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
