sem 2 phar Flashcards
(27 cards)
gels meaning
solid-like substance that contains a significant amount of liquid in a 3D matrix
difference between ointments, creams, gels and pastes
ointments: highest oil content between all of the options, ideal for trapping moisture in skin
creams: a balance between oil and water, a more easily absorbed moisturiser
gels: water-based but a solid-like substance, clear or transparent appearance with quick absorption
pastes: very thick and stiff formulations that are ideal for absorbing secretions on the skin
what are ointments
Very high oil content that is used externally for medicinal purposes
types of ointments
hydrocarbon/oleaginous bases
absorption bases
water-removable bases
water-soluble bases
hydrocarbon/oleaginous bases effects
applied for emollient effects (softening or soothing the skin)
effective as occlusive dressing
remains on skin for long periods of time
difficult to wash off
examples of hydrocarbon/oleaginous bases
hard paraffin –> enhances rheology of ointment
white/yellow soft paraffin
liquid paraffin (mineral oil)
microcrystalline wax –> enhances viscosity and stability to formulation with liquid paraffin
absorption bases effects
emollient (softening an soothing on skin)
no occlusive effects (unlike hydrocarbons)
not washable from skin
contains 1 or more paraffins and sterol base emulsifiers (lanolin (wool fat), lanolin alcohols, beeswax)
generally results in better skin penetration than oleaginous
water washable/removable ointments effects
o/w emulsions
ability of accomodate large volumes of water
not occlusive
easily washable
aesthetically pleasing
water soluble bases
difference between water soluble bases and water removable bases
stability of ointments
relatively stable
stability is reduced when water is present
true solution
<1nm
particles are fully dispersed in continuous phase
example includes salt in water
colloids
between 1nm and 500nm
particles are suspended but do not settle
example include milk
coarse dispersions
> 500nm
particles are visible and settle out
example includes sand in water
3 main types of colloids
sol –> solid in liquid (paint)
emulsion –> liquid in liquid (milk)
foam –> gas in liquid (whipped cream)
key properties of colloids
- Tyndall effect
- Brownian motion
- Sedimentation rate
DLVO theory
explains colloidal stability considering 2 main forces; electrostatic repulsion (positive energy) and van der Waals attraction (negative energy)
Too high of van der Waals attraction results in clumping and
High electrostatic repulsion is ideal because it prevents molecules from aggregating
Types of gels
Hydrogel –> liquid phase is water and can either be physical or chemical
Organogels –> liquid phase is oil and can either by physical or chemical
physical gels –> non-covalent bonds with a self-assembled network
chemical gels –> covalent bonds with polymerisation networks
Gelling agents
used to thicken a liquid into a gel
examples include:
- gelatin (polymer)
- collagen (protein)
- bentonite (inorganic)
- carbopol (polymer) (pH sensitive)
- poloxamer (temp sensitive)
Pros of suspensions
- masks bitter tastes
- sustained release of drug
- improved stability of drug
- bioavailability is typically higher in suspension
- helps to deliver poorly soluble drugs
desirable features of a suspension
- particles do not settle out quickly
- if it does settle, it should redisperse easily
- suspension should flow from bottle easily
- acceptable to patient
- particle size of suspended solid should remain constant
primary minimum in suspensions
BAD!!!!!!
shows higher energy of attraction, therefore will eventually aggregate irreversibly
primary maximum in suspensions
BAD!!!!!!
high energy of repulsion causing particles to remain separate, however, because this prevents flocculation, there is potential for hard caking to occur
secondary minimum in suspensions
IDEAL
Provides weak flocculation and reversible aggregation which is easily redispersible
