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Illustration showing the hepatic portal vein system. 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.
Furthermore, after absorption from the gastrointestinal tract, such drugs must pass to the liver, where they may be extensively altered; this is known as the first pass effect of drug metabolism. Due to the digestive activity of the stomach and intestines, the oral route is unsuitable for certain substances, such as salvinorin A
In addition, the rectal route bypasses around two-thirds of the first-pass metabolism as the rectum's venous drainage is two-thirds systemic (middle and inferior rectal vein) and one-third hepatic portal system (superior rectal vein). This means the drug will reach the circulatory system with significantly less alteration and in greater ...
Enterohepatic circulation of drugs. Enterohepatic circulation is the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver.
Due to the first pass through the liver, disproportionate and supraphysiological levels of estrogens occur locally in the liver with oral estradiol. [ 117 ] [ 12 ] These levels are approximately 4- to 5-fold higher than in the circulation, based on differences in hepatic estrogenic potency for oral estradiol relative to transdermal estradiol.
Effect of digestive juices and the first pass metabolism of drugs. Condition of the patient. In acute situations, in emergency medicine and intensive care medicine, drugs are most often given intravenously. This is the most reliable route, as in acutely ill patients the absorption of substances from the tissues and from the digestive tract can ...
Extensive metabolism on the first pass through the liver leads to average bioavailability of about 50% (45% [5]-53% [6]). Amitriptyline is metabolized mostly by CYP2C19 into nortriptyline and by CYP2D6 leading to a variety of hydroxylated metabolites, with the principal one among them being ( E )-10-hydroxynortriptyline [ 9 ] (see metabolism ...
Conversely, if it is absorbed by the upper portion of the rectum, progesterone is subject to hepatic first-pass metabolism due to entry into the hepatic portal system via the superior rectal vein. [18] As such, although rectal administration is a parenteral route, it may still be subject to some first-pass metabolism similarly to oral ...