Biotransformation and Enzyme Induction
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Questions and Answers

The phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation is known as ______.

first pass effect

The process of removing an absorbed drug from the body is called ______.

excretion

Drugs that prolong the action of medications can do so by increasing ______ protein binding.

plasma

Half-life (t ½) is the time it takes for the plasma concentration of a drug to be reduced to ______ %

<p>50</p> Signup and view all the answers

In steady state, the amount of drug administered equals the amount of drug ______.

<p>eliminated</p> Signup and view all the answers

Biotransformation refers to the chemical alteration of a drug in the body's ______.

<p>metabolism</p> Signup and view all the answers

Phase-I reactions involve the conversion of the parent drug to more polar metabolites through ______.

<p>oxidation</p> Signup and view all the answers

Phase-II reactions are also known as ______ reactions.

<p>synthetic</p> Signup and view all the answers

Glucuronide conjugation is an important Phase-II reaction that often involves ______ acid.

<p>glucuronic</p> Signup and view all the answers

Decreased intensity and/or duration of action of drugs may occur due to microsomal enzyme ______.

<p>induction</p> Signup and view all the answers

Tolerance can occur when a drug induces its own ______.

<p>metabolism</p> Signup and view all the answers

The accumulation of bilirubin in congenital nonhaemolytic jaundice is addressed by hastening its clearance using ______.

<p>phenobarbitone</p> Signup and view all the answers

Cushing's syndrome manifestations may be reduced by enhancing degradation of adrenal ______.

<p>steroids</p> Signup and view all the answers

Study Notes

Biotransformation (Metabolism)

  • Biotransformation is the chemical alteration of a drug in the body.
  • Phase I reactions involve non-synthetic modifications:
    • Oxidation (e.g., barbiturates)
    • Reduction (e.g., chloramphenicol)
    • Hydrolysis (e.g., procaine)
  • Phase II reactions are synthetic or conjugation reactions:
    • Involve coupling with endogenous substrates (e.g., glucuronic acid, sulfuric acid)
    • Important reactions include:
      • Glucuronide conjugation (e.g., chloramphenicol)
      • Sulfate conjugation (e.g., steroids)
      • Glycine conjugation (e.g., aspirin)
      • Acetylation (e.g., sulfonamides)
      • Methylation (e.g., histamine)

Enzyme Induction

  • Enzyme induction is the increased production of drug-metabolizing enzymes.
  • Consequences of microsomal enzyme induction:
    • Decreased drug action for drugs inactivated by metabolism (e.g., contraceptives)
    • Increased drug action for drugs activated by metabolism (e.g., paracetamol toxicity)
    • Tolerance can develop if a drug induces its own metabolism (e.g., carbamazepine)
    • Increased metabolism of endogenous substrates (e.g., steroids)
    • Intermittent use of an inducer can affect the dosage of other drugs (e.g., warfarin)

Possible Uses of Enzyme Induction

  • Congenital nonhaemolytic jaundice: Phenobarbitone can accelerate bilirubin clearance.
  • Cushing's syndrome: Phenytoin can reduce symptoms by enhancing adrenal steroid degradation.
  • Chronic poisonings: Enzyme induction can accelerate the metabolism of accumulated poisons.
  • Liver diseases: Enzyme induction can potentially aid in liver disease management.

Enzyme Inhibition

  • Enzyme inhibition is the reduction in the activity of drug-metabolizing enzymes.
  • Drugs that inhibit drug metabolizing enzymes include:
    • Allopurinol
    • Omeprazole
    • Erythromycin
    • Ketoconazole
    • Ciprofloxacin
    • Isoniazid

First Pass Effect

  • The first pass effect is the significant reduction in drug concentration before reaching systemic circulation due to metabolism in the liver.
  • Examples of drugs affected by first-pass metabolism:
    • Phenobarbitone
    • Aspirin
    • Isoprenaline
    • Propranolol
    • Lidocaine
    • Hydrocortisone
    • Sulbutamol

Excretion

  • Excretion is the process of drug elimination from the body.

Methods to Prolong Drug Action

  • Prolonging absorption from the administration site.
  • Increasing plasma protein binding.
  • Retarding metabolism.
  • Retarding renal excretion.

Contraindicated Drugs for Lactating Mothers

  • Sulfonamides
  • Tetracycline
  • Chloramphenicol
  • Isoniazid
  • Morphine
  • Sedative and hypnotic drugs (e.g., diazepam)
  • Phenothiazines
  • Lithium
  • Antithyroid drugs
  • Radioactive iodine
  • Senna and related purgatives
  • Metronidazole
  • Anticancer drugs
  • Corticosteroids

Clearance

  • Clearance is the theoretical volume of plasma from which a drug is completely removed per unit time.
  • Calculation: Clearance = Rate of elimination / Concentration of drug in plasma.

Half-Life (t½)

  • Half-life is the time required for the plasma concentration or the amount of drug in the body to reduce by 50%.

Steady State

  • Steady state is reached when the rate of drug administration equals the rate of elimination.
  • Approximately 5 times the half-life is required to reach steady state.

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Description

This quiz covers the essential concepts of biotransformation and enzyme induction in drug metabolism. It examines Phase I and Phase II reactions, detailing the various modifications and conjugation processes. Additionally, it highlights the implications of enzyme induction on drug effectiveness and metabolism.

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