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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 ______ %
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In steady state, the amount of drug administered equals the amount of drug ______.
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Biotransformation refers to the chemical alteration of a drug in the body's ______.
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Phase-I reactions involve the conversion of the parent drug to more polar metabolites through ______.
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Phase-II reactions are also known as ______ reactions.
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Glucuronide conjugation is an important Phase-II reaction that often involves ______ acid.
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Decreased intensity and/or duration of action of drugs may occur due to microsomal enzyme ______.
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Tolerance can occur when a drug induces its own ______.
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The accumulation of bilirubin in congenital nonhaemolytic jaundice is addressed by hastening its clearance using ______.
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Cushing's syndrome manifestations may be reduced by enhancing degradation of adrenal ______.
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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.
