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What is the main purpose of Phase II metabolism reaction?
What is the main purpose of Phase II metabolism reaction?
What is the factor that determines the bioavailability of a drug?
What is the factor that determines the bioavailability of a drug?
What is the primary reason why water soluble drugs cannot filter into the CSF or brain?
What is the primary reason why water soluble drugs cannot filter into the CSF or brain?
What is the term for the process by which a drug is converted into a more water soluble product?
What is the term for the process by which a drug is converted into a more water soluble product?
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What is the equation for calculating the volume of distribution of a drug?
What is the equation for calculating the volume of distribution of a drug?
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What type of reaction occurs in Phase I metabolism?
What type of reaction occurs in Phase I metabolism?
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What is the purpose of glucuronidation in Phase II metabolism?
What is the purpose of glucuronidation in Phase II metabolism?
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What is the term for the process by which a drug is absorbed into the systemic circulation?
What is the term for the process by which a drug is absorbed into the systemic circulation?
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What is the process that occurs in the intestinal lumen and intestinal wall during first pass effect?
What is the process that occurs in the intestinal lumen and intestinal wall during first pass effect?
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Which of the following is an example of a drug that is affected by enzyme induction by rifampine?
Which of the following is an example of a drug that is affected by enzyme induction by rifampine?
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What happens to the first pass effect in the presence of hepatic diseases?
What happens to the first pass effect in the presence of hepatic diseases?
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Which of the following is an example of a drug that is affected by enzyme induction by barbiturates?
Which of the following is an example of a drug that is affected by enzyme induction by barbiturates?
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What is the result of saturation of metabolizing enzymes on the first pass effect?
What is the result of saturation of metabolizing enzymes on the first pass effect?
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Which of the following is an example of a conjugation reaction in biotransformation?
Which of the following is an example of a conjugation reaction in biotransformation?
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What is the result of enzyme induction on drug efficacy and plasma half-life?
What is the result of enzyme induction on drug efficacy and plasma half-life?
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Which of the following is an example of an enzyme inducer that affects the metabolism of benzodiazepines and paracetamol?
Which of the following is an example of an enzyme inducer that affects the metabolism of benzodiazepines and paracetamol?
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Which of the following enzymes is induced by cimetidine?
Which of the following enzymes is induced by cimetidine?
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Which of the following drugs is a prodrug that is converted to its active metabolite?
Which of the following drugs is a prodrug that is converted to its active metabolite?
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What is the main mechanism of drug elimination by the kidney?
What is the main mechanism of drug elimination by the kidney?
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Which of the following enzymes is responsible for the metabolism of sulphonamides?
Which of the following enzymes is responsible for the metabolism of sulphonamides?
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What happens to the biological activity of a drug during metabolism?
What happens to the biological activity of a drug during metabolism?
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Which of the following factors affects drug metabolism?
Which of the following factors affects drug metabolism?
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What is the route of excretion of lithium?
What is the route of excretion of lithium?
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Which of the following enzymes is inhibited by erythromycin?
Which of the following enzymes is inhibited by erythromycin?
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Which of the following drugs does not follow a single compartment distribution model?
Which of the following drugs does not follow a single compartment distribution model?
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What is the characteristic of 'hit and run' drugs in terms of their half-life?
What is the characteristic of 'hit and run' drugs in terms of their half-life?
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What is the time required to reach the steady-state level for most drugs that follow first-order kinetics?
What is the time required to reach the steady-state level for most drugs that follow first-order kinetics?
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What is the factor that determines the steady-state level of a drug?
What is the factor that determines the steady-state level of a drug?
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What is the primary consideration in designing a dosage regimen for a drug with a short plasma half-life?
What is the primary consideration in designing a dosage regimen for a drug with a short plasma half-life?
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Which of the following is a characteristic of a multi-compartment distribution model?
Which of the following is a characteristic of a multi-compartment distribution model?
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What is the primary reason why the half-life of a drug is not always indicative of its duration of action and dosage schedule?
What is the primary reason why the half-life of a drug is not always indicative of its duration of action and dosage schedule?
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What is the term for the level of a drug reached when its intake is equal to its elimination?
What is the term for the level of a drug reached when its intake is equal to its elimination?
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What is the effect of plasma protein-binding on the rate of renal excretion of drugs?
What is the effect of plasma protein-binding on the rate of renal excretion of drugs?
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Which of the following routes of excretion is responsible for the elimination of volatile gases and gaseous anesthetics?
Which of the following routes of excretion is responsible for the elimination of volatile gases and gaseous anesthetics?
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What is the total clearance of a drug equivalent to?
What is the total clearance of a drug equivalent to?
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Which of the following drugs has a clearance less than the glomerular filtration rate?
Which of the following drugs has a clearance less than the glomerular filtration rate?
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What is the characteristic of first-order kinetics?
What is the characteristic of first-order kinetics?
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Which of the following factors determines the duration of the half-life of a drug?
Which of the following factors determines the duration of the half-life of a drug?
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What is the effect of highly distributed and sequestrated drugs in tissue on the half-life?
What is the effect of highly distributed and sequestrated drugs in tissue on the half-life?
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Which of the following drugs follows zero-order kinetics?
Which of the following drugs follows zero-order kinetics?
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Study Notes
Pharmacokinetics
- Bioavailability: The fraction of the administered dose that reaches the systemic circulation, defined as unity (or 100%) in the case of intravenous administration.
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Factors determining bioavailability:
- Biological factors: GIT degradation, food and other drugs, absorption, first pass metabolism, entero-hepatic circulation.
- Pharmaceutical factors: particle size, disintegration agents, type of excipient.
Distribution
- Volume of Distribution (Vd): The volume of distribution is calculated by dividing the dose of the drug by the estimated plasma concentration per liter at the time of plasma-tissue equilibrium after i.v. injection.
- Blood-brain and CSF barriers: Water-soluble drugs cannot filter into CSF or brain, crossing occurs either by diffusion or carrier-mediated transport.
- Placental barrier: Important for drug distribution in pregnant women.
- Plasma protein binding: Important for drug distribution and elimination.
Metabolism (Biotransformation)
- Metabolic processes: Convert lipid-soluble drugs into water-soluble products, which are easily eliminated either in the urine or through the bile.
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Types of chemical reactions:
- Phase I reaction: Non-synthetic, occur by microsomal enzymes, including oxidation, reduction, and hydrolysis.
- Phase II reaction: Synthetic, involving the addition of an endogenous water-soluble group (conjugation) by transferases enzymes.
- First pass effect: Pre-systemic elimination, occurs only with oral administration, includes intestinal and hepatic first pass effects.
- Enzyme induction: Increases the metabolism of drugs, leading to decreased efficacy and plasma half-life.
- Enzyme inhibition: Decreases the metabolism of drugs, leading to increased efficacy and plasma half-life.
Elimination
- Rout of excretion: Renal, liver, lungs, gastro-intestinal tract, breast milk, and miscellaneous.
- Clearance: The volume of plasma cleared of the drug in a unit of time, total clearance is the sum of renal, liver, and other clearances.
- Kinetics of clearance: First-order kinetics (non-saturable) and zero-order kinetics (saturable).
- Half-life (t ½): The time taken for the circulatory plasma concentration to fall by 50%, determined by the rate of clearance, distribution, and storage, and plasma protein binding.
Pharmacokinetic Models
- Multi-compartment distribution: Many drugs undergo an early distribution phase followed by a slower elimination phase, modeled by a "two compartment model".
- Single compartment distribution: A few drugs may behave as if they are distributed to only one compartment.
Steady State (SS) Level
- Steady state level: When the intake of a drug is equal to its elimination, reached after 5 half-lives (t ½) in most drugs that follow first-order kinetics.
- Significance of steady state level: The time to reach SS level is a function of t ½, and the SS level reached is a function of the dose and dose interval.
Dosage Regimen
- Variables to consider: Amount of single dose, route of administration, dose interval, and total duration of therapy.
- Types of treatment: Single dose treatment (e.g., hypnotics, analgesics, purgatives) and multiple dosing (better to give smaller doses at shorter intervals).
- Variants in dosage schedule: Drugs with short plasma t ½ (e.g., dopamine) require different dosage schedules.
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Description
This quiz covers the essential concepts of pharmacokinetics, including bioavailability, oral plasma concentration-time curve, and factors that determine bioavailability of a drug.
