Zilpaterol

Zilpaterol

Clinical data
Trade names	Zilmax
Routes of administration	Oral
ATC code	none
Pharmacokinetic data
Biological half-life	11.9–13.2 hours (first phase)
Excretion	Urine (88.2–84.3%) and feces (8.6–8.7%) (in cattle)
Identifiers
IUPAC name (±)-trans-4,5,6,7-Tetrahydro-7-hydroxy-6-(isopropylamino)-imidazo[4,5,1-jk]-[1]benzazepin-2(1H)-one
CAS Number	117827-79-9 Y
PubChem (CID)	9992825
ChemSpider	2343170 N
UNII	S384A1Y12J Y
ECHA InfoCard	100.215.148
Chemical and physical data
Formula	C14H19N3O2
Molar mass	261.148 g/mol
3D model (Jmol)	Interactive image
SMILES CC(C)N[C@@H]1CCN2C3=C([C@H]1O)C=CC=C3NC2=O
InChI InChI=1S/C14H19N3O2/c1-8(2)15-11-6-7-17-12-9(13(11)18)4-3-5-10(12)16-14(17)19/h3-5,8,11,13,15,18H,6-7H2,1-2H3,(H,16,19)/t11-,13-/m1/s1 N Key:ZSTCZWJCLIRCOJ-DGCLKSJQSA-N N
NY (what is this?)

Zilpaterol (zilpaterol hydrochloride; codenamed RU 42173) is a β₂ adrenergic agonist. Under its trade name, Zilmax, it is used to increase the size of cattle and the efficiency of feeding them. Zilmax is produced by Intervet, a subsidiary of Merck & Co., and marketed as a "beef-improvement technology". Zilpaterol is typically fed in the last three to six weeks of cattle's lives, with a brief period (three days in the US) before death for withdrawal, which allows the drug to mostly leave the animal's tissues.

Concerns have been raised on the impact of zilpaterol on flavor; however, studies have confirmed that overall tenderness, juiciness, flavor intensity, and beef flavor remain within the normal variation observed in the beef industry and differences are smaller than what can be detected by the consumer. However, several studies have shown the use of zilpaterol leads to increased size, feed efficiency, and value.

Merck reported Zilmax-fed cattle do not produce beef with a difference in taste or quality compared to cattle not fed the drug, but elsewhere, concerns have been raised about the beef's tenderness. Studies have variously found a slight reduction in tenderness, an increase in shear force, and a lower percentage of intramuscular fat (marbling).

Tyson Foods was the first among the largest U.S. meatpackers to adopt Zilmax. Because of concerns about tenderness and loss of marbling, Cargill and other meatpackers resisted the practice. The next adopters were JBS and National Beef, with Cargill finally joining them in mid-2012.

On August 6, 2013 Tyson Foods banned Zilmax-fed cattle from its processing plants after cattle began arriving with missing hooves in large numbers during hot weather.

This drug is banned in China, Taiwan, Russia, and many countries in the European Union.

Zilpaterol has two chiral carbons and consequently four optical enantiomers. These enantiomers are: (6R,7R)-, (6R,7S)-, (6S,7R)- and (6S,7S)-. RU 42173 corresponds to racemic trans-zilpaterol hydrochloride, a mixture of the (6R,7R)-(−)- and (6S,7S)-(+)-enantiomers.