Analeptics Drugs | Definition, Classification, Side effects, Example

Analeptics Mechanism of action

Strychnine - blockade of inhibition - post-synaptic - blocks postsynaptic NT, glycine

Picrotoxin - blockade of inhibition - pre-synaptic - blocks presynaptic NT, GABA

Doxapram - facilitating excitation - direct - stimulate respiratory center

Nikethamide - facilitating excitation - reflex - stimulate via chemoreceptors

(diagram 8)

Strychnine

Strychnine is an alkaloid and has been used for centuries as poison

It is a powerful convulsant and cause violent extensor spasms

It works by blocking receptor for glycine which is the main inhibitory transmitter acting on motor neurons)

The sequence of strychnine effects are

§  tightness of neck and jaw muscles

§  hyper-reflexia

§  tonic extension

§  tetanic symmetrical convulsions (opisthotonos)

Bicuculine

BIcuculine is a plant alkaloids which resemble strychnine but it acts by blocking receptors for GABA instead of glycine (confines to GABAa-antagonist). Its main effect is on brain rather than spinal cord

Picrotoxin

Picrotoxin is obtained from fishberry which also block the action of GABA on chloride channel (block the ion channel). It can cause convulsion.

Doxapram

Doxapram has bigger margin of safety between respiratory stimulation and convulsion

It is occasionally used as IV infusion in patients with acute respiratory failure.