Suspensions Flashcards
What are the three types of dispersed systems?
Molecular dispersion
Colloidal dispersion
Coarse dispersion
What is a dispersed system?
A system containing a dispersed phase (internal) and a continuous phase (dispersion medium)
What are the main differences between the dispersion systems?
Colloidal dispersion particles are 0.5μm. They are visible under….
What type of dispersion systems are pharmaceutical suspensions and emulsions?
Coarse dispersion systems
What is the difference between an emulsion and a suspension?
The difference between an emulsion and a suspension is based on the nature of the dispersed (internal) phase.
The dispersed phase of an emulsion is liquid
The dispersed phase of a suspension is solid
What is the difference between a colloidal dispersion and a coarse dispersion?
The difference between colloidal and coarse dispersions depends on the size of the dispersed phase.
A colloidal dispersion is between 1nm and 0.5μm
A coarse dispersion is >0.5μm
Why do we formulate pharmaceutical suspensions?
Drug insoluble in delivery vehicle
Mask the bitter taste of the drug by keeping it in solid form
Increase drug stability
Achieve controlled/sustained drug release
What are some pharmaceutical applications of suspensions?
Oral drug delivery,
Topical administration
Pareneteral use
What are the advantages of having a suspension in oral drug delivery?
- offers solution for patients with difficulty swallowing
- offer finely divided dispersed phase hence offering high surface area e.g. Mg stearate and Mg carbonate as antacids
- provide taste marking e.g. Paracetamol suspension more palatable than solution
Why are suspensions used in topical adminstration?
Can be used as liquid preparations e.g. Calamine lotion which contains ZnO and FeO
Is used as an astringent.
Can also be used as semi solid suspensions which often contain a high concentration of powder (20-50%) in an ointment base. Usually paraffin, Vaseline or lanolin
Why are suspensions used pareneterally?
We can control the rate of drug absorption and duration of action e.g. Eligard acetate (3month sustained release injectable suspensions for treatment of prostate cancer)
For SC and IM use only
Why are pharmaceutical suspensions not used for the IV route?
Dispersed phase may be too large and will clog up capillaries. If a suspension MUST be used for IV, the particles must be small enough to avoid emoblism
What factors will the suspension drug absorption be dependent on?
Drug absorption of a suspension depends on the solid drug particles dispersed in medium.
These need to be solubilised to be dissolved.
The rate limiting factor is therefore its dissolution
Compare a solution vs. Suspension in terms of onset and duration of action after IM injection
Solution has faster onset as drug is already in solubilised form and ready for absorption suspension:drugs will take longer to have effect as the solid particles need to be dissolved and then absorbed,
but a suspension has longer duration of action due to slower rate of dissolution.
What are the advantages of suspensions?
Allows us to formulate poorly water soluble drugs
Provides taste marking as unpleasant tastes are less obvious in suspensions than in solutions
Offers rapid absorption (compared to solid dosage forms)
Provides a sustained release option
Improves drug stability (compared to solutions)
Why is a well formulated suspension second only to a solution in terms of superior bioavailability ?
A solution is a uniform molecular dispersion, the active ingredient is already dissolved and will absorb into cells immediately.
A suspension contains the active drug in solid form in a liquid medium. It will still require some time to dissolve into solution and then be absorbed.
This means that in terms of bioavailbility, a suspension is better than a solid dosage form, but not as good as that of a solution
Why is the absorption of a suspension dissolution limited?
The solid particles of the suspension require time to dissolve into the medium.
If this does not occur, the suspension formulation will not be absorbed
What type of suspension will have a faster onset of action?
Aqueous suspensions as they are dissolved first. Oily suspensions have poor aqueous solubility, so their dissolution is still their rate limiting step
What type of suspension will have a longer duration of action?
Oily suspensions as they will dissolve slower. The active ingredient will be absorbed over a longer period of time, resulting in a prolonged duration of action
What can be added to suspensions to improve dispersion and absorption of fine particle size suspensions
Surfactants
What are the properties of the dispersed phase? (Particles)
- Finely dispersed particles have a tendency to aggregate, addition of surfactants tend to decrease this aggregation
- Chemical form of suspended drug (its solubility) can be increased if the particle size decreases (due to NW equation where the the rate of dissolution is proportional to surface area.)
But you need a balance between the surface area and particle size to prevent aggregation
What are the desirable qualities of an ideal suspension?
- Remain sufficiently homogenous for a period to allow removal of dose.
- Suspended materials should not settle too rapidly
- Suspended materials must be easily resuspendable
- not too fluid and not too viscous.
- must be an acceptable colour and odor
- uniform particle size
Why is the viscosity of the suspension important?
Suspensions should not be too viscous as this would hinder transfer onto skin, pouring, and flow through a syringe needle.
However suspensions should not be too fluid that it runs off the skin surface without giving the medicament a chance to have an effect
Why is the size of suspended particles important?
The size should be small and uniform to give a smooth, elegant product which is free from gritty texture