Granulation is the process of particle size enlargement by forming agglomerates (granules) to improve flowability, compressibility, and uniformity of powders before tablet compression.
It is classified into wet granulation, dry granulation, and direct compression.
Wet Granulation Methods:
Definition:
Involves the use of a liquid binder to form granules by agglomerating the powder particles.
Suitable for drugs that are not sensitive to moisture or heat.
Process:
Weighing and Mixing:
API and excipients are blended uniformly.
Binder Addition:
A liquid binder (e.g., starch paste) is added to form a wet mass.
Wet Sieving:
Wet mass is passed through a sieve to form granules.
Drying:
Granules are dried using an oven or fluid bed dryer.
Sieving (Sizing):
Dried granules are resized to ensure uniformity.
Lubrication and Blending:
Lubricants and glidants are added for compression.
Advantages:
Improves flow and compressibility.
Uniform drug distribution for low-dose drugs.
Disadvantages:
Time-consuming and costly.
Not suitable for moisture- or heat-sensitive drugs.
Dry Granulation:
Definition:
Granules are formed without using liquid binders.
Suitable for moisture- or heat-sensitive drugs.
Process:
Weighing and Mixing:
API and excipients are blended.
Slugging or Roller Compaction:
Powders are compacted using high-pressure rollers (roller compactor) or slugging (tablet press) to form large sheets or slugs.
Milling and Sizing:
Compact material is broken down into granules of desired size.
Lubrication and Blending:
Lubricants are added before final compression.
Advantages:
Suitable for moisture- and heat-sensitive drugs.
Faster and cost-effective (no drying).
Disadvantages:
High-pressure equipment needed.
Poor binding properties and dust generation.
Direct Compression:
Definition:
Tablets are made by directly compressing powdered materials without prior granulation.
Suitable for drugs with excellent flowability and compressibility.
Process:
Weighing and Mixing:
API and excipients are blended.
Lubrication:
Lubricants and glidants are added.
Compression:
Direct compression into tablets using a tablet press.
Advantages:
Simple, fast, and economical.
Ideal for heat- and moisture-sensitive drugs.
Disadvantages:
Requires excellent flowability and compressibility.
Not suitable for low-dose drugs due to segregation.
compressibility requirements.
Lack of uniformity for low-dose drugs.
Comparison Table
Aspect | Wet Granulation | Dry Granulation | Direct Compression |
Process Complexity | Complex, multiple steps. | Moderate, fewer steps. | Simplest, no granulation. |
Cost | High (equipment, time). | Moderate (no drying). | Low (minimal processing). |
Suitability | Not for heat/moisture-sensitive drugs. | Suitable for sensitive drugs. | Ideal for free-flowing powders. |
Tablet Strength | Strong and uniform. | Moderate strength. | Depends on powder properties. |