Review questions answers
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Pharmaceutical Drugs and Dosage: Dosage forms - Suspensions - Review questions answers
Review questions
16.1 Indicate
which statements are TRUE and which are FALSE?
A. Flocculation is
desirable for pharmaceutical suspensions.
B. Deflocculation is
not desirable for pharmaceutical suspensions.
C. Motion of dispersed
particles in a suspension is induced by ther-mal and gravitational forces.
D. Viscosity of the
suspension affects the settling of particles
E. Crystal growth of
particles in a suspension is due to temperature fluctuation on storage and due
to wider particle size distribution
16.2 How does
the increase in viscosity of the suspending medium affect the rate of
sedimentation when assuming the density of the particles is larger than that of
the suspending medium?
A. Sedimentation rate
will not change
B. Sedimentation rate
will be slower
C. Sedimentation rate
will be faster
D. No particle
sedimentation will take place
16.3 Which
one of the following phenomena is undesirable in pharmaceuti-cal suspensions?
A. Slow settling of
particles
B. Particles
agglomerate to dense cake
C. Particles readily
redisperse upon agitation
D. Suspension pours
readily
16.4 Define
and differentiate flocculated and deflocculated suspensions. Why is deflocculation not
desirable, whereas flocculation is an acceptable characteristic for
pharmaceutical suspension dosage forms?
16.5 A course
powder with a true density of 2.44 g/cm3 and a mean diam-eter, d,
of 100 μm was dispersed in a 2% carboxymethylcellulose dispersion having a
density, ρ0, of 1.010 g/cm3.
The viscosity of the medium at low shear rate was 27 poise. Using Stokes’ law,
calculate the average velocity of sedimentation of the powder in cm/s.
16.6 Using
Stokes’ law, compute the velocity of sedimentation in cm/s of a sample of zinc oxide
having an average diameter of 1 μm (radius of 5 × 10−5
cm), a true density, ρ, of 2.5 g/cm3 in a suspending medium
having a density, ρ0, of 1.1 g/cm3,
and a Newtonian viscosity of 5 poise.
16.7 Which of
the following parameters control the rate of sedimentation of particles in a
suspension?
A. Particle diameter
B. Viscosity of the
suspending vehicle
C. Surface charge on
the particles
D. Density of the
particles
16.8 Under
what circumstances would a powder for suspension preferred dosage form for
commercialization compared to a ready-to-use sus-pension dosage form?
A. High settling volume
of suspension
B. Low viscosity of
vehicle
C. Poor stability of
API in suspension
D. High viscosity of
vehicle
16.9 Which of
the following ingredients in a suspension could help in floc-culating the
dispersed particles?
A. Surfactant
B. Hydrophilic polymer
C. Electrolyte
D. Cosolvent
16.10 Which of
the following is not a typical requirement for lotions?
A. Must dry quickly
B. Must be fluid, not
highly viscous
C. Must have a smooth
feel to the skin
D. Must be sweet
Answers:
16.1 A. True
B. False
C. True
D. True
E. True
16.2 B. In
flocculated systems, forces of attraction are predominant over repulsive forces.
16.3 B.
According to Stokes’ law, sedimentation rate will increase with an increase in the particle
density.
16.4 Flocculated
suspension has dispersed phase as loose, light, fluffy flocs (associations of
particles) held together by weak van der Waals forces. Deflocculated suspension
has dispersed phase in the form of aggre-gates, which are formed by growth and
fusion of crystals in the pre-cipitates to form a solid cake.
Flocculation
is an acceptable characteristic for pharmaceuti-cal suspension dosage forms as
flocculated suspension form loose flocs, which are easy to redisperse at the
time of dose administra-tion as compared to redispersion of hard cake in a
deflocculated suspension.
16.5 Because
= 2gr2(ρ1 − ρ2)/ 9η , V = 2 ∗
981 ∗ (100/1000/2)2 ∗
[(2 .44 − 1. 010)/ (9 ∗
27)]
=
0.0288 cm/s
16.6 V = [ 2gr2
(ρ1 − ρ2) ] /9η ,V =2 ∗981∗(100/1000/2)2
∗ [(2.5 −1.1)/ (9 ∗
5)]
= 1 .53×105 cm/s
16.7 A, B, C, and D.
16.8 C.
16.9 A, B, and C.
16.10 D.
