first-pass metabolism the intestinal and hepatic degradation or alteration of a drug or substance taken by mouth, after absorption, removing some of the active substance from the blood before it enters the general circulation. Synonym(s): first-pass effect first-pass me·tab·o·lism , first-pass effect (fĭrst-pas mĕ-tab'ŏ-lizm, e-fekt') The ...
A first-pass effect is defined as a low systemic availability of the drug as a result of significant metabolism. Although a first-pass effect can occur in a variety of tissues, including the intestines Doherty and Pang (1997) and uterus De Ziegler et al (1997), it is most often observed with the liver.
The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation. It is the fraction of drug lost during the process of absorption which is generally related to the liver and gut wall.
Because the liver is the primary organ of metabolism, the consequence of first-pass metabolism is the break down of significant amounts of a drug before it can reach the systemic circulation, so those drugs never reach the site of action!
The First Pass Effect. When you take a medication by mouth, it doesn't just magically get into your body and start doing its thing. It actually has to go through a whole host of organs and a big ...
After oral administration, many drugs (morphine, pentazocine) are absorbed intact from the small intestine and trasported first via the portal system to the liver, where they undergo extensive metabolism. This process is called the first-pass effect. Although every tissue has some ability to metabolize drugs, the liver is the principal organ of drug metabolism.
If the major proportion of an active drug is converted to inactive metabolites then the effect of first-pass will markedly reduce the effect of the drug (as explained above) and the oral dose may ...
First-pass elimination takes place when a drug is metabolised between its site of administration and the site of sampling for measurement of drug concentration. Clinically, first-pass metabolism is important when the fraction of the dose administered that escapes metabolism is small and variable ...
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