Dicloxacillin
Dicloxacillin is an oral, narrow-spectrum, **penicillinase-resistant** (isoxazolyl) penicillin. It is primarily used in veterinary medicine for the oral treatment of soft tissue, skin, and bone infections caused by beta-lactamase-producing *Staphylococcus* species. > **Clinical Pearl**: Because of its bulky isoxazolyl side chain, dicloxacillin resists degradation by staphylococcal beta-lactamases. However, its poor oral bioavailability (~23% in dogs) and short half-life necessitate frequent dosing (q6-8h), which can make owner compliance challenging. Due to these pharmacokinetic limitations, other anti-staphylococcal drugs (like cephalexin or amoxicillin-clavulanate) are often preferred in small animal practice.
Mechanism: Dicloxacillin is a **bactericidal** beta-lactam antibiotic. * It binds to specific **Penicillin-Binding Proteins (PBPs)** located inside the bacterial cell wall. * This binding inhibits the third and final stage of bacterial cell wall synthesis → blocks the cross-linking of peptidoglycan. * The weakened cell wall leads to the activation of autolysins → **cell lysis** and bacterial death. * Its bulky side chain prevents the beta-lactam ring from being hydrolyzed by staphylococcal penicillinase.
Dosing by species
- Localized soft tissue infections or skin infections caused by susceptible (non-beta-lactamase producers) bacteria · 25 mg/kg PO q6h · PO · q6h · 14-84 days
- Localized soft tissue infections or skin infections caused by susceptible (non-beta-lactamase producers) bacteria · 25 mg/kg PO q6h · PO · q6h · 14-84 days
- Dermatologic infections · 22 mg/kg PO q8h · PO · q8h
- Recurrent skin infections · 20-30 mg/kg PO three times daily · PO · q8h · Food may decrease absorption
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Hypersensitivity to penicillins
- Septicemia, shock, or other grave illnesses (oral absorption may be significantly delayed or diminished)
Adverse effects
- Anorexia
- Vomiting
- Diarrhea
- Antibiotic-associated diarrhea (superinfections)
- Hypersensitivity reactions (rashes, fever, eosinophilia, anaphylaxis)
- Neurotoxicity (ataxia at very high doses)
- Elevated liver enzymes
- Tachypnea
- Dyspnea
- Edema
- Tachycardia
Drug interactions
- Aminoglycosides · In vitro evidence of synergism with dicloxacillin against S. aureus strains; however, penicillins can inactivate aminoglycosides in vitro, so do not mix in the same syringe/fluid line.
- Cyclosporine · Dicloxacillin may reduce cyclosporine levels.
- Probenecid · Competitively blocks the tubular secretion of dicloxacillin, thereby increasing serum levels and serum half-lives.
- Tetracyclines · Theoretical antagonism; concurrent use is usually not recommended.
- Warfarin · Dicloxacillin may cause decreased warfarin efficacy.
Monitoring
- Clinical efficacy (resolution of infection)
- Toxic clinical signs (GI upset, hypersensitivity)
Overdose
Acute oral penicillin overdoses are unlikely to cause significant problems other than **GI distress** (vomiting, diarrhea). In humans, very high dosages of parenteral penicillins, especially in patients with renal disease, have induced **CNS effects** (neurotoxicity).
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.