Beta Agonists
This covers the inhaled β-agonists used for bronchodilation. Information on catecholamines and sympathomimetics with activity on β-receptors is covered under adrenergic vasoactives.
Common Features
| Pharmacodynamic Effects | β-agonists |
|---|---|
| Resp | Bronchodilatation, ↓ HPV causing ↑ shunt and potential ↓ PaO2 if O2 is not co-administered. |
| CVS | ↑ HR (β1 with higher doses), ↓ BP (β2 with lower doses) |
| GU | Tocolytic. |
| Metabolic | Hypokalaemia from β2 stimulation of Na+/K+ ATPase, hyperglycaemia. |
| Other | Potentiates non-depolarising muscle relaxants |
Differences
| Property | Salbutamol | Salmeterol |
|---|---|---|
| Class | Synthetic sympathomimetic amine | Synthetic sympathomimetic amine |
| Uses | Acute asthma/bronchospasm, hyperkalaemia | Nocturnal and exercise-induced asthma |
| Presentation | MDI (100µg), solution at 2.5-5mg.ml-1 for nebulisation | MDI |
| Route of Administration | Inhaled, IV | Inhaled |
| Dosing | 1-2 puffs via MDI, 5mg nebulised. 0.5mcg.kg-1.min-1 as IV infusion. | |
| Onset | Rapid | Slow |
| Distribution | Low protein binding | |
| Metabolism | High first pass hepatic to inactive metabolites, t1/2β 6 hours. | Extensive hepatic via CYP3A4 |
| Elimination | Urinary elimination of active (30%) drug and inactive metabolites | Renal of metabolites |
References
- Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
- Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.