Dicloxacillin
Dicloxacillin sodium
Also known as: Dynapen · Dicloxin · sodium dicloxacillin · dichlorphenylmethyl isoxazolyl penicillin sodium · methyldichlorophenyl isoxazolyl penicillin sodium · dicloxacilina sodica · dicloxacillinum natricum · P-1011
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 |
|---|---|---|---|---|---|
| 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 | 🌎 NA |
| Dermatologic infections | 22 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Recurrent skin infections | 20-30 mg/kg PO three times daily | PO | q8h | — | 🌎 NA |
- Recurrent skin infections: Food may decrease absorption
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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 | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
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 of action
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.
Safety & warnings
Contraindications
- Hypersensitivity to penicillins
- Septicemia, shock, or other grave illnesses (oral absorption may be significantly delayed or diminished)
Adverse effects
- Anorexia
- Vomiting
- Antibiotic-associated diarrhea (superinfections)
- Hypersensitivity reactions (rashes, fever, eosinophilia, anaphylaxis)
- Neurotoxicity (ataxia at very high doses)
- Elevated liver enzymes
- Tachypnea
- Dyspnea
- Edema
- Tachycardia
Precautions
Use cautiously in patients with documented hypersensitivity to other beta-lactam antibiotics (e.g., cephalosporins, cefamycins, carbapenems) due to potential cross-reactivity. Do not administer systemic antibiotics orally in patients with septicemia, shock, or other grave illnesses; parenteral routes should be used.
Drug interactions
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.
Dicloxacillin may reduce cyclosporine levels.
Competitively blocks the tubular secretion of dicloxacillin, thereby increasing serum levels and serum half-lives.
Theoretical antagonism; concurrent use is usually not recommended.
Dicloxacillin may cause decreased warfarin efficacy.
Monitoring
- Clinical efficacy (resolution of infection)
- Toxic clinical signs (GI upset, hypersensitivity)
Pharmacokinetics
Half-life
Absorption
Resistant to acid inactivation in the gut but only partially absorbed. Bioavailability in dogs is ~23%. Food decreases both the rate and extent of absorption.
Distribution
Distributes to liver, kidneys, bone, bile, pleural, synovial, and ascitic fluids. Minimal amounts distribute into the CSF. Approximately 95-99% bound to plasma proteins in humans.
Metabolism
Partially metabolized to both active and inactive metabolites.
Elimination
Rapidly excreted in the urine via both glomerular filtration and tubular secretion mechanisms. A small amount is excreted in the feces via biliary elimination.
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).
Available products
Formulations
- Capsules
- Oral suspension
Veterinary
- Dicloxin® 100 mg and 500 mg capsules (Historically approved for dogs; no products apparently currently marketed in the USA)
Human-labeled
- Dicloxacillin Sodium Capsules: 250 mg & 500 mg (generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules should be stored at temperatures less than 40°C and preferably at room temperature (15-30°C). Reconstituted oral suspensions should be kept refrigerated and discarded after 14 days.
Client information
Important: Give this medication on an empty stomach (1 hour before or 2 hours after meals) to ensure proper absorption. If your pet vomits or acts sick after receiving it, you may give it with a small treat or meal.
- Compliance is key: Give exactly as prescribed and finish the entire course, even if your pet looks better. Missing doses can lead to resistant infections.
- If using a reconstituted liquid suspension, keep it in the refrigerator and throw away any unused portion after 14 days.
- Watch for signs of an allergic reaction (hives, facial swelling, difficulty breathing) or severe diarrhea, and contact your veterinarian 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.