Pharmacokinetics and Drug Metabolism

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.