Dimercaprol (BAL): veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

BAL, British Anti-Lewisite, Dimercaprol in oil

Species with doses

Dogs, Cats, Cattle and Horses

General dose range

2.5–5 mg/kg IM q4h tapering (per protocol) — check the species tables for the indication

Routes

IM

Last reviewed

1 October 2026

Indications

• Arsenic poisoning (the classic indication)
• Inorganic mercury and gold toxicosis
• Lead poisoning — IN COMBINATION with calcium-EDTA (especially with CNS signs)

Dimercaprol (BAL) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Arsenic / mercury / (lead with EDTA): Plumb’s p.411: 2.5–5 mg/kg deep IM (5 mg/kg only on day 1 of acute cases) q4h for 2 days, q8h on day 3, then twice daily up to 10 days, with sodium thiosulfate 40–50 mg/kg IV (Neiger); 4 mg/kg IM q4–6h for no more than 4 days (Grauer & Hjelle). Papich 5e: 4 mg/kg IM q4h. Deep IM in oil only — never IV. Keep well hydrated.

Cats

• Arsenic poisoning: Plumb’s p.411 (Reid & Oehme): 2.5–5 mg/kg IM q4h for the first 2 days, then q12h until recovery, with fluid therapy; start if ingestion was within 36 h. Papich 5e: 4 mg/kg IM q4h. For lead, succimer or Ca-EDTA are preferred. Monitor renal function.

Cattle

• Arsenic poisoning: Plumb’s p.411: ruminants 2.5–5 mg/kg IM q4h for 2 days (Osweiler); arsenic — 3 mg/kg IM q8h if no signs, 6 mg/kg IM q8h for 3–5 days with signs (Post & Keller); mercury 3 mg/kg IM four times daily for 3 days then twice daily for 10 days. Papich 5e: 4 mg/kg IM q4h. No food-animal withdrawal available — obtain FARAD advice. Efficacy is doubtful unless given early.

Horses

• Arsenic poisoning: Plumb’s p.411 (Oehme; Rees): 5 mg/kg IM initially, 3 mg/kg IM q6h for the rest of day 1, then 1 mg/kg IM q6h for 2 or more days; only effective within hours of ingestion. Also sodium thiosulfate 50–75 g PO q6–8h. Papich 5e: 4 mg/kg IM q4h. Painful IM.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Arsenic poisoning: Plumb’s p.411: ruminants 2.5–5 mg/kg IM q4h for 2 days (Osweiler); arsenic — 3 mg/kg IM q8h if no signs, 6 mg/kg IM q8h for 3–5 days with signs (Post & Keller); mercury 3 mg/kg IM four times daily for 3 days then twice daily for 10 days. Papich 5e: 4 mg/kg IM q4h. No food-animal withdrawal available — obtain FARAD advice. Efficacy is doubtful unless given early.

Contraindications

IRON, CADMIUM or SELENIUM poisoning (the dimercaprol-metal complex is MORE toxic — contraindicated). Significant hepatic impairment (relative; it is hepatically processed). Peanut/oil-vehicle allergy (formulated in peanut oil). G6PD-type oxidative susceptibility (haemolysis). Renal failure with anuria (chelate not excreted). Known hypersensitivity.

Species-specific warnings

Cats: Cats are prone to oxidative haemolysis — monitor PCV; dose carefully and maintain hydration.

Adverse effects

• Pain/sterile abscess at the IM injection site (oil vehicle)
• Hypertension and tachycardia, vomiting, hypersalivation, restlessness (dose-related)
• Nephrotoxicity (the chelate is nephrotoxic — maintain urine flow/alkalinise)
• Haemolysis (oxidative); fever

Drug interactions

• Iron / cadmium / selenium: form MORE toxic complexes — contraindicated; do not give iron supplements concurrently
• Calcium-EDTA: complementary (combined for lead poisoning)
• Alkaline urine: stabilises the chelate and protects the kidney

Pregnancy and lactation

Reserve for serious heavy-metal poisoning where maternal benefit outweighs risk; limited data.

Monitoring

• Renal function (BUN/creatinine, urine output) and hydration — nephrotoxic chelate
• Blood metal levels / clinical response
• PCV (haemolysis), blood pressure, injection sites
• Urine pH (keep alkaline)

Toxicity and overdose

Dose-related toxicity includes hypertension/tachycardia, vomiting/hypersalivation, fever, injection-site pain/abscess, oxidative haemolysis, and NEPHROTOXICITY (the chelate damages the kidney, especially in acidic urine/dehydration). The dangerous error is using it for iron/cadmium/selenium, where the complex is more toxic than the metal alone.

Management: No specific antidote. Discontinue; supportive care — maintain hydration and urine output, alkalinise urine to protect the kidney and stabilise the chelate, manage hypertension/tachycardia, and monitor renal function and PCV (haemolysis). Antihistamine/antipyretic for febrile reactions.

Clinical pearls

• The antidote for ARSENIC and inorganic MERCURY — and the intracellular/CNS partner for calcium-EDTA in LEAD poisoning (it mobilises brain lead so EDTA can excrete it)
• Deep, PAINFUL IM in oil only — never IV; keep the patient hydrated and the urine alkaline to protect the kidney
• NEVER use for iron, cadmium or selenium poisoning — the chelate is more toxic than the metal
• For stable lead poisoning, oral succimer (DMSA) has largely replaced the EDTA/BAL combination

Mechanism of action

Dimercaprol has two free sulphydryl (thiol) groups that bind heavy-metal ions (arsenic, mercury, gold, lead), forming a stable, water-soluble metal-dithiol chelate that is excreted in the urine — protecting essential sulphydryl-containing enzymes the metals would otherwise inactivate. Being lipophilic, it distributes into cells and the CNS (useful for mobilising intracellular/brain lead), which is why it is paired with calcium-EDTA for lead to avoid redistributing mobilised lead to the brain.

Formulations and products

• Injection 50 / 100 mg/mL in oil (deep IM only)
• Dimercaprol (BAL in Oil) — 50 / 100 mg/mL in oil, IM injection (in oil) (human-label)

Storage

Ampoules (in oil): 15–30 °C, protect from light; do not freeze. For deep IM use only.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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Frequently asked questions