Clenbuterol
**Clenbuterol** is a potent, long-acting **beta-2-adrenergic agonist** primarily utilized in equine medicine as a bronchodilator to manage airway obstruction diseases such as **Recurrent Airway Obstruction (RAO)**, formerly known as Chronic Obstructive Pulmonary Disease (COPD) or "heaves". Beyond its respiratory applications, it is occasionally used as a **uterine relaxant (tocolytic)** to assist in the management of dystocia in mares. ### Key Clinical Points: * **Strictly Banned in Food Animals**: Clenbuterol acts as a repartitioning agent (increasing muscle mass and decreasing fat) at high doses. Its use in food-producing animals is strictly prohibited globally due to severe, well-documented **relay toxicity** in humans consuming tainted meat (causing severe tremors, tachycardia, and hospitalization). * **Abuse Potential**: Due to its anabolic-like effects, it is frequently abused in human bodybuilding and weight-loss circles. Veterinarians must be vigilant against drug diversion. * **Endocrine & Cardiac Effects**: Chronic administration in horses can lead to decreased aerobic performance, cardiac hypertrophy, myocardial collagen infiltration, and altered immune function.
Mecanismo: Clenbuterol selectively binds to and activates **beta-2 adrenergic receptors** on smooth muscle cells. ### Primary Pathway: **Beta-2 Receptor Activation** → Stimulates **G_s proteins** → Activates **Adenylyl Cyclase** → Increases intracellular **cyclic AMP (cAMP)** → Activates **Protein Kinase A (PKA)** → Decreases intracellular calcium concentrations → Results in **smooth muscle relaxation** (bronchial, vascular, and uterine). ### Secondary Mechanisms: * **Anti-inflammatory Effects**: Inhibits the release of pro-inflammatory cytokines (such as **Interleukin-1β** and **Tumor Necrosis Factor-α**) from pulmonary macrophages. * **Mucociliary Clearance**: Increases ciliary beat frequency in the respiratory tract, enhancing the clearance of excessive mucus associated with RAO.
Dosificación por especie
- Bronchodilator · Initially, 0.8 micrograms/kg (practically: 0.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 1.6 micrograms/kg (practically: 1 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 2.4 micrograms/kg (practically: 1.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 3.2 micrograms/kg (practically: 2 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement discontinue therapy. · PO · q12h · Recommended duration of therapy is 30 days; then withdraw therapy and reevaluate. · ARCI UCGFS Class 3 Drug
- Adjunctive treatment for dystocia emergencies · 300 micrograms per 500 kg mare IV slowly · IV · Single dose · Parenteral formulation not available commercially in the USA. Fast onset allows quick decision if uterine relaxation will correct the problem. May be used with sedatives/analgesics; xylazine or detomidine may potentiate uterine relaxant effects.
- Adjunctive treatment for dystocia emergencies · 10 mls of clenbuterol syrup orally as the mare walks in the door. · PO · Single dose · Author's hospital protocol upon arrival of a dystocia.
Las dosis son una referencia clínica para médicos veterinarios. Confirme siempre con la información vigente del producto y el paciente individual.
Vías de administración
Contraindicaciones
- Food-producing animals (strictly banned by law)
- Horses suspected of having cardiovascular impairment
- Pregnant mares near full-term (unless used specifically for dystocia management)
Efectos adversos
- Muscle tremors
- Sweating
- Restlessness
- Urticaria
- Tachycardia
- Creatine kinase (CK) elevations
- Ataxia (rare)
- Abortion in pregnant animals
- Cardiac hypertrophy and collagen infiltration (with chronic use)
Interacciones farmacológicas
- Inhalant Anesthetics (halothane, isoflurane, methoxyflurane) · May predispose the patient to ventricular arrhythmias, particularly with preexisting cardiac disease.
- Beta-Blockers (e.g., propranolol) · May antagonize clenbuterol's bronchodilating and tocolytic effects.
- Digoxin · May increase the risk of cardiac arrhythmias.
- Dinoprost (Prostaglandin F2alpha) · Clenbuterol may antagonize the ecbolic effects of dinoprost.
- Oxytocin · Clenbuterol may antagonize the uterine contracting effects of oxytocin.
- Other Sympathomimetic Amines (terbutaline, albuterol) · Concomitant administration may enhance the adverse cardiovascular and neurologic effects of clenbuterol.
- Tricyclic Antidepressants or MAOIs · May potentiate the vascular effects of clenbuterol.
Monitoreo
- Clinical efficacy (improvement in respiratory rate, effort, and reduction of cough)
- Heart rate and rhythm (monitor for tachycardia or arrhythmias)
- Signs of muscle tremors, sweating, or restlessness
- Creatine kinase (CK) levels if myopathy is suspected
Sobredosis
Overdoses can cause severe sympathomimetic toxicity (extreme tachycardia, arrhythmias, severe muscle tremors, hypertension followed by hypotension, and hypokalemia). **Treatment**: * **Decontamination**: Emptying the gut (gastric lavage/activated charcoal) may be appropriate depending on the dosage and timing of ingestion. * **Medical Management**: Provide supportive therapy. Administration of parenteral **beta-blockers** (e.g., propranolol, esmolol) may be considered to control heart rate, rhythm, and elevated blood pressure.
La referencia de fármacos de VetSheet está destinada a médicos veterinarios como apoyo a la decisión clínica; no sustituye el juicio profesional ni la información vigente del fabricante.