Chemistry, Storage/Stability - A beta-2-adrenergic agonist, clenbuterol HCl’s chemical name is 1-(4-Amino-3,5-dichlorophenyl)-2-tert-butyl aminoethanol HCl. The commercially available syrup is colorless and should be stored at room temperature (avoid freezing). The manufacturer warns to replace the safety cap on the bottle when not in use.
Pharmacology - Like other beta-2 agonists, clenbuterol is believed to act by stimulating production of cyclic AMP through the activation of adenyl cyclase. By definition, Beta-2 agonists have more smooth muscle relaxation activity (bronchial, vascular and uterine smooth muscle) versus its cardiac effects (Beta 1).
Uses/Indications - Clenbuterol is approved for use in horses as a bronchodilator in the management of airway obstruction, such as chronic obstructive pulmonary disease (COPD).
It has been used as a partitioning agent in food producing animals, but its use for this purpose is banned in the USA as relay toxicity in humans has been documented.
Pharmacokinetics - After oral administration to horses, peak plasma levels of clenbuterol occur 2 hours after administration and the average half life is about 10 hours. The manufacturer states that the duration of effect varies from 6-8 hours.
Contraindications/Precautions/Reproductive Safety - The drug is contraindicated in food producing animals (legal ramifications). It should not be used in pregnant mares near full term as it antagonizes the effects of dinoprost (prostaglandin F2alpha) and oxytocin and can diminish normal uterine contractility. The label states that the drug should not be used in horses suspected of having cardiovascular impairment as tachycardia may occur. Clenbuterol’s safety in breeding stallions and brood mares has not been established.
Adverse Effects/Warnings - Muscle tremors, sweating, restlessness, urticaria and tachycardia may be noted, particularly early in the course of therapy. Creatine kinase elevations have been noted in some horses and rarely ataxia can occur.
Clenbuterol has been touted in some body building circles as an alternative to anabolic steroids for muscle development and body fat reduction, however its safe use for this purpose is in serious question. Be alert for scams to divert legitimately obtained clenbuterol for this purpose.
Overdosage - Some case reports of clenbuterol overdoses have been reported in various species. Depending on dosage and species, emptying gut may be appropriate; otherwise supportive therapy and administration of parenteral beta blockers to control heart rate and rhythm, and elevated blood pressure may be considered.
Drug Interactions - Concomitant administration with other sympathomimetic amines (e.g., terbutaline) may enhance the adverse effects of clenbuterol. Beta blockers (e.g. propranolol) may antagonize clenbuterol’s effects. Tricyclic antidepressants or monoamine oxidase inhibitors may potentiate the vascular effects of clenbuterol. Use with inhalation anesthetics (e.g., halothane, isoflurane, methoxyflurane), may predispose the patient to ventricular arrhythmias, particularly in patients with preexisting cardiac disease—use cautiously. Use with digitalis glycosides may increase the risk of cardiac arrhythmias. Clenbuterol may antagonize the effects of dinoprost (prostaglandin F2alpha) and oxytocin.
As a 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. Recommended duration of therapy is 30 days; then withdraw therapy and reevaluate. If signs return, reinitiate therapy as above. (Package Insert; Ventipulmin®)
Monitoring Parameters - 1) Clinical efficacy; 2) Adverse effects (primarily cardiac rate)
Client Information - Clients should be instructed on the restricted use requirements of this medication and to keep it secure from children or those who may “abuse” it. The drug may prohibited from use by various equine associations (e.g., racing or show).
Dosage Forms/Preparations/FDA Approval Status -
Clenbuterol HCl Oral Syrup 72.5 mcg/ml in 100 ml and 330 ml bottles; Ventipulmin® Syrup (Boehringer Ingelheim Vetmedica); (Rx). Approved for use in horses not intended for use as food. Extralabel clenbuterol use is prohibited by federal (USA) law.
Human-Approved Products: None
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