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64 Cards in this Set
- Front
- Back
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What are the disadvantages of having tablets as a dosage form? |
-Poor bioavailability of poorly water-soluble drugs or poorly absorbable drugs -Difficult to swallow for some patients -Irritation to the GI tract |
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What are some general attributes of good tablets? |
-Correct dose -Consistent weight and size (elegant) -Drug release controlled -Biocompatible -Sufficient mechanical strength to survive transport and handling -Stable (physically, biologically and chemically) -Acceptable for intended use -Properly packed |
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What does biocompatible mean? |
Non-toxic excipients, no contaminants or microorganisms |
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How are tablets formed? |
Particles are forced into close proximity to each other by powder compaction> particles cohere into a porous solid of defined shape. |
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What are the three stages in tablet formation? |
1) Filling 2) Compression 3) Ejection |
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What happens during powder compression? |
Powder volume is reduced due to the application of a force |
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What happens during powder compaction? |
A porous specimen of defined geometry is formed |
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What happens during the filling stage? |
Powder fills the die by gravity or centrifugal force |
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What happens during the compression stage? |
The upper punch lowers into the die and the powder is compressed; the upper punch then moves up |
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What happens during the ejection stage? |
The lower punch moves up to eject the tablet |
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What are the features of a single punch tablet press? |
-One die and one pair of punches -Hopper shoe moves to and from the die by translational or rotational movement -Tablet weight is controlled by the position of the lower punch (remains stationary) |
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How many tablets can a single punch tablet press produce a minute? |
About 200 tablets a minute |
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How many tablets can a rotary tablet press produce per minute? |
About 10,000 tablets a minute |
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What are the features of a rotary tablet press? |
-Many dies on the die table and many pairs of punches -Die table and punches rotate together> the same punches always work with the same die |
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What is recorded during compression? |
-Forces from the upper and lower punches -Forces transmitted to the die -Displacement |
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Why is it useful to record forces and displacement during compression? |
-To investigate the relation between applied force and the properties of tablets produced -To describe and analyse compression properties of powders |
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What does a variation in force during compression indicate? |
A variation in tablet weight |
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Why are tablets produced via granulation? |
-Improve flowability of powder -Improve mixing homogeneity and reduce segregation -Improve compactability of powder -Improve density of powder -Ensure homogenous colour of tablets -Improve dissolution of poorly soluble drugs |
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How is the dissolution of poorly soluble drugs improved during granulation? |
By dispersing fine powders of the drug in hydrophilic diluent |
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What are the disadvantages of tablet production via wet granulation? |
-Long production time -Consumes energy in drying process -Stability problems in wet environment and during drying -Expensive |
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What are the advantages of tablet production by direct compaction? |
-Simple production, only 2 steps: powder mixing and tableting -Reduced production time -Reduced energy consumption -Lower cost -Fewer stability issues -Faster dissolution (potentially) due to quick disintegration into primary particles |
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What are the disadvantages of tablet production by direct compaction? |
-Need special grade of excipients -Higher risk of powder segregation -Powders of high drug content difficult to form into tablets (poor compactability) |
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What two types of drugs is direct compaction useful for? |
-Drugs that have good flowability -Potent drugs that are of low content (powder properties are mainly controlled by excipients in this case) |
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What are the different types of tablet excipients? |
-Diluent -Disintegrant -Binding agent -Glidant -Lubricant -Antiadherent -Sorbent -Taste adjusting agent |
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When are diluents used? |
Low dose drugs need diluent so that tablets of certain weight (>50mg) can be produced |
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What are the desired features of a diluent? |
-Biocompatible -Chemically inert -Non-hygroscopic -Low cost -Good compressability and compactability -Acceptable taste -Low cost |
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List some commons diluents |
Lactose, Cellulose Powders, Microcrystalline Cellulose, Dextrose/glucose, Sucrose, Mannitol and Inorganic Salts (Calcium Carbonate and Phosphates etc...) |
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What are the features of lactose? |
-Common tablet filler -Pleasant taste -Available as anhydrous and crystalline -Anhydrous lactose dissolves faster than crystaline -Anhydrous lactose has good compaction properties, so used for direct compression |
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What are the disadvantages of lactose? |
-Some people are lactose intolerant -Anhydrous lactose may spontaneously convert to the more stable crystalline form if humid and high temperature |
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What are the features of cellulose powders? |
-Biocompatible -Inert -Good disintegrating property -Good compatability |
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What is the main disadvantage of cellulose powders? |
Hygroscopic |
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What are the properties of Microcrystalline cellulose? |
-Prepared by hydrolysis of cellulose, followed by spray drying -Particles formed are aggregates of smaller cellulose fibres -Particles have crystalline and amorphous regions -Crystallinity varies depending on the source of the cellulose and preparation -Crystallinity affects properties of the particles, such as hygroscopicity and powder compactability |
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What is dextrose/glucose usually used in? |
Chewable tablets |
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What are the properties of sucrose? |
-Carcinogen- used less -Was widely used as a sweetener/dileunt in effervescent tablets and chewable tablets |
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Why is mannitol used as an excipient? |
It has a good taste and produces a cooling sensation when sucked or chewed |
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Why are inorganic salts used as diluents? |
They're insoluble in water and hydrophilic (easily wetted) |
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Why are disintegrants added to tablets? |
To ensure that tablets break up to small particles when in contact with liquid |
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What are the mechanisms by which disintegrants work? |
-Facilitate water uptake -Rupture tablets by swelling of the disintegrant -Deformed particles restore to their original shape upon contact with water -Particle repulsion upon contact with water -Producing CO2 (effervescent tablets) |
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List some common tablet disintegrants |
-Starch -Cellulose -Modified starch or modified cellulose -Gas generating disintegrants |
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What are some examples of gas generating disintegrants? |
-Bicarbonate or carbonate salts together with a weak acid (eg: citric acid and tartaric acid) CO2 is generated when in contact with water, used in effervescent tablets
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Why are binding agents added to tablets? |
To ensure that tablets can be formed with required mechanical strength. |
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When can binding agents be added? |
-As a dry powder before wet granulation -As a solution to producde wet granules -As a dry powder which is mixed with other powder before compaction |
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Which binders are the best? |
Solution binders |
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List some examples of solution binders |
Sucrose, starch, PVP, cellulose derivatives |
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List some examples of dry binders |
Microcrystalline cellulose and crosslinked PVP |
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Why are glidants added to tablets? |
To improve the flowability of the powders/granules |
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What is Colloidal silica and what are its main features? |
It's a glidant. Most widely used, used in low quantity (0.2%), improves flow by adhering to the surface of other particles and reducing interparticulate friction |
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What is Talc (1-2%) and what are its properties? |
A glidant. Hydrophobic; a large quantity of it can reduce dissolution rate |
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Why are lubricants added to tablets? |
To ensure low friction between tablets and die wall. |
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What can happen if there is high friction between tablets and the die wall? |
-Vertical scratches on tablet edges -Capping or fragmentation of tablets during ejection process |
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What are the two different mechanisms of lubrication? |
-Fluid lubrication> rarely used (Eg: liquid paraffin in effervescent tablets) -Boundary lubrication> fine particulate solid eg: magenisum stearate. Used in low quantity <1% |
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What can lubricants end up reducing? |
Tablet strength, as they reduce the bonding between particles |
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Why are antiadherents added to tablets? |
To reduce the adhesion between the powder and the punches (avoids sticking and picking) |
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What are sorbents? |
Substances that are capable of absorbing some quantities of liquid and appears to be "dry powder" (Microcrystalline cellulose and silica) |
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What are the common problems that occur during tableting? |
-High dose and weight variation of the tablets -Low mechanical strength of tablets -Capping and lamination of the tablets -Adhesion or sticking of powder to punches -High friction during tablet ejection |
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What problems can arise if powder properties aren't controlled? |
-Homogeneity and segregation tendency -Flowability -Compression properties and compactability -Friction and adhesion properties |
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What happens during particle compression? |
-Particles in die rearranged so they're closer to each other -After interparticle spacing at minimum, any further increase of pressure results in deformation. -Big particles break into smaller ones if pressure further increased -Smaller particles rearranged and deformed; the same cycle of events may repeat several times during one compression -Eventually particle surface will be at proximity and the particles will stick to each other |
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Which two types of deformation can occur during the compression of particles? |
Elastic and Plastic deformation |
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What are the features of elastic deformation? |
-Temporary deformation -Due to small movement of the cluster of molecules or ions
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What are the features of plastic deformation? |
-Permanent deformation -Sliding of molecules along sliding planes within the particle |
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Under what circumstances can elastic deformation become plastic? |
If the stress is applied for a prolonged period of time |
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What processes occur during compression? (With regards to the machine) |
-When pressing, upper punch descends whilst the lower punch remains stable (upper punch force= Fa) -Whilst ejecting the tablets, lower punch pushes the tablet out (lower punch force= Fb) -Transmission of force from upper punch to lower punch depends on die-wall friction |
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What does Fe stand for? |
Maximum ejection force from the lower punch |
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What are the equations for die-Wall friction during compression? |
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