PSII Exam II Flashcards
Define a dispersed system
A mixture of one phase in another largely immiscible phase.
Define a suspension
Solid particles dispersed in a liquid medium.
Define an emulsion
Liquid droplets dispersed in a liquid medium.
Define a molecular dispersion
A true solution; particle size less than 1 nanometer.
Define a colloidal dispersion
Particle size less than half a micron.
Define a coarse dispersion
Particle size greater than half a micron.
What are three important stability characteristics of PHARMACEUTICAL dispersed systems?
- Uniform distribution
- Aggregation rate controlled.
- Flocculation controlled.
What are three fundamental physical chemistry concepts for PHARMACEUTICAL dispersed systems?
- Interfacial properties
- Vehicle viscosity
- Dispersed particle properties
What are two (2) mechanisms to impart stability common to pharmaceutical dispersed systems?
- Repulsion of particles due to surface charge (zeta potential) [Electrical Barrier]
- Physical hindrance by surfactant. [Mechanical Barrier]
What are three (3) de-stabilization mechanisms for a pharmaceutical dispersed system?
- Temperature changes (solubility, freezing)
- Microbial growth (degredation)
- Addition of chemical agents (pH-solubility, ionic strength).
What are two ways to assess a suspension?
- SEDIMENTATION VOLUME, F (ratio of final sedimentation height and original height -> magnitude increases as sediment height increases [due to greater # of settled particles].
- DEGREE OF FLOCCULATION, Beta (ratio of flocculated height to unflocculated height -> magnitude increases as sediment height increases [due to greater space between particles].
According to Stokes Law, what are two methods for decreasing the rate of settling (velocity of creaming)?
- Decrease mean particle diameter. At
What are two methods for increasing the degree of flocculation?
- Electrolyte interaction with shear plane (affecting zeta potential).
- Mechanical barrier with polymer or surfactant. (Requires optimal concentration for ‘bridging’)
What are three (3) useful characteristics of surfactants?
- Decrease interfacial tension
- Promote wetting of solids
- Facilitate dispersion
Define a Newtonian liquid
Viscosity stays constant. Therefore, rate of shear increases proportionally to shear stress.
What are three (3) classes of Non-Newtonian rheology?
- Plastic flow
- Pseudoplastic flow
- Dilatant Flow
Define plastic flow behavior
- Below yield value, system exhibits elastic behavior.
2. Above yield value, system exhibits Newtonian behavior.
Define pseudoplastic flow behavior
Viscosity decreases with increase in shear stress – shear-thinning behavior.
Define dilatant flow behavior
- Viscosity increases with increase in shear stress – shear-thickening behavior.
Define thixotropy
Thixotropy is related to the time-dependent restoration of structure following shear stress for shear-thinning systems.
How is thixotropy useful in pharmaceutical formulations?
Example: Shaking a nasal spray before use allows delivery into nasal cavity; viscosity recovery prolongs residence.
What kinds of mechanical barriers can emulsifying agents form?
- Monomolecular films
- Polymolecular films
- Adsorbed solid particles
What is a necessary chemical property for an emulsifying agent to be effective?
It must have an affinity for both phases so that it is active at the interface.
Describe the hydrophilic-lipothilic balance (HLB)
Scale of 1-60 that defines relative affinity for water and oil.
What is the HLB value of a lipophilic emulsifying agent?
1-10
What is the HLB value of a hydrophilic emulsifying agent?
> 10
What is Bancroft’s Rule?
The phase in which an emulsifying agent has the greater affinity constitutes the continuous phase.
Discuss two (2) important considerations when combining emulsifying agents.
- The ‘effective’ HLB is a weighted average of agents.
2. Structural characteristics (e.g. double bond) may result in incompatibility.
Define a pharmaceutical gel
Semisolid system consisting of a condensed mass (matrix) enclosing a liquid.
Define a jelly
A gel in which the matrix contains a high water content.
Give two (2) examples of a single phase gel
- Carbomer
2. Hypromellose
What is a hydrogel?
Liquid phase is water – gel network is inorganic or organic
Give three (3) examples of organic hydrogels
- Carbomer
- Poloxamer
- Sodium carboxymethylcellulose
What are four (4) types of structures seen in a gel matrix?
- Random coils
- Helix
- Stacks
- ‘House of Cards’
What are four (4) factors related to gel formation?
- Gelling agent concentration
- Solution pH
- Ion cross-linkage
- Thermal gelation
Give an example of a gel formed with ion cross-linkage
Calcium alginate gels are formed with Ca2+ and Sodium Alginate.
Give an example of a gel formed with solution pH
Carbopol gels are ionized (pKa 5-6) and electrostatic repulsion results in a gel network forming.
Give an example of a gel formed with thermal gelation
Poloxamer is dehydrated at increased temperatures to form micelles which aggregate to form a gel network.
What is a special consideration when using hydrogels of cellulose derivatives?
Levigation is required to help wet the clumped polymer when added to water..
What is a special consideration when using sodium carboxymethylcellulose?
Optimal viscosity for NaCMC is observed at pH 7-9.
Define an ointment
Semisolid preparation intended for external use. API is dissolved, suspended or emulsified.
What are the four (4) USP classifications of ointment bases?
- Hydrocarbon (oleaginous) – oily with limited aqueous.
- Absorption – oily with enhanced aqueous.
- Water removable – oil in water emulsions.
- Water soluble – only water components.
Define a cream
A semisolid emulsion.
Define a paste
A semisolid with a large solid concentration.
Give two (2) examples of oleaginous bases
- 95% petrolatum + 5% wax
2. Liquid petrolatum with low density polyethylene resin.
Give three (3) examples of an absorption base
- Aquaphor – a commercially refined hydrophilic petrolatum.
- Nivea Cream
- Eucerin
Give three (3) examples of water-washable bases
- Dermabase
- Cetaphil
- Aquaphilic
Give an example of a water-soluble base
Polybase
What are four (4) characteristics of ointment bases?
- Composition
- Occlusiveness
- Incorporation of API
- Feel and Washability
Characterize hydrocarbon (oleaginous) bases (4 components)
- Composed of oily compounds
- Occlusive
- Incorporates hydrophobic API
- Greasy, non-washable
Characterize absorption (anhydrous) bases (4 components)
- Composed of oily base + w/o emulsifier
- Occlusive
- Incorporates hydrophobic and small amounts of hydrophilic
- Greasy, non-washable
Characterize water-washable bases (4 components)
- Composed of oil + water + o/w surfactant
- Non-occlusive
- Solids and small amount of aqueous solution – poor hydrophobic.
- Non-greasy and washable.
Characterize water-soluble bases (4 components)
- Water soluble ingredients
- Non-occlusive
- Solids and aqueous solutions
- Non-greasy and washable.
What are two (2) methods of preparing suppositories?
- Hand-rolling
2. Fusion molding
Why are dosage calculations required for preparing drug-filled suppositories with fusion molding?
Components are measured by weight but dosage unit (suppository mold) is created by volume.
Define Density Displacement Factor (DDF)
The weight of a drug in gram required to displace 1 g of base.
What three (3) pieces of information are necessary to calculate a DDF?
- Weight of blank suppository.
- Weight of medicated suppository.
- Weight of drug per suppository.
