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What is the rate limiting step in drug absorption? |
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Definition
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Term
What two steps must a solid dosage form undergo before absorption? |
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Definition
1. Disintegration 2. Dissolution |
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Term
Define diffusion film theory |
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Definition
A representation of the dissolution process where interfacial reactions create a film of saturated solution around the tablet (diffusion layer) that gets sloughed off with movement |
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Term
Give the Noyes Whitney equation |
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Definition
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Term
Does a large diffusion layer make diffusion faster or slower? |
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Definition
A larger diffusion layer impairs diffusion
(See Noyes-Whitney equation) |
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Term
What is the value of C, Bulk Concentration, in the Noyes Whitney equation? |
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Definition
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Term
What are advantages of testing dissolution rate in vitro? |
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Definition
-Fast -Inexpensive -Calibrated -Correlated with performance in humans |
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Term
What are the three variables in determination of dissolution rate? |
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Definition
1. What apparatus? 2. Dissolution medium? 3. Conditions? |
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Term
Describe the Levy and Hayes Beaker method to determine dissolution rate? |
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Definition
A tablet in a glass beaker is spun at a constant rate (60rpm).
A sampling pipette measures the dissolution medium concentration at intervals.
Slope of line is dissolution rate. |
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Term
Describe Dissolution Apparatus 1 |
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Definition
Rotating mesh basket
Used for capsules/products that float or disintegrate
Fluid samples are collected filtered |
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Term
Describe Dissolution Apparatus 2 |
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Definition
A paddle stirs the medium
Sample (usually tablet) is allowed to sink to the bottom (sometimes attached to sinkers) |
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Term
Describe Dissolution Apparatus 3 |
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Definition
A reciprocating cylinder is agitated with intensity
Used for modified release dosage forms |
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Term
Describe Dissolution Apparatus 4 (Flow through cell) |
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Definition
A laminar flow pump forces dissolution medium through cells that hold the sample
Difference because the medium is now agitated instead of the sample
Used for modified release forms with active ingredients of very poor solubility |
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Term
Describe Dissolution Apparatus 5, 6, and 7 |
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Definition
Modifications of previous apparatuses
For drug release studies of transdermal products |
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Term
What kind of dissolution medium is used for testing? |
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Definition
Cheap and practical
-Distilled water -0.1N HCl -Buffered medium
-Medias with sequential pH for enteric-coated dosage forms |
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Term
What is a disadvantage of using acidic dissolution media for testing? |
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Definition
It has a corrosive effect on machinery, so water or acidic buffers are usually used instead |
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Term
How do surfactants increase dissolution? |
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Definition
They reduce interfacial tension and lower contact angle
May be added in testing to speed up the process |
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Term
How does viscosity influence dissolution? |
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Definition
In diffusion controlled dissolution, rate decreases with increase in viscosity
In interfacial controlled dissolution, viscosity has little effect |
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Term
Define agitation and give a formula that relates it to dissolution rate |
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Definition
Agitation changes the liquid-solid interface
Dissolution rate = a(agitation rate)b |
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Term
If interfacial tension is a slower process than diffusion, which is the rate limiting step? |
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Definition
Interfacial tension
This would be seen a very insoluble drug |
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Term
Describe "rapid dissolution" |
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Definition
The interfacial layer is basically nonexistant so diffusion and interfacial tension are at the same rate |
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Term
What are "sink conditions" |
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Definition
In the Noyes Whitney equation, when conditions are that C<<Cs |
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Term
Does dissolution rate depend on solubility? |
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Definition
No, solubility is a measure of how much a substance will dissolve. Dissolution rate is a measure of the speed at which a substance will dissolve. |
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