A Comparison of the Molecular Pharmacological Properties of Current Short, Long, and Ultra‐Long‐Acting β₂‐Agonists Used for Asthma and <scp>COPD</scp>

β-agonists have been used in asthma for 120 years. There are two recent changes: ultra-long-acting agonists for COPD and new asthma guidelines recommending formoterol/ICS inhalers phasing out short-acting salbutamol inhalers. Few studies directly compare the molecular pharmacological properties of short (salbutamol, terbutaline, fenoterol), long (formoterol, salmeterol), and ultra-long-acting (indacaterol, olodaterol, vilanterol) β₂-agonists. Here, the in vitro molecular pharmacological properties of affinity, selectivity, intrinsic efficacy, and duration of β₂-agonists at human β₂ and β₁-adrenoceptors and the 4 β₂-polymorphisms stably expressed in CHO cells were directly compared using radioligand binding and functional studies. Whilst short-acting drugs were similar, there was huge variation and complete overlap in the molecular pharmacological properties of drugs labeled as long and ultra-long-acting β₂-agonists. Salmeterol and vilanterol were highly β₂-selective (> 1000-fold) whereas indacaterol was similar to salbutamol (40-fold). Formoterol and indacaterol were the most efficacious, whereas salmeterol had the longest duration of binding. Salmeterol and vilanterol utilize a β₂-specific exosite (β₂-H296-K305) for high affinity and selectivity (that does not affect intrinsic efficacy or duration) whilst the β₂-selectivity of formoterol and olodaterol resides elsewhere. Duration of binding closely correlated with lipophilicity. β₂-polymorphisms had no substantial effect on β₂-agonist properties. Comparison with other β-ligands suggests that affinity and duration could both be improved further. However, given the very wide range of molecular pharmacological properties of β-agonists that are clinically effective and widely used, non-pharmacological properties (physiochemical, patient factors, devices and combination inhaler availability) may be as important in final clinical patient outcomes as the molecular pharmacological properties of the individual β₂-agonists themselves.