Microencapsulation

Question 1

what is microencapsulation?

Answer 1

it is a method of enclosing drugs in protective/ modified release coatings or membranes

Question 2

describe the difference between a reservoir and matrix system

Answer 2

reservoir has a drug core surrounded by a polymer shell.
whilst the matrix has drug dispersed throughout the polymer

Question 3

list some uses of microencapsulation

Answer 3

1. dosage forms
2. mask unpleasant tastes of drugs
3. protects against oxidation and hydrolysis.
4. GI tract targeting
5. can provide modified release

Question 4

eudragit RL and RS is a degradable polymer. how does it differ from ‘eudragit L & S’?

Answer 4

rate of release only. L & S is gastro resistant so that controls location release in gi tract

Question 5

what are some factors that makes polymers ideal for microencapsulation? (5)

Answer 5

1. biocompatable
2. biodegradable
3. easy to produce
4. relatively cheap
5. no adverse reactions with drug

Question 6

explain how microencapsulated particles are manufactured.

Answer 6

particles formed when polymers solidify (as solvent is removed).
Faster this is done the greater the amount of drug that can be encapsulated.
However the faster the polymer solidifies the more likely a porous microsphere/incomplete coating will be produced.
This can result in fast, uncontrolled and premature release

Question 7

explain what phase separation is (coacervation)

Answer 7

• dissolve coating material(polymer) in a solvent
• add core drug to form dispersion
• solubility of polymer reduced to deposit coating on the core
• then hardening process occurs.
  *only used for microcapsules aka reservoir systems. useful for encapsulating hydrophobic/ poorly soluble drugs

Question 8

how do you reduce the solubility of a polymer?

Answer 8

1. temp control
2. add a third component (adding a non solvent

Question 9

explain how emulsion solvent evaporation/extraction works

Answer 9

1. dissolve polymer in organic solvent then drug added to make solution
2. emulsifies in aqueous continuous phase containing an emulgent/surfactant.
3. emulsion agitated by stirring and heat to evaporate organic solvent or addition of continuous phase for extraction.
4. polymer solidifies around drug and microsphere produced.

Question 10

explain what an oil-in-water emulsion is and why its used

Answer 10

organic phase of containing drug and polymer in organic solvent, then place into a separate solution of water and surfactant.

usually used for hydrophobic drugs

Question 11

why cant you use an oil-in-water emulsion for hydrophilic drugs

Answer 11

the drug will partition from oil phase to water phase. therefore, it will no longer be encapsulated.

Question 12

what emulsion systems can you use for a hydrophilic drug?

Answer 12

oil-in-oil emulsion. two oil phases however they are immiscible with each other.

or preferably a water-in-oil-in-water emulsion. it is quicker to perform than o/o. harder to make a more stable emulsion as three phases rather than two.

however it is quicker and cheaper.

Question 13

list some factors that affect particle size

Answer 13

1. stirring speed
2. surfactant conc.
3. polymer and drug concs.
4. volume of phases

Question 14

factors affecting drug encapsulations

Answer 14

1. surfactant conc
2. polymer : drug ratio
3. volume of phases
4. drug solubility in each phase

Question 15

explain what spray drying is

Answer 15

1.Drug is dispersed or dissolved in a solution of the coating material.
2.Drug-polymer solution/suspension is fed as atomised droplets into heated chamber.
3. They are rapidly desolvated producing dry microparticles, which are drawn through to the collector.

Question 16

list some advantages of spray drying

Answer 16

1. fast process
2. large yield is common
3. allows use of hydrophilic and hydrophobic polymers & drugs
4. easier to scale up than

Question 17

some limitations of spray drying

Answer 17

1. pretty expensive
2. cant use highly heat sensitive materials.