March 01, 2019 Friday
Bedtime Story
Biological Half-Life
This branch of pharmacology namely
pharmacokinetics tries to study the fate of any drug right from the point where
it is consumed or administered into the body of any organism to its complete
elimination which includes its metabolism by the body and therefore its
breakdown to simpler substances.
One of the very important parameters among
the many that is evaluated in the drug kinetics is its biological half-life.
The word “biological” has been introduced to
the concept of half-life in pharmacology for two reasons.
Firstly, it is done so as to signify that
this half-life is related to living organisms in contrast to anything else.
Secondly, the “biological” distinguishes it
from the same term that is used in nuclear physics in relation to radioactive substance
that undergoes radioactive decay.
Biological half-life is denoted by the term
t1/2 which surprisingly is no different from the one used is nuclear
physics.
Biological half-life of a substance is the
time it takes for half of it to be removed from the body of the organism.
When the rate of elimination is exponential
then the term first-order elimination is used for which there have been derived
mathematical formulae that form important testing grounds for medical students.
Many medical students dread them as already
their brains are burnt out from the immense strain of memory overload that
pharmacology (and the other pre-clinical subjects that accompany it namely the
dreaded microbiology, pathology and forensic medicine) demands and the fun of
mathematical calculations in this tense environment where survival is all that
matters is lost.
Most of the drugs that are administered to
the body are eliminated through the metabolic chemical processes that occur in
the liver and kidneys.
A small part of them are also excreted out
through the digestive tract.
In medicine instead of biological half-life
it is the plasma half-life that is of far greater use and interest and the
relation between biological and plasma half-life can be rather complicated.
In biological half-life (in contrast to
plasma half-life) other factors come into play such as tissue binding, receptor
binding, protein-binding, active metabolites and so on and which vary for each
particular drug.
Many of you may not be aware that even the water
that you consume either through drinking or eating has a half life that varies
from 7 to 14 days.
So phase 0 of the clinical research gives a
fair assessment how the organism or the body treats the drug.
Phase 0 is followed by phase 1 where again
sub therapeutic dosages of the new drug is administered to healthy volunteers
for getting information about its safety and toxicity profile.
In this phase the number of volunteers is increased
to hundred or even two hundred and even though the dose is sub therapeutic attempt
is made to gradually increase the dosage on the volunteers with their consent.
Stay tuned to the voice of an
average story storytelling chimpanzee or login at http://panarrans.blogspot.com
Good night Mon Ami and my fellow cousin ape.
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Another great educator and a teacher that I am aware of is
Professor Subhashish Chattopadhyay in Bangalore, India.
While I narrate stories, Professor Subhashish an electronic
engineer and a former professor at BARC, does and teaches real mathematics and
physics.
He started the participation of Indian students at the
International Physics Olympiad.
Do visit him here:
All his books can be downloaded for free through this link:
For edutainment and English education of your children, I
recommend this large collection of Halloween Songs for Kids:
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