Clenbuterol is a long-acting beta-2 agonist that can be administered orally, by inhalation, and intravenously. It is well-absorbed from the GI tract, and has a bioavailability of 70 percent to 80 percent. It also has a remarkably long half-life of 25 to 39 hours. (By comparison, the half-life of albuterol is three to six hours.) It can take up to five days to clear completely from the body. The therapeutic oral dose for asthma is 20 mcg to 30 mcg twice daily. As with all beta-2-specific adrenergic agonists, at high doses clenbuterol also has significant cardiac-stimulating beta-1 activity.
While not a steroid, clenbuterol possesses significant anabolic activity. When given in high doses to steers for 98 days, it increased muscle mass, decreased fat deposition, and improved the USDA yield grade of the meat. By using clenbuterol, farmers can get up to 20 percent more meat and 20 percent less fat from the same amount of feed. In addition, studies have shown that chronic use of clenbuterol decreases the number of slow-twitch (Type I) muscle fibers and increases the number of fast-twitch (Type II) muscle fibers.
Although studies of these anabolic and lipolytic actions have not been carried out in human subjects, it is easy to see why such a drug would become popular in weightlifting, bodybuilding, and athletics. Obtaining clenbuterol through the Internet is not difficult; a recent Google search for “buy clenbuterol” returned 135,000 hits. Emergency physicians should be aware of the signs and symptoms of clenbuterol overdose, which are similar to those caused by excessive amounts of any beta-2 agonist. (See table.)
In a particularly dramatic case reported by Daubert et al (J Med Toxicol 2007;3:56), a 31-year-old man ingested 110 mcg of Ventipulmin syrup, the veterinary preparation of clenbuterol intended to treat airway disease in horses. He presented to the emergency department complaining of palpitations and dyspnea. On exam, his pulse rate was 254 beats per minute. Laboratory testing showed hypokalemia (2.1 mmol/L) and hyperglycemia (209 mg/dl). His heart rate did not respond to adenosine doses of 6 mg and 12 mg, but decreased to 150 beats per minute after 10 mg diltiazem IV.
Following the recommendation of the local poison control center, he was treated with esmolol. Unfortunately, the paper does not make clear how effective that treatment was. On the third hospital day, the patient was electrically cardioverted from rapid atrial fibrillation. Interestingly, this patient was also taking tamoxifen, a drug used by some body builders to suppress the gynecomastia caused by estrogenic metabolites of anabolic steroids.
Recently, Hoffman et al described an outbreak of heroin adulterated with clenbuterol diagnosed at five medical centers along the east coast. (Ann Emerg Med May 23, 2008; Epub ahead of print.) Thirty-four probable or confirmed cases were identified, and these patients presented with features atypical for pure heroin exposure, including chest pain, palpitations, agitation, tachycardia, hyperglycemia, hypokalemia, and metabolic acidosis with increased lactate.
All 10 patients who were treated with beta-blockers (metoprolol, labetalol, or esmolol) improved. There were no adverse effects attributed to this treatment. The authors advise against the use of a beta-blocker in patients who may have recently used cocaine because the resulting unopposed alpha-adrenergic stimulation could theoretically cause vasoconstriction, coronary artery spasm, and hypertension.
One other potential route of exposure to clenbuterol comes from contaminated meat. When farmers illegally feed their animals large doses of clenbuterol, the drug gets concentrated in the liver and to a lesser extent in the skeletal muscle and tongue. The drug is heat-stable, and survives exposure to most cooking temperatures. In Shanghai, where the common name for clenbuterol is “lean meat powder,” clenbuterol-tainted pork caused symptoms in more than 330 people in 2006.
Similar outbreaks occurred in Spain (1990 and 1994), Italy (1997), and France (1991). These outbreaks were traced back to contaminated liver, veal slices, and tongue. In general, symptoms began within 15 minutes to six hours of ingestion, and lasted 90 minutes to six days. No deaths were reported. I am not aware of any such cases in the United States.
So enjoy your veal scaloppini or beef liver smothered in onions. But if your hands start to shake and your heart beats faster, it may not be because you're in love with the chef's preparation.
Manifestations of Clenbuterol Toxicity
▪ Chest pain
▪ Nausea and vomiting
▪ Elevated blood lactate
▪ Cardiac ectopy
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