00:02
Okay. So, in the previous lectures, we looked at receptors and also enzymes.
And now, what I would like to do is consider the journey that a drug makes;
breaking down the different parts of the journey of a drug into the different
phases: the pharmaceutical phase, the pharmacokinetic phase and also, the
pharmacodynamic phase. In the pharmaceutical phase, a drug is
disintegrated from its dosage form by dissolution of the active substrate.
Pharmacokinetically, it is then either absorbed, then distributed, metabolised
and excreted. The pharmacodynamic phase pertains directly to the efficacy of
the drug receptor interaction, specifically in the target tissue. When we
consider the purpose of the pharmaceutical phase, this is to optimise the
pharmaceutical availability, making sure that there is drug available for
absorption in the first place. Within the pharmacokinetic phase, optimisation of
biological availability i.e. for example, a drug’s availability to be absorbed
and also, to travel to the right tissue where it is supposed to function.
01:15
And finally, the pharmacodynamic phase, the objective, of course, to optimise
the required biological effect which is the induction of therapeutic effect. In
other words, time to reduce the amount of material we are actually need to
achieve a desired effect without causing damage to surrounding tissues or
interfering with other receptors.
01:40
The pharmacokinetic phase for the drug to be useful. The compound with the
best binding affinity for a target is not necessarily the best drug. And indeed, it
may actually show poor activity in vivo. There are many instances of this. For
a drug to be useful, it must first reach the target site. It must be absorbed in
sufficient quantity, distributed correctly into the target tissue and should not be
metabolised too quickly or extensively, for example, via first-pass metabolism
in the liver. We need to design drugs that can satisfy the above. And so,
therefore, having something that works in vitro and actually interferes directly
with an enzyme is of no use from a drug perspective unless it can
actually reach the target within an organism. In terms of absorption, which is
the first instance of pharmacokinetic journey, most drugs are given via the oral
route. And why is that? If a drug is typically given via a non-intravenous route,
not all of it may be absorbed into circulation. Poor oral absorption of the active
drug can lead to poor bioavailability.
,03:01
And this can be due to a number of factors: drug lipophilicity, solubility,
ionisation, degradation, metabolism and physiology.
00:01
Welcome to Pharmacology by Lecturio.
00:04
My name is Dr. PJ Shukle and I'm going to introduce you to the science of
Pharmacology which is the science of drugs.
00:11
Today, we're going to talk about introduction to kinetics which is the way drugs
interact with the human body.
00:17
One of the things that I wanna put forward to you for your board exams and
when you're practicing for your tests, is you don't need to know the brand
names.
00:27
I will put them there because they are useful in real practice.
00:30
But remember that brand names are going to differ with time.
00:34
Sometimes some brand names expire and other brand names come into
play and they're also different in different regions of the world.
00:42
Let's start with a question.
00:45
The following dose response curve was isolated from a substance.
00:49
Choose the number that defines each substance.
00:52
So you have a green curve.
00:55
,You have a black curve. You have a yellow curve, and you have a plum
coloured curve.
00:59
So, we're going to define which one each is.
01:03
So, one of them is an allosteric activator. One of them is an active drug.
01:09
One of them is a competitive inhibitor. And one of them is an allosteric
inhibitor.
01:14
So what do these terms mean? Before we answer the question, let's take a
look at how drugs act on a receptor.
01:21
So you can see the grey ball which is the agonist.
01:25
It goes into a receptor bay and it fits perfectly. That is an agonist. That's a
drug.
01:31
A competitive inhibitor will also fit into the same bay, and block the agonist
from binding to that receptor.
01:38
An allosteric activator is something that binds to a different place on the same
molecule.
01:45
So, allo means different, and steric means shape.
01:48
So it's a different shape, it's a different place on the molecule, but it activates
the activity of the drug.
01:55
An allosteric inhibitor is something that acts on the different part of a
molecule, but inhibits the action of the drug.
02:03
So now that we understand what each of those types of molecules how they
are going to react with your receptor, let's try and answer the question.
02:12
, So, A, number 3 is the allosteric activator. So let's take a look at the green
curve.
02:19
The green curve is 1 and 3. One is the active drug, and 3 is the allosteric
activator.
02:27
So you can see that the curve is much higher.
02:30
So you get a much greater response when you have an activator that is
allosteric.
02:36
Let's take a look at C. C, this substance is the competitive inhibitor.
02:41
Notice how the yellow curve is shifted over on the graph.
02:45
That means that you need a higher dose to overcome that competitive
inhibitor.
02:50
Now compare that to D which is the allosteric inhibitor.
02:54
Notice that the purple or the plum curve actually starts at the same point, but
the total response is much lower and it never gets higher than a certain
point and it is always less than 1 alone. So here is a very important
difference between competitive inhibitors and allosteric inhibitors.
03:13
Guarantee this is going to be a question on your exam.
03:16
Guarantee this is going to come up again and again.
03:19
When we talk about how cells interact with drugs or how drugs interact with
cells, we wanna talk about different structural components.
03:29
So, I'm gonna introduce you to the structures of the cell.
03:32
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