Phase 1 and phase 2 refer to the KINDS of metabolism. … In terms of first-pass metabolism in the liver – hydrolysis of pharmacologically inactive esters (prodrugs) to active drugs are important phase 1 reactions.
What is meant by first pass metabolism?
The first pass effect is a phenomenon in which a drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug upon reaching its site of action or the systemic circulation.
What happens after first pass metabolism?
The drug is absorbed from the GI tract and passes via the portal vein into the liver where some drugs are metabolised. Sometimes the result of first pass metabolism means that only a proportion of the drug reaches the circulation.
Where does phase 1 metabolism occur?
Although Phase I drug metabolism occurs in most tissues, the primary and first pass site of metabolism occurs during hepatic circulation. Additional metabolism occurs in gastrointestinal epithelial, renal, skin, and lung tissues.
Does IV bypass first pass metabolism?
It is the fastest and most certain and controlled way. It bypasses absorption barriers and first-pass metabolism.
What is the importance of first pass metabolism?
Knowledge of first pass metabolism can assist the prescriber when deciding on doses and dose schedules to ensure that patients receive their medications at the correct dosing, by the correct route for optimum therapeutic effect.
What is the site of first pass metabolism?
First pass metabolism may occur in the liver (for propranolol, lidocaine, clomethiazole, and GTN) or in the gut (for benzylpenicillin and insulin). After a drug is swallowed, it is absorbed by the digestive system and enters the hepatic portal system.
What is the difference between Phase 1 and Phase 2 metabolism?
Phase I reactions of drug metabolism involve oxidation, reduction, or hydrolysis of the parent drug, resulting in its conversion to a more polar molecule. Phase II reactions involve conjugation by coupling the drug or its metabolites to another molecule, such as glucuronidation, acylation, sulfate, or glicine.
What is a Phase 1 reaction?
Phase 1 metabolism involves chemical reactions such as oxidation (most common), reduction and hydrolysis. There are three possible results of phase 1 metabolism. The drug becomes completely inactive. … One or more of the metabolites are pharmacologically active, but less so than the original drug.
What organ is responsible for metabolism in the first pass effect?
The first-pass effect can occur in the gastrointestinal tract, the liver and lung. Although the liver is the main drug metabolizing organ in the body, the gut wall can play an important role in the first-pass metabolism of certain drugs.
Where does Phase 1 and 2 metabolism occur?
The liver is the primary site for metabolism. Liver contains the necessary enzymes for metabolism of drugs and other xenobiotics. These enzymes induce two metabolism pathways: Phase I (functionalization reactions) and Phase II (biosynthetic reactions) metabolism.
What is Phase II reaction?
Phase II reactions include glucuronidation, sulfation, acetylation, methylation, conjugation with glutathione, and conjugation with amino acids (such as glycine, taurine, and glutamic acid). – It is important to understand that these Phase I and II. reactions may occur simultaneously or sequentially.
What are the 2 phases of drug metabolism?
Drug metabolism reactions comprise of two phases: Phase I (functionalization) reactions such as oxidation, hydrolysis; and Phase II (conjugation) reactions such as glucuronidation, sulphate conjugation.
How do you prevent first pass metabolism?
Bypassing First Pass Metabolism
Two ways to bypass first pass metabolism involve giving the drug by sublingual and buccal routes. The drugs are absorbed by the oral mucosa in both methods. In sublingual administration the drug is put under the tongue where it dissolves in salivary secretions.
Do injections bypass the liver?
Thus, only about 50% of a rectal dose can be assumed to bypass the liver. To parenteral routes we consider injections, inhalations, and transdermal route. The first one includes injection under the skin, intro the muscles (i.m.), in veins (i.v.) and arteries.
How does IV administration relate to first pass metabolism?
First pass metabolism takes place in the liver(mainly*). As the drug that is taken orally gets absorbed, it is absorbed 1st into the portal venous system. … As IV route means the drug enters systemic circulation directly, no drug enters the liver. So there is no first pass effect in the IV route drug medication.