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The brain consumes over 20% of
whole body's energy supply and nearly 15% of the blood of cardiac output. so
the brain is one of the important organ and we know the complete body and other
organ activity directly or indirectly controlled by the brain. so it is very
necessary a barrier must be there to check unwanted chemicals/materials from
the blood which is not suitable or harmful for the brain.[1]
·
same for few drugs, as prodrug (an
inactive form of drug which converts into active drug after
metabolism in body )and xenobiotics (a compound that is
foreign to body) can be harmful to the brain so they prevent and blocked by
the blood-brain barrier (BBB).
looking
at chemical nature
·
Generally, the NON-LIPID
SOLUBLE DRUG ( example-streptomycin, neostigmine, etc) don’t
penetrate BBB while the LIPID-SOLUBLE DRUGS is able
to cross BBB and have action central nervous system.
·
Dopamine is an important
neurotransmitter /neurochemical that doesn’t enter the brain as it is a polar
molecule.
in
parkinsonism, dopamine concentration decreases. both levodopa and dopamine is
part in drug mechanism, but dopamine can’t cross BBB while levodopa can
cross BBB, so levodopa is given to the patient which further get convert
into dopamine, beside an enzyme name monoamine oxidase (MAO) and
few other don’t allow catecholamines,5-HT, etc to enter brain in active form.
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