Students in BMS 444 have asked the following questions about
the practice problems. Here is an attempt to answer them.
General
Some students feel that they "understand the
material," but do not understand my questions. BE CAREFUL!
If you do not understand the questions there is a strong
possibility that you do not "really" understand the
material. However, because there is also the possibility that the
problem is truly opaque, you can help your instructor and future
students by pointing out exactly how the problem is confusing.
Then it can be fixed.
Exam questions will be similar to those in the practice set.
Information needed will be supplied except for the key formulas
identified in the Key
Formulas page.
- Question 2.
- The intent of this question is to drive home that
fact that Vd can be expressed in two ways, i.e.,
- Vd per unit mass (weight) as in L/kg
- Vd per whole individual / animal, as in
L.
- One should pay attention to how it is expressed
and how it is to be used in the problem
presented.
- Question 4.
- The following question was asked: Which F are you
looking for (bioavailability or fraction of
absorption)?
- There is only one "F", the
bioavailability of the drug from the site
of administration to the systemic
circulation. Bioavailability is defined
as the fraction of drug absorbed from the
site of administration to the systemic
circulation. In other words, there is no
difference in the two choices presented
by the students asking the question.
- A potential point of confusion was the
shift from the way bioavailability was
initially described in class and these
notes as being measured using relative
AUCs. This is the way it is done in
practice. However, to make the point of
what the "F" is doing in the
formula we use to predict Cp(0), I posed
problem #4. If one knows Dose, Vd, and
the zero-time intercept of drugs given by
two routes, one should be able to compare
their relative bioavailability. As
pointed out in the answer to the
question, this is not an accurate way to
do it, but it does give one practice in
using the various components of the
formulas we have been studying.
- Question
3:
- This is a tricky question, but not meant to be
mean or perverse. The way we actually do this in
practice is to take a sample at the time we give
the drug and then again 4 hours later. This makes
it easier to get the peak and trough
concentrations. If you were to see the forms we
use with practitioners you would see that they
are often expressed in this way. The question to
ask yourself is -- How long after the previous
dose was the trough sample taken? How long after
the dose was the peak sample taken. The answers
are 12 hours and 4 hours. Thus, the time
difference between the two samples is 8 hours.
This only works if the regimen is in steady state
and the dose of drug is not changing. I hope this
helps.
Send suggestions /
questions
Last modified: 12 Nov 1996 15:31 glc