| Class | Anticholinergic |
|---|---|
| Chemistry |
Tropane alkaloid |
| Routes of administration |
Oral or IV |
| Absorption |
Minimal oral bioavailability, approximately 1%, mostly because of poor lipid solubility |
| Solubility |
pKa 8.1, highly water-soluble |
| Distribution |
VOD = 1.7L/kg, minimally protein bound (4.4%) |
| Metabolism |
50% metabolised by the liver, via hydrolysis of the ester bond, into inactive metabolites |
| Elimination |
Clearance is 50% renal, as unchanged drug, but of an administered oral dose more than 90% will be eliminated unchanged in the faeces |
| Time course of action |
Half-life after IV administration is about 1-5 hours |
| Target receptor |
Muscarinic receptors (M1-M5), which are mainly Gq-coupled receptors (hyoscine binds to all of them with equal affinity) |
| Mechanism of action |
By compettively blocking the effets of acetylcholine on Gq-coupled muscrinic receptors, hyoscine decreases the intracellular concentration of ioniased calcium and cAMP. This results in numerous downstream clinical effects |
| Clinical effects |
- Decreased airway secretions |
| Literature reference |
Corsetti et al, 2021 |
| CICM details of understanding | Not specifically listed in the CICM syllabus |
| Mentioned around Deranged Physiology | |
| Related SAQs |