Suspensions Flashcards
Define ready to use form
Drug is already dispersed in the vehicle with or without any preservativese or any other additives
Define dry powders for suspension
Drug is mixed with suitable suspending and dispersing agents, that can be dissolved in a vehicle by simple agitation
Application of suspensions
- Used if can’t swallow solid dosage forms
- Drugs are unstable in aqueous solutions
- Mask the taste
- Produce high surface area in the GIT, drugs are administered in a finely divided form
Dosage forms?
Oral, ocular, topical and parenteral
- Liquid or semisolid
- parenteral suspension control rate of absorption
- Increase duration of action, vary particles size
Suspensions used as?
Vaccines
Diagnostic tests
Desired properties of suspensions?
Sufficiently homogenous Settle slowly Easily resuspended Pour readily and evenly Particle size constant even in undisturbed standing Optimal viscosity
Suspended particles?
Thermodynamicallly unstable
Van der Waals interactions
Define flocculation
Process of forming flocs
- London and van der Waals + repulsion forces
- Settle rapidly
- easily resuspended
- Clears as flocs settle
- inaccurate dosing
- Unstable
Define aggregation
Particles adhere to each other by stronger forces to form aggregates
Define caking
Due to growth and fusion of crystals in the precipitates and produce a solid aggregate
Deflocculated suspension?
Repulsive energy is too high
- Settle slowly
- Hard cake
- Difficult to re-suspend
- Cloudy
- Stable
- Uniform dosing
Define ideal situation
Deflocculated suspension with a sufficiently high viscosity to prevent sedimentation
Define controlled flocculation
- Balance flocculation
- Underflocculation: deflocculated
- Over flocculation is irreversible
- Particle size control and electrolytes to control zeta potential
Define flocculating agents
Excipients used to achieve controlled flocculation
Define electrolytes
Addition of inorganic electrolytes to an aqueous suspension can change the zeta potential
Define Schulze-Hard Rule
The flocculating power of a chemical rises rapidly with its valance
Define surfactants
Ionic surface active agents cause flocculation by neutralization of the charge
Nonionic surfactant adsorb on to more than one particle and form loose flocculated strucutre
Define polymeric flocculating agents
Form gel like structures and become adsorbed on the surface of particles
Suspending agents?
Usually negatively charged
Positively charged suspened particle that is flocculated with an anionic electrolyte?
Use of negatively charged hydrocolloids may help avoid incompatibility
Use of oppositely charge flocculating agent may result in incompatibility
Sedimentation of suspended particles
Particles size should be as small as possible
Increase the density of the liquid
- When equal to density of solid, sedimentation rate = 0
Increase viscosity of the dispersion medium
F < 1
Final volume of sediment is smaller than the orignal
F = 1
Final volume of sediment is equal to the original
F > 1
Final volume of sediment is greater than the original
- loose and fluffy flocs
Define degree of flocculation
Ration of sedimentation volume for flocculated suspension to the sedimentation volume of deflocculated suspension or as the ratio of ultimate sediment volumes
(U over O)
Temperature of suspensions
Increase lead to under or over flocculation
- heated: energy of repulsion tends to decrease
- freezing and thawing: strong attraction and forms aggregates
- Size is inversely related to freezing rate
- Fluctuation can alter particle size and polymorphic form
Excipients of suspensions
Adversely affect the stability o fa suspension
- Change reversal
Dry powders for suspensions
Do not contain the vehicle
Add exactly the right amount of water
