| Class | Bronchodilator |
|---|---|
| Chemistry |
Synthetic sympathomimetic amine, structurally analogous to catecholamines |
| Routes of administration |
IV, nebulised |
| Absorption |
Poor oral bioavailability; but it is still somehow available as a syrup. When given as a nebuliser, approximately 10% of an inhaled salbutamol dose is deposited in the lungs. |
| Solubility |
Alkaline drug with two ionisable groups, phenolic hydroxyl group (pKa = 9.3) and |
| Distribution |
VOD is 1.3L/kg; minimally protein bound |
| Metabolism |
Metabolised in the liver (extensive first-pass metabolism); The main metablite is the biologically inective salbutamol-o-sulphate. It can also be de-aminated by oxidative |
| Elimination |
The elimination half-life of salbutamol is 118 minutes (range 69 to 162 minutes); unchanged drug and metabolite are 72% excreted in the urine within the first 24 hours. |
| Time course of action |
Airway resistance decreases within 5 to 15 minutes after inhalation of salbutamol; maximum effect is seen at 60 to 90 minutes, and some level of activity persists for 3 to 6 hours. |
| Target receptor |
Beta-2 receptor; less selective for beta-1 |
| Mechanism of action |
Beta-adrenoceptors are coupled to Gs-proteins, which activate adenylyl cyclase to form cAMP from ATP. This results in increased protein kinase A activity, which results in the inhibition of phosphoinositol hydrolysis, which in turn results in decreased intracellular Ca2+ levels. With less intracellular calcium, the bronchial smooth muscle tone decreases. |
| Clinical effects |
Bronchodilation, tachycardia, hypokalemia, hyperlactataemia, insomina, muscle cramps |
| Literature reference |
Sandoz product monograph |
| CICM details of understanding | Level 2 |
| Mentioned around Deranged Physiology |
Pharmacology of drugs used to treat asthma. Also, structure in Structure of synthetic catecholamines, and mechanism in Sympathomimetics. Also as a cause of lactate. |
| Related SAQs |
Question 10 from the first paper of 2023, as a stand-alone, but also many others obliquely. |