Exam questions Flashcards
(37 cards)
List three unique structures of the small intestine that account for its large surface area.
- Circular folds
- Villi
- Microvilli
Which of the following BCS classes is the poorest candidate for oral administration? A. Class I B. Class II C. Class III D. Class IV
D
The absorption of BCS Class II drugs (poor solubility and high permeability) can be improved in the presence of fatty foods. Why?
Fatty foods induce the secretion of bile
enhances drug solubility
Define diffusion layer.
Stationary layer of solvent in which the solute molecules exist in concentrations Cs to C
What is assumed to exist at the surface of a solid undergoing dissolution?
Aqueous diffusion layer
In the Noyes and Whitney equation (diffusion layer model), (dM/dt) = [DS(Cs-C)]/h. Describe what each variable represents.
D= diffusion coefficient S= SA of particle Cs= saturation concentration in diffusion layer / drug solubility C= concentration in GI fluid / conc of released drug in medium h= thickness of diffusion layer
In the Noyes and Whitney equation for the diffusion layer model, is h constant? Is S constant?
No, they decrease with time
What is the driving force for dissolution across a diffusion layer?
Concentration gradient
What is the purpose of the dissolution test?
Demonstrates the rate at which a drug in vitro is released from a solid dosage form
What are the applications of a dissolution test?
- Development of solid dosage formulations
- Quality control test for batch-to-batch consistency
- Determination of bioequivalence (i.e. generic vs. brand)
- Demonstrates to FDA that post scale-up products are bioequivalent to the originally approved formulation
Describe sink condition in vivo.
Drug molecules absorbed in the small intestine are immediately carried away by blood circulation
• In sink condition in vivo, the drug concentration in the blood is always much lower than the drug concentration in the GI tract, and concentration gradient is preserved.
• Sink conditions in vivo arise when the drug absorbed into the body from its solution in the GI fluids is at a faster rate then it dissolves in those fluids
Describe sink condition in vitro.
• Released drug molecules are accumulated in the dissolution medium; as the concentration of dissolved drug increases, the driving force/conc gradient of dissolution is reduced
Define sink condition.
Describes a dissolution system where concentration of the drug at the site if absorption is much greater than the concentration of drug in plasma
Sink conditions maintained when Cgit»_space; C
The drug concentration in the receptor compartment is much lower than the drug concentration in the donor compartment
What is assured by the presence of sink condition?
Complete dissolution of the drug
What are two methods of maintaining sink condition?
Frequently change the medium in the receiver Include additives (i.e. surfactants) that can increase the apparent solubility of the drug
List four strategies used to prevent the oxidation of pharmaceutical products.
- Remove oxygen from container and replace with inert gas
- Add a chelating agent, such as EDTA
- Lower the storage temperature
- Add antioxidants
What is the purpose of controlled drug release?
To achieve a release profile that would yield a therapeutic blood level of the drug over an extended period of time
What are some of the advantages of controlled release systems?
- Can be formulated to last for long periods of time (24 hours, 1 month, several years)
- Can respond to changes in environment (i.e. pH)
- Can be targeted (i.e. tumor-targeted delivery)
- Less frequency of doses so improves patient compliance
- Better safety margin so less side effects
- Reduces healthcare costs because less monitoring needed, and the treatment time is shorter
- Efficient use of the drug means overall less amount is used or needed
- Minimised peaks and troughs- steady state therapeutic levels to better manage the disease
What are the three types of polymers used in controlled drug release?
- Rate-controlling membrane
- Diffusion matrix
- Biodegradable carrier
Describe a rate-controlling membrane.
Membrane polymer controls release of drug held internally; acts as a reservoir device
Describe a diffusion polymer matrix.
Drug is dispersed in a rate-controlling polymer, which allows concentration-dependent diffusion of drug (less applicable for high molecular weight drugs such as proteins); polymer is not degradable
Describe a biodegradable polymer matrix.
Drug is dispersed in a biodegradable polymer, which releases drug upon polymer degradation via hydrolysis or enzymatic activity (can be used for large molecules)
What are the therapeutic advantages of controlled release systems?
- Reduced dose frequency
- More effective drug utilization
- Drug is stabilized inside the polymer matrix
- Reduced side effects
What are possible disadvantages of controlled release systems?
- Possibility of dose dumping if controlled release system fails
- Deactivation of drug inside the polymer
- Costly manufacturing process
