1. The document discusses various gases used as inhalants including oxygen, carbon dioxide, and nitrous oxide. It describes their chemical and physical properties, methods of preparation, storage requirements, assays for testing purity, and pharmaceutical uses. 2. Key pharmaceutical uses include oxygen as an inhalant to support respiration, carbon dioxide as a respiratory stimulant and to promote absorption, and nitrous oxide as a general anesthetic along with oxygen, especially in dental procedures. 3. Proper storage of these gases requires metal cylinders painted in identifying colors and labeled with the gas name or formula for safety.

1. INHALANTS
Presented By
G.Revathi., M.Pharm.,
Assistant Professor
Dept. Of Pharmaceutical Chemistry, SVCP

2. INHALANTS
• Drugs used as inhalants may be inhaled or administered as solid or nebulized
particles from solution or in the form of vapours.
• Sprayed as fine droplets which deposite over the mucous membrane producing
local effects
• Eg; salbutamol  used in bronchial asthma
• Also administered as gases i.e) volatile general anaesthetics

3. Mechanism of Inhalation
Drugs for inhalation
Rapidly absorbed
Produce rapid local & systemic effects
Arrive directly to heart through veins
Produce cardio toxicity
Further, local irritation
Result in increase in respiratory tract secrestions

4. 1.OXYGEN
Molecular formula: O2
Molecular weight: 32 gm
Standard: contains not less than 99% of O2
• Remaining portion consists of
Argon
Nitrogen and
Hydrogen
• It occurs free in air up to 21%.

5. Preparation:
By three methods
1. Fractional distillation of liquified air yields oxygen at – 1830C (90K).
2. Electrolysis of slightly alkaline water (pure water is bad conductor of
electricity).
2H2O → 2H2 + O2
3. O2 is prepared by heating some oxygen containing salts, metallic oxides.
2KClO3  2KCl + 3O2

6. Properties:
1. Colourless, odourless and tasteless gas.
2. It supports combustion but is not inflammable.
3. When mixed with equal volumes of nitric oxide, red fumes of
nitrogen dioxide is formed.
2NO + O2 → 2NO2
4. It is soluble 1 in 32 parts by volume of water.

7. Assay:
Assay is based on its complete absorption by alkaline pyrogallol
solution using specific apparatus for determination of medicinal gases.
Storage:
• Oxygen is usually stored in metal cylinders under compression, should be
painted black. The shoulders of the cylinder should be painted white. The
name of the gas or the symbol “O2” properly stenciled on it. The cylinders
are recommended to be stored in cool room free from other inflammable
materials.

8. Pharmaceutical and Medicinal Uses:
1. as inhalant for supporting respiration during anaesthesia or post
operative conditions.
2. inhalant for poisoning due to other gases.
3. Diluent for volatile and gaseous anaesthetics.

9. 2. CARBON DIOXIDE
• Molecular formula: CO2
• Molecular weight: 44gm
• Synonym: Carbonic acid gas, carbonic anhydride.
• Occurrence: present in atmosphere to the extent of about 0.03%
Is a product of;
Combustion
Respiration and
fermentation reaction

10. • Preparation
• Obtained from calcium carbonate (lime stone) either by direct strong
heating or by treatment with dilute mineral acids
• Commercial Method
• Large quantities of the gas are obtained as by – products of fermentation
industries  CO2 also formed from products of combustion of coke from
fermentation and during manufacture of lime by burning limestone in lime
kilns
CaCO3  CaO + CO2 (g)
CaCO3 + 2HCl  CaCl2 + H2O + CO2 (g)

11. • Physical Properties:
1. Colourless, odourless gas.
2. Does not support combustion.
3. It is heavier than air, soluble in water.
4. The solution is slightly acidic due to the formation of carbonic acid.
CO2 + H2O → H2CO3
5. It can be liquified under compression.
6. It can be solidified called as dry ice.
7. It extinguishes fire.

12. • Chemical properties:
1.When Co2 passed into the solution of calcium hydroxide (lime water) it
turns milky due to formation of calcium carbonate
Ca(OH)2 + CO2  CaCO3 + H2O
2.On passing the CO2 again  becomes clear due to the formation of calcium
hydrogen carbonate due to formation of calcium bicarbonate
CaCO3 + H2O + CO2  Ca(HCO3)2
3.If it is heated  CO2 liberated again gets reprecipitation of calcium
carbonate turns milky appearance
Ca(HCO3)2  CaCO3 + H2O + CO2

13. 4. When passed to reduced coke  CO2 reduced to carbon monoxide
CO2 + C  2CO
• Official test for Identity:
1.When gas passed through Barium hydroxide  white precipitate (barium
carbonate) is formed- dissolves with effervescence with addition of acetic acid
2.CO2 extinguishes as burning splinter
Test for Purity:
Acidity
Carbonmonoxide
Hydrogen sulphides

14. Storage:
It is stored in metal cylinders painted grey. The name of the gas or
the formula CO2 should be stenciled on the shoulder of the cylinder.
Assay:
Assay is based on its absorption by 50% KOH solution. The un
absorbed gas is measured.
Standard:
contains not less than 99% of CO2

15. Pharmaceutical and Uses:
1. Essential for regulating acid base balance in the body.
2. Respiratory stimulant(5%).
3. To give relief in hick-up, soda water produces carminative – promotes absorption.
4. For rapid excretion of inhalation anaesthetics.
5. Liquid orals treated with CO2 gas are used to mask the taste.
6. It can also be used as an inert gas in the containers containing easily oxidization
substances.

16. 3. NITROUS OXIDE
Molecular Formula: N2O
Synonym: Laughing gas
Standard: contains Not less than 95% of nitrous acid
Physical Properties:
1. Colourless, odourless and tasteless gas.
2. Soluble in water, alcohol, chloroform ether and in oils.

17. 3. It supports combustion.
4. It is not absorbed by alkaline pyrogallol solution (differ from oxygen).
5. It is heavier than air and can be compressed to a liquid.
Chemical properties:
On heating, it decomposes into nitrogen & oxygen
2N2O  2N2 + O2
Nitrous oxide is reduced to nitrogen when it passed over hot copper
Cu + N2O  CuO + N2

18. Preparation:
1. It is obtained by heating ammonium nitrate to about
1700C.
NH4 NO3  N2O + 2H2O
2. It can also be prepared by heating a mixture of sodium
nitrate and ammonium sulphate.
2NaNO3 + (NH4) SO4  Na2SO4 + 2N2O + 4H2O

19. Official test for Identity:
1. When gas introduced into flame  bursts glowing wood splinter
2. Not absorbed by alkaline pyrogallol solution
Test for purity
• CO2
• CO
• Halogens
• Oxidizing substances
• NO2

20. Assay:
Assayed by determining un-condensible gas in
a particular apparatus (gaseometric set up) using
liquid nitrogen for condensation of N2O-
uncondensible part should not exceed 5% V/V.
Storage:
1. It is stored in metal cylinders painted blue and
temperature not exceeding 370C
2. The name of the gas or the formula N2O should
be stenciled on the shoulder of the cylinder.

21. Medicinal and Pharmaceutical Uses:
• Used as general anaesthetic along with oxygen (20 to 50%) in dental practice.
• Mixture with oxygen 1:1 ratio used for pain relief in child birth and pain in
myocardial infarction
• Strong analgesic with mild muscle relaxation
• When administered it without oxygen or nitrogen  produce deep anaesthesia
in upto 1 minute but hypoxia occurs.
• Also used for calming the excited mental patients.
• Also used to measure the cerebral and coronary blood flow.