CLENBUTEROL

Introduction

Clenbuterol is a substituted phenylaminoethanol and a long-acting β-2 adrenergic agonist with sympathomimetic activity.^[1] Clenbuterol selectively binds to and activates β-2 adrenergic receptors in bronchiolar smooth muscle, thereby causing stimulation of adenyl cyclase, the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-3',5'-adenosine monophosphate (cAMP).^[2] Increased intracellular cAMP levels cause relaxation of smooth muscle. In addition, clenbuterol also stimulates central nervous system (CNS), and causes an increase in blood pressure and heart rate due to both β-2 and β-1 adrenergic activities.^[3] This agent may also exert an anabolic or anti-catabolic effect due to as of yet unidentified mechanisms. It is most commonly available as the hydrochloride salt, clenbuterol hydrochloride.^[4]

History and Occurrence

Clenbuterol currently serves as an important compound in a prescribed respiratory treatment in horses. The drug, NADA for Ventipulmin® Syrup (Boehringer Ingelheim Vetmedica, Inc.) was approved by the FDA in 1988 for use solely by veterinarians. Because the drug is a product of Boehringer Ingelheim Vetmedica, Inc., clenbuterol can only be found in bulk in the United States under the supervision of this company for use of NADA.^[5] Particularly, NADA treats airway obstruction in horses and is given in the dosage of 0.8-3.2 µg/kg twice daily.^[6] “The Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA) allows veterinarians to prescribe extralabel uses of certain approved animal drugs and approved human drugs for animals under certain conditions. Extralabel use refers to the use of an approved drug in a manner that is not in accordance with the approved label directions.” According to Section 530.41, clenbuterol is banned as an extralabel compound and is therefore prohibited from usage in food animals. Of the several uses surrounding clenbuterol, the use most significant to this discussion involves utilizing the drug for repartitioning effects in food animals. The compound was used to increase mean muscle mass and decrease body fat in show and food animals, similar to the effect in humans. These animals include calves, lamb, chicken and swine.^[7]
To exemplify, in the 1990’s the HFA, the Humane Farming Industry, protested against the use of clenbuterol in veal production. The drug was used as a growth stimulant to increase the growth rate of calves. By doing so, meat producers in the veal industry produce meat quickly and therefore increase profits, all the while compromising the health of consumers. After detrimental human side effects were discovered, the FDA banned clenbuterol in food products in 1991.^[8]
The FDA seemingly takes several precautions in regulating clenbuterol in the United States. For example, Chromatography and immunoassay screening are used to detect traces of clenbuterol in products. Also, the FDA works with the Justice Department to charge clenbuterol violators under the Federal law.^[9][10]

Formation

Clenbuterol hydrochloride was synthesized from 4-amino acetophenone. Initially 4-amino acetophenone was reacted with chlorine to afford 4-amino-3,5dichloro acetopheneone which was further reacted bromine to give 1-(4-amino-3,5-dichlorophenyl)-2-bromoethanone. The obtained bromo compound was reacted tertiary butyl amine to afford 2-(tertbutylamino)-1-(4-amino-3,5-dichlorophenyl)ethanone, which was further reduced with sodium borohydride to give clenbuterol base and converted in to hydrochloride salt by using alcoholic HCl to get clenbuterol hydrochloride.^[11]

 

Application

Clenbuterol is a steroid-like chemical that was initially developed to treat asthma in horses, working by relaxing the airways in the animals' lungs. The drug is both a decongestant and a bronchodilator. A decongestant thins the blood to reduce blood pressure while a bronchodilator widens the vessels that carry oxygen, so the volume of oxygen in the blood increases. In some European and Latin American countries, clenbuterol is approved as an asthma drug for humans too. But, in the United States, it is a banned substance for this purpose. In the U.S. in the past, clenbuterol has been used in animal rearing as well as by vets. In 1991, the U.S. Food Safety and Inspection Service found it had been fed to livestock, so the animals gained more muscle and less fat. But, again, in many countries, clenbuterol is illegal for animal use. The drug is now controversial because of its use in bodybuilding and weight-loss programs.
Uses of Clenbuterol in Food
Although Clenbuterol is more modernly associated with human use as a pharmacological stimulant, uses of Clenbuterol have dated back since the early 90’s as a stimulant used for show animals. Many show animals such as dogs and horses are given Clenbuterol mixed into their feed as a drug to enhance the performance, muscle rearing, and appearance of show animals. Although show animals make up less than 1% compared to livestock slaughtered for human consumption, the FDA, Food and Drug Administration, and the FSIS, Food Safety and Inspection Service, have been banning the use of Clenbuterol and have been pushing towards stopping the use of Clenbuterol even for show animals. The fear lies in the fact that there is possibility that animals used in shows could become slaughtered for consumption, or that if Clenbuterol is allowed to be given to animals, its usage could become evasive to livestock farmers. More recently however, Clenbuterol has been used by countries in Europe and even some livestock in the US as a means of increasing leanness and protein content. The use in Europe has been more pervasive amongst the general population but is deemed illegal in the states. By increasing the leanness and protein content, farmers are able to yield a higher quality of meat.^[12][13]
Treatment of urinary incontinence
Clenbuterol can be effective only when sfincter activity is preserved, which is proved by means of urodynamic tests. The durability of treatment was stable in 86% of treated women, and in 76.3% of treated men. The authors determine the indications and contraindications of administration of celbuterol. They analise the changes in the hydrodynamic of the lower urinary tract in the patients with urinary incontinence after clenbuterol therapy.^[14]

Processing

Clenbuterol Hydrochloride was first synthesized at Thomae; a Boehringer Ingelheim research facility in Biberach, Germany, in 1967. The synthesis of Clenbuterol Hydrochloride was patented in the United States in 1970. After comprehensive clinical trials, Clenbuterol Hydrochloride was approved for the treatment of reversible airway obstruction in Germany in 1976 and later as a veterinary pharmaceutical for the treatment of bronchiolytic disorders in Germany in 1980. Boehringer Ingelheim markets Clenbuterol Hydrochloride as Spirospent for Human Pharmaceuticals and as Ventipulmin for Veterinary Pharmaceuticals. Clenbuterol Hydrochloride is not approved by the Federal Drug Administration for human use in the United States.^[11]

Future trends

The effects that clenbuterol can have on the heart and muscles will depend on how high a dose someone has been taking and for how long. The risks increase with the dose and duration. Those taking high doses can experience long-term side effects quickly, such as a decrease in the size, weight, strength, and activity of the heart. Clenbuterol is illegal for human consumption in the U.S. for a good reason, and anyone buying the drug online should be extremely cautious. While some may choose to take the risk because of the less harmful side effects, they should always remember the potentially extreme side effects as well.^[15][16]

References

1. https://www.medicalnewstoday.com/articles/319927.php
2. https://www.healthline.com/health/clenbuterol
3. Zeman, RICHARD J., R. O. B. E. R. T. Ludemann, and JOSEPH D. Etlinger. "Clenbuterol, a beta 2-agonist, retards atrophy in denervated muscles." American Journal of Physiology-Endocrinology And Metabolism 252.1 (1987): E152-E155.
4. https://www.drugbank.ca/drugs/DB01407
5. “Illegal Compounding of Clenbuterol,” U.S. Food and Drug Administration, FDA Veterinarian Newsletter 2002, Volume XVII, No II, 10/28/2009
6. “Drugs of Chemical Concern: Clebuterol,” U.S. Department of JusticeDrug Enforcement Adminstration, October, 2009
7. Derksen, F. J. "Anecdotes and clinical trials: the story of clenbuterol." Equine veterinary journal 26.4 (1994): 256-258.
8. “Clenbuterol,” Food and Saftey Inspection Service, July 1995 10 October 2011
9. “Clenbuterol,” Food and Saftey Inspection Service, July 1995 10 October 2011
10. Prezelji A, Obreza A, Pecar S.,“Abuse of clenbuterol and its detection,” PubMed.gov February 3003 12 October 2011
11. Med Chem (Los Angeles), Volume 6(8): 546-549 (2016) 546
12. The Effects of Clenbuterol on the Human Body, Jessie Yeh
13. https://food.r-biopharm.com/news/clenbuterol-food-risk/
14. Int Urol Nephrol. 2001;33(3):413-6.
15. Jonathan Brett, Andrew H Dawson and Jared A Brown, Med J Aust 2014; 200 (4): 219-221.
16. https://examine.com/supplements/clenbuterol/

Description

Clenbuterol is a long-acting, potent, and specific β2 stimulator that is used orally.

Chemical Properties

White Crystalline Solid

Originator

Spiropent,Thomae,W. Germany,1977

Uses

Substituted phenylethanolamine with β2 sympathomimetic activity. Bronchodilator.

Uses

bronchodilator, beta2 adrenergic agonist

Definition

ChEBI: Clenbuterol is a primary arylamine that is 2,6-dichloroaniline in which the hydrogen at position 4 is substituted by a 2-(tert-butylamino)-1-hydroxyethyl group.

Manufacturing Process

127 g of 1-(4'-aminophenyl)-2-t-butylaminoethanol-(1) hydrochloride were dissolved in a mixture of 250 cc of glacial acetic acid and 50 cc of water, and chlorine added while stirring the solution and maintaining the temperature of the reaction mixture below 30°C by cooling with ice water. After all of the chlorine had been added, the reaction mixture was stirred for thirty minutes more, then diluted with 200 cc of water, and made alkaline with concentrated ammonia while cooling with ice, taking care that the temperature of the reaction mixture did not rise above 40°C. The alkaline mixture was extracted three times with 200 cc portions of chloroform, and the chloroform extract solutions were combined, dried with sodium sulfate and evaporated. The residue, the free base 1-(4'-amino-3',5'-dichlorophenyl)-2-tbutylaminoethanol-(1), was dissolved in absolute ethanol, gaseous hydrogen chloride was passed through the solution, and the precipitate formed thereby was collected. It was identified to be 1-(4'-amino-3',5'-dichlorophenyl)-2-tbutylaminoethanol-(1) hydrochloride, melting point 174.0°C to 175.5°C (decamp.).

Therapeutic Function

Anti-asthmatic

Side effects

The risks of misusing a drug like clenbuterol include its lack of proven effectiveness and its hazardous side effects. Clenbuterol is well-known to cause symptoms such as rapid heart rate (tachycardia), palpitations, tremors, anxiety, lowered blood potassium (hypokalemia), and elevated blood sugar (hyperglycemia). Adverse effects happen more often with the large doses used for performance enhancement and weight loss. Because the drug has a long half-life in the body, toxic symptoms can last from 1 to 8 days.