the medicine Flashcards
what are sink conditions?
1) where the solute may be removed from solution at a faster rate than it is produced
2) the volume of the solution maybe so large that C does not exceed 10% of Cs
in this case (Cs-C)≈Cs
What are non-sink conditions
where C exceeds 10% of Cs
When does the overall dissolution rate equal zero
when C=Cs
The solution is saturated with solute
what is the significance of Noyes-Whitney
The Noyes-Whitney function is used to represent how the solid material is dissolved into solution
what is dissolution?
Dissolution is the process where a solute in gaseous, liquid, or solid phase dissolves in a solvent to form a solution.
what is the Noyes-whitney equation
dm/dt = D.A.dC/dx
what is dm
change in mass [mg]
what is dt
Change in time [seconds.]
what is D
The diffusion coefficient (cm^2/s)
what is A
surface area (cm^2)
what is dC
change in concentration (mg/cm^3)
what is dx
change in distance (cm)
what does dC/dx describe
The concentration gradient
where: dC/dx = Cs-C/h
what is the notes-whitney equation for a single Spherical particle
dm/dt = D.A.(Cs-C)/h
What is viscosity?
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of “thickness”: for example, syrup has a higher viscosity than water.
What happens to the rights of dissolution when the diffusion coefficient is decreased?
The rate is also decreased [this can happen when viscosity is increased.]
what happens to the rate of dissolution if the particle size is increased? (A)
The rate decreases
what is Cs
the saturation solubility of the drug in solution in the diffusion layer
what is C
Drug concentration in bulk solution
at time t (g/mL)
What is a solution?
A special type of homogenous mixture, composed of two or more substances
What are some advantages of a solution in pharmacy?
easier to swallow than solids
Absorption is rapid
The onset of action is faster than solid dosage forms
Homogenous dosage
Attractive mouth feel and appearance
What are some disadvantages of a solution in pharmacy?
they are bulky to transport
The dosage is dependent on the patient’s ability
Possible microbial contamination
May require taste mashing
Less stable than solid dosage forms
what are some examples of a solvent [aqueous solutions]
water, is the most widely used solvent/cosolvent
What are some examples of a solvent [nonaqueous solution]
oils, alcohols, glycols
what is dissolution? [uni definition.]
It is a process/transfer of molecules and ions from a solid state to a solution
What is solubility?
A Physio chemical property of molecules [drugs]
It depends on the balance of lipophilic and hydrophilic groups
And how much of a drug is dissolving in a specific volume?
What does having a higher intrinsic solubility mean?
there are more hydroxyl groups, more hydrophilic groups. Which increase the affinity between the molecule and the solvent.
More of the molecule in the solvent is packed in before reaching saturation
what is the effect of pH on the solubility of acids? Increasing the pH:
This will increase solubility due to increased interaction of the ionized form with water. The acids will donate to the protons, and become more charged.
what is the effect of pH on the solubility of bases?
Decreasing the pH of a solution containing bases
decreasing the pH of solutions, containing bases will cause ionization This will increase solubility, due to an increased interaction of the ionized form
What is a partitioning coefficient?
They describe the distribution of solvents between a mixture of immiscible liquids
What is an immiscible liquid?
where to liquids stay as two different layers
What is the partition coefficient equation?
P=Co/Cw
[] of the top / [] of the bottom liquid
How do we know if the molecule is more hydrophilic or lipophilic by using the partition coefficient?
we logP
logP>0 = the molecule is more lipophilic
logP<0 = the molecule is more hydrophilic. [polar].
Gastrointestinal absorption the two main classes
there are two main classes of transport through the gastrointestinal tract/membrane
1) passive
2) carrier mediated
Passive transport [diffusion] is driven by a concentration gradient
Why is the gut membrane more permeable to un ionized forms of drugs?
due to a greater liquid solubility, and they are usually smaller molecules. That is also no charge effects
There is rapid absorption when the drugs is un ionized
when are acids usually absorbed
from a low pH
For example, the stomach
when are bases usually absorbed
from a higher pH/environment
For example, the intestine
Why is absorption from the stomach not extensive?
because of the muscle lining, small surface area, short residence time
Why is the small intestine a more favorable environments for absorption?
because of a large surface area, thin barrier, long residence time
what is residence time
the duration of persistence of a mass or substance in a medium or place
The amount of time, a molecule or substance has stayed in somewhere (the longer it has stayed the more likely it is favorable for absorption)
what is the %ionized calculation
%ionised = (I/I+U) X 100
I=amount of ionised drug
U= amount of unionized drug
what is the % ionised equation for acids
% ionised = 100/1+10^pKa-pH
what is the % ionised equation for bases
% ionised = 100/1+10^pH-pKa
