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Kirsty - Y3S2 > TD: Microencapsulation > Flashcards

TD: Microencapsulation Flashcards

1
Q

What is microencapsulation?

Why is it used?

A

Microencapsulation is a method of enclosing drugs in protective/modified release coatings/membranes.

It is used to control the rate of release of the drug

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2
Q

What size are microparticles?

What could 2 terms could microparticle mean?

A

Size: 1-1000um

Microparticle could mean either:

  • Microcapsule: reservoir system
  • Microsphere: matrix system
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3
Q

What does microencapsulation involve?

A

Microencapsulation involves a number of processes that entrap an active material in (mainly) spherical particles/ in a reservoir (if reservoir system) or matrix (if matrix system) in order to immobilise it, protect it, control its release and provide new physical properties or functions.

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4
Q

What are applications of microencapsulation?

A

Applications are wide-ranging: controlled release of drugs and drug targeting, encapsulation of inks, glues, detergents and enzymes.

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5
Q

What is the polymer and drug ratio like?

A

Very rare if drug ratio greater than polymer. Typically always greater portion of polymer

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6
Q

What in terms of coating will affect drug release rate?

A

Thickness of coating and type of polymer used

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7
Q

What are uses of microencapsulation?

A
  • May be used in conventional dosage forms, e.g. compressed into tablets, enclosed in hard gelatine capsules, formulated as a parenteral.
  • Mask unpleasant taste of drugs.
  • Protects against oxidation and hydrolysis.
  • GI tract targeting - pH sensitive coating to prevent release in stomach
  • Produces modified release preparations.
  • Drug targeting by parenteral route to target tissues
    • Can modify size of particles to target disposition in certain parts of the body, e.g. 2-5 µm to target liver
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8
Q

What are examples of:

  1. Water soluble polymer?
  2. Water insoluble non-biodegradable polymer
  3. Water insoluble biodegradable polymer?
  4. Gastro-resistant polymer?
A
  1. Water soluble:
    • Soluble cellulose derivatives, gelatin.4
  2. Water insoluble Non-degradable:
    • Ethylcellulose
  3. Water insoluble Degradable:
    • Eudragit RL and RS
    • copolymers of lactic and glycolic acids (e.g. polylactic-co-glycolic acid (PLGA))
    • waxes
  4. Gastro-resistant:
    • Enteric polymers (Eudragit L & S)
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9
Q

What is the difference of functions between Eudragit RS and RL and Eudragit S and L?

A

RS & RL are not pH depent release so do not control place release just release rate

S & L are suitable for pH depenet release therefore place release and release rate

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10
Q

Which polymer is most used for microencapsulation and why?

A

PLGA

  • Readily available
  • Relativey cheap
  • Biodegradable
  • but hydrophobic
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11
Q

What are the ideal characterisitics for a polymer used in microencapsulation?

A

Ideal polymer for use in microencapsulation would need to be:

  • Biocompatible
  • Biodegradable* or soluble
  • Easily produced
  • Relatively inexpensive
  • Has no adverse interactions with the drug
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12
Q

Which polymers and not regularly used now and why?

A

Non-degradable polymers (ethylcellulose) not used frequently as they reduce patient acceptability and tend to not M/R well, i.e. produce burst release

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13
Q

What is the basic principle behind microencapsulation?

A
  • 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.

Dissolve the polymer in drug in one or more solvents then perform some kind of manipulation that causes the drug and polymer to precipitate out and the polymer solidify. This solidifiying process causes encapsulation of the drug in the polymer.

  • Reservoir: Polymer dissolved but drug not
  • Matrix: Polymer and drug dissolved
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14
Q

What methods are available for microencapsulation?

A
  1. Phase Seperation (coacervation)
  2. Emulsion Solvent Evaporation/Extraction (ESEv/ESEx)
  3. Spray Drying
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15
Q

Describe the basic process of phase seperation

A

The coating polymer is dissolved in a solvent to form a solution, to which the solid drug is added. This forms a suspension with the drug uniformly disperesed throughout the polymer solution. A process occurs which causes the polymer to have reduced solubility and form a coating around the core. Further hardening process then occurs.

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16
Q

What can phase seperation only be used for?

A

Only suitable for microcapsules (Reservoirs)

17
Q

What types of drugs is phase seperation particularly useful for?

A

Particularly useful to encapsulate hydrophobic/poorly soluble drugs as they are not required to dissolve in the polymer solution

18
Q

What 2 processes in phase seperation method can be used to solidify the polymer?

Describe these?

A

(a) Temperature control

Uses temperature to reduce solubility, e.g. ethylcellulose dissolved in cyclohexane at high temperatures. Drug dispersed in solution. On cooling, ethylcellulose precipitates and settles around core. Filtration or centrifugation to harvest. Drying to remove solvent.

(b) Addition of a third component

  • Solubility reduced by adding a non-solvent.
  • E.g. Gelatin (polymer) dissolved in water - finely-divided drug is added to form a suspension.
  • A non-solvent, e.g. absolute alcohol (polymer insoluble in), is added causing the gelatin to precipitate. Gelatin coalesces around the particles and forms hardened microcapsule.
19
Q

Describe Emulsion Solvent Evaporation/Extraction (ESEv/ESEx) method

A
  • Polymer dissolved in organic solvent then drug added to form solution
  • Solutoin emulsified in an aqueous continuous phase containing an emulgent/surfactant.
  • Emulsion agitated by stirring (and application of heat or pressure) to evaporate organic solvent or add additional continuous phase to extract solvent. Polymer and drug and polymer encapsulates drug. Particles filtered, washed, dried.
20
Q

What can the 2. Emulsion Solvent Evaporation/Extraction (ESEv/ESEx) method be used for?

A

Microspheres (Matrix systems)

21
Q

What types of emulsions can be used?

A
  • Oil in water
  • Oil in Oil
  • Water in Water
22
Q

Describe oil in water emulsions used

A

Disperse/ Internal phase is made of polymer and drug dissolved in a water immiscible solvent (oil).

The Continuous phase/ External phase is made of water and surfactant.

The continuous phase is added to the disperse phase to form a oil in water emulsion

23
Q

In an oil in water emulsion what type of drugs can be used?

Why is this method most common?

A

most common as it is particularly useful for hydrophobic drugs/drugs with poor aqueous solubility and is relatively quick to carry out (1-4 h). However cannot be used for hydrophilic drugs.

Only hydrophobic drugs as otherwise a hydrophilic drug would partition into waterphase and less drug encapsulated

24
Q

What is the problem with oil in water emulsions?

A

•Problems can arise when surfactants used to stabilise emulsion lead to increased solubility of the drug in the water phase. This can cause it to diffuse out of the internal phase before polymer solidification and so a large mass of the drug can be lost during manufacture.

25
Q

What can oil in oil emulsion be used for?

Describe an oil in oil emulsion

A

Used for hydrophillic drugs

Both internal and external phases are oils but are immiscible - this means drug wont partion from disperse phase.

As these are less volatile the process is more time consuming to produce particles (up to 12hrs) therefore more costly.

26
Q

What can Water in oil in water emulsion be used for?

Describe this emulsion

Problems and benefits

A
  • Used for hydrophillic drugs. Process is quicker and therefore cheaper than O/O.
  • Problem: As 3 phases needed this is a more complicated proceedure and also requires 2 surfactants to stablilize the phases
  • Water in oil emulsion is combined with another water phase
27
Q

What are factors affecting microparticle properties from emulsion systems in terms of:

  1. Factors affecting particle size
  2. Factors affecting drug encapsulation
A

Affecting particle size:

  • Stirring speed
  • surfactant concentration
  • polymer and drug concentrations
  • volume of each phase

Affecting drug encapsulation:

  • Surfactant concentration
  • polymer:drug ratio
  • volume of each phase,
  • drug solubility in each phase
28
Q

How does spray drying work?

A

Drug is dispersed or dissolved in a solution of the coating material.

Drug-polymer solution/suspension is fed as atomised droplets into heated chamber. They are rapidly desolvated producing dry microparticles, which are drawn through to the collector.

29
Q

What systems can be produced from spray drying?

A

Produce microcapsules or microspheres.

30
Q

What type solvent is preferred to use and why?

What benefits does the other type of solvent have?

A

•If possible aqueous solutions are used (organic solvents are flammable and toxic).

–Use of organic solvents can lead to problems in patient use – limits very tightly controlled

•However organic solvents are sometimes unavoidable and can produce a higher yield of particles at low temperatures than water (most have boiling points well below water and so evaporate to produce particles much more readily). Can also reduce costs and allow use of some heat labile materials.

31
Q

Advantages of spray drying

A

•Advantages:

–Fast process (0.5-1h or less)

–Large yields common (80%+) and encapsulation will always be very high (nowhere to lose drug to during manufacture unlike (o/w) emulsion systems)

–Allows use of both hydrophilic and hydrophobic polymers and drugs

–Much easier to scale up than an emulsion or coacervation

32
Q

Negatives of spray drying

A
  • Specialist equipment - Spray drier required which is expensive compared to for the other techniques
  • Cannot use highly heat sensitive materials
33
Q

What testing of microparticles should be done

A
34
Q

What are the 4 stages of degradation of a water soluble polymer?

A
  1. Polymer hydration on contact with GI fluid
  2. Cleaveg on bonds within polymer structure reducing polymer molecular weight
  3. Erosion of polymer once molecular weight has fallen to a critical point
  4. Dissolution of remaining polymer
35
Q

Explain the difference between surface and bulk degradation of a polymer and why this is important in drug release

A

Degradation is important microparticle delivery system as the rate of degradation can control release and dictate whether or not the release is consistent (Zero order) or Variable (Non-first order).

Surface only degradation can be thought of as like peeling an onion. As the layers of polymer degrade the drug is released.

Bulk degradation results in less consistent/controlled release as the drug is released from the interior earlier than desired. I.e. at the same time as the drug near the surface of the device

36
Q

How does stirring speed effect particle size?

A

Increasing speed causes decrease in particle size as there is an increase in shear forces acting on the internal phase therefore reduce size of internal phase droplets. The opposite is true if decrease speed.

37
Q

How does surfactant conc affect particle size

A

Surfactatns reduce interfacial tension between phases of an emulsion and therefore allow mixing of the water and oil phases. Increaseing surfactant concentratoin will further reduce interfacial tension and in doing so reduce the size of the internal phase resulting in smaller particles being formed. The opposite is true if surfactant reduced

38
Q

How does surfactant conc affect drug encapsulation?

A

Increasing surfactant concentration increases drug solubility in aqueous phase of an emulsion therefore reduces encapsulation (as more drug diffused out or internal phase before polymer solidifies)

39
Q

How does drug solubility in each phase affect drug encapsulation?

A

If a drug is highly water soluble then it will diffuse out of the oil and into the water phase of a oil-in-water emulsion and so encapsulation will be low. Therefore for those type of drugs an oil-in-oil or water-inoil-in water emulsion would be used

Kirsty - Y3S2 (40 decks)

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