Physical Pharmacy week 8 Flashcards
What is a dispersed and continuous phase?
f.e. in SUSPENSION:
Dispersed phase: particles within the medium
Continuous phase: f.e. water, where particles are dissolved in
Difference between dispersed phase formulations and solutions?
Dispersed phase formulations: particles are not dissolved in single molecules, rather there are chunks dispersed in the continuous phase
Solutions are also seen as dispersed formulations but dissolved in a single molecular form
Describe characteristics, size, and one example of molecular dispersions!
pass through semipermeable membrane and undergo diffusion, < 1 nm, Oxygen molecules and glucose
so well put together that considered as 1 phase
Describe characteristics, size, and one example of colloidal dispersions!
do not pass semipermeable membrane but filter paper, diffuses slowly and visible in electron microscope; 1-500 nm; Colloidal silver sol and polymers
in water, homo or heterogeneous system 1 or 2 phases
Describe characteristics, size, and one example of coarse dispersions!
do not pass membrane or paper filter and no diffusion, > 500 nm, RBC and most pharmac. suspension and emulsion
in water, heterogenous system with 2 phases
Characteristics of LyoPHILIC colloids
Colloidal particles interact with dispersion medium - low interfacial tension
dissolve well and provide stable formulation
often hydrophilic organic: albumin, methylcellulose, gelatin –> viscosifying agents
Why are hydrocolloids used as continuous phase in suspensions?
Because they exhibit sol-gel transition (thixotropy)
Example of hydrocolloids in medicine
Albumin or gelofusine used as plasma expander in critical care patients -> increase volume when in case of blood loss, because the heart keeps pumping blood when blood volume is high enough (circulatory shock)
increase because present in the blood vessel and exter osmotic pressure and draw fluid back from the tissues
(Albumin also prevents adsorption (sticking) of drug to packing material)
Characteristics of LyoPHOBIC colloids
high interfacial tension -> dispersed phase has low affinity to continuous phase, more unstable
inorganic molecules, f.e. colloidal gold/silver in water
specialized methods needed to prepare
LyoPHOBIC applications in medicine
TPN total parental nutrition, for patients in critical care to feed, essential oils in emulsion - the oil molecules may block arteries after long-term care
Megestrol (formulation of progesterol) counters weight loss in chemo and increases appetite
What differences are observed when giving coarse and nanodispersion of Megestrol?
Colloidal VS Coarse dispersion
The Megestrol preparation given in nanosize colloidal dispersion was way more effective in bioavailability than coarse dispersion
Characteristics of amphiphilic colloids
it likes water and oil, and it locates at the interface between water and air, lifting up the tail in the air and hydrophilic head to the water, once the interface is covered and minimum surface tension is reached (critical concentration) micelles are formed
How are amphiphilic colloids used?
used as Liposomes (a bigger form of micelles) to deliver lipophilic drugs
Microemulsion (emulsion with nm particles) increase droplet stability and bioavailability
for very lipophilic drugs with poor bioavailability
What is the function of liposomes?
used to target the drug to a specific area: drugs normally go everywhere
the liver f.e. more likely to take up liposomes, thereby you can target the liver in a therapy
Explain one unique property of colloids
High surface area as a catalyst -> using the bigger sized platinum has no action - because it has not the surface area to catalyze the reaction
bring the small particles together, in a way that works
thermodynamically better
Other properties of colloids: Optical (unique to colloidal dispersions)
Where is it used?
If you pass light through colloidal dispersion it will be scattered –> Tyndall effect
(particles in solutions are too small)
can be used to estimate the molecular weight of the colloid -> Turbidity (a measure of cloudiness)
Property of colloids: Brownian motion
-> Random motion of particles
there is enough kinetic energy to keep the small molecules moving to defy gravity
factors acting against Brownian motion: lower the temperature to take out the kinetic energy, particle size higher than 5 nm, viscosity
What other properties are shared with other dispersed systems?
Brownian motion -> molecular dispersions
electriacl double layers -> coarse dispersion
Explain Sedimentation of suspension
The rate of settling is defined by Stokes Law:
r = particle size radius (larger than 5 nm, it will settle)
p(rho) = particle density - p0 = density of the medium (if the particle is denser than density of the medium it will settle, if it is equal it will neither float nor sink, if its density is lower then it will float
g = gravity
n0 = viscosity
How can Stokes Law be applied to small particle systems?
particles lower than 5 nm don’t obey Stokes Law because Brownian motion keeps particles moving -> you have to increase gravity by centrifuging
added factors: w = angular velocity and x = distance of particle to the center of rotation
if you spin milk, particles will settle although Brownian motion
