Pharmaceutical Suspensions Overview
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Questions and Answers

What is the typical particle size range for a suspension?

  • 1µm to 100µm (correct)
  • 100µm to 1mm
  • 0.1µm to 1µm
  • 1mm to 10mm

Which of the following is NOT a type of suspension classified in the content?

  • External suspension
  • Intravenous suspension (correct)
  • Oral suspension
  • Injectable suspension

Which property is essential for the suspended particles in a pharmaceutical suspension?

  • They must be larger than 1mm.
  • They need to remain in suspension without shaking.
  • They should be non-visible to the naked eye.
  • They should be small and uniform in size. (correct)

What must happen to the sediment in a suspension during storage?

<p>It must be easily resuspended with shaking. (C)</p> Signup and view all the answers

What is a common use for suspensions in pharmaceuticals?

<p>To provide a form for patients with difficulty swallowing solids. (B)</p> Signup and view all the answers

Which of the following agents is NOT typically added to a suspension?

<p>Solubilizing agents (A)</p> Signup and view all the answers

What is the maximum concentration of solid particles typically allowed in a parenteral suspension?

<p>30% (A)</p> Signup and view all the answers

Why are eye drops often formulated as suspensions?

<p>Due to the insolubility of certain drugs. (A)</p> Signup and view all the answers

What happens to the total surface area when a solid is divided into smaller particles?

<p>It increases, resulting in higher surface free energy. (C)</p> Signup and view all the answers

What is the role of surface-active agents in charging solid particles?

<p>They may ionize to give the particles a charge. (C)</p> Signup and view all the answers

How does pH influence the charge of particles with ionizable groups?

<p>Both B and C may occur depending on the pH level. (B)</p> Signup and view all the answers

What are potential-determining ions in a colloidal system?

<p>Anions that are selectively adsorbed by particles. (A)</p> Signup and view all the answers

What is the primary function of counter-ions in a colloidal system?

<p>They repel anions from the particle surface. (D)</p> Signup and view all the answers

What effects do small particle sizes have on interfacial tension?

<p>Smaller particle sizes increase interfacial tension. (D)</p> Signup and view all the answers

How does selective adsorption influence the charge of dispersed particles in a suspension?

<p>By forming charged particles based on adsorbed ionic species. (C)</p> Signup and view all the answers

What is the primary cause of surface potential in dispersed solid particles?

<p>The presence of charge in relation to the surrounding liquid medium. (A)</p> Signup and view all the answers

What is the primary role of buffers in a suspension?

<p>Control isotonicity and maintain stability (D)</p> Signup and view all the answers

Which of the following substances is commonly used as a humectant?

<p>Glycerol (B)</p> Signup and view all the answers

What is the effect of sweetening agents on the physical properties of a suspension?

<p>They can adversely affect rheological properties (B)</p> Signup and view all the answers

What is the purpose of using preservatives in a suspension?

<p>To prevent bacterial growth (C)</p> Signup and view all the answers

Which of the following describes a process used for large-scale preparation of suspensions?

<p>Utilization of a colloidal mill (A)</p> Signup and view all the answers

What characterizes the Stern layer in relation to charged particles?

<p>It consists almost entirely of counter-ions tightly bound to the particle surface. (A)</p> Signup and view all the answers

What does a high zeta potential indicate about a dispersion?

<p>It indicates a high degree of electrostatic repulsion between similarly charged particles. (D)</p> Signup and view all the answers

What is the primary effect of particle size on the rate of sedimentation?

<p>Reducing particle size retards the rate of sedimentation. (B)</p> Signup and view all the answers

What happens when the zeta potential is low?

<p>Attractive forces may outweigh repulsive forces, leading to flocculation. (B)</p> Signup and view all the answers

What defines the Nernst potential in a suspension system?

<p>It represents the difference between the charged surface and the electroneutral region. (C)</p> Signup and view all the answers

How can large particles affect injection products?

<p>They can block hypodermic needles if greater than 25µm in diameter. (C)</p> Signup and view all the answers

What is the role of the diffuse layer in relation to charged particles?

<p>It contains relatively mobile ions that are influenced by thermal energy. (D)</p> Signup and view all the answers

What aspect does not affect the stability of suspensions?

<p>The ambient temperature of the suspension. (D)</p> Signup and view all the answers

What is the degree of flocculation β a ratio of?

<p>The sedimentation volume of a deflocculated suspension to the deflocculated system's ultimate volume (A)</p> Signup and view all the answers

Which statement best describes the behavior of deflocculated suspensions?

<p>Their particles remain as separate units leading to slow sedimentation (B)</p> Signup and view all the answers

What is a potential disadvantage of a deflocculated suspension?

<p>Difficulties in maintaining homogeneity during shelf life (B)</p> Signup and view all the answers

Which describes the sedimentation characteristics of a flocculated system?

<p>Produces loose, fluffy floccules with high porosity (D)</p> Signup and view all the answers

What happens to the supernatant in a deflocculated system?

<p>It remains cloudy because of slow settling of small particles (B)</p> Signup and view all the answers

How does the viscosity of a deflocculated system affect sedimentation rate?

<p>High viscosity can lead to low sedimentation rates (D)</p> Signup and view all the answers

What is a common physical stability problem in deflocculated systems?

<p>Entrapment of liquid within the compacted sediment (D)</p> Signup and view all the answers

What defines the ideal behavior of an ideal suspension in terms of rheology?

<p>High apparent viscosity at low rate of shear (B)</p> Signup and view all the answers

What is the primary factor affecting the velocity of sedimentation according to Stokes' Law?

<p>The density difference between particles and the medium (C)</p> Signup and view all the answers

What characterizes a dilute pharmaceutical suspension?

<p>Contains less than 2 g of solids per 100 mL of liquid (B)</p> Signup and view all the answers

Under what condition does Stokes' Law fail to apply?

<p>In concentrated suspensions with more than 2% solid content (C)</p> Signup and view all the answers

What is the effect of adding a diluent to a concentrated suspension?

<p>Impacts flocculation and deflocculation in the system (D)</p> Signup and view all the answers

Which situation would cause Stokes' equation to yield a negative density difference?

<p>Particles being lighter than the dispersion medium (D)</p> Signup and view all the answers

In the context of sedimentation, what is hindered settling?

<p>Particles interacting and impeding each other's movement (B)</p> Signup and view all the answers

What parameter does Stokes' equation assume about particles in a suspension?

<p>They are spherical and monodisperse (B)</p> Signup and view all the answers

What is the ideal concentration of solids in a suspension for maintaining physical stability?

<p>From 0.5% to 2% (A)</p> Signup and view all the answers

Flashcards

Suspension Definition

A mixture of a solid and a liquid where the solid particles are not dissolved and are spread throughout the liquid.

Suspension Particle Size

The size of the solid particles in a suspension is larger than in a colloid, ranging from 1 micrometer to 100 micrometers.

Oral Suspension

A suspension taken by mouth, often for medication.

External Suspension

A suspension used on the skin or other external surfaces.

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Injectable Suspension

A suspension for injection into the body.

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Suspension Uses

Used when a drug is insoluble, difficult to swallow, or needs sustained release.

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Suspension Homogeneity

Suspension must stay consistent between shaking and use.

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Suspension Sedimentation

Solid particles settle over time. Suspensions need to be easily resuspended.

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Surface Potential of Colloidal Systems

Charge on solid particles within a suspension or dispersion, which affects stability.

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Potential-Determining Ions

Ions that determine the overall charge of a particle.

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Counter-ions

Ions with the opposite charge to potential-determining ions in solution.

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Electric Double Layer

Layer of oppositely charged ions formed around a charged particle in solution.

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Charged Particles (Colloidal)

Particles in a colloidal system possessing an electrical charge due to adsorption of ions.

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Surface Free Energy

Energy associated with the surface area of a substance.

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Interfacial Tension

Force acting at the boundary between two phases (e.g. liquid and solid).

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Stability of Lyophobic Colloids and Suspensions

Stability of colloids and suspensions is related the existence of surface potential and the double electric layer.

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Suspension Stability

Maintaining uniformity of dispersed particles in a suspension over time.

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Sedimentation Velocity

The speed at which particles settle in a suspension.

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Stokes' Law

An equation that predicts the velocity of sedimentation based on particle size, density, and medium viscosity.

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Dilute Suspension

A suspension with low solid concentration (less than 2g/100ml).

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Free Settling

Particles settle independently without interference in a dilute suspension.

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Hindered Settling

Particles interfere with each other during sedimentation in a concentrated suspension.

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Stokes' Law Limitations

Stokes' Law only applies to dilute suspensions with spherical particles and where the particles are denser than the medium.

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Sedimentation Rate for Concentrated Suspensions

Stokes' Law doesn't accurately predict the rate of sedimentation for concentrated suspensions.

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Zeta Potential

The potential difference between the shear plane and the electroneutral region, indicating dispersion stability.

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Stern Layer

The tightly bound layer of solvent and counter-ions surrounding a particle in a suspension.

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Diffuse Layer

The layer surrounding the Stern layer containing mobile ions.

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Particle Size and Stability

Smaller particle sizes in suspensions result in greater stability, resisting aggregation.

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Flocculation

Aggregation of particles in a suspension due to attractive forces.

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High Zeta Potential

Indicates a stable suspension due high electrostatic repulsion between particles.

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Low Zeta Potential

Indicates a less stable suspension where attractive forces overcome repulsion, leading to flocculation.

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Degree of Flocculation (β)

The ratio of the sedimentation volume of a flocculated suspension (F) to the sedimentation volume of a deflocculated suspension (Fo). It quantifies the extent of particle aggregation.

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Deflocculated Suspension

A suspension where particles remain individually dispersed, leading to slow sedimentation and a compacted sediment.

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Flocculated Suspension

A suspension where particles aggregate into larger flocs, leading to rapid sedimentation and a loose, easily re-dispersed sediment.

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Caking/Claying

A serious stability problem in deflocculated suspensions where compacted sediment becomes difficult to re-disperse.

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Supernatant

The liquid layer above the sediment in a suspension.

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Apparent Viscosity

The resistance to flow of a suspension, which can be influenced by factors like particle size and concentration.

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Rheology of Suspensions

The study of flow and deformation of suspensions, focusing on how viscosity changes with shear rate.

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Buffers in Suspensions

Buffers are added to suspensions to control the pH (acidity) and maintain chemical stability. They also help to prevent the particles in the suspension from clumping together (flocculation) and ensure the suspension has the correct concentration of dissolved substances.

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Density Modifiers in Suspensions

Density modifiers are added to suspensions to influence the thickness (viscosity) of the mixture. This helps to prevent the solid particles from settling to the bottom (sedimentation).

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Humectants in Suspensions

Humectants are substances that help attract and retain moisture to the suspension. This prevents the suspension from drying out, especially after application to the skin or other surfaces.

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Preservatives in Suspensions

Preservatives are added to suspensions to kill or inhibit the growth of bacteria and other microorganisms. This helps to keep the suspension safe and effective for longer.

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Sweeting Agents in Suspensions

Sweetening agents are added to suspensions to improve their taste, making them more palatable. They can be sugar-based like sucrose or sorbitol, or artificial sweeteners.

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Study Notes

Suspensions

  • Liquid mixtures where solid particles are dispersed throughout the liquid.
  • Particles are visible and settle out over time.
  • Dispersed particles are larger than colloids (typically 1μm to 100μm).
  • Classified as oral, external, or injectable.
  • Parenteral suspensions contain 0.5-30% solid particles.

Physical Properties of a Well-Formulated Suspension

  • Remains homogenous between shaking and use.
  • Sediment easily resuspends with shaking.
  • Viscous enough to reduce settling rate.
  • Small, uniform particle size for smooth texture.

Pharmaceutical Applications of Suspensions

  • Used for drugs difficult to swallow as solid dosage forms.
  • Used for insoluble drugs.
  • Used for drugs that degrade in water.
  • Used to deliver drugs for topical application (e.g., calamine lotion).
  • Used for vaccines (dispersed killed microorganisms).
  • Used for x-ray contrast media (e.g., barium sulfate).

Interfacial Properties of Suspended Particles

  • Knowledge of thermodynamic requirements is necessary for stabilization of suspended particles.
  • Work must be done to reduce a solid to small particles and disperse them in a continuous medium.
  • The large surface area of particles associated with surface free energy that makes the system thermodynamically unstable.
  • Tendency to regroup to decrease surface area and surface free energy
  • Flocculation (formation of light, fluffy aggregates held together by van der Waals forces).
  • Formation of aggregates or caking (due to stronger forces of aggregation).
  • Defined by ΔE = γ . ΔΑ, where γ is the interfacial tension.

Surface Potential

  • Stability explained by presence or absence of surface potential.
  • Solid particles in suspension may become charged through different ways, possibly by selective adsorption of ions, or ionization of functional groups.
  • Solid particles have a negative or positive charge.
  • Surrounding the Stern layer, is the diffuse layer containing mainly counter-ions.

Electric Double Layer

  • Formation of an electric double layer to neutralize charged particles in a suspension.
  • Potential at any point depends on location; potential changes as one moves away from the particle.
  • Difference in potential between the actual surface and the electroneutral region is called the Nernst potential (E).
  • Difference in potential between the shear plane and the electroneutral region is the electrokinetic or zeta (ζ) potential.

Zeta Potential

  • Measures the stability of dispersions.
  • Indicates the degree of electrostatic repulsion between charged particles.
  • High zeta potential = stable dispersions; low zeta potential = tendency to coagulate or flocculate.

Formulation of Suspensions

  • Particle Size Control: Reducing particle size can slow settling rate. Particles over 5um can cause irritation.
  • Wetting Agents: Used to reduce interfacial tension between solid and liquid, helping dispersed particles mix thoroughly.

Viscosity Modifiers

  • Polysaccharides: (e.g., Acacia gum, Tragacanth, Alginates) increase viscosity, but may have limitations based on pH or other factors.
  • Starch: Used less frequently as a viscosity modifier in suspensions.

Formulation Additives

  • Buffers: Maintain chemical stability.
  • Density Modifiers: Increase viscosity and decrease sedimentation.
  • Flavors, Colors, Perfumes: Enhance palatability.
  • Humectants: (e.g., glycerol, propylene glycol) prevent drying.
  • Preservatives: (e.g., sodium benzoate, benzoic acid, parabens) prevent microbial growth.
  • Sweetening Agents: Improve taste (e.g., sucrose, sorbitol, glycerol).

Settling in Suspensions

  • Sedimentation Volume (F): Ratio of final sediment volume to initial suspension volume.
  • Flocculation: Aggregation of particles; leads to a higher sedimentation volume. It is a rapid sedimentation rate when the volume of the sediments will larger and easy redispersed even if stirred moderately.
  • Deflocculation: Particles remain individual; a slow sedimentation rate, and the supernatant remains cloudy. It leads to a low sedimentation volume and sediment difficult to redisperse.
  • Stokes' Law: Equation predicting sedimentation velocity (v=Kd²(ps-po)g/18η). This law is valid for dilute suspension (typically less than 2% solids).

Difference Between Flocculation and Deflocculation

  • Flocculated suspensions show rapid settling.
  • Deflocculated suspensions show slow, separate particle settling.
  • Flocculation leads to a sediment that's easy to redisperse.
  • Deflocculation leads to a compacted sediment that is difficult to redisperse.

Rheology of Suspensions

  • Ideal suspensions should show high apparent viscosity at low shear rates and settle slowly.
  • Sufficient viscosity to remain in desired form on storage but low enough to flow easily.
  • Flocculated suspensions often exhibit thixotropy (reversible loss of structure with time).
  • Deflocculated suspensions often exhibit Newtonian behavior (constant viscosity independent of shear rate).

Brownian Movement

  • Random movement of particles that can affect sedimentation.
  • Significant for very small particles.

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Suspensions PDF

Description

Explore the concept of pharmaceutical suspensions, including their physical properties, applications, and interfacial characteristics. This quiz covers the essentials of liquid mixtures with solid particles and the unique requirements for effective formulation. Test your knowledge on how suspensions are utilized in various drug delivery methods.

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