Dimercaprol — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	IM	2.5-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable, depending on response Notes: For lead poisoning, use in combination with calcium EDTA. Administer deep IM to reduce pain.
Cat	IM	2.5-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable, depending on response Notes: Use with caution in cats due to increased sensitivity to adverse effects.
Horse	IM	3-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Monitor for local reactions at injection site.
Cattle	IM	3-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Observe withdrawal times for food animals.
Small Ruminants	IM	3-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Use with caution; monitor for adverse effects.
Rabbit	IM	2.5-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Limited data; use cautiously.
Birds/Poultry	IM	2.5-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Limited data; use cautiously.
Exotic/Other	IM	2.5-5 mg/kg	q4h for 2 days, then q8h for 1 day, then q12h for 10 days or until recovery	Duration: Variable Notes: Dose based on extrapolation; monitor closely.

Clinical Indications & Species Uses

General Indications

Acute heavy metal poisoning (arsenic, mercury, lead, gold)

Dog (Canine)

Arsenic poisoning
Mercury poisoning
Lead poisoning (as adjunct to EDTA)
Gold poisoning (rare)

Cat (Feline)

Arsenic poisoning
Mercury poisoning
Lead poisoning (as adjunct to EDTA)

Horse (Equine)

Arsenic poisoning
Mercury poisoning

Cattle (Bovine)

Arsenic poisoning
Mercury poisoning

Small Ruminants (Sheep / Goat)

Arsenic poisoning
Mercury poisoning

Rabbit & Small Mammals

Arsenic poisoning
Mercury poisoning

Avian & Poultry

Arsenic poisoning
Mercury poisoning

Exotic & Other Species

Arsenic poisoning
Mercury poisoning

Pharmacology & Mechanism of Action

Drug Class: Chelating Agent | Pharmacological Group: Antidote

Mechanism of Action: Dimercaprol (2,3-dimercaptopropanol) is a dithiol compound that chelates heavy metals by forming stable, water-soluble complexes with arsenic, mercury, gold, and lead. The two sulfhydryl groups bind to the metal ions, preventing them from interacting with cellular enzymes and proteins. The resulting chelate is excreted in the urine and bile, reducing the toxic effects of the metal. Dimercaprol is particularly effective in acute poisoning with inorganic arsenic and mercury, and it can also be used for lead poisoning, though it is less effective than other agents like EDTA.

Pharmacodynamics: Dimercaprol acts by competing with sulfhydryl-containing enzymes for binding to heavy metals. It forms a stable ring structure with the metal, which is then eliminated. The drug is most effective when given early after exposure, before the metal has become tightly bound to tissues. It can also reactivate enzymes that have been inhibited by the metal. Dimercaprol has a narrow therapeutic index and can cause significant adverse effects, including hypertension, tachycardia, and vomiting.

⚡ Pharmacokinetics Summary

Absorption: Dimercaprol is administered intramuscularly (IM) or intravenously (IV). After IM injection, it is rapidly absorbed, with peak plasma concentrations occurring within 30-60 minutes. Oral absorption is poor and erratic, so it is not used orally.

Distribution: Dimercaprol is widely distributed throughout the body, including the brain and cerebrospinal fluid. It crosses the placenta and is distributed into milk. It is extensively bound to plasma proteins and tissues.

Metabolism: Dimercaprol is rapidly metabolized in the liver to inactive metabolites. The metabolism involves oxidation and conjugation.

Excretion: The drug and its metabolites are excreted primarily in the urine, with some biliary excretion. The elimination half-life is short, approximately 2-4 hours in most species.

Half-Life: Approximately 2-4 hours in dogs and cats; similar in other species.

Bioavailability: Not applicable for oral use; IM administration provides rapid and complete absorption.

Protein Binding: Not well documented, but it is known to be extensively bound to plasma proteins and tissues.

Available Formulations & Strengths

Injectable Solution 100 mg/mL in peanut oil (with benzyl benzoate) (IM)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to dimercaprol or any component
Hepatic insufficiency (unless due to arsenic poisoning)
Iron poisoning (dimercaprol-iron complex is toxic)
Cadmium poisoning (ineffective and may be toxic)
Selenium poisoning (ineffective)

Warnings & Clinical Precautions:

Use with caution in animals with renal impairment, as the chelate is excreted renally.
May cause hemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Administer deep IM to minimize pain and sterile abscess formation.
Do not use orally due to poor absorption and GI irritation.
In lead poisoning, use in combination with calcium EDTA; do not use alone.
Monitor blood pressure and heart rate during administration.
Use in pregnant animals only if clearly needed, as it crosses the placenta.
In food animals, observe withdrawal times.

Adverse Effects & Reactions

Common:

Pain at injection site
Vomiting
Nausea
Tachycardia
Hypertension
Salivation
Restlessness

Serious / Severe:

Seizures
Coma
Respiratory depression
Nephrotoxicity
Hemolysis
Anaphylaxis

Rare:

Sterile abscess at injection site
Hepatotoxicity
Bone marrow suppression

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Iron supplements	Formation of toxic dimercaprol-iron complex; do not use concurrently.	High
Calcium EDTA	Synergistic chelation for lead poisoning; use in combination for severe lead poisoning.	Moderate
Other nephrotoxic drugs (e.g., aminoglycosides)	Increased risk of nephrotoxicity.	Moderate
Antihypertensive agents	May potentiate hypotensive effects; monitor blood pressure.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Severe hypertension
Tachycardia
Seizures
Respiratory failure
Coma
Metabolic acidosis

Emergency Treatment Protocol: Discontinue the drug immediately. Provide supportive care including intravenous fluids, oxygen therapy, and anticonvulsants (e.g., diazepam) for seizures. Monitor vital signs and renal function. There is no specific antidote for dimercaprol overdose. In severe cases, hemodialysis may be considered to remove the drug.

Food Animal Withdrawal Times

🥩 Meat: 30 days🥛 Milk: 7 days

Withdrawal times are not officially established for dimercaprol in food animals. The values provided are conservative estimates based on the drug's half-life and potential for residues. Consult regulatory authorities for specific guidance.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (15-30°C or 59-86°F).

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

Handling & Special Conditions: Protect from light. Keep container tightly closed. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use.

Extra-Label (Off-Label) Use: In the US, dimercaprol is not FDA-approved for veterinary use, but it may be used under the Animal Medicinal Drug Use Clarification Act (AMDUCA) with a valid veterinarian-client-patient relationship. Extra-label use requires a withdrawal period established by the veterinarian, and residues must be within tolerance levels.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Dimercaprol is a critical antidote for acute heavy metal poisoning, particularly arsenic and mercury. It is most effective when administered early after exposure. The drug has a narrow therapeutic index and significant adverse effects, so it should be used with caution and under close monitoring. In lead poisoning, it is often used in combination with calcium EDTA to enhance chelation. Due to its painful injection and potential for tissue damage, it should be administered deep IM and the injection site rotated. In food animals, withdrawal times must be observed. Always consult a veterinary toxicologist or poison control center for the most current treatment protocols.

References & Literature

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