Clenbuterol Hydrochloride — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.8-1.6 mcg/kg	q12h	Duration: As needed for respiratory signs Notes: Start at low end and titrate to effect. Monitor for tachycardia.
Cat	PO	0.8-1.6 mcg/kg	q12h	Duration: As needed for respiratory signs Notes: Use with caution in cats with cardiac disease.
Horse	PO	0.8 mcg/kg	q12h	Duration: 5-14 days or as needed Notes: Commonly used for RAO. May be combined with corticosteroids.
Horse	IV	0.8 mcg/kg	q12h	Duration: As needed Notes: For acute bronchospasm, slow IV administration.
Cattle	IM	0.8 mcg/kg	q12h	Duration: For tocolysis, as needed Notes: Use only under veterinary supervision. Withdrawal times must be observed.

Clinical Indications & Species Uses

General Indications

Bronchodilator for reversible bronchospasm
Tocolytic agent in some species

Dog (Canine)

Bronchodilator for chronic obstructive pulmonary disease (COPD)
Tracheal collapse
Bronchitis

Cat (Feline)

Bronchodilator for feline asthma
Chronic bronchitis

Horse (Equine)

Recurrent airway obstruction (RAO) / heaves
Inflammatory airway disease (IAD)
Bronchospasm associated with respiratory disease

Cattle (Bovine)

Tocolytic agent to delay parturition
Respiratory disease (off-label in some countries)

Pharmacology & Mechanism of Action

Drug Class: Beta-2 Adrenergic Agonist | Pharmacological Group: Sympathomimetic Amine

Mechanism of Action: Clenbuterol is a selective beta-2 adrenergic receptor agonist. It binds to beta-2 receptors on bronchial smooth muscle, leading to activation of adenylate cyclase, increased intracellular cyclic AMP (cAMP), and subsequent activation of protein kinase A. This results in relaxation of bronchial smooth muscle, bronchodilation, and inhibition of mediator release from mast cells. Additionally, it has tocolytic effects on uterine smooth muscle and anabolic effects on skeletal muscle, though the latter is not a primary clinical use in veterinary medicine.

Pharmacodynamics: Clenbuterol produces dose-dependent bronchodilation, with effects lasting several hours. It also increases mucociliary clearance, reduces airway inflammation, and may have anti-inflammatory properties. In horses, it is used for its bronchodilatory effects in respiratory conditions. In cattle, it has been used as a tocolytic agent to delay parturition. Its anabolic effects are not clinically utilized in veterinary medicine due to regulatory concerns.

⚡ Pharmacokinetics Summary

Absorption: Clenbuterol is well absorbed after oral administration in most species. In horses, oral bioavailability is approximately 70-80%. In cattle, oral absorption is rapid, with peak plasma concentrations within 1-2 hours.

Distribution: Clenbuterol is widely distributed throughout the body, with high concentrations in the lungs, liver, and kidneys. It crosses the placenta and is excreted in milk. It has a volume of distribution of approximately 1-2 L/kg in horses.

Metabolism: Clenbuterol undergoes hepatic metabolism, primarily via sulfation and glucuronidation. In horses, it is metabolized to inactive metabolites. In cattle, metabolism is similar, with some species differences in the rate of metabolism.

Excretion: Clenbuterol is excreted primarily in the urine as metabolites and unchanged drug. In horses, the elimination half-life is approximately 10-14 hours. In cattle, the half-life is longer, around 24-48 hours, which is important for withdrawal times.

Half-Life: Horse: 10-14 hours; Cattle: 24-48 hours; Dog: 6-8 hours (estimated); Cat: 8-12 hours (estimated)

Bioavailability: Oral bioavailability: Horse ~70-80%, Cattle ~60-70%, Dog ~50-60% (estimated)

Protein Binding: Approximately 89-98% bound to plasma proteins in horses and cattle.

Available Formulations & Strengths

Oral Syrup 72.5 mcg/mL (as clenbuterol hydrochloride) (PO)

Oral Tablet 20 mcg, 40 mcg (PO)

Injectable Solution 0.02 mg/mL (20 mcg/mL) (IV, IM)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to clenbuterol or other beta-agonists
Cardiac arrhythmias
Tachycardia
Hypertension
Hyperthyroidism
Concurrent use with monoamine oxidase inhibitors (MAOIs)
Use in animals with known beta-agonist sensitivity

Warnings & Clinical Precautions:

Use with caution in animals with cardiovascular disease, diabetes mellitus, or seizure disorders.
May cause hypokalemia; monitor serum potassium in prolonged therapy.
In food animals, observe withdrawal times to avoid residues.
Not approved for use in animals intended for human consumption in some countries.
Use in pregnant animals should be based on risk-benefit analysis, especially in cattle for tocolysis.
In horses, use with caution in those with a history of cardiac disease.

Adverse Effects & Reactions

Common:

Tachycardia
Tremors
Nervousness
Restlessness
Sweating
Increased heart rate

Serious / Severe:

Cardiac arrhythmias
Hypokalemia
Hyperglycemia
Pulmonary edema (rare)
Myocardial ischemia

Rare:

Paradoxical bronchospasm
Allergic reactions
Muscle cramps

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Beta-blockers (e.g., propranolol)	May antagonize the bronchodilatory effects of clenbuterol.	High
Corticosteroids	Additive bronchodilation and anti-inflammatory effects; may increase risk of hypokalemia.	Moderate
Diuretics (e.g., furosemide)	Increased risk of hypokalemia.	Moderate
Xanthines (e.g., theophylline)	Additive bronchodilation but increased risk of cardiac arrhythmias.	Moderate
MAOIs	Risk of hypertensive crisis.	High

Overdose & Toxicity Management

Signs of Toxicity:

Severe tachycardia
Hypertension
Tremors
Hyperactivity
Hypokalemia
Cardiac arrhythmias
Seizures

Emergency Treatment Protocol: Discontinue drug immediately. Administer supportive care: IV fluids, electrolyte replacement (potassium), and cardiac monitoring. In severe cases, use a beta-blocker (e.g., propranolol) cautiously to counteract cardiac effects, but be aware of potential bronchospasm. Symptomatic treatment for seizures may be necessary.

Food Animal Withdrawal Times

🥩 Meat: 14 days🥛 Milk: 7 days

Withdrawal times vary by country and formulation. In the US, clenbuterol is not approved for food animals; extra-label use requires extended withdrawal times. Consult regulatory guidelines.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

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

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

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use in the US. Approved in some countries for horses and cattle (e.g., Canada, UK).

Extra-Label (Off-Label) Use: In the US, clenbuterol is not approved for veterinary use in food animals. Extra-label use in food animals is prohibited under AMDUCA due to public health concerns. In horses, it is approved in some countries for respiratory conditions. Use in performance animals may be subject to doping regulations.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Clenbuterol is a potent bronchodilator used primarily in horses for recurrent airway obstruction and in small animals for bronchospastic diseases. It has a long duration of action and is administered orally or parenterally. Due to its beta-2 selectivity, it has fewer cardiac side effects than non-selective beta-agonists, but tachycardia can still occur. In cattle, it is used as a tocolytic, but its use is controversial due to residues. In performance animals, it is banned by most racing authorities. Always monitor heart rate and serum potassium during therapy. For food animals, strict withdrawal times must be observed to prevent violative residues.

References & Literature

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