Tablets are one of the most widely used solid pharmaceutical dosage forms. They are an important topic in Pharmaceutics for B.Pharm, D.Pharm, GPAT and pharmacist examinations.

A tablet contains one or more active pharmaceutical ingredients (APIs) along with suitable excipients and is generally prepared by compression or moulding.

Tablets can be designed for immediate, delayed or modified drug release depending on the formulation and therapeutic requirement.

What Are Tablets?

A tablet is a solid dosage form containing one or more active ingredients with suitable excipients, generally prepared by compression of powders or granules into a definite shape and size.

Common tablet ingredients include:

Active pharmaceutical ingredient
Diluent
Binder
Disintegrant
Lubricant
Glidant
Antiadherent
Colouring/flavouring agents
Coating materials, when required

Advantages of Tablets

Accurate and convenient dosing
Easy to carry, store and transport
Generally good physical and chemical stability
Convenient packaging
Suitable for large-scale production
Can be formulated for modified drug release
Coating can mask unpleasant taste and odour
Generally economical to manufacture

Disadvantages of Tablets

May be difficult to swallow for some patients
Large-dose drugs may require large tablets
Some drugs may have poor absorption when administered orally
Bitter drugs may require taste masking
Improper formulation or compression can produce defects

Classification of Tablets

1. Uncoated Tablets

These tablets do not contain an external coating and are generally intended to be swallowed.

2. Sugar-Coated Tablets

These tablets have a relatively thick sugar-based coating that can improve appearance and mask unpleasant taste.

3. Film-Coated Tablets

Film coating applies a thin polymeric layer around the tablet. It can improve appearance, swallowing and protection.

4. Enteric-Coated Tablets

Enteric-coated tablets are designed to resist disintegration in the stomach and release the drug under appropriate intestinal conditions.

5. Chewable Tablets

These tablets are intended to be chewed before swallowing. They commonly contain sweeteners and flavours.

Examples: Antacid chewable tablets, vitamin chewable tablets.

6. Effervescent Tablets

These tablets are dissolved or dispersed in water before administration and commonly produce carbon dioxide through an acid–carbonate/bicarbonate reaction.

Examples: Effervescent vitamin C tablets, electrolyte tablets.

7. Dispersible Tablets

These tablets are intended to be dispersed in water before administration.

8. Soluble Tablets

These tablets are designed to dissolve in water before administration.

9. Sublingual Tablets

Sublingual tablets are placed under the tongue and are designed for absorption through the oral mucosa.

Example: Nitroglycerin sublingual tablets.

10. Buccal Tablets

Buccal tablets are placed between the cheek and gum for drug release and/or absorption through the buccal mucosa.

11. Modified-Release Tablets

These tablets are designed to alter the rate or timing of drug release.

Examples: Sustained-release, extended-release and delayed-release tablets.

Excipients Used in Tablet Formulation

Excipients are substances added to improve the manufacturing, stability, appearance or performance of tablets.

1. Diluent

Diluents increase the bulk of a formulation when the quantity of drug is too small.

Examples: Lactose, microcrystalline cellulose, starch, dicalcium phosphate.

2. Binder

Binders promote adhesion between particles and help produce mechanically strong tablets.

Examples: Starch paste, povidone, HPMC, hydroxypropyl cellulose.

3. Disintegrant

Disintegrants help tablets break apart after administration.

Examples: Starch, sodium starch glycolate, croscarmellose sodium, crospovidone.

4. Lubricant

Lubricants reduce friction during compression and tablet ejection.

Examples: Magnesium stearate, stearic acid, sodium stearyl fumarate.

5. Glidant

Glidants improve the flow of powders or granules.

Examples: Colloidal silicon dioxide, talc.

6. Antiadherent

Antiadherents reduce adhesion of tablet material to punch surfaces.

Examples: Talc, starch.

7. Colouring Agents

Used to improve appearance and product identification.

Examples: Approved pharmaceutical colours, iron oxides.

8. Flavouring and Sweetening Agents

Used mainly in chewable or orally disintegrating preparations to improve taste.

Examples: Peppermint flavour, fruit flavours, saccharin, aspartame.

Methods of Tablet Manufacturing

The three major methods are:

Direct compression
Wet granulation
Dry granulation

1. Direct Compression

Direct compression is the simplest tablet manufacturing method. Suitable powders are blended and compressed directly into tablets without a separate granulation step.

Steps

Weighing → Sieving → Mixing → Lubrication → Compression → Dedusting → Inspection → Packaging

Advantages

Simple process
Fewer manufacturing steps
Less processing time
No drying step
Suitable for materials with good flow and compression properties

Limitations

The formulation should have suitable flowability, compressibility and compactability.

2. Wet Granulation

Wet granulation converts powders into granules using a suitable granulating liquid or binder solution.

Steps

Weighing → Sieving → Mixing → Binder Addition → Wet Massing → Granulation → Drying → Sizing → Lubrication → Compression

Advantages

Improves powder flow
Can improve compressibility
Reduces segregation
Useful for formulations unsuitable for direct compression

Limitations

More processing steps
Requires additional equipment
Drying is generally required
May not be suitable for moisture- or heat-sensitive materials without an appropriate process

3. Dry Granulation

Dry granulation produces granules without using a liquid granulating agent.

The two common approaches are:

Slugging
Roller compaction

Steps

Weighing → Sieving → Mixing → Compaction → Milling/Sizing → Lubrication → Compression

Advantages

No liquid binder solution required
Useful for moisture-sensitive materials
No conventional drying step required

Limitations

Can produce fines
Requires suitable compaction properties
Granule quality depends on processing conditions

Tablet Compression Process

During compression, powder or granules are converted into a compact tablet.

The major stages are:

Die filling
Weight adjustment
Compression
Decompression
Tablet ejection

Types of Tablet Compression Machines

Single-Punch Machine

Produces tablets one at a time and is commonly used for laboratory and small-scale work.

Rotary Tablet Machine

Contains multiple compression stations and is used for high-speed, large-scale tablet production.

Tablet Manufacturing Process: Quick Flow

Instead of a large flow chart, remember the process as:

1. Raw material weighing → 2. Sieving → 3. Blending → 4. Granulation if required → 5. Drying & sizing if required → 6. Lubrication → 7. Compression → 8. Dedusting → 9. Inspection → 10. Coating if required → 11. Packaging

Evaluation of Tablets

Tablet evaluation is performed to ensure that tablets meet appropriate quality and performance requirements.

Important tests include:

General appearance
Weight variation
Thickness
Diameter
Hardness/mechanical strength
Friability
Disintegration
Dissolution
Assay
Content uniformity

1. General Appearance

Tablets are examined for:

Shape
Colour
Surface
Cracks
Chipping
Mottling
Other visible defects

2. Thickness and Diameter

Thickness and diameter are measured using suitable instruments such as a thickness gauge or vernier caliper.

These parameters are important for tablet appearance, packaging and manufacturing consistency.

3. Weight Variation

Weight variation evaluates the consistency of tablet weight within a batch.

Variation can be affected by:

Powder flow
Granule flow
Die filling
Machine settings
Segregation

Acceptance requirements depend on the applicable pharmacopoeial standard.

4. Hardness / Mechanical Strength

Mechanical strength indicates the ability of a tablet to withstand handling, packaging and transportation.

A tablet that is too weak may break or chip, while excessive hardness can affect disintegration and drug release.

5. Friability Test

Friability measures the tendency of tablets to lose mass due to mechanical stress.

The tablets are weighed before and after tumbling in a friabilator.

Formula

% Friability = [(Initial weight − Final weight) / Initial weight] × 100

For many conventional tablets, approximately 1% or less is commonly used as a general benchmark, but the applicable specification depends on the product and pharmacopoeial requirements.

6. Disintegration Test

Disintegration testing determines how rapidly a tablet breaks into smaller particles under specified conditions.

Factors affecting disintegration include:

Type and concentration of disintegrant
Compression force
Binder concentration
Tablet porosity
Lubricant concentration
Drug properties

7. Dissolution Test

Dissolution testing measures the release of drug from a tablet into a specified test medium under controlled conditions.

Dissolution depends on factors such as:

Drug properties
Formulation
Particle size
Tablet hardness
Disintegration
Release mechanism

8. Assay / Drug Content

Assay determines the amount of active pharmaceutical ingredient present in the finished product.

It helps confirm that the tablet contains the intended amount of drug.

9. Content Uniformity

Content uniformity determines whether individual tablets contain the drug within the specified limits.

It is particularly important for low-dose medicines.

Tablet Coating

Tablet coating involves applying a layer of coating material around the tablet.

Purposes of Coating

Improve appearance
Mask unpleasant taste or odour
Improve swallowing
Protect the drug
Improve stability
Modify drug release
Provide enteric protection

Types of Tablet Coating

1. Sugar Coating

Sugar coating produces a relatively thick coating around the tablet.

Major stages may include:

Sealing → Subcoating → Smoothing → Colouring → Polishing

2. Film Coating

Film coating applies a thin polymeric layer over the tablet.

It generally requires fewer processing steps than traditional sugar coating and can also be designed for functional drug-release purposes.

3. Enteric Coating

Enteric coating is designed to resist the acidic stomach environment and permit drug release under appropriate intestinal conditions.

Common Tablet Defects

Important tablet defects include:

Capping
Lamination
Sticking
Picking
Binding
Mottling
Chipping
Cracking
Double impression

1. Capping

Capping occurs when the upper or lower portion of a tablet separates from the main tablet body.

Causes: Air entrapment, excessive fines, insufficient binding, unsuitable moisture and improper compression.

2. Lamination

Lamination occurs when a tablet separates into two or more layers.

Causes: Air entrapment, excessive compression, poor formulation properties and improper lubrication.

3. Sticking

Sticking occurs when tablet material adheres to the punch surface.

Causes: Excess moisture, sticky formulation, inadequate lubrication and unsuitable punch surfaces.

4. Picking

Picking occurs when material is removed from the tablet surface and sticks to the punch, particularly around engraved areas.

Causes: Sticky formulation, excess moisture and inadequate lubrication.

5. Binding

Binding occurs when tablet material adheres to the die wall, causing difficulty during ejection.

Causes: Insufficient lubrication, excess moisture and high friction.

6. Mottling

Mottling is the unequal distribution of colour on the tablet surface.

Causes: Poor mixing, colour differences and colour migration during drying.

7. Chipping

Chipping occurs when a portion of the tablet breaks away, usually from the edge.

Causes: Weak binding, excessively dry granules, poor compression conditions and worn tooling.

8. Cracking

Cracking appears as cracks on the tablet surface.

Causes: Improper drying, granule properties, excessive compression and elastic recovery.

Factors Affecting Tablet Quality

Particle Size

Affects flow, mixing, segregation, compression and dissolution.

Moisture Content

Improper moisture can contribute to sticking, capping, cracking and poor compression.

Compression Force

Affects tablet strength, porosity, thickness, disintegration and dissolution.

Lubricant Concentration

Insufficient lubrication can cause sticking and binding, while excessive lubrication may affect tablet properties and drug release.

Binder Concentration

Controls granule and tablet strength. Excessive binder may delay disintegration.

Disintegrant Concentration

Influences tablet breakup and subsequent drug release.

Important Terms in Tablet Manufacturing

Compressibility: Ability of a powder bed to decrease in volume under pressure.

Compactability: Ability of a powder to form a mechanically strong compact.

Flowability: Ability of powder or granules to flow consistently.

Granulation: Conversion of powder particles into larger aggregates called granules.

Tabletability: Ability of a material to form a tablet with adequate strength under a given compression condition.

Quick Revision: Tablets

Definition

A tablet is a solid dosage form containing one or more active ingredients and suitable excipients, generally prepared by compression.

Major Manufacturing Methods

Direct compression • Wet granulation • Dry granulation

Important Excipients

Diluent → bulk
Binder → adhesion
Disintegrant → tablet breakup
Lubricant → reduces friction
Glidant → improves flow
Antiadherent → reduces sticking

Important Evaluation Tests

Appearance • Weight variation • Thickness • Hardness • Friability • Disintegration • Dissolution • Assay • Content uniformity

Major Tablet Defects

Capping • Lamination • Sticking • Picking • Binding • Mottling • Chipping • Cracking

Major Coating Types

Sugar coating • Film coating • Enteric coating

Frequently Asked Questions

1. What are tablets?

Tablets are solid pharmaceutical dosage forms containing one or more active ingredients and suitable excipients, generally prepared by compression.

2. What are the three major methods of tablet manufacturing?

The three major methods are direct compression, wet granulation and dry granulation.

3. What is the function of a binder?

A binder promotes adhesion between particles and helps produce strong granules and tablets.

4. What is the function of a disintegrant?

A disintegrant helps the tablet break apart after administration.

5. Why are lubricants used?

Lubricants reduce friction during compression and tablet ejection.

6. What is friability?

Friability is the tendency of a tablet to lose mass due to mechanical stress.

7. What is disintegration?

Disintegration is the breaking down of a tablet into smaller particles under specified test conditions.

8. What is dissolution?

Dissolution is the release of drug from a dosage form into a specified medium under controlled conditions.

9. What is capping?

Capping is the separation of the upper or lower portion of a tablet from the main tablet body.

10. What is enteric coating?

Enteric coating is designed to resist disintegration in the stomach and allow drug release under appropriate intestinal conditions.

Conclusion

Tablets are one of the most important solid dosage forms in Pharmaceutics. Their quality depends on proper formulation, excipient selection, manufacturing process and compression conditions.

For pharmacy examinations, focus especially on tablet types, excipients and their functions, manufacturing methods, evaluation tests, coating and common tablet defects.