What factors affect first pass metabolism?

The four primary systems that affect the first pass effect of a drug are the enzymes of the gastrointestinal lumen, gut wall enzymes, bacterial enzymes, and hepatic enzymes. In drug design, drug candidates may have good druglikeness but fail on first-pass metabolism because it is biochemically selective.

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.

At which organ first pass metabolism occur?

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.

Is first pass metabolism the same as Phase 1?

Phase 1 reactions are often oxidations or hydrolysis reactions, although reductions also occur. In terms of first-pass metabolism in the liver – hydrolysis of pharmacologically inactive esters (prodrugs) to active drugs are important phase 1 reactions.

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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 meaning of 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 are the two phases of 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. Oxidation reactions are the most common and vital. These may occur at carbon, sulfur or nitrogen centre.

What is a Phase 1 reaction?

Phase I reactions are broadly grouped into three categories, oxidation, reduction, and hydrolysis. As most small molecule drugs are lipophilic in nature, drug metabolism converts these hydrophobic compounds into more water soluble compounds that can be excreted. Typically, oxidation is the most common phase I reaction.

What is first pass metabolism of alcohol?

First-pass metabolism of ethanol is observed only after administration of small doses of ethanol, and it is characterized by the difference of the rate of alcohol (= ethanol) elimination occurring after either oral or intravenous application of identical doses of ethanol.

What is second pass metabolism?

GC -> Liver. Second-pass metabolism is where the drug comes back to the liver from the circulation.

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Where does Phase 2 metabolism occur?

Conjugation. Glucuronidation, the most common phase II reaction, is the only one that occurs in the liver microsomal enzyme system. Glucuronides are secreted in bile and eliminated in urine. Thus, conjugation makes most drugs more soluble and easily excreted by the kidneys.

How are drugs excreted from the body?

Most drugs (or metabolites) are excreted by the kidneys. Three process can occur in renal excretion: glomerular filtration, tubular secretion and passive reabsorption. Some drugs are eliminated by the liver in the bile and excreted in feces.

Which route of drug administration is most likely to lead to the first pass effect?

Oral route of drug administration is most likely to lead to the first-pass effect.

What does it mean to have a first pass?

It just means “the first time you read/move through a text/process/location, etc.” It implies an initial casual review, before you get into the details or complexities of something.

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