Antioxidants are compounds that can act as reducing agents and prevent oxidation reactions. They are used in pharmaceuticals to maintain easily oxidized substances in their reduced form. Oxidation causes damage to cells through free radicals but living organisms contain antioxidant systems like glutathione and vitamins C and E to prevent oxidative damage. Antioxidants prevent reactive oxygen species from being formed or remove them before they can harm cells. Hypophosphorous acid, sulfur dioxide, and sodium thiosulfate are official antioxidants used pharmaceutically to prevent oxidation.

2. Definition:
Antioxidants may be described as compounds which have
the capability of functioning chemically as reducing
agents.
Use:
They are used in pharmaceutical preparations containing
easily oxidized substances (e.g. iodide or ferrous ions) in
order to maintain these substances in their reduced form.

3. What is oxidation?
• Oxidation is a chemical reaction that transfers electrons or
hydrogen from a substance to an oxidizing agent.
• Oxidation reactions can produce free radicals. In turn,
these radicals can start chain reactions.
• When the chain reaction occurs in a cell, it can cause
damage or death to the cell.

4. Oxidants and antioxidants in living body
• Although vast majority of complex life on Earth requires
oxygen for its existence, oxygen is a highly reactive molecule
that damages living organisms by producing reactive oxygen
species.
• The reactive oxygen species produced in cells include
hydrogen peroxide (H2O2),
hypochlorous acid (HClO), and
free radicals such as the hydroxyl radical (·OH) and the
superoxide anion (O2
−).

5. Oxidants and antioxidants in living body (cont…)
• These oxidants can damage cells by starting chemical chain
reactions such as lipid peroxidation, or by oxidizing DNA or
proteins.
Damage to DNA can cause mutations and possibly cancer, if not
reversed by DNA repair mechanisms, while damage to proteins
causes enzyme inhibition, denaturation and protein degradation.
• As oxidative stress appears to be an important part of many
human diseases, the use of antioxidants in pharmacology is
intensively studied, particularly as treatments for stroke and
neurodegenerative diseases.

6. Oxidants and antioxidants in living body (cont…)
• Living body contains a complex network of antioxidant
metabolites and enzymes that work together to prevent
oxidative damage to cellular components.
These includes glutathione, vitamin C, and vitamin E as well
as enzymes such as catalase, superoxide dismutase and
various peroxidases.

8. Generation of free radicals

17. Mechanism of action of antioxidants
• In general, antioxidant systems either prevent these reactive species
from being formed, or remove them before they can damage vital
components of the cell.
• So, the mechanism of antioxidant action may be seen in two ways,
both achieving the same net result:
a) either the antioxidant is oxidized in place of the active
constituent;
or
b) if the active component is oxidized, the antioxidant reduces
it back to its normal oxidation state
*** However, since reactive oxygen species do have useful functions in
cells, such as redox signaling, the function of antioxidant systems is
not to remove oxidants entirely, but instead to keep them at an
optimum level.

18. Official antioxidants
Hypophosphorous Acid (HPH2O2):
- It is a very powerful reducing agent
- It can easily reduce many compounds to form phosphorous acid
- Its mixture with any oxidizing agent in concentrated form can
produce an incompatibility and explosion. So, its dilute solution
(0.5-1%) is used.
Use:
1) Used to prevent the formation of free iodine in diluted
Hydrochloric Acid and Hydroiodic Acid syrup.
2) Also used in Ferrous Iodide Syrup to prevent the formation of both
ferric ions and molecular iodine.
3) Salts of hypophosphorous acid also used as preservatives in
foods and many preparations.

19. Official antioxidants (cont….)
Sulfur Dioxide (SO2):
- It protects many susceptible compounds from oxidation by reducing
the oxidized form back again or probably by reacting with oxygen
before the susceptible compounds do.
- Its usual concentration is about 0.1% and seldom exceeds 1.0%
Use:
1)Because of the gaseous nature of the compound, sulfur Dioxide is
usually used in injectable preparations enclosed in single dose
ampules or multiple-dose vials
2) Also extensively used in industry for such processes as bleaching,
fumigating grains, and arresting fermentation
3) Used to fumigate houses where it is given off in the burning of sulfur
candles

20. Official antioxidants (cont….)
Sodium thiosulfate(Na2S2O3.5H2O):
- Officially used as an antidote.
- The only salt soluble with sodium thiosulfate are the alkali metals
- As antioxidant its use is limited to solutions containing iodides. The
allowed concentration is 0.5% in Potassium Iodide solution.
Use:
1) It can readily converts colored molecular iodine to colorless sodium
iodide, thus used to remove iodine stains and traces of chlorine
from industrial bleaching operations.
2) Used somewhat less frequently in combination with acids to treat
various dermatological problems