Dosage Forms II Exam 1 Flashcards
What are the types of liquid dosage forms?
Solution, Emulsion, Suspension
What are the advantages of solutions?
homogeneous, no problems of content uniformity
easy to manufacture
good bioavailability
What are two things to know when designing a buffer?
important for stability, controls pH
Why is a weak acid with a pKa close to the desired pH selected?
because the reaction they undergo will not significantly change the concentration of the solution and allows only a small change in pH
How do you design a buffer with a specific pH and buffering capacity?
by adding a weak acid with a pKa similar to the desired pH of the solution and provides maximum stability
What can be done to minimize irritation if pH of solution cannot match the pH of body fluid?
minimize buffering capacity, minimize volume, and administer slowly
What are antimicrobial preservatives mechanism of action?
they absorb to the bacterial membrane and disrupt it; membrane is lipophilic and has a negative surface charge
What is the function of each excipient in a solution dosage form?
alcohols- Ethanol, Benzyl Alcohol, Chlorobutanol
acids- Benzoic acid, Sorbic acid
parabens- Propyl paraben, butyl paraben, methyl paraben, and ethyl paraben
quaternary ammonium compounds- Benzalkonium Chloride(Zephirin), Cetyltrimethylammonium chlroide(Cepryn)
antioxidants- Free-radical scavengers(Propyl, octyl, dodecyl esters of gallic acid, BHA, BHT, Tocopherols, Vitamin E, Reducing agents(Sodium bisulfite, Ascorbic acid, Thiols)
chelating agents (Citric acid, EDTA)
What are the type of emulsions?
Oil in water; Water in oil (dispersed & continuous phase)
What are the clinical applications of Emulsions?
Oral, External, Intravenous lipid emulsion
What is the molecular basis of interfacial tension and how do surfactants alter the interfacial tension?
less molecules are at the interface then in the bulk phase; these molecules at the interface contact other molecules and experience different forces of attraction
-surfactants have both a hydrophilic and hydrophobic region and lower the overall interface tension (form micelles)
What is the role of interfacial tension in production of an emulsion and stability of the emulsion?
lower the interfacial tension the more stable the emulsion is
How do micelles form in solutions of surfactants and their utility?
form at the liquid-liquid or liquid-air interface to lower the interfacial tension which causes micelles as surfactant concentration is increased
What is the mechanism by which surfactants, hydrophilic colloids, and finely divided solids act as emulsifying agents?
surfactants form micelles, hydrophilic colloids form a multi molecular film and increase the viscosity of water, finely divided solid particles forms a film of fine particles and absorb at the interface
What is the basis of physical instability of emulsions?
Creaming (how quickly it will float to surface or sediment; reversible), Coalescence (droplet size increases; irreversible) Phase inversion (O/W emulsion stabilized by W/O using hard water)
What are the typical components of an emulsion and how to manufacture an emulsion?
Benzyl Alcohol-Preservative
Cetyl Alcohol- Emulsifier, Thickening agent
Glycerin- Humectant
Liquid Petrolatum- Oil Phase
Magnesium aluminum silicate- Emulsifier
Water- Aqueous phase
Why would you select a suspension dosage form rather than a solution?
There is more chemical stability than solutions, can taste better, and can be more soluble
When is a suspension preferred to a tablet dosage form?
easier to swallow, dose is more flexible, dissolution rate is faster
What are the desirable properties of an ideal suspension?
-not settle rapidly
-particles settled should be redispersed easily
-easy to administer
-particle size remains constant during storage
What factors affect the velocity of sedimentation of a suspension dosage form?
the diameter, density of the liquid and solid, viscosity of the liquid, gravity
What are the common methods of particle size reduction?
-Micropulverization
-Fluid energy grinding
-Spray drying
What processes occur during aging of a suspension to bring G toward zero?
aggregation and crystal growth
What interparticle forces are important in suspension dosage forms?
Van der Waals attractive force, Hydration repulsive force, Electrostatic repulsive force, Steric repulsive force
Differentiate dispersion vs. flocculation
dispersion has repulsive forces as dominant force; repel eachother and do not aggregate; usually hard to redisperse
flocculation- repulsive and attractive forces are in balance; easy to redisperse
