Medicinal suspensions Flashcards
Definition of suspension
Dispersion of fine, insoluble, oslid particles(dispersed phase) within a liquid (continuous phase or dispersion medium)
Why may suspensions be required over solutions?
The low solubility of many useful drugs means the requirement for a suspension is necessery
What is the difference between between course suspensions and colloidal suspensions
Course suspensions refer to solid particles of drug with a mean size above 1um however colloidal suspensioins refer to solid particles of drug lower than 1um.
The continuous phase is usually ___ but can be ___ or ___
The continuous phase is usally aqeous but can be organic or oil based.
What are properties of a well forumalted suspension?
(1) Dispersed phase particles should be smal, uniformly sized, and not settle too rapidly.
(2) Settled particles should not form a compact sediment which is difficult to disperse.
(3) Succesive doses should contain the same amount of suspended solid and hence the same dose of drug.
(4) Products should have an agreeable odour, colour, taste, and texture.
(5) Continuous phase should not support microbial growth on storage.
What are advantages of well formulated suspensions?
(1) Used where patient struggles to swallow other dosage forms
(2) Bitter taste of many drugs is less noticible in the solid state than solution state
(3) High surface area of fine suspension is desirable for fast drug dissolution in the GI track
(4) High surface area is required for fast action of toxin absorbing compounds or antiacids.
Is dissolution faster in suspensions or solutions?
Small particles have a larger surface area to volume ratio so dissolution and ultimately drug absorption is faster, but not faster than a solution.
Why might an oral suspension be made instead of solution?
Some drugs hydrolyse in the presence of water and lose their efficacy if prepared as solutions. In some cases it is possible to synthesise an insolluble derivitive that can be formulated as an oral suspension.
Disadvantages of oral suspension
flocculated and deflocculated sedimentation - can lead to innacurate dosage and inelegence.
What is deflocculated sedimentation
Slow sedimentation to form a firm mass that can be impossible / extremely difficult to resuspend (caking) (laying)
What is flocculated sedimentation?
Fast sedimentation to form a loose cake that can be resuspended relatively easily.
Disadvantages of oral suspensions
(1) Presence of water, even with insoluble drugs, can result in hydrolytic degredation with time
(2) Ostwald Ripening (crystal ripening) - Dissolution of smaller particles that can recrystallize on the surface of larger particles, causing a shidt in the mean particle size distribution. This is considered an instability.
What is aggregation / aglomeration?
Aggregation is a collection of individual particles into groups
Aggregation and aglomeration are used interchangably.
What is coagulation?
Coagulation occurs when particles approaching eachother have sufficient energy to overcome repulsive forces - more commonly used when discussing proteins and blood.
hard agglomeration
particles held at short distances from eachother by very strong net forces (VDV). These agglomerates cannot be pulled apart or broken down easily.
