Pharmacology
Respiratory
Selective beta-2 agonists predominantly have which of the following clinical effects:
Answer:
Selective beta-2 agonists act directly on beta-2 receptors, causing smooth muscle relaxation and dilation of the airways.Selective Beta-2 Agonists
Pharmacology / Respiratory
Last Updated: 28th March 2019
Selective beta-2 agonists act directly on beta-2 receptors, causing smooth muscle relaxation and dilation of the airways.
Indications
Mild to moderate symptoms of asthma respond rapidly to the inhalation of a selective short-acting beta2 agonist such as salbutamol or terbutaline sulfate. Short-acting beta-2 agonists have a rapid onset of action (15 minutes) and their effects last for up to 4 hours. Salbutamol or terbutaline sulfate can be given intravenously for severe or life-threatening acute asthma; patients should be carefully monitored and the dose adjusted according to response and heart rate.
Short acting beta-2 agonists are used for immediate relief of asthma symptoms, while some long-acting beta-2 agonists (e.g. salmeterol) are added to an inhaled corticosteroid in patients requiring prophylactic treatment.
Cautions
Beta-2 agonists should be used with caution in people with:
- Cardiovascular disease including arrhythmias and hypertension (beta-2 agonists may cause an increased risk of arrhythmias and significant changes to blood pressure and heart rate)
- Diabetes (risk of hyperglycaemia and ketoacidosis, especially with intravenous use)
- Hyperthyroidism (beta-2 agonists may stimulate thyroid activity)
- Hypokalaemia (potentially serious hypokalaemia may result from beta-2 agonist therapy; this effect may be potentiated in severe asthma by concomitant treatment with theophylline, corticosteroids, diuretics and by hypoxia)
- Susceptibility to QT-interval prolongation
- Convulsive disorders
Interactions
Hypokalaemia may be potentiated by concomitant treatment with theophylline and its derivatives, corticosteroids, and diuretics. This in turn may predispose to toxicity in patients taking digoxin.
Side Effects
Side effects are usually dose related and include:
- Fine tremor — occurs particularly in the hands and is usually worse in the first few days of treatment.
- Palpitations and tachycardia
- Headache
- Seizure
- Anxiety
- Hypokalaemia
- Cardiac arrhythmia and paradoxical bronchospasm (rare)
- Acute angle-closure glaucoma
- QT-interval prolongation
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
