18. PHARMACEUTICAL AIDS

Introduction to Pharmaceutical Aids

Pharmaceutical Aids (PAs) are substances that have minimal or no therapeutic activity but are essential in the manufacturing of various pharmaceutical formulations such as ointments, creams, tablets, injections, and suspensions.

Their purpose includes preservation, stabilization, acidification, alkalinization, adsorption, absorption, filtration, and tonicity adjustment. Pharmaceutical aids are also known as Pharmaceutical Necessities (PNs).

Functions and Classification of Pharmaceutical Aids

Pharmaceutical aids are used in almost every dosage form for specific functions:

  • Acidifiers and Alkalisers: Used to adjust the pH of formulations.
  • Buffers: Maintain the pH of a formulation. Examples include hydrochloric acid buffer, borate buffer, phosphate buffer, and ammonia buffer.
  • Absorbents: Materials that take up liquids or gases uniformly (e.g., activated charcoal).
  • Adsorbents: Substances that accumulate molecules on their surface.
  • Antioxidants: Prevent deterioration of the formulation (e.g., sodium bisulphite).
  • Preservatives: Inhibit microbial growth and stabilize formulations.
  • Desiccants: Absorb moisture to prevent spoilage.
  • Excipients: Provide bulk and improve formulation properties (e.g., lactose, binders, lubricants).
  • Suspending Agents: Prevent particle settling and caking in liquid formulations.
  • Colorants: Provide aesthetic appeal and easy identification.
  • Tonicity Adjusters: Maintain isotonicity in eye drops and injectables.
  • Solvents and Vehicles: Used as carriers for drugs (most commonly water).
  • Flavoring and Sweetening Agents: Improve palatability of oral preparations.
  • Ointment and Suppository Bases: Help in even distribution of drugs in semisolid dosage forms.
  • Binders, Lubricants, and Disintegrants: Used in tablet formulation for cohesion and controlled disintegration.

1. Sodium Bisulphite (NaHSO₃)

Synonym: Sodium Hydrogen Sulphite
Molecular Formula: NaHSO₃

  • Properties: White granular powder with a sulfur dioxide odor; soluble in water and slightly soluble in alcohol.
  • Preparation: Formed by passing sulfur dioxide through a solution of sodium carbonate.
  • Assay: Redox titration using iodine as the oxidizing agent and starch as the indicator. The endpoint changes from blue to colorless.
  • Uses: Acts as an antioxidant and stabilizer in injections such as epinephrine and vitamin C. Also used as an antiseptic, bleaching agent, and in removing permanganate stains.

2. Sodium Metabisulphite (Na₂S₂O₅)

Synonyms: Sodium Pyrosulphite, Disodium Pyrosulphate
Molecular Formula: Na₂S₂O₅

  • Properties: Light yellow crystalline powder with a faint sulfur odor.
  • Preparation: Produced by passing sulfur dioxide over hot concentrated sodium hydroxide to form sodium bisulphite, which loses water to form sodium metabisulphite.
  • Assay: Redox titration using iodine and starch as indicator.
  • Uses: Used as an antioxidant and preservative in acidic solutions, syrups, and injectable formulations (e.g., adrenaline and morphine injections).

3. Zinc Stearate [Zn(C₁₇H₃₅COO)₂]

Synonym: Zinc Soap
Limits: 13–15.5% zinc content

  • Properties: White, fine amorphous powder with a slight odor; insoluble in water.
  • Preparation: Formed by reacting zinc sulfate with sodium stearate to produce zinc stearate precipitate, which is then washed and dried.
  • Assay: Complexometric titration with disodium EDTA using ammonia-ammonium chloride buffer and eriochrome black T as indicator (color change: wine red → blue).
  • Uses: Acts as lubricant, astringent, and antimicrobial agent. Used in tablet manufacturing, dusting powders, and water-repellent formulations.

4. Magnesium Stearate [Mg(C₁₈H₃₅O₂)₂]

Synonyms: Octadecanoic Acid Magnesium Salt
Molecular Formula: Mg(C₁₈H₃₅O₂)₂

  • Properties: White amorphous powder; insoluble in water.
  • Preparation: Obtained by reacting sodium stearate with magnesium sulfate.
  • Assay: Complexometric titration with disodium EDTA using ammonia buffer and eriochrome black T indicator.
  • Uses: Used as anti-adherent and lubricant in tablet formulations and dry powder coatings. Also found in baby products and mint tablets.

5. Aluminium Sulphate [Al₂(SO₄)₃]

Molecular Formula: Al₂(SO₄)₃
Limits: 51–59% Al₂(SO₄)₃ content

  • Properties: White, odorless, crystalline powder; soluble in water but insoluble in alcohol.
  • Preparation: Produced by reacting aluminum hydroxide with sulfuric acid.
  • Assay: Complexometric titration with disodium EDTA using eriochrome black T indicator.
  • Uses: Used in dental preparations, antiperspirants, creams, and deodorants. Also serves as a mild astringent and clarifying agent.

Detailed Notes:

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