agents with primary beta 2 adrenergic agonist activity form the 1st line medications for acute asthma exacerbations owing to their potent bronchodilator effects.
they are also used in premature labour to inhibit uterine contractions
most have some beta 1 adrenergic activity which results in:
increased myocardial oxygen demand
beta 2 adrenergic actions:
hypokalaemia from increased movement of K into cells
hyperglycaemia due to increased glycogenolysis & gluconeogenesis
may cause hypoxia in asthmatics by vasodilation of pulmonary vessels in unventilated alveoli resulting in V/Q mismatch
tocolytic effect in obstetric labour ie. inhibits uterine contractions and thus used in Mx of premature labour, although this role has been largely replaced by the calcium channel blocker, nifedipine, which is better tolerated and orally administered.