Pharmacokinetics is a
branch of pharmacology which explains
the fate of substances administered to a living organism. Pharmaceutical drugs,
food additives, cosmetics pesticides are the chemical xenobiotics. It aims in discovering
the fate of a chemical from the moment that it is administered up to the point
at which it is eliminated from the body and helps in analyzing the chemical
metabolism. Pharmacokinetics is the study
of how an organism affects a drug.
Route of administration
and the dose of administered drug affects the properties of chemicals. Metabolic
changes of the substance in the body, routes of excretion of the metabolites of
the drug after administration through the mechanisms of absorption and
distribution are described by the pharmacokinetics. These may affect the
absorption rate.
Following are the
five-process involved in Pharmacokinetic process:
·
Liberation –It is the process of release
of drug from the formulation.
·
Absorption – which includes the process of
a substance entering the blood circulation.
· Distribution – which includes the
dispersion or dissemination of substances throughout the fluids and tissues of
the body.
· Metabolism – which includes the
recognition of the foreign substance by the organism and the process of
irreversible conversion of parent compounds into daughter metabolites
· Excretion – which includes the removal of
the substances from the body. In rare cases, some drugs irreversibly accumulate
in body tissue.
The role of the liver in drug distribution:
Hepatic portal
system takes the part of the blood stream after the drug is absorbed by the GI
tract. Lipids are absorbed by the lymphatic system whereas most of the drugs
are absorbed into hepatic portal system and then delivered into the blood by
the thoracic duct into the superior vena cava.
Digested food
is taken to the liver by hepatic portal system. Where it is stored in the
liver, processed and distributed. In the same way this may happen to the drug
and the drug would be metabolized before reaching the rest of the body. Drugs
metabolized by the liver will have high hepatic first pass. Drugs with a very
high hepatic first pass are metabolized by the liver which are not given
orally.
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