Lecture 14: Suspensions Oral Products, Calculations, Changing Doses When Dispensing

Question 0

Why do suspensions require a shake the bottle label?

Answer 0

The suspended solids slowly separate on standing and can usually be redispersed with shaking

This may be difficult if they form a compacted sediment

Question 1

What are suspensions?

Answer 1

Pharmaceutical suspension is a disperse system in which one substance (disperse phase) is distributed in particulate form throughout another (continuous phase)

Question 2

Are suspensions aqueous or oily?

Answer 2

Most pharmaceutical suspensions are aqueous but sometimes an oily vehicle is used

Question 3

What are suspensions used for?

Answer 3

Oral administration, 
inhalation, 
topical application, 
opthalmic preparations, 
parenteral administration,
aerosols

Question 4

What are some pharmaceutical uses of suspensions?

Answer 4

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

Question 5

How is low water solubility overcome in suspensions?

Answer 5

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.

Question 6

How can we tell if sedimentation has occurred in a suspension?

Answer 6

Use the formula Vfinal /vinitial

If this = 0, then no sedimentation has taken place

Question 7

What are some examples of suspending agents?

Answer 7

Tragacanth, compound tragacanth, methylcellulose, starch, alginates (internal)

Bentonite (external)

Question 8

How can we determine the stability of a suspension?

Answer 8

Using stoke’s law:
This tells us the rate of sedimentaiton

Where V = 2r^2(density solid - density liquid) g / 9η

Question 9

What can we do to decrease the sedimentation rate?

Answer 9

Reduce the particle size of suspended solids

Increase the viscosity of the liquid phase

Question 10

How can stability be increased?

Answer 10

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

Question 11

What are common additives that are added to suspensions?

Answer 11

Buffers, flavourants, colourants, preservatives

Question 12

What are some other uses for suspensions?

Answer 12

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

Question 13

What are some advantages of having suspensions?

Answer 13

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

Question 14

What are some disadvantages of suspensions?

Answer 14

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,

Question 15

What are the properties of a good suspension?

Answer 15

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,

Question 16

Why are suspending agents needed?

Answer 16

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)

Question 17

How are suspensions compounded?

Answer 17

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.

Question 18

How is a bottle precalibrated?

Answer 18

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

Question 19

Why is a precalibrated bottle necessary

Answer 19

Suspensions are thick so when you transfer too many times you always leave some behind and the patient doesnt get all of it

Question 20

What are mucilages?

Answer 20

Colloidal dispersions
Hydrophilic colloids disperse in water.

The temperature of the water is important

Question 21

How is a methylcellulose mucilage prepared?

Answer 21

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

Question 22

Which new products are now funded from 1 dec 2010?

Answer 22

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)

Question 23

Can glycerol be used as a suspending agent?

Answer 23

Yes because it has a high viscosity

Question 24

What is important when we make suspensions from tablets?

Answer 24

We must always use whole tablets.
If it turns out we require a fraction of a tablet, we must go up to the next whole tablet, re-calculate all the ingredients to give the correct strength and then discard the volume which we dont need

Question 25

What are parabens?

Answer 25

Hydroxygenzoates

Including
Methylhydroxybenzoate solution
Propylhydroxybenzoate solution
Compound hydroxy benzoate solution
We need 0.1%w/v MIC in final product

Question 26

What are propylhydroxybenzoates?

Answer 26

They are poorly water soluble (500parts water required)
PH range up to 9
0.1%w/v

Question 27

What are methylhydroxybenzoates?

Answer 27

The APF sln = 5%
The pharmac methylhydroxybenzoate solution is 10%
Compound hydroxybenzoate is also 10%

Question 28

What is benzoic acid solution?

Answer 28

A preservative.
At a strength of 0.1%w/v it is suitable for oral administration.

Its effectiveness is pH dependent,
It has a pKa of 4.2 so at pH 4.2, there will be an equal amount of dissociated and undissociated ions

Question 29

Wha do you do if you find the dose is inaccurate?

Answer 29

Check again, look at another reference,

Contact the prescriber

Question 30

Why must you contact the prescriber when you find a dose is inaccurate?

Answer 30

Only the prescriber can change the dose on a prescription

Question 31

What is the role of the pharmacist in dose changing?

Answer 31

Recommend dose to prescriber, give reasons, suggest options, be professional

Question 32

What is the procedure of a dose change?

Answer 32

Phone the doctor to discuss what needs to be done

Question 33

How is the dose change documented?

Answer 33

Document the change on the Rx. Send this back to the doctor to get it signed off