[Music]
now why do we talk about hydrophilic and
hydrophobic drugs hydrophilic drugs or
lipo phobic drugs are drugs that love of
water so hydro means water philic means
love now any drug that loves water is
going to hate oil so lipophobic and
hydrophilic are the same thing
hydrophilic drugs are usually polar
hydrophobic drugs are usually not polar
hydrophilic drugs dissolve in water so
it's aqueous diffusion hydrophobic drugs
dissolve in lipid or oil so there have
they have lipid diffusion hydrophilic
drugs would need a pore or a transporter
to get across that lipid bilayer
hydrophobic drugs or lipophilic drugs
often can cross barriers without the
need of pores or transporters this is an
important distinguish distinguishing
feature between these two types of drugs
hydrophilic drugs because they can't
cross that cell membrane usually don't
cross the blood-brain barrier or the
blood uterine barrier so generally
speaking which isn't always true
hydrophilic drugs don't affect cerebal
function and usually are safer in
pregnancy hydrophobic drugs or
lipophilic drugs are almost always drugs
that have some kind of a central effect
and almost always have some kind of a
fetal effect now when we talk about
aqueous diffusion we're talking about an
well molecule movement through water and
lipid diffusion is through oil aqueous
diffusion is always dependent on the
passages of water between cells or the
passage of water through pore it is a
passive process when you have aqueous
diffusion and similarly with lipid
diffusion you have movement through
membranes and it is also a passive
process all of the passive processes are
governed by ficks law now before we get
too bogged down on the on the equation
let's just remember that it is
proportional to the diffusion constant
of the drug the surface area of the
member
the thickness of the membrane and the
concentration difference between the say
the inside of the cell and the outside
of the cell usually the outside being c1
so let's apply this information that we
just learned to drugs choose the best
answer a drug that is hydrophilic a can
permeate a cell without pores or
transporters B will cross the
blood-brain barrier C is always nonpolar
D will always affect the fetus and a
pregnant patient and II will passively
permeate into a cell by ficks law which
one's correct so the answer is e all of
the other ones are wrong all of the
other ones describe a lipophilic drug so
a lipophilic drug permeates a cell
without pores or transporters a
lipophilic drug will cross the brain
barrier and will often affect a fetus
because it crosses the blood uterine
barrier and is almost always nonpolar
all drugs generally will passively
permeate into a cell by ficks law
whether it's through an open channel or
through the membrane in the case of a
lipophilic drug it's a hard question and
I'll tell you why people get this
question wrong because people assume
that just because you're hydrophilic you
can't permeate into a cell that's not
true it a hydrophilic drug can passively
permeate into a cell it doesn't always
need an active transporter and the
reason why it can passively permeate is
because it can go through that cell pore
that we had talked about earlier
[Music]