How Medicines Work: Drug Actions Part 1

Uploaded by AusmedEducation on 17.02.2011

Louis Roller joined the Faculty of Pharmacy and Pharmaceutical Sciences in 1963.
He was the Associate Dean Teaching, 1992 to 2006 of the Faculty,
and Head of the Department of Pharmacy Practice 1992 - 2001
Louis was the Director of the Bachelor Pharmacy Program until his retirement from the University
in December 2008.
He has served on the Pharmacy Board of Victoria for twenty two years
and has significantly contributed to the various editions of the Australia Pharmaceutical Formulary
and Handbook, and the Therapeutic Guidelines Antibiotic and Oral & Dental.
Louis Roller was the first academic
to push for and achieve a more patient-orientated course of pharmacy.
Since his retirement at the end of 2008
he is a highly utilised sessional lecturer at
the Faculty of Pharmacy and Pharmaceutical Sciences
and has developed and delivered courses at La Trobe University
and the Podiatrists Board of Australia.
During his long career, he has and still teaches
varying aspects of therapeutics to pharmacy, dental,
medical, podiatry,
and nursing students
as well as many postgraduate lectures
to various professional organisations.
today we're going to look again at how medicines work, but specifically
drug actions
and within that particular parameter we are going to look at the concept of biopharmaceutics
pharmacokinetics and pharmacodynamics.
All of these "-ics" terms can be very confusing, so we'll try to shed some light on that.
We're going to look drug absorption
drugs distribution
drug elimination: hepatic metabolism, renal excretion
and excretion generally, which includes the kidney of course.
We're going to look at multiple dose regimens
and therapeutic drug monitoring.
and that generally covers the areas of pharmacokinetics, pharmacokinetics and pharmacodynamics
and biopharmaceutics to some extent.
Biopharmaceutics, that's the relationship between physical and chemical properties of the drug
the dosage form
the route of administration on rate and extent of drug sorption.
That's an official definition
and it probably sounds a bit confusing.
pharmacokinetics, or PKs, as it's often called: mechanics of drug absorption, distribution,
and elimination.
Clinical pharmacokinetics is the application of pharmacokinetic theory
to the clinical situation. That is,
the person that you, as a nurse, are dealing with. Pharmacokinetics in simplistic terms is
the study of the movement off drugs into
and out of the body
and again to simplify: what does that mean? that is what the body actually does to the
drug or medicine.
Pharmacodynamics, on the other hand,
is the study of drug effects
and the mechanisms of action that is acting on the receptor sites and so on and the
actual effect that we end up with.
Conversely to pharmacokinetics, this is what the drug does to the body
So in very simplistic terms you could sum up by saying
pharmacokinetics is what the body does to the drug or the medicines, and
pharmacodynamics case what the drug does to the body.
So let's look at pharmacokinetics. This graph represents the ADME curve --
metabolism and excretion.
And here you see the absorption curve...
When you take your medication, if you look at time
after taking the medication, you can measure the amount
of the medication that's measured in the blood.
and what we see with the absorption curve, that is, the time taken for the medication or
the drug to get to a certain level,
and then it reaches what we call a peak height.
After that period of time
the various processes of distribution
and elimination
cause the concentration of the drug to decrease. This is known as
the elimination curve, as you can see there.
And for every particular medication
there is what we call a therapeutic range. What that means
again, in very simple terms,
is the difference between
where the drug for this has an action
that is measurable when one way or another and right up to the toxic concentration that is
represented by those theoretical horizontal lines that are drawn there.
and so anything within that is considered to be the therapeutic range
for the average person under average conditions. Of course, individuals will vary.
There are various other terms that we need to consider sometimes and one of them you
see at the bottom of the graph -- a little arrow
that says "onset"
and the onset of the effect
is a
period in time, in this case it looks like 0.5 hours or half an hour
that it reaches the lowest level