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First-pass metabolism may occur in the liver (for propranolol, lidocaine, clomethiazole, and nitroglycerin) or in the gut (for benzylpenicillin and insulin). [4] The four primary systems that affect the first pass effect of a drug are the enzymes of the gastrointestinal lumen, [5] gastrointestinal wall enzymes, [6] [7] [8] bacterial enzymes [5] and hepatic enzymes.
This is known as the first pass effect. As a consequence, certain drugs can only be taken via certain routes. For example, nitroglycerin cannot be swallowed because the liver would deactivate the medication, but it can be taken under the tongue or transdermally (through the skin) and thus is absorbed in a way that bypasses the portal venous system.
Drugs given by enteral administration may be subjected to significant first pass metabolism, and therefore, the amount of drug entering the systemic circulation following administration may vary significantly for different individuals and drugs. Rectal administration is not subject to extensive first pass metabolism.
Whether a drug is taken with or without food will also affect absorption, other drugs taken concurrently may alter absorption and first-pass metabolism, intestinal motility alters the dissolution of the drug and may affect the degree of chemical degradation of the drug by intestinal microflora.
The greater potency of vaginal estradiol relative to oral estradiol is due to the lack of the first pass associated with oral estradiol and due to low local metabolism of estradiol in the vagina. [10] Because of the high estradiol levels achieved, LH and FSH are more strongly suppressed with vaginal estradiol than with other routes. [72]
Let's take VShred's first claim: that Harvard-backed weight-loss loophole. The "loophole" is actually the hormone irisin, which, yes, Harvard studied way back in 2012, but there's been very little ...
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
Health & Place ] (]]]]) ]]]–]]] Proximity to point sources of environmental mercury release as a predictor of autism prevalence Raymond F. Palmera,, Stephen Blanchardb, Robert Wooda