Biotransformation of Drugs Quiz
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Questions and Answers

Explain how the first-pass effect impacts the bioavailability of orally administered drugs.

The first-pass effect reduces the concentration of a drug significantly before it enters systemic circulation, thereby decreasing its bioavailability.

What are two methods to prolong the action of drugs in the body?

Prolonging absorption from the site of administration and increasing plasma protein binding are two methods to prolong drug action.

Define clearance in the context of drug metabolism.

Clearance is the theoretical volume of plasma from which a drug is completely removed per unit time.

What is the significance of a drug's half-life, and how is it calculated?

<p>Half-life indicates the time required for the plasma concentration of a drug to reduce by half, calculated as $t_{1/2} = rac{ ext{ln}(2)}{ ext{elimination rate}}$.</p> Signup and view all the answers

Name three categories of drugs contraindicated for lactating mothers and explain why.

<p>Sulfonamides, tetracyclines, and lithium are contraindicated due to potential adverse effects on the infant.</p> Signup and view all the answers

What is biotransformation in the context of drug metabolism?

<p>Biotransformation refers to the chemical alteration of a drug in the body, converting it into more polar metabolites.</p> Signup and view all the answers

What are Phase-I reactions in biotransformation?

<p>Phase-I reactions, or nonsynthetic reactions, involve the conversion of parent drugs to more polar metabolites through oxidation, reduction, or hydrolysis.</p> Signup and view all the answers

Can you provide an example of a drug undergoing hydroxylation as a Phase-I metabolic reaction?

<p>An example of a drug undergoing hydroxylation is Procaine.</p> Signup and view all the answers

What role do Phase-II reactions play in drug metabolism?

<p>Phase-II reactions involve the conjugation of drugs or their metabolites with endogenous substrates, making them more water-soluble for excretion.</p> Signup and view all the answers

How does enzyme induction affect the efficacy of oral contraceptives?

<p>Enzyme induction can decrease the intensity and duration of action of oral contraceptives, potentially leading to contraceptive failure.</p> Signup and view all the answers

Describe the phenomenon of autoinduction with an example.

<p>Autoinduction occurs when a drug induces its own metabolism, such as carbamazepine, which increases the rate at which it is metabolized.</p> Signup and view all the answers

What is the consequence of enzyme induction on the metabolism of endogenous substrates?

<p>Enzyme induction can lead to faster metabolism of endogenous substrates like steroids and bilirubin.</p> Signup and view all the answers

What is the therapeutic use of phenobarbitone in the context of jaundice?

<p>Phenobarbitone is used to hasten the clearance of bilirubin in congenital nonhaemolytic jaundice by inducing glucuronidation.</p> Signup and view all the answers

Study Notes

Biotransformation

  • Biotransformation or metabolism is the chemical alteration of a drug in the body.
  • It involves two main phases: Phase I (Nonsynthetic reactions) and Phase II (Synthetic or conjugation reactions).

Phase I Reactions

  • Involve converting the parent drug into more polar metabolites.
  • Examples: Oxidation (Barbiturates), Reduction (Chloramphenicol), Hydrolysis (Procaine).

Phase II Reactions

  • Involve coupling between the drug or its metabolites and endogenous substrates (glucuronic acid, sulfuric acid, acetic acid, amino acid).
  • Key conjugation reactions:
    • 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 refers to the increased synthesis of enzymes that metabolize drugs.

Consequences of Microsomal Enzyme Induction

  • Decreased intensity or duration of action of drugs inactivated by metabolism (e.g., contraceptive failure).
  • Increased intensity of action of drugs activated by metabolism (e.g., paracetamol toxicity).
  • Tolerance: Drug induces its own metabolism (autoinduction) (e.g., carbamazepine, rifampin).
  • Increased metabolism of endogenous substrates (steroids, bilirubin).
  • Intermittent use of inducers can interfere with the dose adjustment of other drugs (e.g., oral anticoagulants (Warfarin)).

Possible uses of enzyme induction

  • Congenital nonhaemolytic jaundice: Phenobarbitone hastens clearance of jaundice (due to deficient glucuronidation of bilirubin).
  • Cushing's syndrome: Phenytoin can reduce manifestations by enhancing adrenal steroid degradation.
  • Chronic poisonings: Faster metabolism of accumulated poisonous substances.
  • Liver diseases.

Drugs that inhibit drug-metabolizing enzymes

  • Allopurinol
  • Omeprazole
  • Erythromycin
  • Ketoconazole
  • Ciprofloxacin
  • Isoniazid

First-pass Effect

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

Excretion

  • Excretion is the passage of a drug out of the body.

Methods to Prolong Drug Action

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

Drugs Contraindicated in Lactating Mothers

  • Sulfonamides, Tetracycline, Chloramphenicol, Isoniazid
  • Morphine, Sedative, hypnotic drugs (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: CL = Rate of elimination / Concentration of drug (in blood or plasma)

Half-life (t½)

  • The time it takes for the plasma concentration or the amount of drug in the body to be reduced by 50%.

Steady State

  • Steady state is achieved when the amount of drug administered equals the amount eliminated.
  • This typically occurs after about 5 times the half-life (t½).

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Related Documents

Pharmacokinetic (II) 2021-2022 PDF

Description

This quiz tests your knowledge on biotransformation, covering essential concepts like Phase I and Phase II reactions, and enzyme induction. Understand how drugs are metabolized in the body, including various conjugation reactions and their implications. Challenge yourself to reinforce your understanding of this critical topic in pharmacology.

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