PDD Quiz Review Flashcards
How can you determine if a compound is a weak acid or weak base based on pH and solubility?
- weak acid: as pH
- weak base: as pH increases, solubility decreases
What is intrinsic solubility (S0) on a graph of pH vs. solubility?
the plateau
What is an amphoteric drug?
has both acid and base properties
What key parameters can be modified in order to obtain a faster release and dissolution from a solid dosage form? (7)
(refer to dissolution rate (dM/dt) equation)
- increasing surface area of drug particles
- decreasing particle size
- increasing solubility Cs of weak acids and bases
- decreasing thickness h of the diffusion layer
- agitating the dissolution medium
- reducing concentration of drug in the bulk medium (Cb)
- constantly removing dissolved drug
What is sodium metabisulphite used for? What could be the consequence of leaving it out?
antioxidant – has higher oxidative potential than the API and is preferentially degraded
- leaving it out may impact stability of the API, especially if it is prone to degradation by oxidation
- alternatives: sodium sulphite, sodium formaldehyde sulphoxylate, ascorbic acid
Differentiate between the 3 types of dispersions.
colloids:
- dispersed particles between 1-500 nm and scatter light
- appear turbid if [API] is high enough
true solutions:
- molecular dispersions with particles < 1 nm in diameter and do not scatter light
- appear clear at all [API]
coarse:
- dispersed particles > 500 nm
- appear cloudy/turbid
How do you determine the order of a reaction?
the sum of the powers
What are the units for k0?
concentration/time
What is shelf-life?
time interval for a product to remain in the accepted specifics as the original
What is the shelf life if 5% degradation of a drug (zero order) is allowed?
t95
- Ct = 95% (C0)
- t95 = (0.05 C0)/k0
What are the units of k1?
1/time
Describe a graph following first order kinetics.
logCt (y) vs. time (x)
- linear relationship
Describe a graph following zero order kinetics.
concentration (y) vs. time (x)
- linear relationship
What are the 2 assumptions for pseudo-zero order reactions?
- only soluble A molecule in the medium (ie. water) undergoes first order degradation (ie. hydrolysis)
- drug A molecules in solid particles do not undergo hydrolysis/degradation until they are released/stabilized in the medium
What is the equation for k0?
k1 x S
Are suspensions formulations more or less stable than solution formations?
suspension formulation is always more stableQ
What does the Arrhenius equation tell us?
degradation rate constant is dependent on temperature
- higher temperature – more collision of molecules, easier to reach sufficient energy
Where do pseudo zero order reactions occur?
in suspensions
What would you recommend to your patients before taking dispersions to ensure accurate dosing?
- shake before using
What happens to particles in O/W emulsions?
oil floats to the top because it is lighter than water
According to Stoke’s law, how can the stability of a suspensions be increased? (3)
- reduce size
- minimize density difference
- increase viscosity of medium – carboxymethylcellulose, methycellulose, microcrystalline cellulose, polyvinyl-pyrrolidone, xanthan gum
What do flocculating agents do?
added to aggregate solid particles into larger, loosely interacting particles to avoid formation of compact cake
What is the function of sorbitol solution?
increase viscosity and palatability
What is the function of syrup (80% sucrose) solution?
increase viscosity and palatability
