Suspensions

What are the primary types of colloidal systems mentioned in the text?

The primary types of colloidal systems are disperse systems and suspensions.

What factors affect the chemical stability of active pharmaceutical ingredients (APIs) in suspensions?

The chemical stability of APIs mainly refers to their decomposition and changes in pH.

What role do preservatives play in the stability of pharmaceutical suspensions?

Preservatives help prevent microbial contamination, thus enhancing microbiological stability.

List some examples of factors impacting the physical stability of suspensions.

Factors include wettability, flocculation/deflocculation, caking, and Ostwald ripening.

Explain the process of Ostwald ripening in suspensions.

Ostwald ripening involves the growth of larger particles at the expense of smaller ones through dissolution and recrystallization.

What is wettability and why is it significant in the context of suspensions?

Wettability refers to how easily a fluid can spread on a solid surface, which is significant for the dispersibility of drug particles in suspensions.

How does the contact angle relate to the wettability of drug particles?

The contact angle, which can range from 0° to 180°, describes how well a liquid droplet spreads on a surface, affecting the wettability of drug particles.

What are the two types of solids based on their wettability mentioned in the text?

The two types of solids are hydrophilic (easily wetted by water) and hydrophobic (repelling water).

Provide examples of hydrophilic and hydrophobic solids.

Hydrophilic solids include Zinc oxide, Talc, and Magnesium carbonate; hydrophobic solids include Sulfur, Charcoal, and Magnesium stearate.

What are the interactions that affect particle-particle interactions in suspensions?

Particle-particle interactions are influenced by repulsive forces due to electrical repulsion and attractive forces due to Van der Waals attraction.

Describe the electric double layer (EDL) and its importance in suspensions.

The EDL consists of a layer of counter-ions attracted to a negatively charged particle surface, essential for maintaining charge balance and influencing particle interactions.

What does DLVO theory explain about particle interactions in suspensions?

DLVO theory explains the balance of attractive and repulsive forces between particles, influencing stability and flocculation behavior.

What happens to particles when they approach each other according to DLVO theory?

As particles approach, their electrical double layers begin to overlap, leading to increased repulsion due to their positive and negative surface charges.

Define time flocculation and deflocculation in the context of drug particles in suspensions.

Time flocculation is when particles form loosely bound aggregates (floccules), while deflocculation refers to particles settling slowly and forming agglomerates.

What are the consequences of deflocculated particles settling in a suspension?

Deflocculated particles may form small sediment that results in a cloudy supernatant, potentially affecting dosage accuracy.

How does Stokes Law relate to sedimentation in suspensions?

Stokes Law describes the sedimentation rate of particles, dependent on particle size, density difference between the particle and medium, and medium viscosity.

How does particle size affect sedimentation velocity according to the text?

If the particle size is reduced by half, the sedimentation velocity decreases fourfold.

What is the effect of changing the density of the medium on sedimentation?

Increasing medium density results in a faster sedimentation rate due to a greater density difference with the particles.

How does viscosity of the medium impact sedimentation in suspensions?

Increasing the viscosity of the medium decreases the sedimentation rate by limiting particle diffusion.

What are the benefits of using suspending agents in pharmaceutical suspensions?

Suspending agents improve rheology by increasing viscosity, which helps maintain a uniform distribution of particles.

Discuss the potential effect of temperature variations on suspensions.

Cyclical temperature variations can lead to Ostwald ripening, affecting the flocculation and sedimentation behavior of particles, potentially impacting drug bioavailability.

What do repeated temperature changes influence in the context of pharmaceutical suspensions?

Repeated temperature changes can affect flocculation, sedimentation, dissolution profiles of drugs, and lead to variability in clinical effects.

Explain the significance of controlled flocculation in drug delivery systems.

Controlled flocculation allows particles to aggregate loosely, ensuring they are easily redisperseable for accurate dosages without caking.

How do the forces that interact between particles change as they approach one another?

As particles get closer, they experience a shift from repulsion (due to electrical forces) to attraction, eventually leading to aggregation if they reach the primary minimum.

What is the outcome when particles coagulate in a suspension?

Coagulated particles may form a cake in the primary minimum, making it difficult to redisperse upon shaking.

What is the primary concern with microbial contamination in suspensions?

Microbial contamination can lead to compromised product integrity and decreased efficacy of pharmaceutical suspensions.

Why is particle size control critical in pharmaceutical suspensions?

Control over particle size is crucial for maintaining consistent therapeutic effectiveness and ensuring uniformity from batch to batch.

How does the addition of non-ionic materials affect the viscosity of the medium?

Adding non-ionic materials increases the viscosity, thus enhancing the suspension's stability by reducing sedimentation.

In what way does the particle density affect the sedimentation rate in a suspension?

Greater differences in density between the particle and the medium lead to faster sedimentation rates.

Define the primary and secondary minima and their significance in suspension stability.

The primary minimum indicates where particles stick together strongly (caking), while the secondary minimum is where weak attractions allow reversible flocculation.

What happens to the interaction between particles when the temperature increases?

Increased temperature can provide enough kinetic energy for particles to overcome energy barriers and enter into closer interactions.

Describe how surfactants function as wetting agents in suspensions.

Surfactants dissolve in water, displacing air around particles and reducing interfacial tension, which lowers the contact angle and improves drug dispersibility.

Explain the role of hydrophilic and hydrophobic interactions in the stability of suspensions.

Hydrophilic interactions promote wetting and dispersion, while hydrophobic interactions can lead to aggregation and instability if not adequately managed.

What is the impact of electric charges on dispersed particles in a suspension?

The electric charges can influence the stability and interactions of particles, modifying the double layer and affecting overall system behavior.

In terms of drug formulation why is it important to consider both physical and chemical stability?

Both physical and chemical stability are essential to ensure that the drug maintains its efficacy, safety, and intended release profile over its shelf life.

How can changing the crystallization method affect particle properties?

Altering the crystallization method can change particle density and size, which in turn impacts sedimentation rates and overall stability of the formulation.

What happens when particles reside in the secondary minimum of the energy interaction curve?

Particles in the secondary minimum exhibit weak attractions, allowing them to form floccules that can easily be redispersed with agitation.

How does the maximum primary energy affect particle interactions?

The primary maximum prevents particles from coming too close together, thus maintaining a level of separation that ensures stability.

Describe the difference between a flocculated and a deflocculated suspension.

Flocculated suspensions contain loosely bound aggregates that are easier to redisperse, while deflocculated suspensions have particles that settle densely and slowly form sediment.

What does the term "packing particles" refer to in the context of pharmaceutical suspensions?

Packing refers to the arrangement and compression of particles under the weight of particles above them, which can affect settling and stability in the suspension.

How do attractive forces play a role in the re-dispersibility of flocculated systems?

Weak attractive forces in flocculated systems allow particles to be easily broken apart and redistributed, facilitating dosage accuracy.

Identify a consequence of insufficient control of particle size distribution in suspensions.

Insufficient control can lead to variability in therapeutic effectiveness and inconsistent drug release profiles between batches.