L50 - liquid dosage forms: suspensions and emulsions 3 Flashcards
what are emulsions?
disperse systems in which insoluble liquid is dispersed in a second liquid phase
what are uses of emulsions?
- cream formulations - offer greater viscosity
- parenteral nutrition
- oral administration
- rectal administration of antiepileptic agents
what are advantages of pharmaceutical emulsions?
- delivery of drugs with low aq sol - in internal phase (o/w), oral admin - oil droplets absorbed
- taste masking - dissolved in internal phase (o/w)
- administration of oils with therapeutic effect
what is good about the drug being dissolved in the internal phase (o/w)?
- red of irritation
- no difficulty swallowing solid dosage forms
- total parenteral nutrition
what are disadvantages of pharmaceutical emulsions?
- thermodynamically unstable - formulation needed to stabilise emulsion from separation of 2 phases
- pharmaceutical emulsions may be difficult to manufacture
what are the types of emulsions?
- o/w - oil is disperse phase, water external
- w/o - water is disperse phase, oil external
- w/o/w (multiple) - disperse phase contains droplets of another
what are properties of acceptable emulsions/creams?
- physical stability - no phase separation
- flow properties - easily removed from container
- formulation spreads easily
- aesthetically and texturally pleasing
- suitable flavour
- correct texture
what are the main components of emulsions?
- oil
- water
- emulsifying agents
what is the emulsion type determined by?
- stability of droplet phase
- phase of lower stability forms external phase
what are determinants of type of emulsions produced?
- phase vol of internal phase
- chem properties of film around internal phase
- viscosity of inter and exter phase
what are the tests for identification for o/w?
- miscible with water
- staining with oil soluble dye - paler than w/o, coloured globules on colourless background
- conductivity - water conducts electricity
what are the test for identification of w/o?
- miscible with oil
- staining with oil soluble dye - intense colouration than o/w, colourless globules in coloured background
- conductivity - won’t conduct in oil
what is the emulsion instability like?
- flocculation = creaming
- coalescence = breaking/cracking
what is cracking?
- coalescence of internal phase = separation of emulsions to 2 layers
- by destruction of mono/multilayer film at interface between droplet and external phase
- irreversible
what can cracking be due to?
- incorrect selection of emulsifying agents
- presence of incompatible excipients
- temperature
- microbial spoilage
what is flocculation like?
- secondary interactions maintain droplets at defined distance of separation
- shaking redisperses
- can enable droplet coalescence
what is creaming caused by?
density difference between oil and water phases (sedimentation/elevation)
what can creaming be prevented by?
density difference between phases is zero
how can you reduce rate of creaming?
- rate = stokes eqn
- reduce avg particle size of disperse phase
- inc viscosity of emulsion
what is phase inversion? when does it occur?
- switching of an o/w to a w/o emulsion (vice versa)
- when critical value of phase vol ratio has been exceeded
what are the frequently cited phase vol ratio?
- o/w 74:26
- w/o 40:60
what happens when you add hydrophilic polymers to emulsions?
- adsorb at interface between disperse phase and external phase
- gel like multilayer produced
what is the type of emulsions dependent on?
- preference of particles for each phase
- if aq phase = o/w
when are o/w used and w/o used?
- o/w - oral, IV, used for water-soluble drugs for local effect
- w/o - moisturising formulations, greasy
