Clenbuterol: A substituted phenylaminoethanol that has beta-2 adrenomimetic properties at very low doses. It is used as a bronchodilator in asthma.Drug Residues: Drugs and their metabolites which are found in the edible tissues and milk of animals after their medication with specific drugs. This term can also apply to drugs found in adipose tissue of humans after drug treatment.Adrenergic beta-Agonists: Drugs that selectively bind to and activate beta-adrenergic receptors.Adrenergic beta-2 Receptor Agonists: Compounds bind to and activate ADRENERGIC BETA-2 RECEPTORS.Receptors, Adrenergic, beta-2: A subclass of beta-adrenergic receptors (RECEPTORS, ADRENERGIC, BETA). The adrenergic beta-2 receptors are more sensitive to EPINEPHRINE than to NOREPINEPHRINE and have a high affinity for the agonist TERBUTALINE. They are widespread, with clinically important roles in SKELETAL MUSCLE; LIVER; and vascular, bronchial, gastrointestinal, and genitourinary SMOOTH MUSCLE.Ethanolamines: AMINO ALCOHOLS containing the ETHANOLAMINE; (-NH2CH2CHOH) group and its derivatives.Fenoterol: An adrenergic beta-2 agonist that is used as a bronchodilator and tocolytic.