Terbutaline, sold under the brand nameBricanyl among others, is a β2adrenergic receptor agonist, used as a "reliever" inhaler in the management of asthma symptoms and as a tocolytic to delay preterm labor for up to 48 hours. This time can then be used to administer steroid injections to the mother which help fetal lung maturity and reduce complications of prematurity. It should not be used to prevent preterm labor or delay labor more than 48–72 hours. In February 2011, the Food and Drug Administration began requiring a black box warning on the drug's label. Pregnant women should not be given injections of the drug terbutaline for the prevention of preterm labor or for long-term management of preterm labor, and should not be given oral terbutaline for any type of prevention or treatment of preterm labor "due to the potential for serious internal heart problems and death." It was patented in 1966 and came into medical use in 1970.
Medical uses
Terbutaline is used as a fast-acting bronchodilator and as a tocolytic to delay premature labor. The inhaled form of terbutaline starts working within 15 minutes and can last up to 6 hours. Terbutaline as a treatment for premature labor is an off-label use not approved by the FDA. It is a pregnancy category C medication and is routinely prescribed to stop contractions. After successful intravenous tocolysis, little evidence exists that oral terbutaline is effective. However, following uterine inversion in the third stage of labor, terbutaline can be used to relax the uterus if necessary prior to uterine replacement.
The tertiary butyl group in terbutaline makes it more selective for β2 receptors. Since there is no hydroxy group on position 4 of the benzene ring, the molecule is less susceptible to metabolism by the enzyme catechol-O-methyl transferase.
Chemistry
Terbutaline is synthesized by brominating 3,5-dibenzyloxyacetophenone into 3,5-dibenzyloxybromoacetophenone, which is reacted with N-benzyl-N-tert-butylamine, giving a ketone intermediate. Reduction of this product with H₂ over Pd/C leads to terbutaline.
Stereochemistry
Terbutaline contains a stereocenter and consists of two enantiomers. This is a racemate, ie a 1: 1 mixture of - and the - form:
Society and culture
Athletics
As with all β2-adrenergic receptor agonists, terbutaline is on the World Anti-Doping Agency's list of prohibited drugs, except when administered by inhalation and a Therapeutic Use Exemption has been obtained in advance.
