This document discusses the gastrointestinal tract and factors that influence drug absorption such as pH and surface area. It also covers modified release drug delivery systems, including their aims to control drug levels and minimize side effects. Various drug release kinetics are defined, including zero-order and first-order, as well as models like Higuchi, Hixson-Crowell, and Korsmeyer-Peppas that can predict drug release profiles from different dosage forms. Key considerations for modified release formulations include matching the drug release rate to absorption.

1. Upgrade
Profi
pharmaceutics 2 test 2: modified delivery systems 1
Terms in this set (86)
transit time for food: mouth 1 min
transit time for food:
esophagus
4-8 sec
transit time for food: stomach 2-4 hr
transit time for food: small
intestine
3-5 hr
transit time for food: colon 10 hr to several days
pH of stomach 1-3
surface area of stomach not too large
drugs absorbed in stomach
lipophilic,
neutral,
acidic
pH of small intestine 5-7.5
surface area of small intestine very large
pharmaceutics 2 test 2: modified delivery systems 1 Study

2. drugs absorbed in small
intestine
all
pH of large intestine 7.9-8
surface area of large intestine small
drugs absorbed in large
intestine
all
approximately how long is the
stomach?
20 cm
approximately how long is the
small intestine?
3 m
approximately how long is the
large intestine?
1 m
what is the aim of modified
release systems?
to deliver the minimum amount of drug necessary to
the site of action to produce the desired
therapeutic response,
to deliver the drug at an optimal rate to maximize
the beneficial response and minimize unnecessary
drug exposure
what are most modified-
release products and how are
they administered?
tablets and capsules,
orally
when are drugs formulated in
an immediate release dosage
form?
long lasting and require only once a day oral dosing
to sustain adequate drug blood levels and desired
therapeutic effect
pharmaceutics 2 test 2: modified delivery systems 1 Study

3. what can multiple daily dosing
result in?
missed doses,
made-up doses,
noncompliance
what is the problem with taking
immediate release drugs
multiple times a day, even if on
schedule?
therapeutic blood level peaks and valleys
what is the minimum effective
concentration (MEC)?
the plasma drug level below which therapeutic
effects will not occur
what is the maximum safe
concentration (MSC)?
the plasma drug level above which toxic effects will
occur
what defines the therapeutic
range?
MEC to MSC
what is it called when the MEC
is reached?
onset of action
what follows the onset of
action?
absorption phase
what ends the absorption
phase?
reaching peak plasma concentration (cmax)
what happens after the Cmax is
reached?
post absorption phase
what ends the post absorption
phase?
returning to MEC
pharmaceutics 2 test 2: modified delivery systems 1 Study

4. what happens after the MEC is
reached the second time?
elimination phase
what type of dose causes an
immediate peak and a gradual
decline in concentration?
IV
what type of dose causes a
peak that reaches above the
minimum toxic concentration?
double
what type of dose causes a
slow increase, a plateau, and a
slow decrease in
concentration?
controlled release
what can happen if doses are
administered too frequently?
minimum
how do extended release
products typically work?
immediate release to produce desired effect
followed by gradual release of drug to maintain
effect over predetermined period
what should be taken into
consideration with modified
release formulations?
release rate
what happens if drug
absorption is slower than the
drug release?
increasing drug dosing will have no effect,
decreasing drug dosing may result to reduced drug
levels in circulation,
slowing drug release without changing drug dosing
may result in prolonged drug presence in
circulation
pharmaceutics 2 test 2: modified delivery systems 1 Study

5. ficks first law J = -D(dC/dX)
ficks first law: J flux (atoms/m2s)
ficks first law: D diffusion coefficient (m2/s)
ficks first law: dC/dX concentration gradient
what is the ideal method of
drug release?
zero order kinetics
what happens to the drug in
zero order kinetics?
drug released in steady rate
does drug release rate depend
on concentration for zero
order kinetics?
no
what does zero order look like
on a graph?
straight line
zero order kinetics Qt = Q + (K0 x t)
what mechanism of drug
release is used in first order
kinetics?
diffusion
what is the mechanism of drug
release for first order kinetics
based on?
noyes-whitney
noyes-whitney equation rate of dissolution
pharmaceutics 2 test 2: modified delivery systems 1 Study

6. what is first order release
kinetics dependent on?
concentration gradient (cs-ct)
what concentration gradient
determines first order kinetics?
between the static liquid layer immediately
surrounding the solid surface and the bulk liquid
when is first order release
kinetics model applied?
no change in shape of solid during dissolution
process
first order kinetics log Qt = log Q0 - Kt/2.303 (Qt = Q0e^-kt)
first order drug release
depends on the ______________
concentration
what scale is a graphical
representation of first order
kinetics on? what does it
produce?
log, straight line
what does first order kinetics
produce graphically when the
numbers are not logged?
hyperbola
Q0 initial amount of drug
Qt amount released at time
K first order release constant
K0 zero order release constant
pharmaceutics 2 test 2: modified delivery systems 1 Study

7. what describes the release of
drugs from systems where
there is a change in the surface
area and diameter of the solid
dosage form?
hixson crowell cube root model
hixson-crowell equation Qi^1/3 - Qr^1/3 = KHC x t
Qi initial amount of drug in solid dosage form
Qr amount of drug remaining in solid dosage form
KHC hixson crowell rate equation
mechanism of drug release for
hixson-crowell
erosion
what is the simplest and most
used model of release
kinetics?
higuchi
how would the hixson cowell
model be graphed linearly?
cube root of particle volume
what model describes the
release of drugs from solid
matrices where drug release is
dependent on square root of
time?
higuchi
mechanism of drug release for
higuchi model
diffusion, erosion
pharmaceutics 2 test 2: modified delivery systems 1 Study

8. how would the higuchi model
be graphed linearly?
square root of time
KH higuchi dissolution constant
what does the hixson crowell
graph normally look like?
hyperbola
what describes the release
behavior of drugs from a
hydrophilic matrix with
changing surface area and
diffusion rate?
korsmeyer peppas equation
what does the higuchi model
graph normally look like?
exponential
mechanism of drug release for
korsmeyer peppas
erosion, diffusion
korsmeyer peppas equation F = (Mt/M) = Km x t^n
F fraction of drug released at time
Mt amount of drug released at time
M total amount of drug in dosage form
Km kinetic constant
n diffusion or release exponent
pharmaceutics 2 test 2: modified delivery systems 1 Study

9. how is the best fitting kinetic
model for dissolution data
evaluated?
by comparing correlation coefficiency (R2 value)
what does a higher R^2 value
mean?
better correlation with model
maximum R^2 value? 1
pharmaceutics 2 test 2: modified delivery systems 1 Study