gels creams and ointments Flashcards
What is a gel
Non-fluid colloidal network or polymer network that is expanded
throughout its whole volume by a fluid.
what is swelling constrained by
constrained by intermolecular interactions or cross-links within
the molecular network, which confers structural rigidity.
what is swelling due to
solvent infiltration into the molecular network, thus
unfolding and expanding the molecular network
gels are what kinds of semi-solids
viscoelastic
name the type 1 gel
chemical gel
name the type 2 gel
physical gel
describe the type 1 chemical gel + give an example
Irreversible polymer network.
– Covalently cross-linked.
– Often uses a covalent cross-linker.
– Example: polyacrylamide gel.
describe the type 2 physical gel + give an example
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
what fluid phase does a hydrogel have
water
what fluid phase does an alcogel have
alcohol
what fluid phase does organogel have
organic solvent
which fluid phase does oleogel have
oil
which fluid phase does xerogel have
none
which fluid phase does aerogel
air
which fluid phase does cryogel have
produced throughfreezing
indications of pharmaceuitcal gels
Analgesic (e.g. ibuprofen). – Anti-inflammatory (e.g. diclofenac). – Anti-bacterial (e.g. clindamycin). – Anti-fungal (e.g. miconazole). – Local anaesthetics (e.g. lidocaine)
advvantages of gel:
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.
what are the basic components of pharmaceuticel gel
Drug.
– Solvent: dissolves drug and excipients, usually aqueous.
– Gelling agent: forms molecular network, provides structural rigidity,
entraps drug.
what other components are in pharmaceutical gels
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.
describe a solid
– Liquid state.
– Colloidal dispersion (two or more components) of freely diffusing gelling
agent.
– Not a solution (single component).
describe a gel
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.
what is the gel point
point of incipient polymer network formation.
what does gel point depend on
chemical composition of the gel formulation,
what are cellulosics
Cellulose and derivatives.
what are carbomers
Cross-linked polyacrylic acid polymers.
how can gel viscosity and swelling be enhanced
by neutralisation
with a base (e.g. triethanolamine) or by adding hydroxyl donors (e.g.
polyols, sugar alcohols) to promote hydrogen bonding.
what is a cream
semi-solid emulsion
Dispersed system stabilised using a suitable emulsifier.
name the two types of cream
hydrophillic
lipophlic
what are the characteristics of hydrophillic cream
Non-greasy.
– Miscible with skin secretions.
– Water-washable.
– Non-occlusive.
characteristics of lipophilic cream
– 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).
what does a cream need
Drug.
– Continuous phase.
– Dispersed phase.
– Emulsifier—stabilise emulsion.
To ensure sufficient dose and even dispersion of ingredients:
Good solubility in either phase.
– Or, incorporate solids homogenously by trituration.
To ensure stable emulsion:
Choice of suitable emulsifiers, commonly amphiphilic surfactants.
– Hydrophile-lipophile balance (HLB) and Bancroft’s rule.
recall bancrofts rule in terms of emulsifier
High HLB emulsifier, O/W emulsion.
– Low HLB emulsifier, W/O emulsion.
recall HLB in terms of emulsifier
Hydrophilic emulsifier: High HLB (>10).
– Lipophilic emulsifier: Low HLB (<10)
what is an emulsion
continuous phase is a gel.
O/W or W/O.
what is an emulgel
Emulsion + gel.
advantages of emulgel:
– 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
what is an ointment
semi-solid dosage form, usually anhydrous with a hydrophobic oily
base, intended for external application to the skin or mucous membran
Types of ointment
Hydrophobic (oleaginous) ointment.
– Water emulsifying ointment.
– Hydrophilic (greaseless) ointment.
describe a hydrocarbon base
Occlusive—emollient effect.
– Not water-washable.
– Greasy.
– Petrolatum (paraffin).
describe a absorption bases
– Form w/o emulsions with skin secretions.
– W/O emulsifier.
– Emollient effect.
– Lanolin and derivatives.
describe a water-removable base for water emulsifying ointment
Form O/W emulsions with skin secretions.
– O/W emulsifier.
– Water-washable.
– Cetostearyl alcohol, cetomacrogol.
describe water-soluble base
Water-washable.
– Non-greasy.
– Macrogols (polyethylene glycols = PEG).
