Suspension Flashcards
definition
Suspension
Liquid preparations that consist of solid particles dispersed throughout a liquid phase in which the particles are not soluble.
Reasons for suspensions
Suspensions vs. Solutions
* solubility
* chemical stability: solution - ___ order, suspension - ___
* palatability (taste) - erythromycin estolate ___ tastes better than the ___
- 1st, 0th
- suspension, solution
Reasons for suspensions
Suspensions vs. Tablets
* ___ of dose
* ease of swallowing
* ___ rate
- flexibility
- dissolution
Suspension vs. other dosage forms
What dose this graph mean?
suspension dissolves faster than a tablet
Suspension vs. other dosage forms
What dose this graph mean?
the graph represents how much of a dosage form is absorbed and excreted in an hour. fastest = solution, 2nd = suspension, 3rd = tablet
Components of suspension
- active ingredient (solid particles)
- vehicle
- buffer
- preservative
- flocculating agent
- structured vehicle system
- wetting agent
- antifoaming agent
- flavor and sweetener
Desirable properties
- do not want rapid settling
- particles that do settle should not form a ___ and must be easily redispersed into a ____ when shaken
- easy to administer (not too ____)
- for lotions, should be fluid enough to spread to the affected area but not so much to where it is dripping off
- want particle size to remain ___ during storage
- hard cake, uniform mixture
- viscous
- constant
What equation is used to find the velocity of sedimentation (settling)?
Stokes Law
T or F: the diameter of the particle is expressed as mcm
False: diameter expressed as cm
What is the maximum particle size (diameter) of bismuth subsalicylate (active ingredient of Pepto Bismol suspension) required to produce
a rate of settling less than 1.85 x 10-6 cm/sec as a 10% suspension in sorbitol solution?
* The density and viscosity of sorbitol solution are 1.3 g/cm3 and 110 cps, respectively. The density of
bismuth subsalicylate is 2.2 g/cm3.
2.03 um
particle size
micropulverization
* 10-__ mcm (most oral and ___ suspensions)
* high speed attrition or impact mills
- 50 mcm, topical
particle size
Fluid energy grinding
* < ___mcm ( ___ or ophthalmic suspensions)
* jet milling, micronizing
* shearing action of high-velocity compressed airstream on the particles in a confined space
- 10 mcm, parenteral
Particle size
Spray drying
* < ___ mcm
* spray dryer - cone shaped machine into which a solution of a drug is sprayed and rapidly ___
- 5 mcm
- dried
Suspension formulation designs
- dispersed phase (____)
- dispersion medium (___)
- solid particles
- liquid
types of suspension
- dispersed suspension
- flocculated suspension
- structured vehicle system
Thermodynamic stability equation
A suspension is stable when ∆G = 0. This can never be reached in a suspension because we usually want small particles (high ∆A ) for rapid dissolution. Over time, a suspension moves toward ∆G= 0 by two processes that reduce the surface area (∆ ): (increase particle size)
1. aggregation
2. crystal growth
2 processes that reduce the surface area (increase particle size)
- aggregation
- crystal growth
Interparticle forces
- Van der Waals attractive force
- Hydration repulsive force
- Electrostatic repulsive force
- Steric repulsive force
only electrostatic repulsive force and steric repulsive force are controlled by the formulation
Net effect of interparticle forces
What does the net graph look like?
Dispersed suspension
* ___ forces are dominant
* particles repel each other and do not ___
* Problem: particles settle as ___ particles. Leads to dense ___ which is difficult to resuspend
- repulsive
- aggregate
- individual, cake
Net dispersion graph
Controlled flocculation
* ___ and __ forces are in balance
* particles are attracted to each other at the secondary minimum to form ___, also known as floccules
* the floccules settle to produce a sediment with high ___
* this type of sediment is ___ to redisperse
- repulsive and attractive
- aggregates
- volume
- easy
Controlled flocculation net graph
Dispersion vs. Flocculation
particle diagram
Dispersion vs. Flocculation
cake types
What is the sediment volume and degreen of flocculation of this picture?
know this graph
Exercise 2
The addition of 2 mmol of sodium chloride to 100 mL of an intramuscular suspension causes
the volume of the sediment to increase from 5 mL to 40 mL. What degree of flocculation was induced by the added sodium chloride?
B=8
Rheology
* Study of ___ characteristics
* Shear rate (dv/dr) - speed of top vs bottom layer of liquid when force is applied to the ___
* Shear stress (F) - the ___ per unit area, F’/A, required to bring about flow.
- flow
- side
- force
Rheology
What does the Newtonian flow graph look like?
What does a plastic flow graph look like?
What does a pseudoplastic flow graph look like?
What does a dilatant flow graph look like?
Newtonian flow equation
What types of non-newtonian flows can undergo thixotropy?
plastic and pseudoplastic
summary
Comparison of different suspension approaches
Contact angle
A ___ contact angle
indicates poor spreading
and that cohesive forces of
the liquid is ___.
- high, strong
