What Is Clenbuterol Used For In Horses?
In May 1998, the U.S. Food and Drug Administration (FDA) approved the use of a branded version of clenbuterol for the management of horses affected with airway obstruction, such as occurs in chronic obstructive pulmonary disease (COPD). In other parts of the world, clenbuterol had been available for many years but, because it was not available in the United States via normal routes (an equine pharmacy, for example), it was sometimes used illicitly.1
Clenbuterol, a bronchodilator and mucokinetic drug, belongs to a class of drugs called beta2-agonists. When administered at recommended dosages, it reaches plasma levels rapidly, relaxing airway smooth (bronchial) muscle. Beta2-agonists are often used to treat asthma in humans. Other drugs in this class include albuterol, pirbuterol and fenoterol.
Mechanisms and Usage
During the “fight or flight” response, catecholamines (epinephrine and norepinephrine) are released from sympathetic nerves and the adrenal gland. The catecholamines activate several types of adrenoceptors so that heart rate and contractility increase, blood flow increases to the muscles and is reduced to splanchnic organs, glycogenolysis and lipolysis increase, the pupils dilate, gastrointestinal motility is decreased, and the uterus and bronchi relax.1
Clenbuterol is not a steroidal medication, but does possess some properties similar to those of anabolic steroids, such as promoting an increase in muscle mass. Due to these properties, clenbuterol has been used (in livestock and horse pharmacy applications) to increase lean muscle mass.
While studies on the efficacy of clenbuterol as a weight loss or performance enhancer in humans have been limited, many studies have been performed in animals and livestock. In research, sources have observed that clenbuterol stimulates muscle growth and repair while preventing atrophy in mice and rats. In livestock applications, some studies have indicated that increases in muscle growth occurs at the expense of fat tissue, part of a process referred to as repartitioning. Further, in horses, studies have found that long-term administration of high doses of clenbuterol increased the expression of genes related to various muscle components and fat metabolism.2
In its most common application (in the U.S. and other countries), clenbuterol is relegated to the use cited in the first paragraph. With stable management that reduces the horse's exposure to dust and to high ammonia concentrations (from urine in poorly-ventilated stalls, for example), clenbuterol is used to manage chronic obstructive pulmonary disease. Clenbuterol is sometimes used with sick foals in respiratory distress due to pneumonia (equimed.com).
Dosage and Administration
Drug side effects are unlikely with clenbuterol, but occasionally include increased heart rate, trembling, excitement, and sweating. For bronchospasm in equines, the recommended dosage via oral route is typically 0.0008 mg/kg at a concentration of 0.0725 mg/ml, 2 times a day for 3 days. The dosage is increased by ~8mg/kg every 3 days until the horse shows improvement, with a maximum of 30 total days of treatment.
1 Robinson, N. & Vet, B.. (2000). Clenbuterol and the Horse.
2Seladi-Schulman, J. (2018). What is Clenbuterol? Healthline.com.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services in Nationwide. Unlike other veterinary compounding pharmacy, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.