The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism at a specific location in the body which leads to a reduction in the concentration of the active drug before it reaches the site of action or systemic circulation.

2023年11月3日 · The first-pass effect is a pharmacological phenomenon in which a medication undergoes metabolism at a specific location in the body. The first-pass effect decreases the active drug's concentration upon reaching systemic circulation or its site of action.

The first pass effect, also known as first-pass metabolism, refers to the phenomenon in which a drug undergoes significant metabolism and reduction in bioavailability during its initial passage through the liver.

2023年11月3日 · The first-pass effect is a pharmacological phenomenon in which a medication undergoes metabolism at a specific location in the body. The first-pass effect decreases the active drug's concentration upon reaching systemic circulation or its site of action.

First pass metabolism describes the metabolism of a drug molecules before it reaches the systemic circulation and can also be referred to as pre-systemic metabolism. Although it is possible via other routes of administration, it is predominant in drugs administered orally.

A workaround to the first-pass effect is to administer medication using alternate routes to the GI tract. Examples of alternative routes that avoid the first-pass effect include transdermal, nasal, inhalation, injection, or intravenous administration of medication.

Before an orally absorbed drug reaches systemic circulation, it must first pass through the intestine, and then the liver where drug metabolism known as pre-systemic metabolism may occur. This is known more commonly as the first-pass effect.

First-pass metabolism occurs primarily in the liver, where enzymes like cytochrome P450 are involved in drug biotransformation. The extent of first-pass metabolism can vary widely among different drugs, influencing their dosing and administration routes.

2022年8月18日 · First-pass/Pre-systemic metabolism of Drugs refers to metabolism of a drug during its passage from the site of absorption into the systemic circulation. The extent of first pass metabolism differs for different drugs and is an important determinant of oral bioavailability.

In other words, the first-pass metabolism effect affects the bioavailability of drugs. The term first-pass effect is often used to refer to drugs given orally, as the intestines and liver are the major sites of drug metabolism.