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Chapter: Pharmaceutical Drugs and Dosage: Dosage forms - Suspensions

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


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 = [ 2gr21 − 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.

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