The final goal of cholinergic agonists is to increase cholinergic transmission. This can be accomplished in many ways. First they can act as agonist directly on the cholinergic receptors and can produce acetylcholine like actions. Second they can also indirectly increase acetylcholine levels at synaptic cleft by inhibiting its metabolism.
Therefore, we can have two main categories of drugs in cholinergic agonists
- Directly acting
- Indirectly acting
These are the drugs which bind to the cholinergic receptors an mimic the action of acetylcholine hence they are also called as directly acting parasympathomimetics.
Drugs in this category include
These drugs doesn't have any affinity towards cholinergic receptors but act on acetylcholinesterase enzyme and inhibit metabolism of acetylcholine increasing it levels at synaptic cleft. Hence these drugs can also be called as acetylcholinesterase inhibitors.
Based on the duration of the action, these drugs can be classified into three categories
- Short acting
- Medium acting
Still few drugs act presynaptically to increase cholinergic transmission but they have no significant clinical use and just considered as experimental tools. These include
- Storage inhibitor
- Uptake inhibitor