Master of Pharmacy: Pharmaceutical Formulations and Dosage Forms Flashcards
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Fick's first law of diffusion relates steady-state flux (J) to which variables?
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.
Which polymorphic form of a drug is generally preferred for formulation due to its thermodynamic stability?
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.
In the Noyes-Whitney equation, which factor most directly increases the dissolution rate of a poorly soluble drug?
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.
A transdermal patch designed for zero-order drug delivery typically uses which design?
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).
Which excipient functions as a glidant to improve powder flow during tablet manufacturing?
Answer: Colloidal silicon dioxide (Aerosil)
Colloidal silicon dioxide reduces interparticle friction by coating powder surfaces, improving flow through hoppers and tablet press feeders.
Zeta potential measurements are used in colloidal dispersions primarily to assess:
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.
The critical micellar concentration (CMC) of a surfactant is defined as the concentration at which:
Answer: Micelles begin to form spontaneously in solution
Above the CMC, additional surfactant monomers self-assemble into micellar aggregates, enabling solubilization of hydrophobic drugs.