Beta 2 Agonists

Question 1

What are the respiratory indications?

Answer 1

1. Asthma - short-acting B2-agonists used to relieve breathlessness.
   Long-acting B2-agonists are used as ‘step 3’ treatment for chronic asthma, but must always be used in conjunction with inhaled corticosteroids
2. COPD - short-acting B2-agonists used to relieve breathlessness. Long-acting B2 agonists can be used as second-line therapy.
3. Hyperkalaemia - nebulised salbutamol may be used as an adjunct (alongside insulin, glucose and calcium gluconate) for the urgent treatment of high serum potassium

Question 2

Where are beta 2 receptors found?

Answer 2

Bronchi smooth muscle
Gi Tract
Uterus
Blood vessels

Question 3

How do B2 agonists work?

Answer 3

B2 receptor is G protein-coupled receptor.
Activation triggers signalling cascade that leads to smooth muscle relaxation.
This improves flow of air and relieves breathlessness.

Question 4

Why are B2 agonists used in hyperkalaemia?

Answer 4

Stimulate Na+/K+ ATPase pump on cell surface membranes, thereby causing a shift of K+ from the extracellular to the intracellular compartment (i.e. removes K+ from the blood)

Question 5

What are the pertinent side-effects of B2 agonists?

Answer 5

Tachycardia, anxiety, tremor and papitations (B2 activates fight or flight).

Also promote glycogenolysis so may increase serum glucose.

At high doses serum lactate may also be raised.

Long-acting B2 agonists can cause muscle cramps.

Serious side effects may include worsening bronchospasm, irregular heartbeat, and low blood potassium levels.

Question 6

What are the two classes of B2 agonists?

Answer 6

Short-acting - salbutamol, terbutaline

Long-acting - salmeterol, formoterol

Question 7

What warnings should be taken into account when prescribing B2 agonists?

Answer 7

Long-acting B2 agonists must only be prescribed in conjunction with inhaled corticosteroids (without steroids they are associated with increased asthma deaths).

Take care when prescribing to patients with cardiovascular disease in whom tachycardia might induce arrhythmia - especially important in hyperkalaemia where large doses may be needed.

Question 8

What are the important interactions for B2 agonists?

Answer 8

B-blockers oppose action therefore reduce effectiveness.

Use of nebulised B2-agonists, theophylline and corticosteroids can cause hypokalaemia - serum K+ should be monitored.

Question 9

Why would you prescribe short-acting inhaled B2 agonists?

Answer 9

PRN - common choice in adults is 100-200 micrograms.

Question 10

How are B2 agonists used in acute exacerbations of COPD or asthma requiring hospital treatment?

Answer 10

2.5mg salbutamol nebulised 4 hrly

Question 11

When are long-acting B2 agonists used?

Answer 11

For maintenance therapy: prescribed regularly (usually twice daily). Often co-administered with steroid in same inhaler (Symbicort, Seretide).
These combinations also used in COPD.

Question 12

How is salbutamol eliminated?

Answer 12

Approximately 72% of the inhaled dose is excreted in the urine within 24 hours, 28% as unchanged drug and 44% as metabolite.

Question 13

Patient information?

Answer 13

Explain the medicine will make their airways relax and therefore improve their breathing. Make sure that they understand that this treats the symptoms, not the disease. Consequently, if they find themselves needing to use the β2-agonists very frequently, then they should seek medical advice, or increase their other treatment (e.g. inhaled corticosteroid) in accordance with a written action plan. Make sure that they are clear on how and when to take the inhaler (e.g. for acute symptoms, pre-emptively before exercise or regularly for long-acting medication).

Make sure they know how to administer the inhaler