MPharm Master of Pharmacy Master of Pharmacy: Pharmaceutical Formulations and Dosage Forms 3 — Questions and Answers
Question 1: Fick's first law of diffusion relates steady-state flux (J) to which variables?
- J = D × C/t (concentration over time)
- J = –D × dC/dx (diffusion coefficient × concentration gradient) (Correct answer)
- J = P × A × ΔC (permeability × area × concentration difference)
- J = k × Cs (dissolution rate constant × solubility)
Correct answer: J = –D × dC/dx (diffusion coefficient × concentration gradient)
Fick's first law states J = –D(dC/dx), where flux is proportional to the diffusion coefficient and the negative concentration gradient across the membrane.
Question 2: Which polymorphic form of a drug is generally preferred for formulation due to its thermodynamic stability?
- Metastable polymorph
- Amorphous form
- Stable polymorph (Correct answer)
- Solvate form
Correct answer: Stable polymorph
The most stable polymorph has the lowest solubility but the highest physical stability, reducing the risk of form conversion during processing and storage.
Question 3: In the Noyes-Whitney equation, which factor most directly increases the dissolution rate of a poorly soluble drug?
- Increasing particle size
- Decreasing the diffusion layer thickness (h) (Correct answer)
- Decreasing the drug's saturation solubility
- Increasing drug crystal density
Correct answer: Decreasing the diffusion layer thickness (h)
The Noyes-Whitney equation shows dissolution rate ∝ D×A×Cs/h; reducing diffusion layer thickness (e.g., by agitation or micronization) directly increases rate.
Question 4: A transdermal patch designed for zero-order drug delivery typically uses which design?
- Matrix-type patch without rate-controlling membrane
- Reservoir-type patch with a rate-controlling membrane (Correct answer)
- Multilayer drug-in-adhesive patch
- Microreservoir patch with suspension
Correct answer: Reservoir-type patch with a rate-controlling membrane
Reservoir patches contain drug in a solution or gel depot separated from skin by a rate-controlling membrane that maintains constant flux (zero-order release).
Question 5: Which excipient functions as a glidant to improve powder flow during tablet manufacturing?
- Magnesium stearate
- Colloidal silicon dioxide (Aerosil) (Correct answer)
- Microcrystalline cellulose
- Crospovidone
Correct answer: Colloidal silicon dioxide (Aerosil)
Colloidal silicon dioxide reduces interparticle friction by coating powder surfaces, improving flow through hoppers and tablet press feeders.
Question 6: Zeta potential measurements are used in colloidal dispersions primarily to assess:
- Drug solubility in the formulation
- Physical stability by predicting electrostatic repulsion between particles (Correct answer)
- Viscosity of the continuous phase
- Particle shape and crystallinity
Correct answer: Physical stability by predicting electrostatic repulsion between particles
A zeta potential beyond ±30 mV indicates sufficient electrostatic repulsion to prevent aggregation and predict colloid physical stability.
Question 7: The critical micellar concentration (CMC) of a surfactant is defined as the concentration at which:
- All surfactant molecules adsorb to the interface
- Micelles begin to form spontaneously in solution (Correct answer)
- Surfactant solubility is exceeded
- Phase inversion of an emulsion occurs
Correct answer: Micelles begin to form spontaneously in solution
Above the CMC, additional surfactant monomers self-assemble into micellar aggregates, enabling solubilization of hydrophobic drugs.
MPharm Master of Pharmacy Master of Pharmacy: Pharmaceutical Formulations and Dosage Forms 3
Fick's first law of diffusion relates steady-state flux (J) to which variables?