DRUGS ACTING CNS-General anesthetics

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DRUGS ACTING ON CENTRAL NERVOUS SYSTEM

GENERAL ANESTHETICS

The term Anesthesia means loss of sensation. General anesthetic is a class of CNS depressant drugs which produce total loss of sense of pain with controlled and reversible loss of consciousness.
General anesthetics bring about descending depression of the CNS starting with cerebral cortex, basal ganglia, cerebellum and finally the spinalcord. General anesthetics are mainly used in surgical operations for relaxation of muscles of patients. These agents are non specific with receptors and used at high concentration to access to all areas of the body.
CLASSIFICATION :
Based on the method of administration, these may divided in to three groups.
1. Inhalation Anesthetics
i) Hydro Carbons – Cyclo propane, Ethylene
ii) Halogenated Hydro carbon – Halothane, Chloroform, Ethyl chloride
iii) Ethers – Di ethyl ether, Vinyl ether, Enflurane, Methoxy flurane, Iso flurane, Desflurane, Sevoflurane.
iv) Alcohols – Trichloro ethanol
v) Miscellaneous – Nitrous oxide

2. Intravenous anesthetics
i) Ultra short acting Barbiturates – Metho hexitol sodium, Thio amylol sodium, Thio pentol sodium
ii) Benzo diazepines – diazepam, Midazolam
iii) Miscellaneous – Ketamine, Etomidate, Propofol, Alphaxalone

3. Basal Anesthetics
Fentanyl citrate, Tribromo ethanol, paraldehyde

Inhalation Anesthetics

These are volatile liquid or Gases and they are administered through inhalation process.

1. Di ethyl ether or Anesthetic ether

C2H5 – O - C2H5
Synthesis

C2H5 OH + H2SO4 C2H5 HSO4 C2H5 – O - C2H5

C2H5 ONa + C2H5Br C2H5 – O - C2H5

2. Vinyl Ether
CH2 CH– O - CH CH2

Synthesis
Cl CH2 CH2OH Cl ----- CH2 CH2O CH2 CH2 Cl ---------CH2 -- CH– O - CH --CH2

3.Halothane

4. Methoxy flurane

5. Enflurane( 2-Chloro- 1,1,2 –tri fluoro ethyl methyl ether )

CHF2 – O - CF2CHFCl

6. Sevo flurane

FCH2 – O – CH(CF3)2

7. Nitrous oxide (Laughing Gas) N2O

8. Cyclo propane
CH2
CH2 CH2

9. Tri chloro ethylene

CCl2 CHCl

II. Intravenous anesthetics

These are administered through intravenously and cause unconsciousness. These are mainly sodium salt of barbiturates. They are ultra short acting barbiturates which duration of action is less than 30 minutes.

1. Metho hexitol sodium

2.Thiamylal sodium

3. Thio pental sodium

Ketamine Hydro chloride


Mechanism of action

General anesthetics are non specific in action because they do not act on specific receptor site.
When General anesthetics are dissolved in lipid layer and membranes , they cause dis ordering or increased fluidity of the membrane. This may inactive the protein essential functioning of CNS or ion channel, which would remain open resulting in chloride ion influx leading to synoptic hyper polarization, which inhibits neuronal function.
Volatile General anesthetics are rapidly evaporates and cooled immediately and skin gets anesthetized.
Barbiturates mainly depress the CNS and decrease specific functional activities in brain. They increase the GABA ergic inhibitory response by influencing conductance at the chloride channel. They are also uncoupling of the oxidative phosphorylation, prevent the electron transport system and inhibit the cerebral carbonic anhydrase activity.