4. Drug acting on autonomic ganglia

Ganglionic Blockers

Ganglionic blocking agents can be classified on the basis of their chemical structure or mechanism of action into three groups

Depolarizing drugs, such as nicotine
Competitive drugs, such as trimethaphan and tetraethylammonium
Noncompetitive agents, such as hexamethonium (C6) and mecamylamine, a secondary amine.

Depolarizing drugs, such as nicotine, which produce initial stimulation and varying degrees of subsequent block through a mechanism analogous to that of succinylcholine (see later).
At higher doses, these agents can stimulate and block other cholinergic receptors, such as those at the neuromuscular junction and in the CNS.

Competitive drugs, such as trimethaphan and tetraethylammonium, which interfere with the binding of ACh to the nicotinic receptor.

Noncompetitive agents, such as hexamethonium (C6) and mecamylamine, a secondary amine.
Hexamethonium interferes with ganglionic transmission by blocking ion channels that have been opened by ACh, whereas mecamylamine seems to share properties associated with both hexamethonium and the competitive blocking agents.

Pharmacologic effects

All the ganglionic blocking drugs, regardless of their structure or their mechanism of action, have the same basic pharmacology,

An ideal ganglionic blocking agent would be a compound that interferes only with ganglionic transmission, blocks without previous excitation, and does not influence the release of transmitter. 

General therapeutic uses

Because of their multiple side effects, ganglionic blockers are rarely used. For most patients, these effects are intolerable except for acute use in recumbent patients. Trimethaphan was used in the past as an adjunct during anesthesia to produce controlled hypotension and in hypertensive emergencies.

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