Pharmacology Drug Absorption and Bioavailability

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Questions and Answers

Which of the following drugs is most likely to alter absorption by changing gastric pH?

Proton pump inhibitors (correct)

Metoclopramide

Vasodilators

Laxatives

A drug's bioavailability is a measure of what percentage of the administered dose that:

is metabolized in the liver.

reaches the blood stream in comparison to the same dose administered intravenously. (correct)

excreted through the kidneys.

is metabolized by the GI tract before reaching the liver.

If a drug is administered intravenously, what is its expected bioavailability?

Less than 75%

75- 100%

100% (correct)

Which route of drug administration is most likely to have its bioavailability affected by 'first-pass' metabolism?

Oral Signup and view all the answers

Which factor does NOT directly influence the speed at which a drug reaches its target?

The drug molecule weight Signup and view all the answers

A drug with high first-pass metabolism could have a bioavailability that is:

Significantly reduced Signup and view all the answers

Which of the following best describes facilitated diffusion?

Does not require energy, but need a protein carrier and is saturable. Signup and view all the answers

If a drug is in an ionized form at a particular site, how does this impact movement across cellular membranes?

Its movement will likely be significantly restricted. Signup and view all the answers

Which of the descriptions below is NOT a characteristic of active transport?

Dependent on the concentration gradient. Signup and view all the answers

A drug administered by a specific route results in a localized effect, what does this indicate about the drug's distribution?

Its distribution is narrow. Signup and view all the answers

What does the therapeutic index (TI) primarily indicate about a medication?

The range of doses that are both effective and safe. Signup and view all the answers

Which of the following factors is NOT a primary determinant in the rate of drug absorption?

The patient's age. Signup and view all the answers

What does a wide therapeutic window suggest about a drug?

The drug has a greater margin of safety. Signup and view all the answers

Which route of administration bypasses the gastrointestinal tract?

Intramuscular Signup and view all the answers

If a drug has a very steep slope on the dose-response curve, it indicates:

The effect of the drug changes dramatically with small changes in dose. Signup and view all the answers

Which of the following is an example of an enteral route of drug administration?

Sublingual tablet Signup and view all the answers

Which factor is most critical in determining both the rate of absorption and distribution of a drug?

The rate and amount of blood flow to the administration area Signup and view all the answers

What is the primary function of the 'absorption' phase in pharmacokinetics?

To move the drug from its site of administration into the bloodstream Signup and view all the answers

What is the primary consequence of a drug being bound to plasma proteins?

Reduced drug efficacy Signup and view all the answers

Which of the following factors does NOT directly affect the first pass effect of a drug?

Drug binding to plasma proteins Signup and view all the answers

What does a high apparent volume of distribution (Vd) indicate about a drug?

Extensive distribution into tissues and compartments. Signup and view all the answers

Which condition would most likely result in a decrease in the percentage of a drug bound to plasma proteins?

Severe liver disease Signup and view all the answers

What is the correct definition of drug distribution?

The movement of a drug from the bloodstream to other body compartments. Signup and view all the answers

Which of the following factors primarily affects a drug's distribution rather than absorption?

Lipophilicity versus hydrophilicity Signup and view all the answers

A drug with a high affinity for plasma proteins will typically demonstrate which characteristic?

Lower apparent volume of distribution Signup and view all the answers

If a 100mg dose of a drug results in 20mg reaching systemic circulation after the first pass effect, what percentage was NOT absorbed or removed by the effect?

80% Signup and view all the answers

What is the primary objective of drug metabolism?

To improve the drug's elimination from the body. Signup and view all the answers

In what organ does the majority of drug metabolism occur?

Liver Signup and view all the answers

What is a key characteristic of Phase I metabolic reactions?

They add a handle for larger, more water-soluble compounds to attach. Signup and view all the answers

Which of the following is a typical Phase II metabolic reaction?

Glucuronidation Signup and view all the answers

What is a possible consequence of increased metabolism of a drug via enzyme induction?

Reduced drug efficacy due to faster elimination. Signup and view all the answers

Which scenario could result in decreased drug metabolism, leading to higher drug levels?

Co-administration of an enzyme inhibitor Signup and view all the answers

What is the potential consequence of a patient having extremely functional CYP2D6 enzymes on the drug codeine?

Reduced therapeutic effect due to rapid drug metabolism. Signup and view all the answers

According to the provided material, what is a common outcome of phase II metabolism?

The metabolite will be more easily excreted. Signup and view all the answers

Which type of inhibitor binds to the same site as the agonist, but can be overcome with a higher concentration of the agonist?

Competitive inhibitor Signup and view all the answers

What is a main consequence of P450 enzyme inhibition regarding a drug's blood levels?

Rapid and profound increase in blood levels of the drug Signup and view all the answers

Which of the following is NOT a primary function of excretion?

Converting drugs into inactive metabolites Signup and view all the answers

What is a key characteristic of drug metabolites that facilitates their excretion?

They are usually charged and water-soluble Signup and view all the answers

Which of the following describes the main difference between renal and biliary excretion?

Renal excretion involves excretion into urine while biliary excretion involves excretion into bile Signup and view all the answers

What are the three primary mechanisms of renal drug excretion?

Glomerular filtration, tubular secretion, and tubular reabsorption Signup and view all the answers

Which of the following is a key feature of glomerular filtration?

It is limited by the structure and size of pores in the glomerulus Signup and view all the answers

How does the binding of a drug to a protein in the blood affect its rate of glomerular filtration?

It limits the rate of filtration since the protein-bound complex is generally too large to pass through the glomerular pores Signup and view all the answers

Study Notes

Overview of ADME

ADME stands for absorption, distribution, metabolism, and excretion
Pharmacology is the study of substances that interact with living systems
Drugs affect biologic function
Pharmacokinetics (PK) describes how the body absorbs, distributes, metabolizes, and eliminates drugs
Pharmacodynamics (PD) is the action and effects of bioactive substances on living organisms

Objectives

Relate dose-response curve to therapeutic index
Compare and contrast effects of drug administration routes on onset, intensity and duration
Describe first-pass effect and its impact on bioavailability
Describe factors influencing drug absorption
Describe factors influencing drug distribution
Describe the pharmacokinetic consequences of drug metabolism
Identify major enzymatic reactions in phases I and II drug metabolism
Explain the roles of filtration, secretion, and reabsorption in renal drug excretion
Predict drug excretion routes based on drug properties
Describe relationships between drug elimination and steady-state drug concentrations

Key Terms

Pharmacology: Study of substances with living systems through chemical processes, especially binding to regulatory molecules
Drug: Substance that changes biological function
Pharmacokinetics (PK): Process of drug absorption, distribution, metabolism, and elimination within the body
Pharmacodynamics (PD): Action and effects of bioactive substances on living organisms
Absorption: Process of a substance entering blood circulation
Distribution: Dispersion of a substance throughout the body's fluids and tissues
Metabolism: Transformation of a substance into other substances
Excretion: Removal of substances from the body

Absorption, Distribution, Metabolism & Excretion

Absorption: Process of drugs entering the bloodstream from the site of administration
Distribution: Dispersion of drugs throughout various tissues and fluids
Metabolism: Transformation of drugs into other substances
Excretion: Removal of drugs or metabolites from the body

The Core of ADME

Active drug must reach the target receptor at sufficient levels and for an adequate duration to modify biological response
Biological response to drugs varies between individuals
Understanding pharmacokinetics and pharmacodynamics is vital for adjusting dosages and selecting appropriate drugs
Drug toxicity is also related to ADME

Dose-Response Curve

Shows relationship between drug dose and response
A minimum dose is needed for a significant response
Response increases with dose until a maximum effect is reached
Variability and slope illustrate the range and speed of response changes with increasing doses

Therapeutic Index

Range of doses creating an effective medication without unacceptable adverse events
Determined from quantal dose-response curves
Therapeutic window is the clinically useful range between the minimum effective and minimum toxic doses

First-Pass Metabolism

Drugs absorbed via the GI tract are metabolized to a varying degree in the liver before reaching systemic circulation
First-pass effect significantly reduces bioavailability for certain drugs

Distribution

The movement of drugs from the bloodstream to different body compartments. Factors affecting distribution include tissue permeability, blood flow, and binding to plasma proteins.

Protein Binding

Albumin, β-globulin, and α-acid glycoprotein bind drugs and play a crucial role in drug distribution and activity within the body
Drugs bound to proteins are inactive

Apparent Volume of Distribution (Vd)

A measure of the volume of body fluid in which a drug is distributed
Vd can be greater than the actual physical body volume

Metabolism

The body's transformation of the drug through chemical reactions
Metabolism can lead to the formation of inactive or active metabolites, which may have varying degrees of activity compared to the parent drug
Metabolism can alter the pharmacokinetic properties of a drug

Phase I Metabolism

Adds chemical groups to drug molecules to make them more water-soluble for excretion
Includes oxidation, reduction, hydrolysis, etc
Enzymes catalyze these reactions

Phase II Metabolism

Involves conjugation reactions with endogenous molecules
These molecules enhance water solubility and facilitate excretion

Renal vs Biliary Excretion

Renal excretion is the removal of drugs via urine routes
Biliary excretion refers to removing drugs via bile into the feces
Glomerular filtration, active secretion, and passive reabsorption are critical to renal excretion
Diffusion and active secretion are important in hepatic excretion

Renal Drug Excretion

Kidney excretes many drugs either unchanged or as metabolites.
Three key transport mechanisms (glomerular filtration, tubular secretion, and tubular reabsorption) regulate renal excretion

Kidney, Nephron and Glomerular Filtration

The kidney is the primary organ for renal excretion
The nephron is the functional unit of the kidney
Glomerular filtration is the non-selective process of removing small molecules, including drugs, from the bloodstream into the nephron

Tubular Secretion

Active transport process for large and ionized molecules for high urine concentrations.
Specific transport systems such as carriers play a significant role in the process

Tubular Reabsorption

Passive diffusion is the process of small, neutral, and lipophilic molecules moving from the urine back into the blood

Biliary Drug Excretion

Drugs enter hepatocytes where they are secreted into bile
Factors like conjugation, molecular size influence biliary excretion
5% of drugs are excreted in bile; however, active secretion can raise this to nearly 95%.

Questions?

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Description

This quiz explores key concepts in pharmacology, focusing on drug absorption, bioavailability, and factors influencing these processes. Test your understanding of how different routes of administration and physiological factors impact drug distribution and effectiveness.