Expansion
Ion channels, G protein coupled, kinase linked and nuclear receptors
Expansion
| Family | Speed | Examples |
|---|---|---|
| Ligand-gated ion channels | Milliseconds | Nicotinic (suxamethonium), GABA-A (benzodiazepines, propofol), NMDA (ketamine) |
| G protein coupled | Seconds | Adrenoceptors, muscarinic, opioid, dopamine, histamine, angiotensin |
| Kinase linked | Minutes to hours | Insulin receptor, growth factor receptors, cytokine receptors (targeted by biologics) |
| Nuclear (intracellular) | Hours | Steroids, thyroid hormone, vitamin D, retinoids |
The speed of onset follows directly from the mechanism, which explains several clinical facts: adrenaline works within seconds in anaphylaxis while hydrocortisone takes hours and cannot be relied on acutely; and propofol acts within one arm-brain circulation time.
Non-receptor mechanisms are worth remembering too, since not every drug acts on a receptor:
- Enzyme inhibition: statins, ACE inhibitors, aspirin, proton pump inhibitors
- Transporter blockade: SSRIs, SGLT2 inhibitors, diuretics
- Ion channel blockade directly: local anaesthetics, calcium channel blockers
- Physicochemical: antacids, osmotic laxatives, chelators