Penicillamine — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	10-15 mg/kg	q12h	Duration: Long-term for copper storage disease; 1-3 months for lead poisoning Notes: Administer on an empty stomach (1 hour before or 2 hours after meals). For copper hepatopathy, monitor liver enzymes and copper levels.
Cat	PO	10-15 mg/kg	q12h	Duration: Variable; for lead poisoning, 2-4 weeks Notes: Use cautiously in cats; may cause anorexia and vomiting.
Horse	PO	3-5 mg/kg	q12h	Duration: Variable Notes: Limited data; use with caution.
Cattle	PO	10-15 mg/kg	q12h	Duration: 2-4 weeks for lead poisoning Notes: Extra-label use; observe withdrawal times.
Small Ruminants	PO	10-15 mg/kg	q12h	Duration: 2-4 weeks Notes: Extra-label use; monitor for adverse effects.
Rabbit	PO	10-15 mg/kg	q12h	Duration: 2-4 weeks Notes: May cause GI upset; administer with a small amount of food if vomiting occurs.
Birds/Poultry	PO	10-15 mg/kg	q12h	Duration: 2-4 weeks Notes: Limited data; use with caution.
Exotic (ferrets, reptiles)	PO	10-15 mg/kg	q12h	Duration: 2-4 weeks Notes: Dose based on extrapolation; monitor closely.

Clinical Indications & Species Uses

General Indications

Heavy metal poisoning (lead, zinc, copper, mercury)
Cystine urolithiasis
Copper storage disease

Dog (Canine)

Copper-associated hepatopathy (e.g., Bedlington Terriers)
Cystine urolithiasis
Lead poisoning
Zinc toxicity
Mercury poisoning
Rheumatoid arthritis (adjunctive therapy)

Cat (Feline)

Lead poisoning
Zinc toxicity
Cystine urolithiasis (rare)
Copper-associated hepatopathy (rare)

Horse (Equine)

Cystinuria (rare)
Lead poisoning
Copper toxicity (rare)

Cattle (Bovine)

Lead poisoning
Copper toxicity (rare)

Small Ruminants (Sheep / Goat)

Lead poisoning
Copper toxicity (rare)

Rabbit & Small Mammals

Lead poisoning
Zinc toxicity

Avian & Poultry

Lead poisoning
Zinc toxicity

Exotic & Other Species

Lead poisoning in reptiles and small mammals
Zinc toxicity in ferrets

Pharmacology & Mechanism of Action

Drug Class: Chelating Agent | Pharmacological Group: Heavy Metal Antagonist

Mechanism of Action: Penicillamine is a thiol-containing amino acid that chelates heavy metals such as copper, lead, mercury, and zinc, forming stable, water-soluble complexes that are excreted in the urine. It also reduces cystine excretion by forming a mixed disulfide with cysteine, which is more soluble than cystine, thereby preventing cystine stone formation. Additionally, penicillamine has antifibrotic and immunosuppressive properties, including inhibition of collagen cross-linking and modulation of T-cell function.

Pharmacodynamics: Penicillamine chelates divalent cations, particularly copper, enhancing their urinary excretion. In copper storage disease (e.g., in Bedlington Terriers), it reduces hepatic copper levels and prevents further accumulation. In cystinuria, it lowers urinary cystine concentration by forming a more soluble disulfide. Its immunosuppressive effects are used in rheumatoid arthritis and other immune-mediated conditions, though the exact mechanism is not fully understood.

⚡ Pharmacokinetics Summary

Absorption: Penicillamine is rapidly but incompletely absorbed from the gastrointestinal tract. Oral bioavailability is approximately 40-70% in humans, but may vary in animals. Food reduces absorption, so it should be given on an empty stomach.

Distribution: Penicillamine is widely distributed in body tissues and fluids. It crosses the placenta and is excreted in milk. It binds to plasma proteins, mainly albumin, to a moderate extent.

Metabolism: Penicillamine undergoes hepatic metabolism to disulfides and other metabolites. It is also metabolized in the intestine by bacteria.

Excretion: The drug and its metabolites are primarily excreted in the urine. In renal impairment, excretion is reduced, requiring dose adjustment.

Half-Life: The elimination half-life is approximately 1-2 hours in dogs, but the chelating effect may persist longer.

Bioavailability: Oral bioavailability is variable, approximately 40-70% in humans; similar in dogs and cats.

Protein Binding: Approximately 80% bound to plasma proteins.

Available Formulations & Strengths

Capsule 125 mg, 250 mg (PO)

Tablet 250 mg (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to penicillamine
Concurrent use with gold therapy
Pregnancy (except in cases of life-threatening poisoning)
Renal insufficiency (severe)
History of blood dyscrasias

Warnings & Clinical Precautions:

Administer on an empty stomach to maximize absorption.
Monitor renal and hepatic function periodically during long-term therapy.
May cause pyridoxine (vitamin B6) deficiency; consider supplementation.
Use with caution in animals with a history of gastrointestinal ulcers.
In cats, use with caution due to increased risk of anorexia and vomiting.
For copper storage disease, monitor liver copper levels and liver enzymes.
For cystinuria, ensure adequate hydration and alkalinization of urine.
May cause immune-mediated reactions; discontinue if severe adverse effects occur.

Adverse Effects & Reactions

Common:

Anorexia
Vomiting
Diarrhea
Lethargy

Serious / Severe:

Immune-mediated hemolytic anemia
Thrombocytopenia
Leukopenia
Proteinuria
Nephrotic syndrome
Systemic lupus erythematosus-like syndrome
Dermatitis (pemphigus-like)

Rare:

Hepatotoxicity
Pulmonary fibrosis
Myasthenia gravis
Alopecia
Pyridoxine deficiency

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Iron supplements	Reduces absorption of penicillamine; separate administration by at least 2 hours.	Moderate
Antacids (aluminum/magnesium)	Decrease penicillamine absorption; separate administration by at least 2 hours.	Moderate
Gold salts	Increased risk of nephrotoxicity and hematologic toxicity; avoid concurrent use.	High
Immunosuppressive agents (azathioprine, cyclophosphamide)	Additive immunosuppressive effects; monitor for bone marrow suppression.	Moderate
Pyridoxine (vitamin B6)	Penicillamine increases pyridoxine excretion; supplementation may be needed.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Nausea
Vomiting
Diarrhea
Anorexia
Weakness
Hypotension
Acute renal failure
Bone marrow suppression

Emergency Treatment Protocol: Treatment is primarily supportive. Induce vomiting if recent ingestion and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain hydration and promote diuresis. Monitor renal function, blood counts, and electrolytes. In severe cases, consider hemodialysis or hemoperfusion. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 30 days🥛 Milk: 7 days

Withdrawal times are not established for penicillamine in food animals; use extra-label with caution and consult regulatory guidelines. A conservative withdrawal period of at least 30 days for meat and 7 days for milk is recommended.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C / 68-77°F).

Handling & Special Conditions: Keep container tightly closed and protect from moisture.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for human use; not specifically approved for veterinary use, but commonly used extra-label in animals.

Extra-Label (Off-Label) Use: In the US, extra-label use of penicillamine in food animals is permitted under AMDUCA with a valid veterinary-client-patient relationship. However, due to lack of established withdrawal times, careful residue avoidance is necessary.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Penicillamine is a valuable chelating agent in veterinary medicine, particularly for copper storage disease in dogs and lead poisoning. It is also used for cystine urolithiasis. Therapy requires careful monitoring of hematologic, renal, and hepatic parameters. Administer on an empty stomach to enhance absorption. For copper hepatopathy, combine with a low-copper diet and possibly zinc supplementation. For cystinuria, encourage water intake and urine alkalinization. Adverse effects are dose-related and may necessitate dose reduction or discontinuation. In food animals, observe withdrawal times and use with caution.

References & Literature

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