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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.
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 ...
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.
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 ...
In particular, the oral route is subject to a high first-pass effect, which results in high levels of testosterone in the liver and consequent hepatic androgenic effects, as well as low potency due to first-pass metabolism in the intestines and liver into metabolites like dihydrotestosterone and androgen conjugates. [2]
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.
This is known as the first pass effect. As a consequence, certain drugs can only be taken via certain routes. 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 ...