L49 - Liquid Dosage Forms: Suspensions And Emulsions 2 Flashcards
What is acceptable suspensions?
- low rate of sedimentation
- disperse phase: easily redispersed with gentle shaking
- flow properties: formulatino easily removed from the container
- aesthetically pleasing
What are advantages of pharmaceutical oral suspensions?
- delivery sys for low sol drugs
- avoid large vol of solvent (solution)
- avoid precipitation upon storage (cosolvent used)
- taste masking of drugs
- difficulty swallowing solid dosage forms
- controlled drug delivery
What are disadvantages of pharmaceutical oral suspensions?
- problems - correct dose?
- unstable: formulation to ensure stability over period of shelf life
- aesthetic suspension: difficult
- bulky, difficult for patient to carry
What are challenges?
- stability - sedimentation = caking, excipients, particle size of dispersed phase
- alt choice - production of solutions with solubilising agents
what are key parameters to be controlled?
- electrical properties of dispersed particles
- effect of distance of separation between particles on interaction (none, agglomeration, floccules)
- viscosity
What are physical properties considerations in formulations?
- particle size
- wetting properties of drugs
how does particle size affect formulation?
- inc stability by modifying rate of particle sedimentation
- particle sizy minimised by:
- chem methods ( controlled precipitation)
- phys methods (milling)
how do wetting properties of drug affect formulation?
- insoluble - hydrophobic not easily wetted
- surface active agents dec interfacial tension
- particles poorly wetted = aggregation
What is crystal growth like?
- small particles > solubility/dissolution rate when dispersed in aq vehicle
- change inc temp, smaller particles dissolve in vehicle
- crystallisation may occur on surface of large particle
How do you decrease crystal growth?
- hydrophilic factors
- adsorption on suspended dug particles
how do you control crystal growth?
- temp cycling (freeze-thaw)
- monitor particle diameter
- physical stability
What are components of pharmaceutical oral suspensions?
- vehicle
- ## excipients
what are vehicles used in pharmaceutical oral suspensions?
- purified water USP
- buffers
What are excipients used in pharmaceutical oral suspensions?
- addition of electrolytes - dec zeta potential
- surface active agents - facilitating flocculation (non ionic preferred)
why do we add hydrophilic polymers to pharmaceutical oral suspensions?
- adsorb to surface of suspended drug particles
- prevents particles coming in close contact
- stabilise suspensions
- inc viscosity
- flow properties
what are the different hydrophilic polymers in oral suspensions?
- cellulose derivatives
- poltvinylpyrrolidine
- Na alginate (ionic)
- acacia, tragacanth, xantham gum
- C of polymer
- hydrated silicates
what do you have to consider when preservatives are added?
- highly pathogenic microorganisms absent
- parabens, organic acids
- interactions with hydrophilic polymers
what is an important determinant in direct incorporation?
mixing rate
what is direct incorporation like if suspensions is flocculated?
high speed mixing
what is direct incorporation like if flocculation properties poor?
- high speed mixing may inc viscosity
- difficult to mix homogeneously
how can you decrease particle size during direct incorporation?
ball milling
What is the precipitation method?
- drug dissolved in vehicle after addition of counterion
- excipients dissolved in vehicle
what is a potential problem of the precipitation method?
- production of ionic byproducts
- if C too high, precipitated drug washed with aq solvent
