Formulation of Tablet Dosage Form: What You Should Know

 There are three methods through which we prepare tablets.

A. Granulation

1. Wet granulation method

2. Dry granulation method

B. Direct compression method

A. Granulation: 

It is a process in which fine powder of drugs is converted into small granules, which are further used to prepare tablets through compression. The size ranges from 0.2 to 4 mm. The reasons for granulation are 

To prevent the components in the powder mixer from segregating.  Segregation is due to the difference in size or density of components. Ideal granules will contain all constituents of the mixture.

To enhance the mixture's flow characteristics as a result of the larger, more isodiametric granules.

To improve compression characteristics of the mixture.

Granulation of toxic material reduces the hazard of toxic dust.

Granules become denser than powder mixes that occupy less volume per unit weight.

1. Wet granulation method:

In this process, we use a binder solution in wet form. The steps required for this are:

• Mixing of API and excipients
• Preparing a damp mass using a binder solution
• Screening-Granulation
• Drying
• Sizing the granulation by dry screening
• Lubrication
• Compression

i. Mixing of API and excipients:

First, we must weigh the required amount of API (medicament) and all participants. Weighing must be done in a clean area with a suitable airflow system to avoid cross-contamination. These excipients, such as diluents and half the disintegrating agents, are mixed with API through the blender. The blenders that can be used are double-cone blenders, planetary mixers, ribbon blenders, and V-blenders.

ii. Preparing a damp mass:

To make a damp mass, we must add a binder solution (in wet form) to this mixture.

iii. wet screening:

Now, this damp mass is screened using a sieve with the help of hand or suitable equipment and forms granules.

iv. Drying:

These wet granules are dried in a hot air oven at 60 degrees C. Depending upon the thermo-labile nature of the drug. It is required for the removal of solvent. It can be done by tray dryers (24 hours of drying and fluid bed dryers (30 minutes).

v. Dry screening:

After drying, these granules are screened through a sieve to get uniform size to get uniform size granules. Mesh size plays an important role.

Tablet Diameter	Mesh Size
3/16”	#20
3.5/16-5/16”	#16
5.5/16-6.5/16”	#14

vi. Lubrication:

Now, these granules are mixed with glidant, then add lubricant and remaining disintegrants. It is blended very gently using a tumbling action to maintain the uniform size of granules.

vii. Compression:

Now compress these granules into the desired punching machine to give the tablets the proper shape and size.

Advantage: 

• Cohesive and compressible properties are improved.
• Good flow properties
• Better uniformity and good distribution

Disadvantage:

• Costly
• More steps required more labor and time.

2. Dry granulation:

In this process, we use a binder in dry form. Cohesive properties are required for this method, either for the active ingredient or the diluent. Asprin and vitamins are formulated for tableting by compression granulation. A roller compactor is used on a large scale, with two rollers revolving over each other. The compaction force of the roller compactor is controlled by hydraulic pressure, the roller's rotational speed, and the feed screen's rotational speed. This method is used when an effective dose of the drug is too high for direct compression. These are the steps required for this.

• Mixing
• Slugging (first compression)
• Crushing (breaking)
• Screening
• Mixing (Lubricant, disintegrating)
• Compression

i. Mixing: 

The required amount of API and all exipients are weighed first. Add these excipients with API and half an amount of lubricant with a dry binder in the blender.

ii. Slugging:

Now, these mixtures are compressed into large flat tablets (pellets) known as "slugs," about one inch in diameter.

iii. Crushing:

Now, these slugs are against breaking into small particles using the mill.

iv. Screening:

These tiny particles are screened to produce uniform-sized granules.

v. Mixing:

Add the remaining lubricant, glidant, and disintegrating agents to granules and mix them into blenders.

vi. Compression:

Now compress these granules into the desired punching machine to give the tablets the proper shape and size and produce tablets.

Advantages of dry granulation over wet granulation

• No use of moisture
• Suitable for moisture and heat-sensitive material.
• It requires less equipment and minimum floor space and energy.
• Better disintegration.

Disadvantages:

• Create more dust than wet granulation.
• They are not allowing uniform color distribution other than wet granulation.
• A heavy-duty tablet press is required to form a slug.

B. Direct Compression Method:

In this process, the drug powder material is directly compressed into tablets. This process is suitable for drug substances with good compressible and flow properties. First, weigh the API (medicament) and suitable excipients such as diluents (e.g., spray-dried lactose, crystalline maltose, etc.). After that, mix and prepare tablets through compression.

Advantages:

• It is simpler and requires less time and equipment.
• Cheap
• Faster dissolution rate due to high disintegration (no involvement of moisture)

Disadvantages:

• Not suitable for high-dose drugs (not easily compressed)
• Sometimes, it needs to be blended uniform.
• Not suitable for all drugs.