Lecture 14: Suspensions Oral Products, Calculations, Changing Doses When Dispensing Flashcards
Why do suspensions require a shake the bottle label?
The suspended solids slowly separate on standing and can usually be redispersed with shaking
This may be difficult if they form a compacted sediment
What are suspensions?
Pharmaceutical suspension is a disperse system in which one substance (disperse phase) is distributed in particulate form throughout another (continuous phase)
Are suspensions aqueous or oily?
Most pharmaceutical suspensions are aqueous but sometimes an oily vehicle is used
What are suspensions used for?
Oral administration, inhalation, topical application, opthalmic preparations, parenteral administration, aerosols
What are some pharmaceutical uses of suspensions?
Can be used as a formulation for low water solubility medicaments e.g. Paracetemol
May be due to having to address swallowing difficulties of patient
Active ingredient may taste unpleasant in solution e.g. Chloraphenicol although is soluble is changed to chlroaphenicol palmitate which is insoluble. As it does not dissolve, the suspension does not have a bitter taste.
Hydrolysis of medicament can be put off
Suspensions can be used as depot injections
Suspensions can also be used externally
How is low water solubility overcome in suspensions?
We can use a wetting agent to reduce ST
Hydrophilic suspending agent coats hydrophobic particles
Sometimes we see flocculation
These are large loose fluffy and dispersible sediment originating from excipients in the tablet. Dont filter these out, leave them in. We dont just want a clear supernatant.
How can we tell if sedimentation has occurred in a suspension?
Use the formula Vfinal /vinitial
If this = 0, then no sedimentation has taken place
What are some examples of suspending agents?
Tragacanth, compound tragacanth, methylcellulose, starch, alginates (internal)
Bentonite (external)
How can we determine the stability of a suspension?
Using stoke’s law:
This tells us the rate of sedimentaiton
Where V = 2r^2(density solid - density liquid) g / 9η
What can we do to decrease the sedimentation rate?
Reduce the particle size of suspended solids
Increase the viscosity of the liquid phase
How can stability be increased?
Have a small surface area (a large surface area is equivalent to high surface free energy which makes it thermodynamically unstable)
Store the suspension under 25°C but do not freeze.
Test the sediment size and re-dispersability
What are common additives that are added to suspensions?
Buffers, flavourants, colourants, preservatives
What are some other uses for suspensions?
A formulation for insoluble drugs,
Can suspend crushed tablets e,g, for paediatric doses
Opened capsules e.g, omeprazole
Can adsorb drugs or microbes in GIT to use in the event of an overdose.
Can be used for eye suspensions, inhaler suspensions
What are some advantages of having suspensions?
Insoluble drugs may be more palatable
Insoluble drugs may be more stable.
Suspended powders easier to swallow
Enables easy administration of bulk insoluble powders
Absorption quicker than in solid dosage forms
Lotions will leave a cooling layer of medicament on the skin
What are some disadvantages of suspensions?
Preparation requires shaking before use
Accuracy of dose likely to be less than equivalent solution
Storage conditions can affect dispersed systems
They are bulky, difficult to transport and prone to container breakages,
What are the properties of a good suspension?
Ready redispersion of any sediment which accumulates on storage
After gentle shaking, the medicament stays in suspension long enough for a dose to be accurately measured
Suspension is pourable
Particles in suspension are small and relatively uniform in size so product is free from gritty texture,
Why are suspending agents needed?
If the solid is indiffusable and is not easily wetted with water, it can form large clumps in the liquid
It is therefore difficult to measure an even dose
So a suspending agent is require
(Diffusable or dispersable solids do not require a suspending agent)
How are suspensions compounded?
Grind solids finely in mortar with pestle
Mix in solid suspending agent
Use a small amount of vehicle or suspending mucilage to make a smooth paste free from lumps.
If glycerol or syrups are in formula, use to make paste
Add wetting agent if in formula
Dissolve soluble ingredients in a vehicle and add to paste gradually until it is pourable then make it up to volume with the vehicle.
How is a bottle precalibrated?
Measure the volume of suspension required in using water in conical measures, get it checked,
Pour into an appropriate amber medicine bottle, and mark the water line. Get this checked.
Then empty the bottle. The suspension must be made up to this line
Why is a precalibrated bottle necessary
Suspensions are thick so when you transfer too many times you always leave some behind and the patient doesnt get all of it
What are mucilages?
Colloidal dispersions
Hydrophilic colloids disperse in water.
The temperature of the water is important
How is a methylcellulose mucilage prepared?
Need to dissolve the methylcellulose in hot water
Add 50mL of boiling hot water to the powder.
Then add ice cold water.
Then add the preservative and make it up to volume
Which new products are now funded from 1 dec 2010?
Oral suspending agents: ora-sweet, ora-sweet SF, ora-blend, ora-blend SF
Methylhydoxybenzoate, propylene glycol and sodium bicarbonate for use in compounding of oral liquid mixtures
Two galenicals (menthol and sulphur)
Can glycerol be used as a suspending agent?
Yes because it has a high viscosity
