 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.
Cat PO 11-15 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.
Horse PO 10-20 mg/kg q6-8h Duration: 5-7 days or as clinically indicated
Notes: Oral absorption may be variable; consider parenteral therapy for severe infections.
Cattle PO 10-20 mg/kg q8-12h Duration: 5-7 days or as clinically indicated
Notes: Oral absorption is poor in ruminants; parenteral therapy is preferred. Not approved for food animals in many countries.
Small Ruminants PO 10-20 mg/kg q8-12h Duration: 5-7 days or as clinically indicated
Notes: Oral absorption is poor in ruminants; parenteral therapy is preferred. Not approved for food animals in many countries.
Rabbit PO 15-25 mg/kg q8-12h Duration: 5-7 days or as clinically indicated
Notes: Administer on an empty stomach. Monitor for gastrointestinal upset.
Birds/Poultry PO Not established Not established Duration: Not established
Notes: Not commonly used; other antibiotics are preferred.
Exotic/Other PO Not established Not established Duration: Not established
Notes: Use with caution; consult a specialist.

Clinical Indications & Species Uses

General Indications
  • Treatment of infections caused by penicillinase-producing staphylococci
  • Skin and soft tissue infections
  • Abscesses
  • Wound infections
Dog (Canine)
  • Treatment of pyoderma caused by penicillinase-producing Staphylococcus spp.
  • Soft tissue infections
  • Abscesses
  • Wound infections
  • Osteomyelitis (as adjunctive therapy)
Cat (Feline)
  • Treatment of pyoderma caused by penicillinase-producing Staphylococcus spp.
  • Soft tissue infections
  • Abscesses
  • Wound infections
Horse (Equine)
  • Treatment of infections caused by penicillinase-producing Staphylococcus spp.
  • Skin and soft tissue infections
  • Respiratory tract infections (when susceptible)
Cattle (Bovine)
  • Treatment of mastitis caused by penicillinase-producing Staphylococcus spp.
  • Skin and soft tissue infections
  • Respiratory tract infections (when susceptible)
Small Ruminants (Sheep / Goat)
  • Treatment of infections caused by penicillinase-producing Staphylococcus spp.
  • Skin and soft tissue infections
Rabbit & Small Mammals
  • Treatment of infections caused by penicillinase-producing Staphylococcus spp.
  • Skin and soft tissue infections

Pharmacology & Mechanism of Action

Drug Class: Antibiotic | Pharmacological Group: Penicillinase-resistant penicillin

Mechanism of Action: Dicloxacillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs) and interfering with the transpeptidation reaction. This leads to weakening of the peptidoglycan layer and ultimately cell lysis. It is resistant to staphylococcal beta-lactamases, making it effective against penicillinase-producing Staphylococcus spp.

Pharmacodynamics: Dicloxacillin is bactericidal against susceptible gram-positive bacteria, including penicillinase-producing staphylococci. It is less active than penicillin G against non-beta-lactamase-producing gram-positive cocci but retains activity against many streptococci. It is ineffective against gram-negative bacteria due to poor penetration and beta-lactamase production.

⚡ Pharmacokinetics Summary

Absorption: Dicloxacillin is acid-stable and well absorbed after oral administration in monogastric animals, but absorption is reduced in ruminants due to ruminal degradation. Food decreases absorption; therefore, it should be given on an empty stomach.
Distribution: Dicloxacillin is widely distributed in body fluids and tissues, but penetration into cerebrospinal fluid is poor unless meninges are inflamed. It is highly protein-bound (approximately 95-98% in humans, similar in animals).
Metabolism: Dicloxacillin undergoes minimal hepatic metabolism; the majority is excreted unchanged.
Excretion: Dicloxacillin is primarily excreted by the kidneys via tubular secretion and glomerular filtration. Biliary excretion also occurs. In renal impairment, dose 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 (estimated); Humans: 0.6-0.8 hours.
Bioavailability: Oral bioavailability in dogs and cats is approximately 50-80% when given on an empty stomach; in ruminants, oral bioavailability is poor due to ruminal degradation.
Protein Binding: Approximately 95-98% in dogs, cats, and other species.

Available Formulations & Strengths

Oral Capsule 250 mg, 500 mg (PO)
Oral Tablet 125 mg, 250 mg, 500 mg (PO)
Oral Suspension (reconstituted) 62.5 mg/5 mL, 125 mg/5 mL (PO)
Injectable Solution (not common in veterinary medicine) Various (IM/IV)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to penicillins or cephalosporins
  • Use in rabbits, guinea pigs, hamsters, and other small rodents (risk of antibiotic-associated enterotoxemia)
  • Oral use in ruminants (poor absorption and disruption of ruminal flora)
Warnings & Clinical Precautions:
  • Use with caution in animals with renal impairment; dose adjustment may be needed.
  • Use with caution in animals with a history of gastrointestinal disease.
  • Prolonged use may result in overgrowth of non-susceptible organisms (e.g., Candida, Clostridium).
  • In food animals, observe withdrawal times; extra-label use requires veterinary oversight.
  • Administer on an empty stomach to maximize absorption.
  • Do not use in animals with known hypersensitivity to beta-lactams.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (vomiting, diarrhea)
  • Allergic reactions (skin rash, urticaria)

Serious / Severe:

  • Anaphylaxis
  • Clostridial enterotoxemia in rabbits and rodents
  • Acute interstitial nephritis (rare)
  • Hepatotoxicity (rare)

Rare:

  • Blood dyscrasias
  • Neurotoxicity (with high doses or renal impairment)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Probenecid Decreases renal tubular secretion of dicloxacillin, increasing its plasma concentration and half-life. Moderate
Bacteriostatic antibiotics (e.g., tetracyclines, macrolides) May antagonize the bactericidal effect of dicloxacillin; avoid concurrent use. Moderate
Methotrexate Dicloxacillin may reduce renal clearance of methotrexate, increasing its toxicity. Moderate
Warfarin Dicloxacillin may enhance the anticoagulant effect of warfarin; monitor coagulation parameters. Moderate
Oral contraceptives (in humans) May reduce efficacy of oral contraceptives; not directly relevant in veterinary medicine. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Gastrointestinal signs (vomiting, diarrhea)
  • Neurological signs (tremors, seizures) with very high doses
  • Allergic reactions

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is stable. Administer activated charcoal to reduce absorption. Provide fluid therapy and monitor for electrolyte imbalances. In severe cases, consider hemodialysis (though not commonly performed in veterinary patients).

Food Animal Withdrawal Times

Dicloxacillin is not approved for use in food animals in many countries. If used extra-label, withdrawal times must be established based on pharmacokinetic data and regulatory requirements. Consult a veterinarian and regulatory authorities.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C) in a tight container.

Handling & Special Conditions: Protect from moisture. Oral suspensions should be refrigerated after reconstitution and discarded after 14 days.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for human use; not FDA-approved for veterinary use, but may be used extra-label in animals.

Extra-Label (Off-Label) Use: In the US, extra-label use of dicloxacillin in food animals is prohibited if an approved drug exists that is labeled for the indication and species. For companion animals, extra-label use is permitted under AMDUCA with veterinary oversight.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Dicloxacillin is a narrow-spectrum penicillinase-resistant penicillin primarily used for infections caused by penicillinase-producing staphylococci. It is a good choice for canine and feline pyoderma, but its use has declined with the availability of other antibiotics such as cephalosporins and fluoroquinolones. It is not effective against methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus pseudintermedius (MRSP). Oral absorption is variable and affected by food; therefore, it should be given on an empty stomach. In ruminants, oral administration is not recommended due to poor absorption and disruption of ruminal flora. For food animals, use is limited and withdrawal times must be observed. Always perform culture and sensitivity testing when possible to ensure efficacy.

References & Literature

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