excipients

Question 1

why do we use excipients ?

Answer 1

to control dose, taste , solubility, stability, rate of absorption etc.
also drugs are often in small doses that would be difficult for a patient to weigh, equally drugs with high doses can be difficult to formulate.

Question 2

how is panadol actifast different to original panidol?

Answer 2

actifast contains the excipient sodium bicarbonate - this increases the rate of tablet disintegration and dissolution as well as the rate of gastric emptying so that the drug reaches the absorption site, the small intestine quicker. actifast is just as effective as regular panadol but provides faster acting pain relief. however for the sodium bicarbonate to work you must take 2 tablets at once with at least 100 ml of water.

Question 3

whats an excipient?

Answer 3

any other component of the formulation other then the api. excipients must be chemically and physically inert and must have an appropriate evaluation for safety.
excipients aid the manufacture process, enhance stability, assist in identification etc.

Question 4

how can excipients effect dissolution?

Answer 4

rates of drug dissolution can be adversely affected by choice of formulation additives, particularly lubricants. insoluble magnesium stearate is a lubricant which imparts hydrophobicity to a formulation hence inhibitng drug dissolution. we therefore want to minimise the percent of lubricant ithin the formulation.

Question 5

what are diluents?

Answer 5

diluents/bulking agents are inert substances added to the formulation to make a reasonable sized tablet. the principle diluent used is lactose as it has a pleasant taste rapidly dissolves in water and it is not hygroscopic.
dicalcium phosphate is also used particularly in wet granulation.
starches are used as diluents and binding agents.
microcrystalline cellulose is a popular direct compression diluent.

Question 6

what is microcrystalline cellulose?

Answer 6

microcrystalline cellulose is produced by partial hydrolysis of cellulose, it has outstanding compressabilityand high tablet strength from low compression force. it has both lubricant and disintegrating properties. however mcc is sensitive to lubricant and moisture sensitive.

Question 7

what are lubricants?

Answer 7

lubricants are used to prevent adherence of the formulation to punches and dies to ensure smooth ejection from the die. they act by interposing a film of low shear strength at the interface between the tablet and the die wall/punch face. some lubricants also act as antiadherents and flow aids. talc and magnesium stearate is most effective as punch lubricantswhilst stearic acid is more effective as a die lubricant.

Question 8

what is magnesium stearate?

Answer 8

magnesium stearate is a lubricant that gets incorporated with dry granules prior to compression.

Question 9

what are the disadvantages of magnesium stearate?

Answer 9

requires additional processing steps, high conc will decrease disintegration time and weaken bond forces due to its hydrophobic nature
its incompatible with many drugs e.g. aspirin requires talc or stearic acid instead.

Question 10

what are glidants?

Answer 10

glidents/flow agents improve flow properties of granules by reducing interparticulate friction. common glidents are fumed silica, a synthetic amorphous colloidal silicon dioxide. flow agents reduce the contact area between granules, reducing the interparticulate cohesion/adhesion which determines flowability

Question 11

what are disintegrants?

Answer 11

disintegrants promote the break up of tablets once ingested. this is the first stage of dissolution. disintegrat=nts are important in the dissolution of insoluble drugs especially those with a high dose. the rolse is to rapidly disintegrate tablets to increase the surface area of the formed deggragetes promoting rapid release of the drug.
a common disintegrant is starch or polyvinylpyrollidone.

Question 12

whats disintegration?

Answer 12

the process by which tablets are broken down into granules.

Question 13

whats deaggregation ?

Answer 13

the process by which granules primarily become drug particles for rapid rate of dissolution.

Question 14

how do disintegrants work?

Answer 14

there are many mechanisms of action, including:

• swelling
• porosity and capillary action, this draws liquid into capillary pathways and ruptures interparticulate bonds
• deformation
• gas production
• inter relationship occurs in most formulations

Question 15

what are super disintegrants?

Answer 15

sometimes faster disintegration is required - modified starch has rapid and extensive swelling with minimal gelling, this also reduces issues relating to compressability and flowability of starch although it is more hygroscopic.

Question 16

what are binding agents?

Answer 16

binding agents /adhesives bind powders togetherin the wet granulation process or granules during direct compression
common binding agents are starch mucilage and gelatin.
pvp is an important binder as its soluble in water and alcohol and rapidly releases the drug.

Question 17

how can binding agents be added?

Answer 17

a powder in formulation - this is known as slugging.
or a solution added to mixed powders in wet granulation.
liquid additives must be remved prior to compression.
adhesives can affect dissolution rate.

Question 18

what are adsorbents?

Answer 18

adsorbents are substances capable of holding quantities of fluids in an apparent dry state. liquid flavourings etc can be mixed with adsorbents for granulation and compression into tablets. fumed silica microcrystalline cellulose and magnesium crabonate arre commonly used absorbents.