Vetdrugs 2.0Clenbuterol is a beta2-adrenergic agonist used mainly as a bronchodilator in horses. Its principal veterinary role is relief of reversible airway obstruction associated with equine asthma. It acts on airway smooth muscle and can improve mucociliary clearance, providing symptomatic support within a broader respiratory treatment plan.
Group
Beta2-adrenergic bronchodilator
Mechanism of Action
Clenbuterol activates beta2-adrenergic receptors coupled to stimulatory G proteins, increasing adenylyl cyclase activity and intracellular cyclic AMP. Downstream protein-kinase signaling reduces smooth-muscle contractile activity, producing bronchodilation. Increased ciliary beat frequency can support mucus clearance. The same smooth-muscle relaxation mechanism can also reduce uterine tone in reproductive applications.
Dose Rates
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Equine asthma — Initial | 0.8 mcg/kg | PO | Every 12 h | |
| Equine asthma — Maintenance | 1.6 mcg/kg | PO | Every 12 h | Escalation step only after inadequate response to the preceding dose; ceiling 3.2 mcg/kg. |
| Equine asthma — Maintenance | 2.4 mcg/kg | PO | Every 12 h | Escalation step only after inadequate response to the preceding dose; ceiling 3.2 mcg/kg. |
| Equine asthma — Maintenance | 3.2 mcg/kg | PO | Every 12 h | Escalation step only after inadequate response to the preceding dose; ceiling 3.2 mcg/kg. |
| Emergency uterine relaxation | Reference only | IV | 300 mcg per 500 kg mare IV slowly is a size-qualified dystocia example, not a universal fixed dose. A suitable parenteral formulation is required; never inject oral syrup. | |
| Historical oral dystocia example | Reference only | PO | An institutional example gives 10 mL oral syrup on presentation for dystocia, but patient weight and product strength are not assigned. It is not a universal calculator dose. |
Indications
- Relief of reversible bronchoconstriction in horses with equine asthma, including recurrent airway obstruction.
- Adjunctive management of equine respiratory disease with a reversible obstructive component and impaired mucus clearance.
- Specialist use as a uterine relaxant during selected obstetrical procedures, where supported by the species and product indication.
Contraindications
- Do not administer to food-producing animals.
- Avoid nontherapeutic muscle-building use.
- Suspected cardiovascular impairment because tachycardia and arrhythmia can occur.
Interactions
- Other adrenergic medicines can increase cardiac stimulation.
- Beta blockers reduce bronchodilation.
- May oppose uterotonic effects of oxytocin and prostaglandin F2alpha; the desired reproductive effect must be considered.
Adverse effects
- Tachycardia and tremors
- Arrhythmias
- Reduced response with repeated use
- Possible impaired cardiac or exercise function
Toxicity
Excess beta-adrenergic stimulation can cause serious cardiac toxicity.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Ventipulmin syrup 72.5 mcg/mL Clenbuterol hydrochloride 72.5 mcg/mL. Store at or below 25°C; avoid freezing. | Oral Liquid | 72.5 mcg / mL | PO |
Monitoring and Administration
Monitor heart rate and respiratory response. If response is inadequate, increase cautiously in separate dose steps.
The starting dose is 0.8 MICROGRAM/kg, equivalent to 0.0008 mg/kg. The printed 0.008 mg/kg conversion is incorrect and is not used.
Dose escalation to 1.6, 2.4 and 3.2 mcg/kg is described. No small-animal dose is established in the supplied monograph.
For the 72.5 mcg/mL Ventipulmin formulation, each escalation step is assessed after 3 days (six treatments). Stop if there is no response at 3.2 mcg/kg twice daily. At the effective dose, the described treatment period is 30 days, followed by withdrawal to reassess signs; if retreatment is needed, repeat the stepwise titration.