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Fei Lectures > L6: Gels > Flashcards

L6: Gels Flashcards

0
Q

How are drugs incorporated into gels?

A

They can be SUSPENDED in the matrix, or DISSOLVED in the liquid

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1
Q

A pharmaceutical gel is a semisolid system of at least two constituents, what are they?

A

A condensed mass, enclosed and interpenetrated by a liquid.

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2
Q

Explain what happens when the particles of drug are added in to the gel.

A

They link together to form INTERLACED NETWORK, imparting the RIGIDITY to the structure, continuous phase is held between the meshes.

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3
Q

In gels, when the coherent matrix is rich in liquid, what is the product called?

A

Jelly.

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4
Q

In gels, if the liquid is removed, and only gel framework remains, what is this called and give an example?

A

Xerogel.

Gelatin sheets, tragacanth flakes

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5
Q

Explain what a single phase gel/system is.

A

Contain linear/branched polymer MACROMOLECULES, that dissolve in water, have no definite boundaries with the dispensing medium.

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6
Q

What are macromolecules classed as?

A

Natural polymers –> tragacanth

Semisynthetic cellulose derivatives –> methyl cellulose

Synthetic polymers –> carbomer polymers

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7
Q

Why do macromolecules not form true solutions?

A

Because of their size.

Form colloidal dispersions instead (sol).

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8
Q

What’s different about a macromolecule (colloidal dispersion) even if it is liquid and appears to be a solution?

A

Sometimes cloudy.

More viscous than base solvent.

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9
Q

What do two phase gels contain rather than macromolecules?

A

Floccules of small particles.

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10
Q

The structure of a two phase gel is not always stable, on shaking, what happens to it?

A

It becomes a liquid.

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11
Q

What is the two phase gel referred to as, if the particles are large?

A

Magma.

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12
Q

Give examples of two phase systems.

A

Aluminium hydroxide gel

Magnesia magma

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13
Q

What are gels that contain water called? And how are they formed?

A

Hydrophilic gels. (Hydrogels).

Formed by lyophilic sols.

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14
Q

Aqueous gels can be divided into 2 groups, depending on what?

A

On the nature of the bonds between the chains of the network.

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15
Q

Explain what ‘type 1 gels’ are.

A

Irreversible systems

With 3D network, Formed by COVALENT bonds between the macromolecules.

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16
Q

Type 1 gels are ‘irreversible systems with a 3D network’ formed by what?

A

By COVALENT bonds between the MACROMOLECULES.

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17
Q

How is the network made in type 1 gels?

A

May be made by POLYMERISING water soluble polymers with a CROSS-LINKING agent.

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18
Q

If the polymers in type 1 gels contain little water, they are said to be…

A

Rigid.

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19
Q

What can happen when the polymers in type 1 gels absorb water?

A

Can swell and become more flexible.

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20
Q

(Type 1 gels) The network polymers can swell in water, but cannot dissolve, why?

A

Due to the stable cross linking structure.

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21
Q

The network polymers in type1 gels have been used in…..

A

…the fabrication of expanding implants.

….the prolonged drug release system.

22
Q

Explain what type 2 gels are.

A

3D network, held together by weaker bonds. E.g. Hydrogen bonds, dipole dipole attraction.

Heat reversible.

23
Q

type 2 gels are heat reversible, what does this mean?

A

They can change from ‘sol’ to gel on either heating, or cooling.

24
Q

Type 2 gels can be used….

A

Topically.

25
Q

What is usually the base in lyophobic gels?

A

Base is usually OILY.

Liquid paraffin
Vegetable oil

26
Q

Aqueous gels are often prepared using what type of gelling agent?

A

Organic gelling agent.

27
Q

Lyophobic gels usually use what type of gelling agent?

A

Inorganic gelling agent.

Usually based on a silicate compound.

28
Q

What type of ‘phase’ is a lyophobic gel?

A

Two phase.

29
Q

Name one pharmaceutical application of gels. T

A

Topical application.

30
Q

What’s different about a gel compared to creams/ointments? (TA)

A

Gels are non greasy formulations.

31
Q

Whats one pharmaceutical area where gels are useful topically?

A

For hairy regions of the body.

E.g. Synalar gel for scalp use.

32
Q

Why are gels useful as lubricants? (Topically)

A

As they spread easily over skin.

33
Q

Name one pharmaceutical application of gels. (O)

A

Ophthalmic application.

34
Q

Why are gels better than ointments? (Ophthalmic)

A

Less visual distortion after application.

35
Q

Explain how (ophthalmic gel) works

A

Forms a protective film over the cornea.

Well tolerated.

36
Q

Why are gels better than solutions? (Ophthalmic)

A

Increased retention time

May result in less frequent administration.

37
Q

Name an ophthalmic gel

A

Viscotears 0.2%

38
Q

Name an anaesthetic gel (topical).

A

Lidocaine gel

39
Q

Name one pharmaceutical application of gels. (Bio)

A

Bioadhesives

40
Q

What are bioadhesives used for?

A

To treat oral lesions

41
Q

Name one pharmaceutical application of gels. (Bu)

A

Buccal application

42
Q

Name one pharmaceutical application of gels. (W)

A

Wound management.

43
Q

Name one consideration of using a gelling agent.

Dispersing medium

A

If it is added to dispersing medium in a haphazard manner, there’s a tendency for the agent to CLUMP.

44
Q

Name one consideration of using a gelling agent

Temperature.

A

Some are more soluble in cold water than hot. Methyl cellulose

Some more soluble in hot than cold water. Gelatin

45
Q

Name one consideration of using a gelling agent

PH

A

Some require a neutraliser, or pH adjusting chemical to create the gel.

46
Q

Name one consideration of using a gelling agent

Time.

A

Most require 24-48 hours to completely hydrate, and reach max viscosity and clarity.

47
Q

Name one consideration of using a gelling agent

Drug

A

Easier to add active drug BEFORE gel is formed.

Only if drug doesn’t interfere with gel formation.

48
Q

Name one consideration of using a gelling agent

Mouth

A

Only a few can be administrated orally.

49
Q

Name another additive for gels. (H)

A

Humectants.

50
Q

Name another additive for gels. (P)

A

Preservatives.

51
Q

What does a humectant do in gels ?

A

Can minimise water loss from a gel.

52
Q

Example of a humectant?

A

Glycerol

Fei Lectures (8 decks)

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