Exam 4 Flashcards
What is the particle size for molecular dispersions?
< 0.001 µm
What is the particle size for colloidal systems?
0.001 – 0.5 µm
What is the particle size for coarse disperions?
10 – 50 µm
What are two types of coarse dispersions?
suspensions, emulsions
What is a pharmaceutical suspension?
coarse dispersion in which insoluble solid particles are dispersed in a liquid dispersion medium
What should the particle size of suspensions be?
> 0.1 µm
What are the different types of administration for suspensions?
oral, topical, transmucosal, parenteral
T/F The stokes law is only applicable to dilute suspensions.
True
What is the concentration for “dilute suspensions”?
< 2 % solid
What is a promoting factor?
a factor that if it is increased then settling will increase
What are examples of promoting factors?
density, particle diameter, gravity
What is the force of attraction?
London-van der Waals type (VA)
What is the force of repulsion?
Electrical double layer (VR)
What is the net potential energy of interaction?
VT = VA + VR
With respect to the DLVO theory, what does it mean when Pmax < Thermal energy of particle?
irreversible aggregation
With respect to the DLVO theory, what does it mean when Pmax > Thermal energy of particle?
the dispersion is stable
With respect to the DLVO theory, what does it mean when Smin < Thermal energy of particle?
loose reversible flocculation
How can you increase the height of Pmax?
increasing zeta potential
How can you decrease the depth of Smin?
adding electrolytes
With respect to the state of the suspension, what are you doing by increasing the height of Pmax / increasing depth of Smin?
making the suspension more stable
What are properties / characteristics of flocculated particles?
weakly bonded, settle rapidly, do not form cake, easily resuspended
What are properties / characteristics of deflocculated particles?
settle slowly, eventually form sediment, form cake, difficult to resuspend
What are the characteristics of sidmentation of a flocculated system?
there is a distinct boundary, flocs carry small particles down
What are the characteristics of sidmentation of a deflocculated system?
there is a turbid supernatant, sediment segregates according to particle size
What is an oral suspension?
aqueous preparations with the vehicle flavored and sweetened to suit the taste preferences of the intended patient
What are the desirable qualities of a pharmaceutical suspension?
Does not settle, no cake formation, high suspendability, able to pour easily, pharmaceutically elegant, dispersed particle size should not change
What are examples of structured vehicles?
Carboxymethylcellulose (CMC), Polyvinylpyrrolidine (PVP), Xanthan gum, Benotnite, Tragacanth gum
What are properties of structured vehicles?
they entrap particles in a deflocculated manner to prevent settling, pseudoplastic/plastic in nature, allows particles to become easily dispersed
Does high sedimentation volume produce a more or less stable solution?
more stable
What does surfactants do?
reduce surface tension on solid-liquid interphase; can provide charge on particle surface; decrease surface free energy
Why is concentration of surfactant important in flocculation?
At low concentrations, they can be used as wetting and deflocculating agents
How does polymers act in flocculation?
part of their chain is absorbed on the particle surface and the remaining part of the chain is projected into the dispersion medium
What does hydrophilic polymers do?
they coat the particles which make them less prone to caking
How can you get the best suspension preparation?
if you know how to use structured vehicles hand in hand with flocculation strategy
_____ powders have low contact angles in water. _____ powders have large contact angles in water.
hydrophilic / hydrophobic
How can wettability be improved?
using surfactants (otoxynol) and wetting agents (glycerin, PG)
What can you use to make your formulation pharmaceutically elegant?
suspending agents, flocculating electrolytes, wetting agents, sweeteners, preservatives, flavoring agents, color
What is a suspending agent?
something that entraps particle in a deflocculated manner
How do you prepare suspensions?
wet the dispersed phase particles with wetting agent; dissolve soluble formulation ingredients in dispersion phase; add dispersion phase in portions to the wetted particles and mix thoroughly
Why must suspensions be refrigerated?
high temperatures may increase solubility and low temp may increase crystallization
How come neonatal suspensions don’t need flavoring?
neonates cannot taste or smell; also have underdeveloped kidney so you don’t want to add anything unnecessary
Under which patient conditions should you not use alcohol in suspensions?
elderly patients with a history of depression, patients with liver problems
What are the common categories of pharmaceutical suspensions?
antacid, antibacterial, rectal, dry powders for suspension
What are characteristics of emulsions?
thermodynamically unstable system; consists of at least two immiscible liquid phases; stabilized by an emulsifying agent
What are the types of emulsions?
- Oil-in-water
- Water-in-oil
What is an oil-in-water phase?
Nonpolar dispersed phase in polar dispersion medium; medicinal emulsions
What is an water-in-oil phase?
Polar dispersed phase in nonpolar dispersion medium; externally applied emulsions
How do you test whether an emulsion is oil-in-water or water-in-oil?
- Dye method (Methylene blue dusting; M.blue dissolves easily in water)
- Dilution of dispersion medium
- Electrical circuit method (electrical current will form in water)
What prevents coalescence?
the emulsifying agent
What is coalescence?
process by which two or more droplets, bubbles or particles merge during contact to form a single daughter droplet, bubble or particle
What is the surface tension theory?
the reduction in interfacial tension prevents coalescence
What is the oriented wedge theory?
the monomolecular film around the droplets prevents coalescence
What is the interfacial film theory?
the particulate film around the droplets prevents coalescence
What type of emulsifier is Sorbitan monooleate (Span 80)?
Nonionic surfactant
What type of emulsifier is Acacia?
Hydrophilic colloid
What type of emulsifier is Veegum (Mg-Al-silicate)?
Solid particle
What are characterstics of hydrophilic colloids as an emulsifier?
Form multimolecular film at the interface; strong film resists coalescence; effect is the increased viscosity; usually promote oil-in-water emulsions
What are characteristics of creaming?
- Negative sedimentation where ρDispersed < ρDispersion
- Gravity-assisted sedimentation where ρDispersed > ρDispersion
- is reversible
How can you prevent the breaking of emulsions?
- have uniform particle size
- have optimal viscosity
- have phase volume of 50/50 but critical point is 74% oil in oil-in-water emulsion
- increase the zeta potential
What can heparin do in an oil-in-water emulsion?
it has to be an oil-in-water emulsion that has been stabilized by lecithin; it undergoes charge reversal; heparin flocculates charge-reversed emulsion by bridging the droplets and destabilizes the droplets
What is phase inversion?
when the dispersion medium becomes dispersed phase and dispersed phase becomes dispersion medium
What are the ways in which you can have a phase inversion?
- O/W Emulsion + Oil -> W/O Emulsion
- W/O Emulsion + Water -> O/W Emulsion
- Addition of salt: O/W emulsion stabilized with Na stearate inverts to W/O emulsion upon addition of CaCl2
T/F Emulsions do not have an effect on what the dispersion medium is.
F. Whatever the emulsifying agent love, it will make that the dispersion medium
What is Bancroft’s rule?
The phase in which the emulsifying agent is more soluble will be the external phase
What does HLB stand for?
hydrophilic lipophilic balance
Describe the values of the HLB system.
Can go up to 40; useful medicinal range is 1-20; the higher the number, the more hydrophilic
T/F: A single emulsifying agent is more effective than a mixture of emulsifying agents.
False: A mixture of emulsifying agents is more effective than a single agent
How is calcium soap formed within an emulsion?
via a reaction between oleic acid and Ca(OH)2
