L50- liquid dosage forms: suspensions and emulsions 3

what is phase inversion

it when the critical value of the phase volume ratio has been exceeded

its when you have the switching of a O/W emulsion into a W/o or vice versa

the usual is 0/w-74:26

w/o-40:60

explain how hydrophilic polymers can help with emusion instability

once u add the polymers they the form a ring around the droplet with the hydrophilic tail around the outside

the film created protect the droplet

explain how the addition of adsorbed particles can help to increase the emulsion instability

these particles have been wetted by both phases, water and oil

it the particles have mainly been wetter by water then will have an oil in water emulsion and vice versa

what type of emulsion is preferred for topical administration

oil in water is preferred for water soluble drugs for local effect, non-greasy

water in oil is preferred for most moisturising formulation and is greasy

what are the steps to creating a stable emulsion

• add a mixture of emulsifying agents

• based on on the HLB value of the emulsifying agents and the emulsifying you want

• then calculate the amount of each emulsifying agents that’s needed

what are emulsifying agents

• they are a choice of a mixture of surfactants and also consider their concentration, how much is needed

• typically add one with a low HLB and one with a higher and then a third can be added for balance

• the surface- active agents used to stabilise the emulsion could be anionic, cationic or amphoteric

explain how emulsions are manufactured

• the oil phase and the aqueous phase are prepared separately

• then they are mixed together under turbulent mixing conditions

• on a lab scale- mechanical scale

• production scale- colloid mills, ultrasonifirers ,mechanical stirrers