Question

Define bioavailability and hepatic first-pass effect, discussing their relationship.

Answer 1

According to pharmacology ,bioavailability is the fraction of drug that reaches to our circulation part. Mathematically its the ratio of the fraction of drug that is absorbed to the drug that is orally consumed.

The first pass effect is a drug metabolism where the concentration of a drug that is orally taken is greatly reduced before it reaches to our systemic circulation. This fraction of drug can be lost during the process of absorption by means of liver and gut wall. The process by means of liver is termed as hepatic first pass effect.

During a hepatic first pass effect the drug from the gastrointestinal tract is reached to our liver by the portal vein.

Relationship between bioavailability and hepatic first pass effect:-

When the drug is absorbed from the gastrointestinal tract,it is first transferred to our hepatic portal system via the portal vein. Hence after only this they reaches to the rest part of our body. This hepatic first pass effect can reduce bioavailability of the drug. Therefore making theat the fraction of drug orally administered and absorbed are nearly same.

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