beta 2 adrenergic agonists

introduction

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:
- tachycardia
- tremor
- 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.
- skeletal muscle vasodilatation
- increased risk of nocturnal leg cramps
  - increased risk with potassium-sparing diuretics, thiazides, and inhaled long acting beta 2 adrenergic agonists (especially if used with corticosteroids, but not with statins or loop diuretics ¹⁾

short-acting beta2 agonists (SABA):
- salbutamol
  - aka albuterol
  - Ventolin
- terbutaline
  - Bricanyl turbuhaler
long acting beta2 agonists (LABA):
- salmeterol - longer acting agent used in inhalant preparations
  - eg. Seretide (salmeterol plus fluticasone)
- eformoterol - long acting agent used in inhalant preparations
  - eg. Flutiform (eformoterol plus fluticasone propionate) introduced Aust. 2013
  - eg. Symbicort (eformoterol plus budesonide)
- vilanterol
  - eg. Breo Ellipta (vilanterol plus fluticasone) - introduced Aust. 2014
  - Anoro Elipta - (vilanterol + umeclidinium)
- indacaterol - LABA+LAMA for once daily dosing for patients with mod-severe chronic obstructive pulmonary disease (COPD)
  - eg. Ultibro Breezhaler 110/50 (indacaterol + glycopyrronium) - introduced Aust. 2014
- olodaterol - long acting agent used in inhalant preparations
  - eg. Striverdi Respimat introduced Aust. 2014

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