(14) pharmaceutical aids and necessities

Pharmaceutical Aids and Necessities

Importance

• Critical for:

  • Preparation of pharmaceuticals

  • Preservation of pharmaceuticals

  • Storage of pharmaceuticals

Classification of Pharmaceutical Agents

• Acids and Bases

• Buffers

• Antioxidants

• Water

• Glass

• No therapeutic value

• Use in dosage forms

Acids, Bases, and Buffers

Bronsted-Lowry Theory

• Focuses on acid-base reactions in aqueous solutions.

• General expression:

  • HA + B → Aˉ + HB˖ (Acid + Base = Conjugate Base + Conjugate Acid)

Electrolytes

• Strong Electrolytes: Strong acids and bases.

• Weak Electrolytes: Weak acids and bases.

• Relation: The strength of acids and bases affects the strength of their conjugate counterparts.

  • Strong acid = weak conjugate base

  • Strong base = weak conjugate acid

Official Inorganic Acids

Boric Acid (H3BO3)

• Synonyms: Boracic acid, hydrogen borate.

• Occurrence: Found in seawater, certain plants, and fruits.

• Properties: Available in various crystalline forms; serves as an antiseptic.

• Use: Eyewash and buffer in ophthalmic solutions; toxicity makes it unfit for oral use.

Hydrochloric Acid (HCl)

• Synonyms: Chlorhydric acid, spirit of sea salt.

• Use: Acidifying agent in pharmaceuticals.

Diluted Hydrochloric Acid

• Found in gastric juice; aids in pepsinogen to pepsin conversion.

• Use: Management of gastric achlorhydria and hypochlorhydria.

Nitric Acid (HNO3)

• Synonyms: Spirit of nitre.

• Properties: Can produce yellow stains on tissue.

• Uses: Manufacture of sulfuric acid, dyes, explosives; treatment of warts.

Phosphoric Acid (H3PO4)

• Synonyms: Orthophosphoric acid.

• Use: Acidifying agent.

Diluted Phosphoric Acid

• Use: Tonic and stimulant for gastric mucous membranes.

Sulfuric Acid (H2SO4)

• Synonyms: Oil of vitriol.

• Preparation: Oxidation of sulfur dioxide to sulfur trioxide.

• Use: Dehydrating agent in pyroxylin preparations.

Acetic Acid (CH3COOH)

• Synonyms: Glacial acetic acid.

• Use: Irrigation solution with bacteriostatic properties.

Official Inorganic Bases

Strong Ammonia Solution (NH4OH)

• Synonyms: Ammonium hydroxide.

• Precautions: Handle with care, as it’s caustic.

Diluted Ammonia Solution

• Known as ammonia water.

• Uses: Circulatory stimulant, external counter-irritant.

Calcium Hydroxide (Ca(OH)2)

• Synonyms: Slaked lime.

• Uses: Fluid electrolyte, topical astringent.

Potassium Hydroxide (KOH)

• Synonyms: Caustic potash.

• Uses: Caustic in veterinary practice, saponifying agent.

Sodium Hydroxide (NaOH)

• Synonyms: Caustic soda.

• Properties: Attacks soft glass.

• Uses: Similar to potassium hydroxide but milder.

Sodium Carbonate (Na2CO3.H2O)

• Use: Forms sodium salts of acidic drugs in preparations.

Soda Lime

• Uses: For metabolism tests, anesthesia, and O2 therapy.

Potassium Bicarbonate

• Synonyms: Potassium hydrogen carbonate.

• Use: Buffering agent for pharmaceutical preparations.

Sodium Bicarbonate

• Synonyms: Sodium hydrogen carbonate.

• Uses: Preparation of effervescent mixtures.

Buffers

Definition

• Solutions that resist drastic pH changes when acids or bases are added. Maintain pH for stability, solubility, and patient comfort.

Mechanism of Action

• H+ ions react with conjugate base to form weak acid;

• OH- ions react with weak acid to form water and conjugate base.

Buffer Selection Considerations

• Should not:

  • Participate in oxidation-reduction reactions.

  • Alter solubility of components.

  • Form complexes with active ingredients.

Inorganic Buffer Systems

Phosphate Buffer System

• Advantage: Contains dihydrogen and monohydrogen phosphate ions.

• Disadvantage: Microbial growth due to metal insolubility.

Borate Buffer System

• Contains metals that precipitate with phosphate; suitable for external use.

Primary Borate Buffer Systems

1. Feldman’s Buffer: pH 7.6-8.2, includes boric acid and NaCl.

2. Atkins and Pantin Buffer: pH 7.6-11, includes sodium carbonate, boric acid, and NaCl.

3. Gifford Buffer: pH 6-7.6, similar to Feldman’s but with KCl.

Standard Buffer Solutions

• Designed for analytical purposes with specific pH ranges. Examples:

• Hydrochloric Acid, Acetic Acid, Potassium Phosphate, etc.

Antioxidants

Function

• Prevent oxidation of active ingredients or reduce oxidized forms back to normal states.

Selection Considerations

• Should be physiologically inert and assessed for toxicity and solubility issues.

Uses

• Hypophosphorous Acid: Prevents oxidation and acts as a preservative.

• Sulfur Dioxide: Protects compounds from oxidation, used in injections and industrial processes.

• Sodium Bisulfite: Prevents oxidation and prepares water-soluble drug derivatives.

• Nitrogen: Acts as an inert atmosphere to retard oxidation.

• Sodium Thiosulfate: Acts as a reducing agent and cyanide antidote.

• Sodium Nitrite: Antidote for cyanide; involved in meat curing with potential carcinogenic risks.

Glass in Pharmaceuticals

Characteristics

• Glass is a preferred material for small volume infusions.

• Composition includes silicon dioxide and various oxides.

Glass Types

1. Type I (Borosilicate Glass): Chemically resistant, low leachability.

2. Type II (Soda-lime Treated Glass): Less resistant; suitable for buffered solutions.

3. Type III (Soda-lime Glass): Suitable for anhydrous liquids or dry substances.

Reagent Modifications

• Glass properties modified for brightness and clarity by adding lead or boron.

Water in Pharmaceuticals

Role of Water

• Acts as a primary solvent due to its properties: high dielectric constant, hydrogen bonding.

Natural Water Types

• Alkaline Water: Contains sodium and magnesium.

• Carbonated Waters: Charged with CO2.

• Saline Waters: Contain sodium and magnesium sulfates.

Official USP Waters

1. Purified Water: Clear liquid, used as a solvent.

2. Bacteriostatic Water: Pre-filled syringes, contains antimicrobial agents but not for neonates.

3. Sterile Water for Injection: Clear liquid, no added substances.

4. Sterile Water for Irrigation: Sterilized water for irrigating solutions only.

5. Sterile Water for Inhalation: Packaged without antimicrobial agents.