Suspensions Flashcards
What is the disperse phase within a suspension?
The particles.
If they have a mean size above 1um are refered to as course suspension.
If they have a mean size below 1um are refered to colloidal dispersions.
What is a suspension?
A dispersion of fine insoluble solid particles( disperse phase) within a liquid( dispersion medium)
What is the continuous phase in suspensions?
The dissolving liquid, usually water but can be organic or oil based
What properties should a well formulated suspension have?
Disperse phase particles should be small, uniformly sized and not settle too rapidly
Settled particles should not form a compact sediment which is difficult to disperse
Successive doses should contain the same amount of suspended solid and hence the same dose of drug
Product should have an agreeable odour,colour,taste and texture.
The continuous phase should not support microbial growth on storage.
What are the advantages of using a well formulated suspension?
Useful where patients have swallowing products
Bitter taste of drugs is less noticeable in the solid state than the solution state.
High surface area of fine suspensions is desirable for fast drug dissolution in the GI tract.
High surface are is required for the fast action of toxin absorbin compounds( ie kaolin) or antacids ( magnesium carbonate)
Useful if the drug hydrolizes, so not really suitable in a solution, as it can sometimes be possiblto synthesise an insoluble derivative that can be formulated as a suspension
What are the disadvantages of sedimentation in oral suspensions?
Can settle in two forms, deflocculated sediment and flocculated sediment.
Deflocculated - slow sedimentation,but forms a firm mass that is hard to re suspend. Caking
Flocculated - fast sedimentation to form a loose cake that can be re suspended relatively easily. Forms loose clumps in solution
Both can lead to inaccurate dosing and look inelegance.
Flocculating agents often used as this is preferred over deflocculated suspensions,
What is Ostwald or crystal ripening?
This is when dissolution of smaller particals that can then re crystallise on the surface of larger particles, which causes a shift in the mean particle size distribution
Can drugs still hydrolyse in water in suspensions?
Over time even insoluble drugs can have hydrolytic degradation.
What is aggregation?
Is when individual particles collect into a group
What is coagulation?
This occurs when particles approach each other and have sufficient energy to overcome the repulsive forces, and form compact aggregates.
What are compact aggregates?
When particles coagulate, they form compact aggregates, where particles are held at a short distance by very strong net attractive forces. They cannot be broken down easily, the effect is irreversible.
Sometimes called hard agglomerates
What is a diffusible solid?
This is an insoluble solid that can be suspended in a continuous phase for a sufficient length of time so that a dose can be measured
What is an indiffusible solid?
A solid that cannot be suspended in a continuous phase for sufficient time to measure a dose without the use of a suspending agent.
What is the difference between suspending agents and viscosity enhancers?
They are the same thing, suspending is increased by increasing viscosity.
What is important to to consider when formulating a suspension?
Particle size, in general as small as possible, as the larger the particle the quicker the a sedimentation.
A narrow particle size distribution is preferred as this reduces the probability of Oswald ripening.
