Multiple compressed tablets are prepared by more than one compression cycle. This process is best suited when separation of active ingredient is needed for stability purposes, or if the mixing process is inadequate to guarantee uniform distribution of two or more active ingredients. They are usually prepared to separate physically or chemically incompatible ingredients or to produce repeat or prolonged action of drugs. They are also known as multiple layered tablets or a tablet within the tablet.

Multiple compressed tablets

There are three categories under this class: compression coated tablets, inlay tablets and layered tablets. Multiple compression tablets, especially layered tablets, tend to solve incompatibility issues between two or more active pharmaceutical ingredients (APIs). Bilayer tablet provides adequate surface separation of two reactive ingredients but there may be some reactivity at the interface. If complete physical separation is required for stability purposes then three layered tablet may be employed.

Compression Coated Tablets

Compression coated tablet has two parts, the first part is internal core and the second part is surrounding coat. Outer layer provides the initial dose while the inner core releases the drug later on. Hence, it is useful for releases of two active pharmaceutical ingredients (APIs), one immediate release formulation which is entrapped in coat and the other sustained or delayed release formulation entrapped in the core. It is also possible to provide loading dose and maintenance dose for one drug using this concept. Sometimes, the inner core may consist of liquid formulation to provide immediate release of the core after the coat dissolves.

Advantages Of Compression Coated Tablet

1. Stable due to absence of water or other solvent

2. Inner core protected from sunlight or oxidation

3. cover a bitter substance, conceal an unpleasant or mottled appearance

4. Provide a barrier to substances that irritate the stomach or destroy by gastric juice

5. Accurate dosing

Disadvantages Of Compression Coated Tablet

1. Expensive than other coating

2. Advance in other coating makes it possible to coat aqueous substances

3. Big size and weight of tablet

Types Of Compression Coated Tablet

a) Sugar Coated Tablets

The sugar coating of the tablets is sugar-coated with an aqueous sugar-coating solution containing about 5 to 30 % by weight. As the name suggests, this method consists of the application of sugar (sucrose) based coating solutions on the tablets. Sugarcoating is the most usual multi-step coating process used in the manufacture of the tablet dosage form in pharmaceutical industries. Widely utilized in preparing multivitamin and multivitamin mineral combinations.

Advantages Of Sugar Coating

1. The sugar coat protects the enclosed drug from the environment

2. provides a barrier to objectionable taste or odour

3. It also produces an elegant, glossy appearance

4. The patient acceptability also increases due to the sweet taste of the tablet

5. Materials use are inexpensive

6. Sugarcoating can enhance the mechanical strength of the dosage form

Disadvantages Of Sugar Coating

1. Equipment use are expensive

2. Coating can interfere with the pharmacodynamic properties of drug formulation

3. Because the process is sling, several film defects can occur which can affect the quality of the product. (Motting, capping, chipping and bridging)

4. Process takes longer than standard compressed tablets

5. Coating increases the weight and size

b) Film Coated Tablets

It is the type of coated tablets in which drugs are not required to be coated. In order to provide more strength to the tablet, film coating is used as an alternative to sugar coating. The polymers such as HPC (hydroxypropyl cellulose), HPMC (hydroxypropylmethyl cellulose), and ethyl cellulose are used for this technique. It is also a faster process than the sugar coating technique. The coating is designed to rupture and expose the core tablet at the desired location in the gastrointestinal tract.

Advantages Of Film Coated Tablet

1. The tablet coating increases the shelf life by protecting it from air, moisture, and light, hence it is more stable and durable in chemical, physical, and microbiological properties

2. It is less bulky

3. Less time consuming to apply

4. Cheaper and high degree of automation than other dosage forms including liquid than sugar coated tablets

5. Release drug at location inside the GIT

6. Reduce dust in the industry

7. The polymer materials are non-toxic and tasteless and significantly enhance the dissolution rate, bioavailability, and the drug's effective time

8. It has been formulated to use with different characteristics, such as controlled release film, gastric film, sustained-release films, enteric film, etc

9. The polymer materials are non-toxic and tasteless and significantly enhance the dissolution rate, bioavailability, and the drug's effective time

Disadvantages Of Film Coating

1. it is less attractive and elegant in physical appearance than sugar coating

2. Not suitable for all drug like hygroscopic drugs, low density, and amorphous as they cannot be compressed in a punching machine

3. Cannot be used in unconscious patient, children and elderly

4. Probability of batch to batch failure or variations is higher than standard compressed tablets

5. More expensive than standard compressed tablets

6. Due to the stability issue, more than two or three APIs can only be formulated in capsules, not tablets

c) Gelatin Coated Tablets

The innovator product, the gel cap is a capsule–shaped compressed tablet that allows the coated product to be about one–third smaller than a capsule filled with an equivalent amount of powder. The gelatin coating facilities swallowing, and gelatin–coated tablets are more tamper evident than an unsealed capsule.

Advantages Of Gelatin Coated Tablet

1. Easy to swallow

2. Prevent counterfeiting by adding printed branding

3. Mask unpleasant odour and taste

4. Improve stability of photosensitive active pharmaceutical ingredient (API)

5. Beautiful in appearance as they can be coloured

6. Protect the GIT from harsh API

Disadvantages Of Gelatin Coated Tablet

1. Moisture-sensitive drugs may not be stable in soft gelatin capsules due to the relatively higher water content in soft gelatin shells (20–30% w/w).

2. Expensive to produce

3. The manufacturing process is relatively tedious and difficult to optimize

4. Gelatin coated tablets in multiple jar container are in constant close contact with each other and expose the whole product to second coating when one of the gelatin breaks

5. There is more interaction between the content and the gelatin coating

d) Enteric Coated Tablets

The enteric coated tablets are coated with the material resistant to acidic medium (stomach environment) and hence are not able to release drugs in the stomach. Whereas, it easily releases drugs in intestine (alkaline) media. Hence, drugs have to pass through the stomach and the time of release of drugs is delayed and hence called delayed action tablets.

Advantages Of Enteric Coated Tablet

1. Protect drug from GIT juice

2. Mask taste and odour

3. Sustain release thereby increasing adherence

4. Beautiful product by adding colour

5. Physical and chemical stability to product

6. Cheaper than some dosage forms

7. Delay release is important for time sensitive drugs

Disadvantages Of Enteric Coated Tablet

1. Time consuming and tedious

2. Can interfere with pharmacodynamic properties of API

3. Cannot be crush or split before using

Layered Tablets

Layered tablets are composed of two or three layers of granulation compressed together. They Have the appearance of a sandwich because the edges of each layer are exposed. When two or more active pharmaceutical ingredients are needed to be administered simultaneously and they are incompatible, the best option for the formulation pharmacist would be to formulate a multilayered tablet. A single tablet composed of two or more layers and usually each layer is of different color to produce a distinctive looking tablet.

There are mainly two type of layered tablets used in pharmaceutical industries: bilayer tablet and trilayer tablet.

Bilayer Tablet

In bilayer tablet release of both drugs start immediately, It solves incompatibility issues between two or more active pharmaceutical ingredients by providing limited contact. sing this technique. Modified drug release can be achieved by preparing bilayer tablets. It is possible to do dose adjustment by splitting of bilayer tablet

Trilayer Tablet

Sometimes, incompatibility can occur in bilayer die to the fact that there is only one layer between two drugs. However, formulating three layers between two or three drugs reduces the chance of incompatibility between two or three drugs.

Advantages Of Layer Tablet

1. Manufacturing of bilayer tablet is easy

2. Require fewer material

3. Thin and light

4. Weight if each layer can easily be controlled

5. Monogram and other distinctive marking can be impressed on the surface

6. Colouring of the different layers makes it possible for identification

Disadvantages Of Layer Tablet

1. Very expensive

2. Chances of cross contamination is high especially in bilayer tablet

Inlay Tablets

A variation of the compression coated tablet is the inlay, dot, or bull's-eye tablet. Instead of the core tablet being completely surrounded by the coating, its top surface is completely exposed. This form can be useful in sustained release preparations to reduce the size and weight of the tablet. Two drugs are incorporated in the tablet, one in core and one in coat. Release of both drugs starts immediately but coating is responsible for slow release and core is responsible for immediate release of incorporated drugs.

Advantages Of Inlay Tablets

1. Less coating material

2. Thinner tablet

3. The core is visible, so coreless tablets are readily detected

4. Reduce weight

5. No concern with the capping of the top coating

Disadvantages Of Inlay Tablets

1. Inlay tablets attain less hardness, which leads to

high friability so more care need to be taken during

transportation and storage

Overview Of Pharmaceutical Multiple Compressed Tablet