Liquid Formulations Flashcards
what are some common solvents
water
alcohol
glycerol (glycerine)
propylene glycol
what are some excipients in solvents
buffers sweetening agents viscosity enhancement preservatives reducing agents/antioxidants flavours and perfumes colours density modifiers isotonicty modifiers
what are buffers
buffers control the pH of the pharmaceutical preparation
common buffers for pharmaceutical solutions are:
phosphate,citrate and acetate buffers
what do you need to achieve a buffer
acid + base to achieve the buffering
what is the sweetening agents used for
increase palatability of the API / Preparation
what are some commonly used sweetening agents
sucrose sorbitol mannitol na and ca salts of saccharin glycerol aspartame
what are viscosity enhancement
hydrophilic polymers are commonlu used for viscosity enhancement
what do preservatives do
control microbial growth
what do antioxidants use
enhances stability of the API have higher oxidative potential than API or inhibit free radical induced decomposition
what are the advantages of solutions
easy to swallow
fast therapeutic response immediately available for absorption
homogeneous
minimal irritation to gastric mucosA
what are the disadvantages of solutions
bulky poorer stability in solution microorganisation growth preservative needed issues with accuracy of dose taste is pronounced
What are the uses of emultions
predominantly topical
IV
Rectal
Oral
what are the desired characteristics of an emulsions
physical stability - no separation
should be easily remove from container and applied
pleasant texture; aesthetically pleasing
what is an emulsion
Anemulsionis mixture of two liquids that would not normally mix, i.e. a mixture of two immiscible liquids. Bydefinition, anemulsioncontains tiny particles of one liquid suspended in another. Chemically, they are colloids where both phases are liquids.
what are the different types of emulsions
o/w for oral and i.v.
Both o/w and w/o for topical; w/o more greasy formulation but more hydrating to the skin
Multiple emulsions – o/w/o or w/o/w
what are the advantages of emulsions
deliver drugs of low aqueous solubility
making taste - flavours added to external phase whilst drug is in the internal phase
employed for total parental nutrition
good for patients with swallowing difficulties
what are the disadvantages of emulsions
fundamentally unstable
may be difficult to manufacture
what is the name of the phase that is disperced into the medium
immiscible phase
what has the lowest surface area per volume
droplets
what does dispersion lead to
high surface area of the dispersed phase
how can we avoid creaming of our emulsion
Reduced droplet size – Smaller droplets flocculate slower!
Increase viscosity (of continuous phase) – make it harder for the droplets to move!
Reduced density difference between phases – Lower difference gravity effects are lowered!
Disperse phase concentration – Lower dispersed phased concentration, slower coalescence.
Prevention of flocculation and coalescence – Additives to reduce creaming.
how can we use surfactants
Amphipathic nature of the surfactant means they are present at the phase boundary
Surfactants keep the droplet size small, hence aid dispersion and stability
Coalescence is prevented by the steric repulsion
Mainly non-ionic surfactants employed for internal use; charged surfactants for skin preparations
use of hydrophilic polymers
Use of hydrophilic polymers – these adsorb at the interface of the phases producing multilayers
The multilayers are highly viscoelastic, so mechanically prevent coalescence
If ionic hydrophylic polymers are used, zeta potential is created – further stability
