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?

It must be easily resuspended with shaking. Signup and view all the answers

What is a common use for suspensions in pharmaceuticals?

To provide a form for patients with difficulty swallowing solids. Signup and view all the answers

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

Solubilizing agents Signup and view all the answers

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

30% Signup and view all the answers

Why are eye drops often formulated as suspensions?

Due to the insolubility of certain drugs. Signup and view all the answers

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

It increases, resulting in higher surface free energy. Signup and view all the answers

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

They may ionize to give the particles a charge. Signup and view all the answers

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

Both B and C may occur depending on the pH level. Signup and view all the answers

What are potential-determining ions in a colloidal system?

Anions that are selectively adsorbed by particles. Signup and view all the answers

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

They repel anions from the particle surface. Signup and view all the answers

What effects do small particle sizes have on interfacial tension?

Smaller particle sizes increase interfacial tension. Signup and view all the answers

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

By forming charged particles based on adsorbed ionic species. Signup and view all the answers

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

The presence of charge in relation to the surrounding liquid medium. Signup and view all the answers

What is the primary role of buffers in a suspension?

Control isotonicity and maintain stability Signup and view all the answers

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

Glycerol Signup and view all the answers

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

They can adversely affect rheological properties Signup and view all the answers

What is the purpose of using preservatives in a suspension?

To prevent bacterial growth Signup and view all the answers

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

Utilization of a colloidal mill Signup and view all the answers

What characterizes the Stern layer in relation to charged particles?

It consists almost entirely of counter-ions tightly bound to the particle surface. Signup and view all the answers

What does a high zeta potential indicate about a dispersion?

It indicates a high degree of electrostatic repulsion between similarly charged particles. Signup and view all the answers

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

Reducing particle size retards the rate of sedimentation. Signup and view all the answers

What happens when the zeta potential is low?

Attractive forces may outweigh repulsive forces, leading to flocculation. Signup and view all the answers

What defines the Nernst potential in a suspension system?

It represents the difference between the charged surface and the electroneutral region. Signup and view all the answers

How can large particles affect injection products?

They can block hypodermic needles if greater than 25µm in diameter. Signup and view all the answers

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

It contains relatively mobile ions that are influenced by thermal energy. Signup and view all the answers

What aspect does not affect the stability of suspensions?

The ambient temperature of the suspension. Signup and view all the answers

What is the degree of flocculation β a ratio of?

The sedimentation volume of a deflocculated suspension to the deflocculated system's ultimate volume Signup and view all the answers

Which statement best describes the behavior of deflocculated suspensions?

Their particles remain as separate units leading to slow sedimentation Signup and view all the answers

What is a potential disadvantage of a deflocculated suspension?

Difficulties in maintaining homogeneity during shelf life Signup and view all the answers

Which describes the sedimentation characteristics of a flocculated system?

Produces loose, fluffy floccules with high porosity Signup and view all the answers

What happens to the supernatant in a deflocculated system?

It remains cloudy because of slow settling of small particles Signup and view all the answers

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

High viscosity can lead to low sedimentation rates Signup and view all the answers

What is a common physical stability problem in deflocculated systems?

Entrapment of liquid within the compacted sediment Signup and view all the answers

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

High apparent viscosity at low rate of shear Signup and view all the answers

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

The density difference between particles and the medium Signup and view all the answers

What characterizes a dilute pharmaceutical suspension?

Contains less than 2 g of solids per 100 mL of liquid Signup and view all the answers

Under what condition does Stokes' Law fail to apply?

In concentrated suspensions with more than 2% solid content Signup and view all the answers

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

Impacts flocculation and deflocculation in the system Signup and view all the answers

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

Particles being lighter than the dispersion medium Signup and view all the answers

In the context of sedimentation, what is hindered settling?

Particles interacting and impeding each other's movement Signup and view all the answers

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

They are spherical and monodisperse Signup and view all the answers

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

From 0.5% to 2% Signup and view all the answers

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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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.