Vancomycin

Overview

Vancomycin is a glycopeptide antibiotic reserved for the treatment of severe, life-threatening infections caused by multidrug-resistant gram-positive bacteria. Because of its critical importance in human medicine, its use in dogs and cats should be restricted to carefully selected cases where culture and susceptibility testing confirm that safer or less critical antimicrobial options are ineffective.

Vancomycin is administered intravenously for systemic infections and orally for selected enteric infections caused by susceptible organisms. Oral vancomycin is not appreciably absorbed from the gastrointestinal tract and therefore is only useful for infections confined to the intestinal lumen. Systemic administration requires intravenous delivery, as subcutaneous and intramuscular administration can cause severe pain and tissue injury.

The drug is primarily active against gram-positive bacteria, including resistant staphylococci and enterococci. It also has activity against Clostridioides difficile, Rhodococcus equi, Listeria monocytogenes, Corynebacterium spp., and Actinomyces spp. Gram-negative bacteria are resistant. Although highly effective against susceptible organisms, its use remains controversial in veterinary medicine because of concerns regarding antimicrobial stewardship and the emergence of resistant bacterial strains.

Mechanism of Action (MOA): Vancomycin inhibits cell wall synthesis and altering membrane permeability; bactericidal action occurs by activating bacterial cell-wall autolysins. It also affects bacterial RNA synthesis. It is generally bactericidal and exhibits time-dependent antimicrobial activity against most gram-positive bacteria.

Indications

Vancomycin should be reserved for carefully selected infections in dogs and cats when culture and susceptibility testing confirm that alternative antimicrobial options are ineffective or inappropriate.

• Multidrug-resistant gram-positive infections: Treatment of severe, life-threatening infections caused by susceptible multidrug-resistant gram-positive bacteria, particularly resistant Staphylococcus spp. and Enterococcus spp.
• Methicillin-resistant staphylococcal infections: May be considered for confirmed methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus pseudintermedius (MRSP) infections when other effective options are unavailable.
• Multidrug-resistant enterococcal infections: May be used for susceptible Enterococcus infections that are resistant to first- and second-tier antimicrobials.
• Clostridioides difficile enteric infection: Oral therapy may be considered for documented C. difficile infections that have not responded adequately to metronidazole treatment.
• Local therapy: Vancomycin may be incorporated into antimicrobial-impregnated implants (PMMA beads, gels), intra-articular injection, and regional limb perfusion. Local routes that do not produce appreciable systemic or enteric concentrations carry less concern for resistance emergence.

Dosage (Reference)

Dog

Vancomycin should only be used when culture and susceptibility testing support its use. Systemic therapy requires intravenous administration, while oral therapy is reserved for susceptible enteric infections.

Cat

Vancomycin should be reserved for confirmed susceptible multidrug-resistant infections when alternative antimicrobial options are not appropriate. Both intermittent infusion and CRI protocols have been described.

Warnings & Precautions

Vancomycin is a critically important antimicrobial that should be reserved for carefully selected cases in dogs and cats. Appropriate patient selection, antimicrobial stewardship, and close monitoring are essential throughout therapy.

• Reserve for multidrug-resistant infections: Vancomycin should only be used when culture and susceptibility testing confirm that other appropriate antimicrobial options are ineffective or unavailable.
• Avoid empirical use: Treatment should not be initiated without a clear indication and microbiological justification whenever possible.
• Infectious disease consultation recommended: Consultation with a veterinary infectious disease specialist is advised before initiating therapy because of the drug’s importance in human medicine.
• Renal impairment: Patients with decreased renal function may require dose reduction or extension of the dosing interval to minimize drug accumulation and toxicity.
• Monitor serum drug concentrations: Peak and trough concentrations should be monitored when possible, particularly during prolonged treatment or in patients with renal dysfunction.
• Intravenous administration only: Systemic therapy must be administered intravenously; subcutaneous and intramuscular administration can cause severe pain and tissue injury.
• Administration rate: Vancomycin should always be administered as a dilute solution over at least 30 minutes and never as a rapid IV bolus.
• Local use considerations: Local administration techniques such as antimicrobial-impregnated implants, intra-articular therapy, or regional limb perfusion may be appropriate in selected cases and are associated with less concern regarding systemic antimicrobial resistance.
• Fatal in rabbits: IV vancomycin can be fatal in rabbits.
• Regulatory restrictions: Use in animals is banned in some countries, and some clinicians believe the drug should never be used in veterinary patients. Not allowed in food animals.
• Pregnancy & lactation: Excreted in milk; because oral vancomycin is not appreciably absorbed, it is unlikely to harm nursing animals, though diarrhoea could occur. For serious infections the potential benefits usually outweigh the risks.

Drug Interactions

Several clinically important drug interactions may increase the risk of toxicity during vancomycin therapy. Concurrent use with other potentially nephrotoxic or ototoxic medications requires careful monitoring and risk-benefit assessment.

• Aminoglycosides: Concurrent use may increase the risk of nephrotoxicity and ototoxicity. Although the combination may be used in selected cases because of potential antimicrobial synergy, enhanced monitoring is recommended.
• Other nephrotoxic drugs (e.g., amphotericin B, cisplatin): May increase the risk of renal injury when administered with vancomycin; use cautiously and monitor renal function closely.
• Anesthetic agents: In children Concurrent administration has been associated with histamine-mediated reactions, including erythema and flushing; monitor patients carefully during anesthesia.
• Infusion incompatibility: Do NOT mix vancomycin with other drugs in the infusion line. Incompatible with beta-lactam antibiotics, fluoroquinolones, aminoglycosides, macrolides, propofol, anticonvulsants, corticosteroids, furosemide, and alkaline solutions , ampicillin, amphotericin B, cefazolin, ceftazidime, diazepam, hydrocortisone, pantoprazole.

Side Effects & Overdose

Side Effects

The most significant adverse effects of vancomycin are associated with systemic administration. Toxicity is more likely in patients receiving prolonged therapy, high doses, or concurrent nephrotoxic medications.

• Nephrotoxicity: The most important adverse effect of systemic therapy and a major factor limiting long-term use. risk is greater after 4–8 days of treatment and often resolves after discontinuation (Papich). One patient developed AKI after 21 days and returned to baseline creatinine over 2 months.
• Ototoxicity: May occur during treatment, particularly when high serum concentrations develop or when administered with other ototoxic drugs.
• Hypersensitivity reactions: Dermatologic and hypersensitivity reactions have been reported in human patients and may occur in veterinary patients.
• Neutropenia: Reversible neutropenia has been reported, especially with high doses or prolonged treatment.
• Infusion-related reactions: Rapid IV administration may result in thrombophlebitis, severe hypotension, and, rarely, cardiac arrest.
• Gastrointestinal effects (oral therapy): Nausea, inappetence, vomiting, and diarrhea may occur during oral treatment.
• Injection-site injury: Severe pain and tissue damage may occur if the drug is administered by SC or IM routes.

Overdose

Vancomycin overdose primarily increases the risk and severity of concentration-dependent toxicities. Treatment is largely supportive and focused on monitoring organ function.

• Nephrotoxicity: Acute kidney injury is the most significant concern following systemic overdose.
• Ototoxicity: Excessive drug exposure may increase the risk of auditory or vestibular toxicity.
• Management: Discontinue therapy and provide supportive care with close monitoring of renal function and hydration status.
• Therapeutic drug monitoring: Serum drug concentrations should be assessed when available to guide ongoing management.
• Hemodialysis: Does not appear to remove clinically significant amounts of vancomycin.
• 24-hour poison consult: For suspected overdose, consult a 24-hour veterinary poison consultation center specializing in veterinary-specific information.

Key Notes

Practical clinical points that can help optimize the use of vancomycin in dogs and cats:

• Culture results drive therapy: Vancomycin should be considered only after bacterial identification and susceptibility testing confirm that it is an appropriate treatment choice.
• Excellent gram-positive activity: The drug is highly effective against many resistant gram-positive pathogens but has no meaningful activity against gram-negative bacteria.
• Time-dependent antimicrobial: Maintaining adequate drug exposure over time is more important than achieving very high peak concentrations.
• Enterococci may respond differently: While vancomycin is usually bactericidal against susceptible organisms, activity against enterococci is often bacteriostatic.
• Purulent infections may be harder to treat: Pus and cellular debris can bind vancomycin and potentially reduce antimicrobial effectiveness at the site of infection.
• Useful for local antimicrobial delivery: The drug can be incorporated into local treatment strategies such as antimicrobial-impregnated materials and other site-directed therapies when appropriate.
• Resistance remains a growing concern: Emergence of vancomycin-resistant enterococci (VRE) and resistant staphylococci underscores responsible antimicrobial stewardship. the global prevalence of VRE in companion animals is estimated at 14.6%, with regional variability.
• WHO Highest Priority: The World Health Organization designates vancomycin as a Critically Important, Highest Priority antimicrobial for human medicine — empirical veterinary use should be discouraged and reserved for confirmed last-resort cases.
• Reconstitution + storage: Reconstitute the 500 mg vial with 10 mL sterile water (20 mL for the 1 g vial), then dilute further with at least 100 mL (500 mg) / 200 mL (1 g) of 0.9% saline, 5% dextrose, or Lactated Ringer’s. Reconstituted solution is stable 14 days refrigerated; further-diluted solution is stable 24 h at room temperature or 2 months refrigerated.
• Newer lipoglycopeptides: Newer human lipoglycopeptides related to vancomycin — dalbavancin (Dalvance), oritavancin (Orbactiv), and telavancin (Vibativ) — have very long half-lives (10–14 days, dosed once every 7–14 days in people) but are expensive and have not been tested for clinical use in animals.