AN OVERVIEW: ON SUPERDISINTEGRANTS
Disintegrants are substances or mixture of substances added to the drug formulation that facilitates the breakup or disintegration of tablet or capsule content into smaller particles that dissolve more rapidly than in the absence of disintegrants. In dosage forms, solid orals gain maximum popularities, about 85%, because of many advantages over others. The therapeutic activity of these formulations is obtained through a typical manner like disintegration followed by dissolution. Hence disintegration has major role for facilitating drug activity and thus gain popularity among other dosage forms. Superdisintegrants are generally used at a low level in the solid dosage form, typically 1- 10 % by weight relative to the total weight of the dosage unit. The present study comprises the various kinds of superdisintegrants which are being used in the formulation to provide the safer, effective drug delivery with patient's compliance. In this review article, more emphasis is given on application and usage of various superdisintegrants comparing with other disintegrants in reference to available scientific studies. The various sources of superdisintegrants and their modification to improve disintegration property are also high-lighted.
REFERENCE ID: PHARMATUTOR-ART-1740
Despite increasing interest in controlled releasedrug delivery systems, the most common tablets are those intended to be swallowed whole and to disintegrate and release their medicaments rapidly in the gastrointestinal tract (GIT) still remains the dosage form of choice. Disintegrates are substances or mixture of substances added to tablet formulations to promote the break-up of the tablet (and capsule “slugs’) into smaller fragments in an aqueous environment thereby increasing the available surface area and promoting a more rapid release of the drug substance. Tablet disintegration has received considerable attention as an essential step in obtaining faster drug release. The emphasis on the availability of the drug highlights the importance of the relatively rapid disintegration of a tablet as a criterion for ensuring uninhibited drug dissolution behaviour. A number of factors affect the disintegration behaviour of tablets . The development of fast dissolving or disintegrating tablets provides an opportunity to take into account the role of disintegrants. Recently, chemically modified disintegrants termed as superdisintegrants have been developed to improve the disintegration processes. Selection of appropriate formulation excipients and manufacturing technology can obtain the design feature of fast disintegrating tablet. The disintegrants have the major function to oppose the efficiency of the tablet binder and the physical forces that act under compression to form the tablet. The stronger the binder, the more effective must be the disintegrating agents in order for the tablet to release its medication. Ideally, it should cause the tablet to disrupt, not only into the granules from which it is compressed, but also into powder particles from which the granulation is prepared . The proper choice of a disintegrant or a superdisintegrant and its consist performance are of critical importance to the formulation development of such tablets. Drug release from a solid dosage form can be enhanced by addition of suitable disintegrants. In more recent years, increasing attention has been paid to formulating not only fastdissolving and/or disintegrating tablets [4,5] that are swallowed, but also orally disintegrating tablets  that are intended to dissolve and/or disintegrate rapidly in the mouth. An ideal disintegrant should have poor solubility, poor gel formation, good hydration capacity, good compressibility, flow properties and no tendency to form complexes with the drugs.
SELECTION OF SUPERDISINTRIGATION:[7,8]
Since superdisintegrant is used as an excipient in the tablet formulation, it has to meet certain criteria other than its swelling properties. The requirement placed on the tablet disintegrant should be clearly defined. The ideal disintegrant should have –
1. Poor solubility.
2. Poor gel formation.
3. Good hydration capacity
4. Good moulding and flow properties.
5. No tendency to form complexes with the drugs.
6. Good mouth feel.
7. It should also be compatible with the other excipients and have desirable tableting properties.
Although some are better than others, the currently marketed superdisintegrants exhibit an optimum combination of properties
METHOD OF ADDITION OF SUPRADISINTEGRANTS
There are three methods of incorporating disintegrating agents into the tablet.
In wet granulation method, the disintegrant is added to other excipients before wetting the powder with the granulating fluid. Thereby, the disintegrant is incorporated within the granules. In dry granulation method, the disintegrant is added to other excipients before compressing the powder between the rollers. In a computer optimized experiment, the study show the effect of incorporating a disintegrant, croscarmellose sodium, intragranularly, extra granularly or distributed equally between the two phases of a tablet in which a poorly soluble drug constituted at least 92.5% of the formulation. The results analyzed by means of a general quadratic response surface model suggest that, tablets with the same total concentration of crosscarmellose sodium dissolve at a faster rate when the super disintegrant is included intragranularly. Tablet friability is not affected by the method of disintegrant incorporation .
In both wet and dry granulation method, the superdisintegrant is added to the granules during dry mixing prior to compression. The effect of mode of incorporation of superdisintegrants (croscarmellose sodium, sodium starch glycolate and crospovidone) on dissolution of three model drugs with varying aqueous solubility (carbamazepine, acetaminophen and cetrizine HCl) from their respective tablet formulations by wet granulation was studied. It is proved that crospovidone is effective in improving the dissolution of the drugs in extra granular mode of addition seems to be the best mode of incorporation, irrespective of the solubility of the main tablet component.
Internal and External Addition
In this method, disintegrant is divided into two portions. One portion is added before granule formation (intra) and remaining portion is added to granules (extra) with mixing prior to compression. This method can be more effective. If both intragranular and extragranular methods are used, extra-granular portion break the tablet into granules and the granules further disintegrate by intra-granular portion to release the drug substance into solution. However, the portion of intra-granular disintegrant (in wet granulation processes) is usually not as effective as that of extra-granular due to the fact that it is exposed to wetting and drying (as part of the granulation process) which reduces the activity of the disintegrant. Since a compaction process does not involve its exposure to wetting and drying, the intragranular disintegrant tends to retain good disintegration activity.
Mechanism of disintegrations by superdisintegrants
There are five major mechanisms for tablet disintegration as follows:-
2. Porosity and Capillary Action (Wicking)
4. Due to disintegrating particle/particle repulsive forces
5. Heat of wetting
6. Due to release of gases
7. Enzymatic reaction
8. Combination action
Swelling is believed to be a mechanism in which certain disintegrating agents (such as starch) impart the disintegrating effect. By swelling in contact with water, theadhesiveness of other ingredients in a tablet is over come causing the tablet to fall apart .E.g. Sodium starch glycolate, PlatagoOvata.(fig.1)[10,11,12]
2. Porosity and Capillary Action (Wicking)
Effective disintegrants that do not swell arebelieved to impart their disintegrating action through porosity and capillary action. Tablet porosity provides pathways for the penetration of fluid into tablets. The disintegrant particles (with low cohesiveness and compressibility) themselves act to enhance porosity and provide these pathways into the tablet. Liquid is drawn up or “wicked” into these pathways through capillary action and rupture the inter particulate bonds causing the tablet to break apart as shown in Fig 1. Crospovidones are synthetic, insoluble, crosslinked homopolymers of N-vinyl-2-pyrrolidone. Crospovidone quickly wicks saliva into the tablet to generate the volume expansion and hydrostatic pressures necessary to provide rapid disintegration. Unlike other superdisintegrants which rely principally on swelling for disintegration, crospovidones uses a combination of swelling, wicking and deformation[13,14] formulated fast dissolving Efavirenz formulation by using three different superdisintegrants such as crosscarmellose sodium (CCS), sodium starch glycollate (SSG) and crospovidone (CP). It is concluded that CP is able to release the drug faster than the other two disintegrants.(fig.2)
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