𝛃2 adrenoceptor agonists

𝛃2 adrenoceptor agonist...

1. EXAMPLES: Short-acting – salbutamol, terbutaline; long-acting – salmeterol, formoterol.
2. MECHANISM OF ACTION: Selective 𝛃2 adrenoceptor agonists in smooth muscle of upper airways that increase intracellular cAMP. This leads to smooth muscle relaxation and bronchodilation.

• Acute asthma (short-acting).
• Chronic asthma/COPD (long-acting).
• Premature labour.

• Hypersensitivity.

• Fine tremor.
• Hypokalaemia (if high doses given).
• Tachycardia.
• Headache.

• The effects of long-acting drugs last 12 h.
• Proportion reaching GI tract is metabolised by the liver. t½ varies; salbutamol 3–7 h and terbutaline 16–20 h.

• Monitor potassium levels if high doses of salbutamol given (especially in acute asthma).

• Should not be given with non-selective 𝛃2 blockers, due to opposing actions.
• In management of acute asthma, hypokalaemia may be potentiated by hypoxia and the use of theophylline, steroids and diuretics.

• Salbutamol can be administered by inhaler, nebuliser or IV in the management of acute asthma.
• Salbutamol can be used in the immediate management of hyperkalemia (increases uptake of potassium into cells).
• BTS guidelines recommend a stepwise approach to the management of chronic asthma. First-line therapy involves the use of short-acting 𝛃2 agonists; if symptoms are uncontrolled this is supplemented with inhaled corticosteroids and then long-acting 𝛃2 agonists.
• 𝛃2 agonists salbutamol and terbutaline can be used to delay uncomplicated premature labour (24–33 weeks gestation) by at least 48 h, by inhibition of uterine contractions.