Wet Granulation Advantages And Disadvantages Biology Essay

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In this lab three different sets of tablets were produced i.e soft, medium and hard using different processes which mainly included i.e Direct Compression Vs Wet Massing ,different excipients which included (Lactose Vs Calcium Phosphate) & and different binders which included (PVP Vs Klucel). Once all the tablets were produced by the above mentioned varying processes, excipients and binders they were studied and compared to see how they would influence a range of tablet testing parameters such as uniformity of weight, friability, crushing strength & disintegration time.

Introduction:

A tablet is perhaps the oldest and the most common pharmaceutical dosage form. Its popularity is due to its convince in the administration of the drug without the help or supervision of a health care practitioner, thus providing patients freedom and a very cost effective means of providing a reproducible medication. A tablet seldom consists of only the active ingredient. In fact , a tablet represents a mixture of one or more active ingredients with a number of "inactive" ingredients or excipients. There are many reasons for formulating a tablet product with excipients, ranging from management of small dosage amounts of active ingredients to esthetic resons of colour and shape of a product. However, the most fundamental and critical objective of a tablet product is to provide/deliver the active ingredient accurately and reproducibly. Therefore, from this perspective, a tablet is now commonly considered as a drug delivery device (Ahmed, 2000).

However all tablets are made by compressing a particulate solid between two punches in a die of a tablet press. For an active ingredient to be transformed into tablets of satisfactory quality , the formulation must have three essential attributes.

First, the formulation must flow into the die space of the tablet press sufficiently rapidly and in a reproductible manner

Second, the particles in the formulation must cohere when subject to a compressing force, and that coherence should remain after the compressive has been removed.

Third after the compression event is complete, it must be possible for the tablet to be removed from the press without damage to either the tablet or the press.

Very few active ingredients possess all three of these essentials and some posses none of them. Hence some preliminary treatment is almost invariably necessary.

Methods of Tablet Manufactures:

There are three main methods of tablet manufacture designed to confer the above mentioned essential attributes to a tablet formulation. Wet granulation and direct compression are the most important, with dry granulation (also termed as precompression or slugging) used in some circumstances. Fig shows the processes of wet granulation and direct compression broken down into their constituent stages.

The relative simplicity of the direct compression process is immediately apparent.

Ease of removal of the tablet from the press is, in theory at least, readily achieved. Friction occurs between the tablet and the die and punches of the press, which can be overcome by including a lubricant in the formulation. Hence every formulation, irrespective of the method of manufacture, will include a lubricant . This will usually be a metallic salt of a fatty acid such as magnesium stearate.

The two other prerequisites-flow and cohesion-can only be achieved by more elaborate technique and are in fact the reasons why wet & dry granulation processes were devised.

As part of its complexity, wet granulation involves the addition of a liquid (usually water), followed by its removal, normally by evaporation. In addition to the energy requirements of this drying process, the presence of water might bring about hydrolysis of the active ingredients, which will be exacerbated at the elevated temperatures used for drying.

If a major component of the formulation such as the diluents were to possess the necessary degree of fluidity and compressibility, granulation would be unnecessary. This is the basis of direct compression method of tablet manufacture.

Wet Granulation: Advantages and Disadvantages:

The wet granulation process is the traditional method of manufacture and is frequently used in the pharmaceutical industry. Expertise in wet granulation is widely available, as in the required equipment. The process improves flow and cohesion reduces dust and cross contamination and permits the handling of powder blends without loss of homogeneity. Though it has been practiced for many years and therefore may be perceived as an old fashioned process., it must be borne in mind that the wet franulation process has itself undergone a transformation in recent decades. High-speed mixer-granulators, fluidized bed granulation and drying and an ever increasing use of automation have served to make wet granulation a much more efficient and economic process than it once was( Marinelli, 2009).

Nevertheless, the wet granulation process still retains many inherent disadvantages. Problems include choice and method of addition of the binder and the effect of drying time and temperature on drug stability and its distribution within the solid mass.

Direct Compression Process: Advantages and Disadvantages

The most striking feature of the direct compression process is its simplicity and hence economy. Less equipment is required and the number of stages in the process, each of which will require validation, is greatly reduced. There are also lower labour costs, reduced processing time and lower power consumption. On top of that since direct compression is a dry procedure therefore there would be no need for a drying stage. Thus, exposure to water and the elevated temperatures needed to remove that water are avoided, resulting in a decreased risk of deterioration of the active ingredient. A further advantage of DC is that tablets disintegrate into their primary particles rather than granular aggregates. The resultant increase in surface area available for dissolution should result in faster drug release. On the other hand talking about disadvantages, the primary limitation on the use of direct compression is that it depends on the fluidity and compressibility of tablet diluents. Therefore it cannot be used for low potency, high dose active ingredients, where the inclusion of sufficient diluents in the formulation to permit direct compression would lead to unacceptably large tablets. Thus, active ingredients such as paracetamol and aspirin do not tend themselves to the DC process. However, as stated earlier, such ingredients are often available in pregranulated form (Holm, 2009)

Thus considering the different ways to produce tablet it is also important to mention here that there has also been an increased emphasis in developing tablets that provide controlled disintegration/release process of the active ingredient.. These tablets are hence known by different names such as slow,extended, controlled, sustained or delayed release tablets to reflect their drug release characteristics. These modified drug release products provide further convenience to patients by reduced frequency of drug administration, thus increasing the chance of compliance as well. However for establishing the quality of a tablet product, the fundamentals remain the same i.e to ascertain that the product delivers the intended active ingredient in an accurate and reproducible manner. Therefore, tablet testing can be broadly divided into three aspects or categories:

Confirmation of the nature of the active ingredient and the product ( Identity, quantity, impurities, integrity etc)

Establishing pharmaceutical availability of the active moiety both in vitro and in vivo in humans and if required also in animals.

Establishing stability profiles to achieve shelf life.

Testing of nature of the tablet products:

As a consequence one seeks to establish whether the tablets are within specifications, for example the nature of the active ingredients (identification) expected amount (assay) purity (related compounds) and uniformity of the amount of drug from tablet to tablet (uniformity of dosage units). Commonly these testing procedures are described in pharmacopeia's under a specific name. In addition to these tests some other tests such as friability, hardness, disintegration etc are also conducted and will be described as below

Uniformity of Dosage Units (B.P Pharmacopoeial Tests)

This test is conducted to establish consistency in the content of active ingredient from tablet to tablet. There are generally two approaches taken in establishing this: weight variation or content uniformity. If the active ingredient represents not less than 50% weight of the tablet and greater than 50 mg, then one may establish uniformity of dosage units using the weight variation method. A sample of 10 tablets are weighed individually and results of these weighing are recorded. In the case of the content uniformity approach, a sample of 10 tablets are individually analyzed using the analytical method described under the assay procedure. It is mandatory to use content uniformity for tablets with less than 50 mg of active ingredient and/ or representing less than 50% total mass of the tablets. The content uniformity approach is preferred over the weight variation approach as it more precisely reflects the variation of the active ingredient from tablet to tablet. The required specification for this test is that uniformity of dosage unit should be within a range of 85%-115% with a relative standard deviation of less than or equal to 6% (Holm, 2009)

Friability ( Non - B.P Pharmacopoeial Test)

This test is intended to determine, under defined conditions, the friability of uncoated tablets, the phenomenon whereby tablet surfaces are damaged and/or show evidence of lamination or breakage when subjected to mechanical shock or attrition. Commercially available apparatuses known as friabilators are used for the test. Basically, it consists of a drum with diameter between 283mm and 291mm and having width of 36 mm-40 mm, made of transparent plastic material The drum is attached to the horizontal axis of a device that rotates at 25_1 rpm. The tablets are tumbled at each turn of the drum by a curve projection with an inside radius of 75.5 mm-85.5mm that extends from middle of the drum to outer wall. Thus, at each turn, the tablets roll or slide and fall onto the drum wall or onto each other. Usually, a sample of 10 tablets are tested at a time, unless tablet weight is 0.65 g or less, where 20 tablets are tested. After 100 turns, the tablet samples are evaluated by weighing. If the reduction in the total mass of the tablets is more than 1%, the tablets fail the friability test. Generally, the test is done once. If cracked, cleaved, or broken tablets are obvious, then the sample also fails the test (Marinelli, 2009).

Hardness Testing ( Non - B.P Pharmacopoeial Test)

A tablet requires a certain amount of mechanical strength to withstand the shocks of handling in its manufacturing, packing, shipping, and dispensing. As discussed before, hardness and friability are most common measures used to evaluate tablet strength. The need for testing hardness or crushing strength, in addition to friability, may be explained with an analogy that friability determines how fragile a tablet is. If a tablet is more fragile than expected, then the friability test will detect its substandard quality. However, on the other hand, if the tablets are more robust than desired, a friability test would not detect this deficiency. It is the tablet hardness test that will detect the deficiency (Holm, 2009)

Disintegration Test (B.P Pharmacopoeial Tests)

A disintegration test is a test to establish how fast a tablet disintegrates into aggregates and/or finer particles.

The test assumes that if product disintegrates within a short period of time, such as within 5 min, then the drug would be released as expected and one should not anticipate a problem in the quality of a drug product. Although this test is in use for some products in pharmacopeias, its use is generally diminishing in favor of drug dissolution testing (Holm, 2009)

Materials & Methods:

Please refer to the Pharmaceutics Handbook for MPharm Year2

4.0 ) Results & Discussion:

A fundamental quality attribute for all pharmaceutical preparations is the requirement for a constant dose of drug between individual tablets. In practice, small variations between individual preparations are accepted and the limits for this variation are defined as standards in pharmacopoeias. For tablets, uniformity of dose or dose variation is tested in two separate tests: uniformity of weight and uniformity of active ingredient. These either reflect indirectly or measure directly the amount of drug substance in the tablet.

Uniformity of active ingredient:

The uniformity of active ingredient is carried out by ensuring a constant dose of drug between individual tablets. Traditionally, dose variation between tablets is tested in two separate tests;

1- Weight uniformity

2- Content uniformity

If the drug forms greater part of the tablet, any variation in the tablet weight obviously indicates a variation in the active ingredient. (Weight uniformity test)

If the drug is potent (USP specifies 50 mg of the active ingredient or less), the excipients form the greater part of the tablet weight and the correlation between the tablet weight and amount of the active ingredient can be poor, in this case another test (Content uniformity) must be performed (Holm, 2009)

In this lab report the weight uniformity test was carried out (which is one of BP requirements) and the following results were obtained. The below table also shows the maximum and minimum percentage error.

Table 4.1: Shows the calculated values for CV% along with maximum and minimum % error for various tablets produced by different processes, binders and excipients.

Method

Excipient

Binder

Mean / mg

Range / mg

% Error  

CV%

Min

Max

Min

Max

Direct Compression

Lactose

169

164

173

2.95

2.36

1.7

Direct Compression

Calcium Phosphate

146

141

148

3.42

1.36

1.5

Wet Massing

Lactose

PVP

122

120

125

1.63

2.45

1.4

Wet Massing

Calcium Phosphate

PVP

175

172

179

1.71

2.20

1.2

Wet Massing

Lactose

Klucel

118

116

119

1.69

0.84

0.9

Wet Massing

Calcium Phosphate

Klucel

149

142

154

4.69

3.35

2.88

Thus by the help of the above table 4.1 it can be clearly seen that all the tablets produced by different processes, different binders and different excipients are within the percentage max and min error & show values below 6% of CV% thus all of them have passed the weight uniformity test.

Different Binders:

Binders are the substances which are added either dry or in wet- form to form granules or to form cohesive compacts for directly compressed tablets.

An ideal binder should have good binding properties, as determined by compressibility under pressure, high plasticity, low elasticity and small particle size. Small particle size facilitates even distribution of the binder through the inter-particulate void spaces in a tablet. Uniform binder distribution in the tablet results in decreased pore structure and subsequent enhancement in tablet crushing strength. To reduce friability, a binder with highly plastic properties (high deformability) is essential. A further requirement for a good binder is low hygroscopicity. Excessive uptake of moisture (greater than 5 percent) or high moisture content can lead to instability and sticking during production (Summers, 2002)

There are many excipients used as binders in the direct compression; these include hydroxypropylcellulose (HPC), methylcellulose (MC), povidone (PVP), hydroxypropylmethylcellulose (HPMC), and starches and their derivatives, such as pregelatinized and granulated starches. These polymers differ in their physico-chemical, mechanical and morphological characteristics. For direct compression, studies suggest highly compactable, plastic, fine particle size binders facilitate compression of drugs at relatively low filler-to-drug ratios, therefore representing ideal properties for tablet binders(Summers, 2002)

The two different binders that were used in this lab were PVP & Klucel XPF. In order to study the effects of different binders the following two figs will be used. Fig one represents the friability & disintegration time Vs Hardness for tablets produced by wet massing with PVP as a binder and Lactose as a filler.

Fig 4.1) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Lactose) & binder (PVP)

Friability : 1.05 %

Hardness: 3.75 Kp

Disintegration Time: 2.12 decimal mins

The above figure represents the friability, Disintegration time and Hradness for a tablet produced the process of wet massing in the presence of lactose (as an excipient) and PVP as a binder. The value of friability as percentage drops from 2% to about 0.75 % as the hardness increases. This is because as friability is the ability to form fines or fragments of the original tablet and since the hardness of the tablet is increasing

therefore consequently less fragmentation of the tablet would occur/ take place. On the other hand however the values for disintegration time augments from 0 to 4.5 with an increase in the value of hardness. This is due to the fact that compacts develop mechanical strength by creation of a surface bonding area between particles. This is mainly achieved by irreversible particle deformation that flattens initial asperity. The decrease of particle surface roughness enables molecular forces to act. Thus, the indentation hardness can be considered as that portion of the compression pressure that contributes to the formation of interparticulate contacts. Accordingly (Hiestand, 2000) proposed the tablet hardness to correspond to the magnitude of the bonding active compression pressure considering these arguments for the strengthening mechanism of tablets, the direct link between hardness and bonding points seems to be a reasonable theoretical approach.

Fig 4.2) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Lactose) & binder (Klucel)

Optimum Hardness: 6.5 Kp

Optimum Friability: 2.70%

Optimum Disintegration Time: 3.45 (time/ decimal mins)

The above figure represents the friability, Disintegration time and Hardness for a tablet produced the process of wet massing in the presence of lactose (as an excipient) and Klucel as a binder. From the above figure 4.2 it can be seen that with increased hardness of the tablet the value of the friability drops down. Whereas a direct relationship can be seen between the hardness and disintegration time.

Comparing the above two fig 4.1 and 4.2 , it can be seen that fig 4.2 has an optimum hardness value of 6.5 whereas that for fig 4.1 has a hardness value of 3.75 .In a similar fashion there is a difference in the values of optimum disintegration time too with fig 4.2 showing higher disintegration time in comparison to that showed by fig 4.1.This difference in the optimum hardness value is due to the difference of binders. From the obtained results it can be seen that using Klucel results in optimum hardness much high in comparison to when PVP is used. But the value for optimum friability is less i.e 1.05% when PVP is used in comparison to Klucel (friability value is 2.70%). In a similar fashion the values for disintegration time is less for tablets produced by PVP whereas it is high for tablets produced by Klucel . Hence from the results obtained above the PVP seems to be a superior binder in comparison to Klucel in terms of lower friability and less disintegration time period.

Fig 4.3) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Calcium Phosphate ) & binder (PVP)

Optimum Hardness: 5.8 Kp

Optimum Friability: 0.78%

Optimum Disintegration Time: 0.38 (time/ decimal mins)

Fig 4.4) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Calcium Phosphate ) & binder (Klucel)

Optimum Hardness: 1.4 Kp

Optimum Friability: 0%

Optimum Disintegration Time: 0.2 (time/ decimal mins)

From fig 4.4 it can be seen that the friability behaves quite unexpectedly with increasing hardness. Normally with the tablets, the increase of compression force causes a reduction of friability. The value of friability falls down from 2.75 % to 0 but then starts to rise again as the hardness augments to 5 Kp. One of the possible explanation for this trend could be due to the fact that When the compression force increases, the particles deform plastically and the tablets become harder and less friable But at higher compression forces the friability of the tablets seemed to increase again although the crushing strength remain stable. This could be explained by some fragmentation of the system.

Thus again by the help of the above two fig 4.3 and 4.8 it can be clearly seen that the results obtained in this comparison case are opposite to the results obtained by the help of the fig 4.1 & 4.2. PVP yielded tablets which have higher optimum hardness in comparison to those produced by Klucel. A similar case is with friability and disintegration time too. Thus in this case Klucel stands out to be a superior binder (with respect to low friability and disintegration value).

However literarure (Ahmed, 2000) shows that K90 grade for PVP used in this lab (more viscous in comparison to that of Klucel) should produce harder granules. Furthermore using a high grade for PVP like K90 , which is highly viscous, would result in higher dissolution time and hence high disintegration time, which would also consequence in the production of harder tablets. Thus the harder the tablet are the lower friability they would have. Klucel on other hand is less viscous, therefore is will produce softer granules hence softer tablets (therefore low disintegration time and high friability of the tablets will be observed)

But this case is not entirely true in all circumstances, as it depends on the grades of the binders used.

For example some (Summers, 2002) shows that some grades of Klucel exhibits a unique combination of thermoplasticity with organic solvent or aqueous solubility, allowing tough tablet preparation using many different formulation techniques. Furthermore a tougher binder with a high degree of plastic flow provides better friability performance. In addition, such binder characteristics allow a tableting process to run at a higher compaction speed without capping process.

Beyond unmatched tablet hardness and friability, benefits of tableting with Klucel include:

• Lower compression and ejection forces; and

• Reduction or elimination of tablet capping.

On top of this (Boyle) also shows that Klucel can be used at lower use levels to yield superior tablets, compared to tablets with higher binders levels of HPMC, MC, PVP (Grade K 70) and pre-gelatinized starch.

(Aqualon) also stated that High-dose acetaminophen formulations using lower levels of poorer binder like PVP (K70) resulted in poorer formulations due to capping. Furthermore, Klucel (Low Grade) has low viscosity due to which it has much lower (almost twice less) the dissolution time in comparison to that for PVP (grade K70). This has a direct impact on disintegration. Thus the lower the dissolution time is, the faster it will disintegrate (hence will show fast effect) (Marinelli, 2009)

Different Excipients:

In this lab only two different types of excipients were used i.e Lactose and Calcium Phosphate

Fig 4.5) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Lactose) & binder (PVP)

Optimum Hardness: 3.78Kp

Optimum Friability: 1.1 %

Optimum Disintegration Time: 2.15 (time/ decimal mins)

Fig 4.6) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Calcium Phosphate ) & binder (PVP)

Optimum Hardness: 5.80 Kp

Optimum Friability: 0.78%

Optimum Disintegration Time: 0.38 (time/ decimal mins)

By the help of the fig 4.5 and 4.6 it can be clearly seen that the value of optimum hardness (for lactose) 3.78 Kp is quite low in comparison to the value of optimum hardness 5.80Kp for tablets which had calcium phosphate as main excipient. However the same figures also show that lactose has a higher value for friability (1.1%) and disintegration time (2.15 decimal min) in comparison to those showed by calcium phosphate. (Friability 0.78%) and disintegration (0.38 time decimal mins). This difference is due to the fact that lactose is more compressible than calcium phosphate and hence requires less amount of compressible force (as this is what the obtained data suggests). However in real time it has been proposed by (Marinelli, 2009) that calcium phosphate has higher density, hence higher compressibility. Therefore in such a case low compression weight would be required to produce hard tablets with less friability. Whereas in case of lactose it has been suggested that it has lower tapped density hence poor compressibility. This suggests that at lower pressures it will be elastic and therefore a higher compression weight will be required to produce hard tablets with lesser/lower friability.

Fig 4.7) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Lactose) & binder (Klucel)

Optimum Hardness: 6.5 Kp

Optimum Friability: 2.70%

Optimum Disintegration Time: 3.45 (time/ decimal mins)

Fig 4.8) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (calcium phosphate) & binder (Klucel)

Optimum Hardness: 1.4 Kp

Optimum Friability: 0%

Optimum Disintegration Time: 0.2 (time/ decimal mins)

Thus by the help of the figures 4.7 and 4.8 it can be seen that the results obtained for lactose and calcium phosphate are opposite to the results obtained in figures 4.5 and 4.6. Fig 4.7 and 4.8 show that tablets produced using lactose had high optimum hardness to those produced by calcium phosphate. In a similar fashion the values for friability and disintegration time for tablets produced using lactose were high in comparison to those produced by calcium phosphate.

However literature (Marinelli, 2009) suggests that lactose is also more water soluble than calcium phosphate therefore it will dissolve and provide a pathway for diffusion of drug and erosion of matrix, leading to a faster (lower dinintegration time) release of drug from matrix tablets (in comparison to calcium phosphate).

Different Processess:

The two different sets of processes used in this lab were direct compression and wet massing

Fig 4.9) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (wet massing) , excipient (Lactose) & binder (PVP)

Optimum Hardness: 3.78 Kp

Optimum Friability: 1.1 %

Optimum Disintegration Time: 2.15 (time/ decimal mins)

Fig 4.10 ) Shows relationship between friability, hardness & disintegration time for tablet produced by the process (Direct Compression) & excipient (Lactose)

Optimum Hardness: 3.00 Kp

Optimum Friability: 0.480 %

Optimum Disintegration Time: 0.15 (time/ decimal mins)

Thus by the help of the figure 4.8 and 4.9 it can be clearly seen that tablets produced by direct compression show lower optimum hardness, lower value for friability and lower value for disintegration time. Wet massing on the other hand results in tablets formed with high optimum hardness value, high friability value and high disintegration time. It is also worth mentioning at this stage that direct compression process required DC lactose and calcium phosphate of higher grades (Direct compression formulations require good flow in order to maintain proper weight uniformity) whereas low grade regular lactose and calcium phosphate were used for wet massing (during wet massing low grade excipients were used however the granules produced could have been affected by sieving)

With regards to wet massing, it is generally agreed that there will exist an optimum range of granule sizes for a particular formulation, and therefore certain generalizations are worthy to note here. Within limits, smaller granules will lead to higher and more uniform tablet weight and higher tablet crushing strength, with subsequent longer disintegration time and reduced friability. The strength of granules has also been shown to influence the tensile strength of the tablets prepared from them, with stronger granules leading, in general to harder tablets (Marinelli, 2009).

Conclusion: Fianlly to sum up everything, it was seen in this lab that all the set of tablets produced (hard, soft & medium) via different processes or by different excipients or binders , all of them passed the uniformity of weight test. Concerning binders, in this lab PVP seem to stand superior to Klucel (however this might not always be the case). Regarding excipients both lactose and calcium phosphate could be used. As , calcium phosphate has higher density, hence higher compressibility. Therefore in such a case low compression weight would be required to produce hard tablets with less friability. Whereas in case of lactose it has lower tapped density hence poor compressibility. This suggests that at lower pressures it will be elastic and therefore a higher compression weight will be required to produce hard tablets with lesser/lower friability. Lastly , both DC and wet massing were used to produce tablets however tablets produced by DC had shorter disintegration time in comparison to those produced by wet massing.

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