MANUFCTURING OF TABLETS

MANUFACTURING OF TABLETS

There are four main methods by which tablets are manufactured:

direct compression

wet granulation

dry granulation

        The choice of manufacturing process employed is dependent on several factors, including the compression properties of therapeutic agent, the particle size of the therapeutic agent and excipients and the chemical stability of the therapeutic agent during the manufacturing process.

Direct Compression.

        It is very simple and cheap method.In this method the active ingrdients and requiered excepients are directly compressed into tablets without undergoing stage of granulation.This method is only suitable for those compound which have good coherecy among particles,good flow in processing units and  excellent compressibility and a specific particle size distribution to ensure uniform mixing.

WET GRANULATION

This is the traditional method of pretreatment of solids prior to tabletting. Despite its complexity and inherent disadvantages, even now about half the tablets produced worldwide are manufactured by this process.

Wet granulation has following steps.

1. MIXING

The first stage in the wet granulation process is often a dry mixing stage in which the active component is mixed with a diluent. The purpose of the mixing stage is to ensure that the powder blend and hence the resulting tablets are homogeneous in content. Thus, the aim is to produce a mixture such that when a sample is removed, the relative proportions of the components of that sample are the same as in the mixture as a whole.

It might be intuitively expected that the homogenecity of a mixture will progressively increase with time, but this is not always the case. Under certain conditions, an optimum mixing time occurs, beyond which the mixture shows a tendency to separate back into its components. This process is known as segregation. The efficiency of mixing is enhanced by the use of powders that have similar average particle size/distribution, although this is often not the case in many mixing operations. Generally the shear rate required to mix pharmaceutical powders is low.This is done by using several types of mixers.

2.Granulation

Granulation is a unit operation in which mixed powders are simultaneously mixed with a suitable fluid, e.g. water, isopropanol or ethanol (or mixtures thereof). To achieve cohesion between the powders, it is necessary to include a binding agent within the formulation, either in the solid state within the powder mix or dissolved in the binding fluid. Powder mixing, in conjunction with the cohesive properties of the binder, enables the formation of granules.

3.DRYING

After the process of granulation, the product exists as a wet mass from which the liquid must be removed, since the presence of water leads to the impairment of flow properties, and perhaps to chemical instability. Wateris usually removed by evaporation for which energy is needed. This is normally provided as heat, thoughmicrowave energy is being increasingly used for drying in tablet manufacture.

4.SEIVING

When the drying process is complete, it is likely that the product will have cohered into relatively large masses, especially if tray drying has been used. The dried material is therefore passed through a sieve (usually 250–700 mm) to break up aggregates and to give a relatively uniformly sized granules.

5.MIXING OF ADDITIVES

. A second mixing stage now follows in which several important ingredients of the formulation are added.

·         Glidant,     To increase flow of material during manufacturing processes

·         Lubricant    To  avoid sticking with wall of dyes.

·         Disintegrating agent  To disintegrate in GIT tract.

6.TABLET MANUFACTING STAGE

Finally material is compressed in to tablets using single punch or multiple punch tableting machines.

This process has owned the advantages and disadvantages.

DRY GRANULATION

The dry granulation process is used to form granules without using a liquid solution because the product to be granulated may be sensitive to moisture and heat. Forming granules without moisture requires compacting and densifying the powders. In this process the primary powder particles are aggregated under high pressure There are two main processes. Either a large tablet (known as a ‘slug’) is produced in a heavy-duty tabletting press (a process known as ‘slugging’) or the powder is squeezed between two rollers to produce a sheet of material (roller compactor or chilsonator). In both cases these intermediate products are broken using a suitable milling technique to produce granular material, which is usually sieved to separate the desired size fraction. The unused fine material may be reworked to avoid waste. Then granuls are compressed into tablets.

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