Routes of Administration Oral (Suspensions) Flashcards
1
Q
What is a disperse system?
A
- A 2 phase heterogenous system in which an insoluble or immiscible dispersed phase is distributed through a continuous phase
- Are classified upon the size of dispersed phase
2
Q
What are the different dispersion classifications?
A
- Molecular (less than 1nm) (Glucose solution)
- Colloidal (between 1nm and 1um) (microemulsions, micelles, milk)
- Coarse (more than 1um) (suspensions, emulsions)
3
Q
What are suspensions?
A
- Liquid disperse system consisting of particles distributed within a liquid vehicle
- Classified as coarse or colloidal depending on size
- Not optically clear = cloudy
4
Q
What are the reasons of suspensions?
A
- Deliver poorly water-soluble drugs which cant be formulated as aqueous solutions
- Mask bitter taste
- Increase drug stability
- Achieve controlled/ sustained drug release
5
Q
To ensure a uniform dose, what properties should an oral suspension have?
A
- Particles settle slowly
- Particles readily and uniformly re-dispersed upon shaking
- Particle size remains consistent over time
- Viscosity is high enough to ensure a uniform dose (not too much or unpourable)
6
Q
What is the Electrical double layer?
Explanation from centre to outside
A
- Negatively charged particle
- Stern Layer: Particle attracts ions of opposite charge (positive), tightly bound around surface
- Hydrodynamic plane of shear (slipping plane)
- Diffuse Layer - ions are diffused freely around particle
7
Q
What is zeta potential?
A
- Governs the degree of repulsion/ attraction between particles
- The electrical potential in the interfacial double layer at the slipping plane
8
Q
What happens if the zeta potential is reduced below a certain value?
A
- The attractive forces between particles due to van der waals overcome the forces of repulsion and the particles come together to form floccules - flocculation
- The magnitude of surface and zeta potentials is related to the surface charge and the thickness of the double layer
9
Q
What happens if the zeta potential is high?
A
- The stronger the electrostatic repulsion and the more stable the system (low viscosity, well dispersed)
10
Q
Excipients (ionic charge NaCl) how do they affect the suspension properties?
A
- At low conc - will only affect the diffuse layer, neutralising the particle charge, thinning diffuse layer
- At high conc - will also affect fixed layer charge. Charge on particle surface will decrease
11
Q
How do micelles affect the electrical double layer? what happens if the concentration is above or below the CMC
A
- Critical micelle concentration is the concentration in which micelles form
- Above CMC, micelles form with a hydrophobic core in which hydrophobic drug may dissolve
- Below CMC, surfactants will cover particle surface and reduce interfacial tension between particle and medium (increase stability)
12
Q
What is the DVLO theory?
A
- It explains the aggregation (cluster) of aqueous dispersions and the forces between charges surfaces interacting with the liquid.
- It calculates the attraction (van der waals) and repulsion energies (electrostatic potential) between particles with energy of the interactions.
13
Q
What is a deflocculated system?
A
- A system in which particles are individually and uniformly dispersed throughout the liquid medium
- Remains deflocculated when repulsive energies are high and may settle slowly producing sediment (not ideal)
- Redispersion is hard
14
Q
What is a Flocculated System?
A
- Forms weakly attracted or weakly bonded aggregates of particles
- When attractive forces are greater than repulsive
- Reducing surface charge of particles can induce flocculation
15
Q
What are the different ways particles move?
A
- Brownian Motion
- Gravity
- External agitation (shaking by patients)
