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CH4106 > Liquid Dosage Forms - Disperse Systems: Suspensions > Flashcards

Liquid Dosage Forms - Disperse Systems: Suspensions Flashcards

1
Q

What is dispersion

A

A system in which a dispersed phase is distributed through a continuous phase

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2
Q

Disperse systems consist of

A
  • Suspensions
  • Emulsions
  • Aerosols
  • Gels
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3
Q

Dispersions can be classified based on size as:

A
  • Molecular dispersion < 50 A, homogeneous system
  • Colloidal dispersion 50-2000A, heterogeneous system
  • Coarse dispersion > 2000A, heterogeneous system
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4
Q

What is aggregation

A

Collection of particles into a group

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5
Q

What is coagulation

A

Particles closely aggregated and therefore, difficult to redisperse

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6
Q

What is flocculation

A

Open aggregates with particles remaining apart by a small distance

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7
Q

What is suspension

A

2 phase systems comprising solid particles (disperse phase) dispersed in a liquid (continuous phase or dispersion medium)

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8
Q

Suspensions can be divided into

A
  • Coarse suspensions - contain visible solids
  • Colloidal suspensions - no visible solids to naked eye - lyophilic (high affinity to the continuous phase)/lyophobic (lack of attraction, thermodynamically unstable and formed by aggregation of small particles/comminution of large particles)
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9
Q

What is a pharmaceutical suspension

A

Preparations containing finely divided drug particles distributed uniformly throughout a vehicle in which the drug exhibits minimum solubility

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10
Q

Advantages of suspensions

A
  • Chemical stability: more stable than in solution
  • For drugs that are insoluble
  • More palatable compared to solution
  • Prolong drug action
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11
Q

Disadvantages of suspensions

A
  • Physical instability - settle over time -> lack of uniformity and accuracy of dose
  • Sedimentation and compaction cause problems
  • Bulkiness of the drug as liquid is added
  • Difficult to formulate
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12
Q

Features desired of suspensions

A
  • Should satisfy the qualities of all pharmaceutical properties - therapeutic efficacy, chemical stability, permanency of the preparation, esthetic appeal
  • Particle size should be small with uniform size and remains fairly constant on standing
  • Should pour readily from its container after shaking
  • Must remain homogeneous for intake
  • Should settle slowly and readily redisperses when shaking
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13
Q

Main ingredients for suspensions

A
  • Drug - drug particles ideally have uniform size or distribution; drug surface (hydrophilic/hydrophobic)
  • Wetting agent - depends on the type of drugs (hydrophilic-solvents/hydrophobic-surfactants) - displace air from the particle surface and separate each particle from adjacent particles for wetting, reduce surface tension of an aqueous medium, partially cost the surface/form a complete monolayer on the suspension particles
  • Flocculating agent - enable suspension particles to link together in loose aggregates/flocs
  • Suspending agent - increase viscosity and retard sedimentation, must be dispersed in the aqueous vehicle to avoid formation of clumps
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14
Q

Examples of suspending agents

A

cellulose derivatives, clays, natural gums, polymers

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15
Q

Examples of flocculating agents

A

electrolytes, surfactants and polymers

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16
Q

Ways to control sedimentation

A
  1. increase the concentration of suspending agent
  2. proper selection of suspending agent
  3. increase viscosity of the suspension vehicle
  4. decrease the particle size -> slow settling rate
  5. increase particle separation -> prevent clumping/caking upon settling
17
Q

Particle size reduction can be done by

A
  • Micropulverization: 10-50um
  • Jet milling/micronizing: <10um
  • Spray drying: extremely small dimensions
18
Q

How to decrease sedimentation rate

A

decrease the differences in densities between the suspended particle and suspension medium

19
Q

Describe suspension interactions

A
  • Surfactants (wetting agents) used to wet the suspension particle will exist in an equilibrium between surfactant adsorbed on the particle surface, monomers in solution, and surfactant in micelles
  • Polymers (suspending agents) will exist in equilibrium with polymers in solution
  • Electrolytes that affect the adsorption of surfactants and polymers can be adsorbed onto the suspension particle surface directly affect the surface charge of the particle
20
Q

2 states that suspension can exist in

A
  • Deflocculated state: each suspension particle exists independently and behaves as a single particle - no interaction
  • Flocculation state: suspension particles attract each other and form loosely bound aggregates/flocs
21
Q

Models to describe flocculation

A
  • Electrostatic model of flocculation
  • Polymer model of flocculation
    (Draw)
22
Q

Deflocculated VS Flocculated

A

Deflocculated

  • Particles exist as separate entities
  • Sedimentation is slow, particles settle separately
  • Sediment is formed slowly from the bottom of the container
  • Sediment eventually becomes caked due to weight of succeeding layers of sediment
  • Remains suspended for relatively long time, remains cloudy

Flocculated

  • Particles are loose aggregates
  • Sedimentation is rapid, particles settle as large flocs
  • Sediment formed rapidly from top of container
  • Sediment is loosely packed and easy to redisperse
  • Somewhat unsightly as there is obvious, clear supernatant
23
Q

Preparation of flocculated suspensions

A

Depends on the drug type and product desired

  • use clays like bentonite: act as a support for the floc
  • alteration in pH to minimize solubility
  • electrolyte - electrical bridge
  • surfactants - induce process and increase sedimentation volume
24
Q

What are important to note about dispersion medium

A
  • Rapid settling can cause it to be difficult to measure accurate dose and produces pharmacologically inelegant preparation
  • Suspending agents give structure to dispersion medium - add viscosity but must ensure that thickener does not bind drug or is too viscous as it prevents agitation and pouring of suspension
25
Q

Steps to prepare suspensions

A
  • Add wetting agent to the particles: Use alcohol, glycerin, propylene glycol, surfactants to displace air
  • Add all water soluble materials to dispersion medium
  • Add dispersion medium to wetted particles in portions
  • Preservatives can be added to prevent bacterial growth
  • Use blender or mixer to ensure uniformity of suspension (liquid phase -> dispersed phase)
26
Q

Packaging and storing suspension

A
  • Wide-mouth containers
  • Containers should have adequate space above the liquid for thorough mixing and pouring
  • Tight containers protected from freezing, excessive heat or light
  • Should be shaken before use
27
Q

Bulk surface properties for disperse systems

A
  • surface tension
  • interfacial tension
  • wetting
  • adsorption
28
Q

Examples of wetting agents

A

acacia, taragacanth, sodium lauryl sulfate (anionic), polysorbate 80 (nonionic)

CH4106 (18 decks)

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