gels creams and ointments

Question 1

What is a gel

Answer 1

Non-fluid colloidal network or polymer network that is expanded
throughout its whole volume by a fluid.

Question 2

what is swelling constrained by

Answer 2

constrained by intermolecular interactions or cross-links within
the molecular network, which confers structural rigidity.

Question 3

what is swelling due to

Answer 3

solvent infiltration into the molecular network, thus

unfolding and expanding the molecular network

Question 4

gels are what kinds of semi-solids

Answer 4

viscoelastic

Question 5

name the type 1 gel

Answer 5

chemical gel

Question 6

name the type 2 gel

Answer 6

physical gel

Question 7

describe the type 1 chemical gel + give an example

Answer 7

Irreversible polymer network.
– Covalently cross-linked.
– Often uses a covalent cross-linker.
– Example: polyacrylamide gel.

Question 8

describe the type 2 physical gel + give an example

Answer 8

Reversible polymer network.
– Weak intermolecular bonds (e.g. H-bonds).
– Sol-gel transition in response to specific stimulus (e.g. heat, pH).
– Example: agarose gel

Question 9

what fluid phase does a hydrogel have

Answer 9

water

Question 10

what fluid phase does an alcogel have

Answer 10

alcohol

Question 11

what fluid phase does organogel have

Answer 11

organic solvent

Question 12

which fluid phase does oleogel have

Answer 12

oil

Question 13

which fluid phase does xerogel have

Answer 13

none

Question 14

which fluid phase does aerogel

Answer 14

air

Question 15

which fluid phase does cryogel have

Answer 15

produced throughfreezing

Question 16

indications of pharmaceuitcal gels

Answer 16

Analgesic (e.g. ibuprofen).
– Anti-inflammatory (e.g. diclofenac).
– Anti-bacterial (e.g. clindamycin).
– Anti-fungal (e.g. miconazole).
– Local anaesthetics (e.g. lidocaine)

Question 17

advvantages of gel:

Answer 17

Topical and parenteral drug delivery.
• Controlled release.
• Dose form retention.
• Environmentally sensitive gels:
– Conditional drug release triggered by changes in environmental
conditions, e.g. pH, temperature.
• In-situ gelling systems:
– Controlled release: administer in liquid form, drug release in semi-solid
form.
– In-situ gelling can be triggered by physiological environment, e.g. body
heat.

Question 18

what are the basic components of pharmaceuticel gel

Answer 18

Drug.
– Solvent: dissolves drug and excipients, usually aqueous.
– Gelling agent: forms molecular network, provides structural rigidity,
entraps drug.

Question 19

what other components are in pharmaceutical gels

Answer 19

Cosolvent—enhance drug solubility.
– pH regulator (buffer)—enhance solubility of ionisable drugs, avoid skin
irritation.
– Preservative—inhibit microbial growth in aqueous gels.
– Penetration enhancer—enhance drug absorption into skin.

Question 20

describe a solid

Answer 20

– Liquid state.
– Colloidal dispersion (two or more components) of freely diffusing gelling
agent.
– Not a solution (single component).

Question 21

describe a gel

Answer 21

Solid-like state.
– Molecules of gelling agent interact covalently or non-covalently, polymer
network develops.
– Constrained by intermolecular bonds, physical entanglement or cross-links.
– Gelling agent not freely diffusing.

Question 22

what is the gel point

Answer 22

point of incipient polymer network formation.

Question 23

what does gel point depend on

Answer 23

chemical composition of the gel formulation,

Question 24

what are cellulosics

Answer 24

Cellulose and derivatives.

Question 25

what are carbomers

Answer 25

Cross-linked polyacrylic acid polymers.

Question 26

how can gel viscosity and swelling be enhanced

Answer 26

by neutralisation with a base (e.g. triethanolamine) or by adding hydroxyl donors (e.g. polyols, sugar alcohols) to promote hydrogen bonding.

Question 27

what is a cream

Answer 27

semi-solid emulsion | Dispersed system stabilised using a suitable emulsifier.

Question 28

name the two types of cream

Answer 28

hydrophillic | lipophlic

Question 29

what are the characteristics of hydrophillic cream

Answer 29

Non-greasy. – Miscible with skin secretions. – Water-washable. – Non-occlusive.

Question 30

characteristics of lipophilic cream

Answer 30

– Somewhat greasy (less so than ointments). – Less miscible with skin secretions than O/W. – Less water-washable than O/W. – Somewhat occlusive (less so than ointments).

Question 31

what does a cream need

Answer 31

Drug. – Continuous phase. – Dispersed phase. – Emulsifier—stabilise emulsion.

Question 32

To ensure sufficient dose and even dispersion of ingredients:

Answer 32

Good solubility in either phase. | – Or, incorporate solids homogenously by trituration.

Question 33

To ensure stable emulsion:

Answer 33

Choice of suitable emulsifiers, commonly amphiphilic surfactants. – Hydrophile-lipophile balance (HLB) and Bancroft’s rule.

Question 34

recall bancrofts rule in terms of emulsifier

Answer 34

High HLB emulsifier, O/W emulsion. | – Low HLB emulsifier, W/O emulsion.

Question 35

recall HLB in terms of emulsifier

Answer 35

Hydrophilic emulsifier: High HLB (>10). | – Lipophilic emulsifier: Low HLB (<10)

Question 36

what is an emulsion

Answer 36

continuous phase is a gel. | O/W or W/O.

Question 37

what is an emulgel

Answer 37

Emulsion + gel.

Question 38

advantages of emulgel:

Answer 38

– Incorporation of poorly water soluble drugs in a water-based formulation. – Non-greasy. – Good patient acceptability. – Dual release control mechanisms. – Viscous continuous phase enhances emulsion stability. – Thixotropy enhances spreadability

Question 39

what is an ointment

Answer 39

semi-solid dosage form, usually anhydrous with a hydrophobic oily base, intended for external application to the skin or mucous membran

Question 40

Types of ointment

Answer 40

Hydrophobic (oleaginous) ointment. – Water emulsifying ointment. – Hydrophilic (greaseless) ointment.

Question 41

describe a hydrocarbon base

Answer 41

Occlusive—emollient effect. – Not water-washable. – Greasy. – Petrolatum (paraffin).

Question 42

describe a absorption bases

Answer 42

– Form w/o emulsions with skin secretions. – W/O emulsifier. – Emollient effect. – Lanolin and derivatives.

Question 43

describe a water-removable base for water emulsifying ointment

Answer 43

Form O/W emulsions with skin secretions. – O/W emulsifier. – Water-washable. – Cetostearyl alcohol, cetomacrogol.

Question 44

describe water-soluble base

Answer 44

Water-washable. – Non-greasy. – Macrogols (polyethylene glycols = PEG).