🌟 Pre-formulation Factors (Detailed Notes)
📌 Definition
Pre-formulation factors wo physical, chemical aur mechanical properties hain jo kisi new drug substance ko formulation banane se pehle study kiye jaate hain.
👉 Purpose: Drug ki solubility, stability, bioavailability, and compatibility samajhna, taki ek safe, effective aur stable dosage form design ho.
1️⃣ Melting Point
- Definition: The temperature at which solid drug changes to liquid.
- Importance:
- Purity test ke liye → pure substance ka sharp MP hota hai, impure ka broad range.
- Drug formulation me → melting point zyada hoga to solubility kam hogi.
- Storage condition decide karne ke liye (high MP drugs stable at room temp).
- Applications:
- Polymorphic form identification (har crystal form ka MP alag hota hai).
- Example:
- Paracetamol: 169°C
- Aspirin: 135°C
2️⃣ Solubility
- Definition: Maximum quantity of drug that dissolves in a given solvent at specific temperature & pH.
- Factors Affecting Solubility:
- Temperature (heat → solubility ↑ for most solids).
- Particle size (smaller → dissolves faster).
- Polymorphism (amorphous more soluble than crystalline).
- pH of medium (weak acids dissolve better in basic medium, weak bases in acidic medium).
- Importance:
- Directly controls absorption & bioavailability.
- Drug selection for dosage form → water soluble drugs prefer oral syrups, poorly soluble drugs need suspensions/nanoparticles.
- Examples:
- Griseofulvin (poor solubility → micronized form use karte hain).
- Ibuprofen is poorly soluble in water → salt forms banayi jaati hain.
3️⃣ Viscosity
- Definition: Resistance offered by a liquid to flow.
- Importance in Pre-formulation:
- Drug dissolution rate ko affect karta hai → high viscosity medium me drug dissolve slow.
- Parenteral (injection) formulation me viscosity control important (too viscous = hard to inject).
- Stability of suspensions: high viscosity → particles settle slow.
- Applications:
- Oral syrups: viscosity adjust for uniform taste & stability.
- Eye drops: viscosity enhancers use to increase contact time.
- Examples:
- Glycerin, honey → viscous liquids.
- Hydroxypropyl methylcellulose (HPMC) → viscosity enhancer in eye drops.
4️⃣ Dissolution
- Definition: The process by which a drug particle dissolves into solvent over time.
- Formula: Governed by Noyes–Whitney equation
- D = diffusion coefficient
- A = surface area of drug
- Cs = solubility
- C = concentration in bulk
- h = diffusion layer thickness
- Importance:
- Determines onset of action of drug.
- Poor dissolution = poor absorption = poor bioavailability.
- Dissolution testing mandatory before launching tablets/capsules.
- Applications:
- Fast dissolving tablets designed for immediate effect.
- Controlled release tablets designed for slow dissolution.
- Examples:
- Paracetamol dissolves fast → quick fever reduction.
- Digoxin dissolves slow → delayed onset.
5️⃣ Particle Properties
- Parameters Studied:
- Particle size
- Shape
- Surface area
- Flow properties
- Importance:
- Small particle size = large surface area = higher dissolution rate.
- Shape influences flow during tablet compression.
- Large irregular particles → poor mixing, segregation in powder blends.
- Applications:
- Micronization & nanonization used for poorly soluble drugs.
- Aerosols need particles 1–5 µm for lung deposition.
- Examples:
- Micronized progesterone → improved absorption.
- Inhalation powders → controlled particle size critical.
6️⃣ Solid State Properties
- Definition: Physical arrangement of drug molecules in solid form.
- Types:
- Crystalline form → molecules arranged in orderly lattice, stable but less soluble.
- Amorphous form → disordered arrangement, less stable but more soluble.
- Polymorphism → drug can exist in more than one crystalline form (different MP & solubility).
- Importance:
- Polymorphic forms may show different bioavailability.
- Wrong form may cause drug formulation failure.
- Examples:
- Ritonavir: one polymorph insoluble → market recall.
- Sulfathiazole exists in several polymorphic forms.
📌 Applications of Pre-formulation Studies
- Selection of right dosage form (tablet, capsule, syrup, injection).
- Improve solubility & dissolution for better absorption.
- Identify stability problems (degradation by heat, light, moisture).
- Helps in bioavailability & bioequivalence studies.
- Prevents formulation failure (wrong polymorph, wrong particle size).
🎯 Mnemonic for Quick Recall
👉 "My Sweet Vanilla Drink Please Serve"
- Melting point
- Solubility
- Viscosity
- Dissolution
- Particle properties
- Solid state properties