ANTIOXIDANTS: In Pharmaceutical Formulation

Introduction:

• Chemically they are reducing agents.
• They oxidize themselves and prevent oxidation of API.
• A substance that inhibits oxidation is called antioxidants.
• The effectiveness of antioxidant can depend on the concentration used and pH of solution.
• Examples: 
• Ascorbic acid, 
• butylated hydroxy anisole (BHA), 
• butylated hydroxyl toluene (BHT)
• Oxidation is a chemical reaction involving the loss of electrons or an increase in oxidation state.
• 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.
• Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions.
• The following are some of the qualities of an ideal anti-oxidant:
• It should be readily soluble or dispersible in the medium.
• It should be effective in low concentration.
• It should be non-toxic.
• It should be non-irritant.
• It should be compatible with other ingredients of emulsion.
• It should be colorless, odorless and tasteless.

Classification of antioxidants:

• On the basis of the source antioxidants are 2 types. They are,
• Natural antioxidants: 
• Tocopherol (Vitamin E), 
• Sesamol, 
• Guaiac resin, 
• Mehionine.
• Synthetic antioxidant: 
• BHA, 
• BHT, 
• Tertiary butyl hydroquinone.
• On the basis of solubility antioxidants are 2 types. They are,
• Water soluble antioxidant:
• Citric Acid, 
• Tartaric Acid, 
• Phosphoric Acid, 
• Ascorbic Acid, 
• Sodium Metabisulfite and 
• thiol derivatives.
• Oil soluble antioxidant: 
• BHA
• BHT

Brief Detail of Some Antioxidant:

• Butylated Hydroxy Anisole (BHA)
• Description: White or slightly yellow. Waxy solid having a faint characteristic odor.
• Solubility: Insoluble in water; 1 g in 4 mL alcohol, 2 mL chloroform or 1.2 mL ether.
• Uses: An antioxidant in cosmetics and pharmaceuticals containing fat and oils.
• Butylated Hydroxyl Toluene (BHT)
• Description: White, tasteless crystal with a mild odor; stable in light or air; melts at 70'C.
• Thermolabile substance and has low toxicity.
• Solubility: Insoluble in water; 1 g in 4 mL alcohol, 1.1 mL chloroform or 1.1 mL ether.
• Uses: An antioxidant employed to retard oxidative degradation of oils and fats in various cosmetics and pharmaceuticals.
• Tocopherol:
• Natural antioxidant.
• Present in vegetable oil in concentration range of 0.1% to 0.01%
• Potassium Metabisulfite
• Description: White crystals or crystalline powder with an odor of SO₂. Oxidizes in air to the sulfate. May ignite on powdering in a mortar if too much heat develops.
• Solubility-Freely soluble in water; insoluble in "alcohol.
• Uses: Antioxidant.
• Sodium Bisulfite:
• Description: White or yellowish white crystals or granular powder with the odor of sulfur dioxide; unstable in air.
• Solubility: 1g in 4 mL water; slightly soluble in alcohol.
• Uses-An antioxidant und stabilizing agent.  Help to solubilize kidney stones.
• Sodium Metabisulfite:
• Description: White crystals or white to yellowish crystalline powder with an odor of sulfur dioxide; on exposure to air and moisture, it is slowly oxidized to sulfate.
• Solubility: 1 gm 2 mL water; "lightly soluble in alcohol; freely .soluble in glycerin.
• Uses: A reducing agent. It is used in easily oxidized pharmaceuticals. Such as epinephrine hydrochloride and phenylephrine hydrochloride injections, to retard oxidation.