This document discusses general anesthetics. It begins by defining general anesthetics as drugs that produce unconsciousness and loss of sensation. It then describes the four stages of general anesthesia produced by inhalation anesthetics: stage I involves analgesia; stage II involves delirium and loss of consciousness; stage III allows for surgery with unconsciousness and reflex paralysis; stage IV involves respiratory and circulatory failure. The document goes on to classify general anesthetics as volatile/inhalation or non-volatile/intravenous, and discusses the characteristics, mechanisms of action, and specific volatile and non-volatile anesthetic agents in more detail over several paragraphs.

1. Presented by
Mrs. Karthika. S, M.Pharm, PhD,
Assistant Professor,
Dept. of Pharmaceutical chemistry,
SVCP.

2. GENERAL ANESTHETICS
 General anesthetics are group of drugs that produces loss of
consciousness, and therefore, loss of all sensations.
 The absolute loss of sensation is termed as Anesthesia.
 General anesthetics bring about reducing the depression of the
central nervous system (CNS), starting with the cerebral
cortex, the basal ganglia, the cerebellum, and finally the spinal
cord.
 These drugs are used in surgical operations to induce
unconsciousness and, therefore, abolish the sensation of pain.

3. STAGES OF GENERAL
ANESTHESIA
 When an inhalation anesthetic is administered to a
patient some of the following well defined stages
are produced by increasing the blood concentration.
They are;
Stage I (Stage of analgesia):
 The patient is conscious and experience sensations
of warmth, remoteness, drifting, falling, and
giddiness.
 There is a marked reduction in the perception of
painful stimuli. This stage is often used in minor
surgery.

4. Stage II (Stage of delirium):
 This stage begins with the loss of consciousness.
 Depression of higher centers produces variety of effects
including excitement, involuntary activity, and increased
skeletal muscle tone, and the respiration is typically irregular.
Stage III (Stage of surgical anesthesia):
 This is the stage of unconsciousness and paralysis of reflexes,
respiration is regular and blood pressure is maintained.
 All surgical procedures are carried out in this stage.
Stage IV (Stage of medullary paralysis):
 Respiratory and circulatory failures take place as a result of
the depression of the vital centers of the medulla, and brain
stem occurs

5. CLASSIFICATION OF GENERAL
ANESTHETICS
The general anesthetics are classified according to their
nature (volatile or non-volatile) at room temperature.
They are:
A. Volatile/Inhalation anesthetics.
They are administered by inhalation and are further
subdivided as;
1. Gases:
Cyclopropane: Ethyl chloride, Nitrous oxide
2. Liquids:
Diethyl ether, Halothane, Chloroform,
Trichloroethylene

6. B. Non-Volatile or Intravenous anesthetics.
They are non-volatile at room temperature and are
administered by intravenous route.
They are;
1. Barbiturates:
Thiopental sodium, Methohexital sodium.
2. Non-barbiturates:
Propanidid, Propofol.

7. CHARACTERISTICS OF GENERAL
ANESTHETICS.
An ideal general anesthetic should possess the following
characteristic features:
a) It should be inert
b) It should be potent and non-inflammable.
c) It should be non-irritating to mucous membrane
d) It should produce rapid and smooth anesthesia
e) It should produce analgesia and muscle relaxation in
addition to anesthesia
f) It should not produce severe hypotension
g) It should not produce nausea and vomiting
h) It should be compatible with adjuvant drugs used in
anesthesia
i) It should be economical
j) It should be stable to heat, light and alkalies

8. MECHANISM OF ACTION.
 General anesthetics target the ligand gated ion channels and
produce the anesthetic action.
 The GABA receptor gated chloride channels are the most
important sites and opens to perform the inhibitory action.
 N2O and Ketamine do not affect the GABA or Glycine gated
Cl– channel,
 But they selectively inhibit the excitatory NMDA-type of
glutamate receptor, which belongs to calcium-gated channels
in the neurons and leads to neuronal hyper-polarization.

9. Structure:
Synthesis:
VOLATILE ANESTHETICS
HALOTHANE
2-bromo,2-chloro,1,1,1-trifluoroethane

10. Properties:
 It is a clear, colourless, heavy, non-flammable liquid,
 Slightly soluble in water, miscible with ethanol, and with
trichloroethylene.
Uses:
 It may produce any depth of anesthesia without causing
hypoxia.
 Being a non-irritant, its inherent hypotensive effect retards
capillary bleeding and renders a comparatively bloodless
field.
 It is a potent, relatively safe general inhalation anesthetic
used in conjunction with N2O.
 For skeletal muscle relaxation, it is used with succinyl
choline or tubocurarine.
Storage:
• It should be stored in well-closed airtight containers,
protected from light, at a temperature not exceeding 25°C in
a nonreactive metal container

11.  It is a clear, colourless liquid, non-inflammable and non-
explosive in air or oxygen in anesthetic concentrations.
 It is the most potent of the inhalational agents.
 It is employed to cause light anesthesia with deep analgesic
and muscle relaxation feature, which makes it convenient for
surgical operations.
METHOXYFLURANE
Structure:
Properties & Uses:
2,2-dichloro,1,1-difluoro methoxyethane

12.  It is a clear, colourless, volatile liquid with pleasant
hydrocarbon-like odour.
 Soluble in water, miscible with organic solvents, chemically
it is extremely stable.
 The induction of an emergence from anesthesia and
adjustment of anesthetic depth during maintenance is smooth
and moderately rapid.
 It is a noninflammable halogenated ether anesthetic and
provides rapid induction with no excitement.
ENFLURANE
Structure:
Properties & Uses:
2-chloro,1,1,2-trifluoroethyl,1-difluoromethylether

13.  Low boiling liquid with a slight odour;
 Miscible with most organic solvents including fats or oils;
practically insoluble in water.
 It is a nonflammable, non-irritating agent.
 The physical properties of this compound result in a more
rapid induction and termination of anesthetic when observed
with the currently used agents.
SEVOFLURANE
Structure:
Properties & Uses:
1,1,1,3,3,3-hexafluoro 1-(fluoro methoxy)Propane

14.  It is a clear, colourless, heavy liquid, insoluble in water,
miscible with ethanol, and trichloroethylene.
 It resembles isomer enflurane in its properties. It is not
flammable in air or oxygen.
 The depth of anesthesia can be rapidly adjusted with it. It is
used for induction and maintenance of general anesthesia.
ISOFLURANE
Structure:
Properties & Uses:
Storage:
It should be stored in well-closed airtight containers and protected
from light
1-chloro,2,2,2-trifluoroethyl difluoromethyl ether

15.  Low boiling liquid with a slight odour;
 Miscible with most organic solvents including fats or oils;
practically insoluble in water.
 It is a non-flammable, non-irritating agent.
 The physical properties of this compound result in a more
rapid induction and termination of anesthetic when observed
with the currently used agents
DESFLURANE
Structure:
Properties & Uses:
1,2,2,2-tetrafluororthyl difluoromethyl ether

16. DESFLURANE
ISOFLURANE
SEVOFLURANE
ENFLURANE
METHOXYFLURANE
HALOTHANE

17. NON-VOLATILE ANESTHETICS
ULTRA SHORT ACTING BARBITUTRATES
METHOHEXITAL SODIUM
Structure:

18. Synthesis:

19. Uses:
 It is more potent and has shorter duration of action.
 It is used for the induction of anesthesia through the
intravenous administration.
 It produces more rapid recovery from unconsciousness
than thiopental.
 Its onset of action is quite speedy comparable to
thiopental sodium while its recovery is more rapid. For
these reasons, this intravenous anesthetic is specifically
useful for short surgical operations, such as oral surgery,
gynaecological investigation, genitourinary procedures,
and electroconvulsive therapy.
Properties:
 White to off-white hygroscopic powder,
 Odourless,
 The solution is alkaline to litmus,
 Soluble in water.

20. THIAMYLAL SODIUM
Structure:
Properties & Uses:
 Thiomylal is a highly hydrophobic thiobarbiturate
having its structural features very much related to
thiopental.
 Its biological activities are almost identical to
thiopental.
 It is used as intravenous anesthetic.

21. THIOPENTAL SODIUM
Structure:
Properties :
 A yellowish-white powder, hygroscopic, freely
 Soluble in water, partly soluble in ethanol.

22. Uses:
 These are usually administered intravenously for the
production of complete anesthesia of a short
duration.
 It belongs to the category of ultra short-acting
barbiturates.
 Onset is rapid (about 30 sec) and duration is brief
(10–30 min).
 By rectal route it is administered as a solution,
suspension, or suppositories as basal anesthetic.
 It is also used as a sedative, hypnotic, and
anticonvulsant.
Storage:
It should be stored in well-closed airtight containers and
protected from light.
Dosage form:
Thiopental injection B.P.

23. DISSOCIATIVE ANESTHETICS
KETAMINE HYDROCHLORIDE
Structure:
Properties & Uses:
 It is a white or almost white crystalline powder,
freely soluble in water, methanol, and ethanol.
 Its another name is ‘dissociative anesthetic’ because
it produces unpleasant hallucinations and strong
feelings of dissociation from the environment.
 It is a rapidly acting non-barbiturate general
anesthetic that produces anesthesia and is
characterized by profound analgesia.
Dosage form:
Ketamine HCl injection I.P., B.P.