L48 - liquid dosage forms: suspensions and emulsions 1 Flashcards

1
Q

what are characteristics of suspensions?

A
  • solubility of drug in vehicle is low
  • diameter of disperse phase: 0.5 to 100mcm
  • particle size <0.5 mcm - colloidal
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2
Q

what is a suspension?

A

dispersion in which the drug is dispersed in the external phase (vehicle)

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3
Q

what do suspensions being unstable lead to?

A
  • sedimentation
  • particle-particle interactions
  • caking (compaction)
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4
Q

what can help understand suspensions’ physical stability?

A
  • electrical properties of dispersed particles
  • effect of distance of separation between particles on their subsequent interaction
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5
Q

why may particles acquire a charge due to?

A
  • ionisation of functional groups
  • adsorption of ions to surface of the particle
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6
Q

what is the electrical double layer?

A

phenomenon referred to following adsorption of ion on to the surface

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7
Q

what is the zeta potential?

A

potential that the boundary of second layer possesses

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8
Q

what does zeta potential measure?

A

degree of electric charge on particles relative to bulk medium in which they are suspended

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9
Q

what can be used to stabilise pharmaceutical suspensions regarding electrical properties of dispersed particles?

A

compression of the electrical double layer by inc conc of electrolyte

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10
Q

what are the three states on interaction possible?

A
  • no interaction
  • coagulation (agglomeration)
  • loose aggregation (termed floccules)
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11
Q

what is the no interaction state like?

A
  • particles sufficiently distant from one another
  • thermodynamically stable (absence of sedimentation)
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12
Q

what is the coagulation state like?

A
  • particles form intimate contact with each other
  • pharmaceutically unacceptable formulation - inability to redisperse the particles upon shaking
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13
Q

what is the loose aggregation state like?

A
  • loose reversible interaction between particles
  • enable particles to be redispersed upon shaking
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14
Q

what are the opposing forces in particle suspensions like?

A
  • thermodynamic instability tends to aggregation = attractive forces (vdw potential eng, Va)
  • electrical charge (zeta potential) tends to separation = repulsive forces (electrostatic potential eng, Vr)
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15
Q

what is the DLVO theory?

A

when dispersed in liquid medium, particles will experience (electrical), repulsive forces and attractive (london/vdw) forces

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16
Q

what is the eqn for the overall energy of interaction between the particles?

A

Vt = Va + Vr

17
Q

what does the potential energy curve for particles show?

A
  • 2 minima
  • 1 maximum
18
Q

what happens as you increase interparticles distance?

A
  • short - attractive forces predominate, particles tend to agglomerate (first minimum)
  • as it increases - repulsive forces predominate, particles remain in suspension (max)
  • increased further - repulsive force decreases, particles weakly attracted (second minimum)
19
Q

what is key to determining the stability of the system?

A

depth of secondary minimum

20
Q

what happens in sedimentation?

A
  • large particles reach bottom initially
  • smaller particles occupy space between larger particles
21
Q

when does sedimentation occur?

A

under the influence of gravity

22
Q

what is caking?

A
  • particles at the bottom gradually compressed by weight of those above
  • sufficient energy available to overcome primary max (repulsive force)
  • particles become sufficiently close to form irreversible interaction at primary min