Int J Curr Pharm Res, Vol 11, Issue 2, 7-13Review Article



Department of Pharmaceutics, T. John College of Pharmacy, Bangalore

Received: 14 Nov 2018, Revised and Accepted: 20 Feb 2019


This review article deals with the various pelletization techniques utilized in the pharmaceutical industry for spheroidal particle production i.e., pellet for mainly oral administration which can be further formulated into several other dosage forms such as tablets, capsules or can be administered as such. Now-a-days oral administration has become the most versatile, convenient and common route of drug administration which ultimately focuses on patient compliance. The technique which is setting horizon in pelletization is “Extrusion Spheronization” because of its simple and easy steps involved in pellet production in a faster way. This review also includes the characterization and evaluation of pellets to ensure its quality, safety and efficacy to give out the required therapeutic activity after administration.

Keywords: Different pellet formation techniques, ITS Evaluation Parameters



In the pharmaceutical industry, pellets are simple small free-flowing spherical particles formed by agglomeration of fine powder or granules, which can be given in the form of tablets and capsules for various disease conditions, although tablets are more convenient than capsules. The size range of pellet size is of 0.5-2.0 mm [1].

Flexibility of pellets in development of dosage form [2]

History of pellets [3]

In the 1950's, pellets came into existence in the field of “Pharmaceutical Industry” with an impact of sustain release dosage form. In terms of formulation, processing methods and equipment used were faster, cheaper and more efficient. It can also be used for sustained release of active constituents.

Properties of pellets

Uncoated pellets [4]

It should have high physical strength and integrity with uniform shaped smooth pellets along with improved flow properties with an optimum size range of 600 and 1000 µm provided with good hardness and low friability.

Coated pellets [5]

Along with uncoated properties of pellets, coated pellets maintains the active ingredient to give the uniform size of final dosage form within its standard limits, and also gives desirable drug release studies.

Formulation aspects of pellets [6]

Advantages of pellets

Technological advantages [3]

Therapeutical advantages [7]

With its large number of advantages, however, there are a few disadvantages

Disadvantages of pellets [8]

Pharmaceutical applications of pellets [9]

Pelletization technique [10]

Agitation [10]

Agitation involves the conversion of finely divided particles into spheroidal particles by the addition of required liquid by a continuous rolling or tumbling motion. The liquid can be added at the beginning of the process, or during the agitation process. Pans, discs, drums or mixers may be used to produce pellets by the balling process. It is the oldest and less efficient technique for production of pellets.

Balling [9]

It can be done either by adding the required volume of liquid into powder or by applying a high temperature. Spherical agglomeration can be divided into two categories, such as liquid-induced agglomerations and melt-induced agglomerations. Instruments like conventional horizontal drum pelletizers, inclined dish pelletizers or tumbling blenders, rotary fluid-bed granulators. This technique is popularly used in iron ore and fertilizer industries. The rate and extent of agglomeration formation depend on formulation variables such as particle size, the degree of liquid saturation, viscosity of liquid phase and solubility of powder.

Compactation [10]

Agglomeration of drug particles or granules takes place in presence of pressure which gives out well-defined shape and size of pellet.

Compression [4]

Blend of active ingredients and number of excipients are compressed with the aid of pressure to give out defined shape and size of the pellet.

Extrusion-spheronization [11]

Extrusion Spheronization is used to produce spheroidal structure or pellets of uniform size. It involves multiple processes such as wet mass extrusion followed by Spheronization to produce matrix pellets or spherical particles or beads. Apart from medical field, it has greater application in other fields such as agrochemicals, detergent additives, sweeteners, food; etc. It is the most commonly used method for pellet formation. “Spheronization" is a primarily used for oral drug delivery system.

Layering [13]

Pellet formation by layering involves the deposition of successive layers of drug molecules from dry powder or granules, suspension, a solution of drug particles.

Powder layering technique [8]

Various steps involved in this technique are as follows.

Solution/suspension layering technique [12]

Various steps involved in this technique are as follows.

Globulation [3]

It is also known as droplet formation, it contains two process, spray drying and spray congealing. It works by atomization of hot melts, suspensions or solutions to form pellet particles.

Spray drying [3]

In this process, drug substances in solution or suspension are sprayed with or without excipients into hot stream of air to generate dry spheroids. When atomized droplets come in contact with hot air, evaporation of the application media takes place, this drying process continues through a series of stages where the viscosity of the droplets continuously increases until the entire application medium is evaporated and finally solid particles are obtained. The spray-dried powder particles are homogenous with uniform size. The design and operation of the spray drier can improve the characteristics of final pellet such as particle size, particle distribution, bulk density, porosity, flow ability, moisture content, and friability.

Spray congealing [9]

It is another globulation technique, where a melt material is sprayed and pellet formation occurs. And it solidifies through a fluid stream of gas or liquid material at a suitable temperature lower than the melting point of the carrier or drug molecule. This method is best suitable for coating of beads and also for small size beads.

Extrusion-spheronization [10]

The extrusion Spheronization is a common technique and widely used method for uniform size pellet production with multiple steps. This process was first devised by Reynolds in the year 1970 and also Conine Hadley gave his contribution to the technique.

It is multiple process of wet mass extrusion which further pursued by spheronization step to produce matrix pellets or beads of spheroids, and mainly used for the production of multiple particle for oral sustained drug delivery system. The extrusion operation densifies the material to saturation point while spheronization is only a shaping process and drying operation finalizes the textural characteristics of the product by densifying the medium through induced shrinkage [4].

It is a worldwide using process due to its simple and fast processing technology.

Pellet formation by extrusion spheronization [14]

Mechanism of pellet formation by extrusion spheronization [14]

Process of extrusion spheronization [4]

Extrusion spheronization follows mainly four steps, they are as

1) Preparation of the wet mass (granulation)

2) Shaping the wet mass into cylinders (extrusion)

3) Breaking up the extrudate, rounding the particles into spheres (spheronization)

4) And drying of pellets

Preparation of the wet mass (Granulation)

It involves, preparation of the plastic mass of the material with different types of granulator’s usage to perform the mixing of the powder blend and the granulation liquid. The most common and simple granulators used are the planetary mixer, high-shear or sigma blade mixer, etc. The wet granulation process plays an important role in extrusion-spheronization. With the Twin Screw Extruder (TSE), it allows the possibility of wet granulation to run continuously.

Shaping the wet mass into cylinders (Extrusion)

The prepared plastic mass undergoes the extrusion process in which pressure is applied to a mass of particles until it flows out through an orifice to produce the extrudates. The extrudate length might vary from each other, depending on the physical characteristics of the materials extruded. Extrusion is performed using five main classes of extruders: screw, sieve and basket, roll, and ram extruders. Details for all types of the extruder are given in table 1 [10].

Types of extruders with schematic representation [10]

Screw Extruder: A) Axial screw extruder

B) Radial screw extruder

A) Sieve extruder

B) Basket extruder

Table 1: Details for all types of the extruder are given in table

Type of extruder Mechanism Comment
Screw extruder Utilizes a screw to develop the necessary pressure to force the material to flow through uniform openings

a) Axial: Screen is placed at the end of the screw, perpendicularly with the axis of the screw

b) Radial: Screen is placed around the screw, discharging the extrudate perpendicularly to the axis of the screw

Sieve extruder A rotating or oscillating arm presses the damp material through a sieve Extrudate falls vertically from the sieve plate
Basket extruder Similar to sieve extruders, except that the sieve or screen is part of a vertical cylindrical wall Extrudate formed in the horizontal plane
Roll extruder Roll extruders operate by feeding material between a roller and a perforated plate or ring die

Type 1: A ring rotates around one or more rollers installed inside the cylindrical die chamber, each of which rotates on its stationary axis.

Type 2: The roller or rollers are mounted on the outside of the ring die and material is fed from a hopper occasionally with a screw, into the region between the roller and the die.

Type 3: Rollers are positioned above and roll along the surface of a flat, stationary die plate.

Ram extruder A piston riding inside a cylinder or channel is used to compress material and force it through an orifice on the forward stroke Extrusion forces recorded with the ram extruder are always greater and force necessary to extrude the wet mass through the ram extruder decreases as the quantity of water added increases

A) Internal roller

B) Roller external to die

C) Roller on the flat die plate

Ram extruder

Spheronization [12]

In this process, the extruded cylindrically shaped particles are uniformly broken into a particular length which gradually leads to the formation of spherical shapes, thus shaping process is due to plastic deformation. Extrudates are first broken into nearly uniform lengths, all three dimensions of agglomerate shape are determined and spheres with uniform diameter are obtained. In spheronization process, different stages can be distinguished depending on the shape of the particles, i.e., starting from a cylinder over a cylinder with rounded edges, dumbbell shape and elliptical particles to eventually perfect spheres.

Schematic diagram of spheronizer

Spheronizer [15]

It is an instrument or a device consisting of a vertical hollow cylinder with a horizontal rotating disk i.e.; friction plate situated inside the cylinder. The extrudates are charged onto the rotating plate and broken into short pieces by contact with the rotating disk, collisions between particles and also collisions with the wall device. Mechanical energy is supplied by the spinning of the rotating disk which is converted into kinetic energy in the form of a mechanically fluidized bed. Continuation of this process causes the extrudate to deform slowly into a spheroidal structure. The rotating disk has a grooved surface to increase the frictional forces. There are two types of grooves available based on geometry, they are “cross-hatch geometry” where the grooves are formed from right angles and “radial geometry “which uses a radial pattern.

Factors affecting pelletization technique [4]

Characterization and evaluation of pellets

The prepared pellets must go through various parameters for characterization and evaluation of pellets.

Characterization of pellets as follows

Particle size analysis [16]

The particle sizes of the formed pellets are to be measured using an optical microscope with ocular and stage micrometer where the particle size distribution can be calculated. The ‘Wesmox model’ with a resolution of 45x may be used.

The particle size distribution study can also be done by ‘Sieve Analysis' technique by using a set US standard sieve of different mesh size known as different sieve numbers such 14,16,18,22 and 44 with a pellet of the load of 10 gm. The sieve set is to be mechanically shaken for 10 min, total net weight of pellets retained on each sieve was determined and these values are used for calculating particle size distribution.

Micrometric properties

θ = tan-1 (h/r)

Where ‘r' is the radius of the pellet pile formed an ‘h' is the height of the pellet pile.

Apparent bulk density was determined by pouring the bulk samples into a graduated cylinder. Tapped density can be determined by placing a graduated cylinder containing a known mass of powder on a mechanical tapper apparatus (Electro lab tap density tester). Carr’s index can be calculated by using the equation given below:

Hausner’s ratio was measured by the ratio of tapped density to bulk density.

Where, WO is the initial weight and W is the weight after100 rotations.

The friability test is performed on the formed pellets to ensure the ability of mechanical strength to withstand the property of strength where lower the friability value indicates good mechanical strength of the spheroids.

Therefore, characterization each individual pellet can be known by the aspect ratio (AR) and two-dimensional shape factor(eR). The equation for pellet sphericity is as follows:

eR = 2πr/Pm-(b/l) 2

Where ‘r' is the radius, 'Pm' is the perimeter, ‘l' is the length and ‘b’ is the width of the pellet.

Evaluation of pellets

The formula for calculation of % yield of a pellet is written below:

% yield= weight of pellets/Weight of drug+weight of polymers×100


In present scenario, pelletization technology in pharmaceutical industry has obtained a prominent role due to its different extent character in novel drug delivery system as well as in conventional system and also incompatible drugs can also be prepared by overtaking granulation process. Pellets can be formulated using various technique but widely used is “Extrusion Spheronization” technique because of its fast working process without complicated design and high efficiency of pellets production with uniform spherical particles.


All the author have contributed equally


Declare none


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