Term
| 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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