Pharmaceutical Inorganic Chemistry — B.Pharmacy 1st Semester
Pharmaceutical Inorganic Chemistry covers the chemistry of inorganic compounds used in pharmacy, including their preparation, properties, testing, and medicinal applications. Understanding these compounds is vital for quality control and therapeutic use.
Unit 1: Impurities in Pharmaceutical Substances
Pharmaceutical substances may contain impurities introduced during synthesis, storage, or handling. These impurities must be detected and controlled to ensure drug safety.
Sources of Impurities
- Raw materials: Impure starting materials
- Manufacturing process: Incomplete reactions, side reactions
- Storage: Degradation, contamination
- Packaging: Leaching from containers
Limit Tests
Limit tests are semi-quantitative tests designed to identify and control impurities in pharmaceutical substances at or below a specified threshold:
- Limit test for Chlorides: Uses dilute HNO₃ and AgNO₃. Comparison with standard NaCl opalescence.
- Limit test for Sulphates: Uses dilute HCl and BaCl₂. Turbidity compared with standard K₂SO₄.
- Limit test for Iron: Uses thioglycollic acid and ammonia. Pink color compared with standard FeCl₃.
- Limit test for Heavy Metals: Uses dilute acetic acid and H₂S gas. Dark color compared with standard lead solution.
- Limit test for Arsenic: Gutzeit test using zinc and HCl to generate AsH₃, detected by stain on HgBr₂ paper.
Unit 2: Acids, Bases, and Buffers
Theories of Acids and Bases
- Arrhenius Theory: Acids produce H⁺ ions, bases produce OH⁻ ions in aqueous solution
- Brønsted-Lowry Theory: Acids are proton donors, bases are proton acceptors
- Lewis Theory: Acids are electron pair acceptors, bases are electron pair donors
Buffer Solutions
Buffer solutions resist changes in pH when small amounts of acid or base are added. They consist of a weak acid and its conjugate base, or a weak base and its conjugate acid.
Henderson-Hasselbalch Equation
For acidic buffers: pH = pKa + log([salt]/[acid])
For basic buffers: pOH = pKb + log([salt]/[base])
Pharmaceutical Applications of Buffers
- Maintain pH of ophthalmic preparations (pH 7.4)
- Stabilize drug formulations
- Control drug absorption and bioavailability
- Maintain physiological pH in parenteral preparations
Unit 3: Major Intra- and Extracellular Electrolytes
Physiological Role of Ions
- Sodium (Na⁺): Major extracellular cation. Maintains osmotic pressure, nerve impulse transmission. Source: NaCl (normal saline — 0.9% w/v)
- Potassium (K⁺): Major intracellular cation. Cardiac function, muscle contraction. Source: KCl
- Calcium (Ca²⁺): Bone formation, muscle contraction, blood clotting. Source: CaCO₃, calcium gluconate
- Magnesium (Mg²⁺): Enzyme activation, neuromuscular function. Source: MgSO₄ (Epsom salt)
- Chloride (Cl⁻): Major extracellular anion. Acid-base balance, gastric HCl production
- Bicarbonate (HCO₃⁻): Buffer system, acid-base balance
- Phosphate (PO₄³⁻): Bone structure, energy metabolism (ATP), buffer system
Unit 4: Gastrointestinal Agents
Antacids
Antacids neutralize excess gastric acid to relieve heartburn and indigestion:
- Sodium bicarbonate (NaHCO₃): Rapid acting but systemic effects, CO₂ production
- Aluminium hydroxide [Al(OH)₃]: Slow acting, constipating effect
- Magnesium hydroxide [Mg(OH)₂]: Moderate acting, laxative effect (Milk of Magnesia)
- Combination antacids: Al(OH)₃ + Mg(OH)₂ — balanced GI effects
Cathartics (Laxatives)
- Saline cathartics: MgSO₄, Mg(OH)₂ — osmotic action draws water into intestine
- Bulk-forming: Calcium polycarbophil — absorbs water, increases bulk
Unit 5: Dental Products and Antimicrobials
Dental Products
- Sodium fluoride (NaF): Anti-caries agent, strengthens tooth enamel
- Stannous fluoride (SnF₂): Anti-caries and anti-gingivitis
- Zinc chloride (ZnCl₂): Astringent in mouthwashes
- Calcium carbonate (CaCO₃): Abrasive in toothpastes
Antimicrobial Agents
- Potassium permanganate (KMnO₄): Oxidizing antiseptic for wound cleaning
- Hydrogen peroxide (H₂O₂): Oxidizing agent for wound cleaning and oral rinse
- Boric acid (H₃BO₃): Mild antiseptic for eye washes
- Silver nitrate (AgNO₃): Caustic and antiseptic
- Iodine and Povidone-iodine: Broad-spectrum topical antiseptics
Important Exam Questions
- Explain the limit tests for chloride, sulphate, and arsenic
- Discuss the Henderson-Hasselbalch equation and its pharmaceutical applications
- Write about the physiological role of sodium, potassium, and calcium
- Classify antacids with examples and mechanisms of action
- Describe inorganic antimicrobial agents used in pharmacy
- Explain different theories of acids and bases