Pharmacology Chapter 5 Quiz

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Questions and Answers

Which factor primarily favors drug absorption from the intestine over the stomach?

Higher concentration of the drug

Longer contact time in the stomach

Greater blood flow to the intestine (correct)

Lower pH levels in the intestine

What is bioavailability?

The amount of drug present in the urine

The rate at which a drug is metabolized

The fraction of drug that reaches systemic circulation unchanged (correct)

The total amount of drug administered

What effect does the presence of food in the stomach have on drug absorption?

Decreases absorption due to rapid gastric emptying

Has no impact on absorption at all

Delays absorption due to dilution and slower gastric emptying (correct)

Increases absorption rate due to dilution

How is bioavailability determined?

By comparing plasma levels post oral administration to IV administration Signup and view all the answers

What primarily limits the absorption of very hydrophilic drugs?

Their inability to cross lipid-rich cell membranes Signup and view all the answers

What is the effect of first-pass hepatic metabolism on drug bioavailability?

It decreases the amount of unchanged drug in systemic circulation Signup and view all the answers

Which of the following is NOT a physical factor influencing drug absorption?

Gut microbiome composition Signup and view all the answers

What is the main reason that absorption from the intestine is more efficient than from the stomach?

Richer vascularization in the intestine Signup and view all the answers

What is the effect of a large volume of distribution (Vd) on the half-life of a drug?

It increases the drug's half-life. Signup and view all the answers

How do bound drugs interact with target sites in the tissues?

They are pharmacologically inactive. Signup and view all the answers

What characteristic of albumin is true concerning drug binding?

It has varying binding capacities and affinities. Signup and view all the answers

What is primarily responsible for the metabolism of drugs in the body?

The liver Signup and view all the answers

What type of reactions does phase I metabolism typically involve?

Oxidation, reduction, and hydrolysis Signup and view all the answers

What is a pro-drug?

An inactive compound that must be metabolized to its active form. Signup and view all the answers

What is one possible result of drug metabolism?

Inactive drugs converting to active metabolites. Signup and view all the answers

Which type of drug is most likely to remain unbound to plasma proteins?

Hydrophilic drugs Signup and view all the answers

What is required for a drug to enter the central nervous system?

It must pass through the endothelial cells of the CNS. Signup and view all the answers

Which type of drug is most likely to penetrate the blood-brain barrier?

Lipid-soluble drugs Signup and view all the answers

How is the volume of distribution (Vd) calculated?

By dividing the total drug dose by the plasma concentration at time zero. Signup and view all the answers

What happens when a drug binds to plasma proteins?

The drug is sequestered and slowed in transfer from the vascular compartment. Signup and view all the answers

Which factor limits the ability of ionized or polar drugs to enter the CNS?

The lack of slit junctions between endothelial cells. Signup and view all the answers

In which compartment is a drug likely to get trapped if it has a large molecular weight?

Plasma compartment Signup and view all the answers

What characteristic of hydrophobic drugs aids their movement across biological membranes?

They possess a uniform distribution of electrons. Signup and view all the answers

What role does plasma albumin play relating to drug distribution?

It acts as a drug reservoir and binds drugs non-selectively. Signup and view all the answers

What is the defining characteristic of first-order kinetics in drug metabolism?

A constant fraction of drug is metabolized per unit time. Signup and view all the answers

Under which conditions do zero-order kinetics occur in drug metabolism?

When the enzyme is saturated by a high free-drug concentration. Signup and view all the answers

What happens during Phase I reactions in drug metabolism?

Lipophilic drugs are converted into hydrophilic substances. Signup and view all the answers

Which of the following statements about the Michaelis-Menten equation is true in the context of first-order kinetics?

The rate of metabolism is proportional to the free drug concentration. Signup and view all the answers

What is the primary role of the cytochrome P-450 system in drug metabolism?

To catalyze Phase I reactions converting lipophilic drugs. Signup and view all the answers

Which of the following drugs is known to follow zero-order kinetics due to saturation of enzymes?

Aspirin Signup and view all the answers

What is the significance of Km (Michaelis constant) in drug metabolism?

It indicates the substrate concentration at which the reaction rate is half of Vmax. Signup and view all the answers

Which of the following best describes the effect of Phase I metabolism on drug pharmacologic activity?

Phase I metabolism may increase, decrease, or have no effect on activity. Signup and view all the answers

What primarily limits the secretion of drugs in premature infants and neonates?

Incompletely developed tubular secretory mechanisms Signup and view all the answers

What is the primary active transport system responsible for the secretion of weak acids in the proximal tubule?

Anion transport mechanism Signup and view all the answers

How does manipulating urine pH help in drug clearance?

It increases the fraction of ionized drug in the lumen Signup and view all the answers

What happens during the process known as ion trapping?

Drugs become ionized, limiting their reabsorption Signup and view all the answers

In the context of renal clearance, what does the extraction ratio measure?

The difference in drug concentration between arterial and venous plasma Signup and view all the answers

What is necessary to facilitate the clearance of weak bases when treating overdose conditions?

Acidification of the urine Signup and view all the answers

What roles do lipid solubility and pH play in drug passage into the glomerular filtrate?

They do not influence drug passage Signup and view all the answers

What primarily occurs in the proximal tubular secretion of drugs?

Active transport of anions and cations Signup and view all the answers

What is the formula to calculate total body clearance?

Cltotal = Ke Vd Signup and view all the answers

How does the half-life of a drug relate to its clearance and volume of distribution?

Inversely related to clearance and directly proportional to volume of distribution Signup and view all the answers

What condition may lead to a longer half-life of a drug in patients?

Renal failure or any abnormality affecting drug elimination Signup and view all the answers

Which of the following describes the extraction ratio of a drug?

The ratio of the concentration of the drug exiting over entering the kidneys Signup and view all the answers

What is typically the major organ responsible for drug excretion?

Kidney Signup and view all the answers

In which circumstance may a patient benefit from a drug excreted through the intestine rather than the kidney?

If they have renal failure Signup and view all the answers

What effect does enterohepatic circulation have on drug half-life?

It can prolong the half-life of certain drugs Signup and view all the answers

What is the typical behavior of drug elimination in the body?

Follows first-order kinetics Signup and view all the answers

Study Notes

General Pharmacology

Pharmacology is the study of interactions between a living organism and external chemicals that alter normal biochemical functions.
Pharmaceuticals are substances with medicinal properties.
Drugs are chemical substances used to treat, diagnose, or prevent disease (prophylaxis).
Pharmacology is a branch of chemical science practiced by pharmacologists.
Sub-divisions of pharmacology include clinical pharmacology, neuro- and psychopharmacology, pharmacogenetics, pharmacogenomics, and pharmacoepidemiology.

Introduction

Toxicology is the study of harmful drug effects, including diagnosing and treating exposures to toxins and toxicants.
Pharmacology can be sub-divided into pharmacodynamics and pharmacokinetics.
Pharmacokinetics describes what the body does to a drug, including absorption, distribution, metabolism, and excretion (ADME).
Pharmacodynamics describes what the drug does to the body, including pharmacological actions and mechanisms.

Routes of Drug Administration

Therapeutic objectives guide the choice of drug administration route, considering factors like rapid onset of action or localized delivery.
Enteral Route (oral):
- Most drugs absorbed through the gastrointestinal (GI) tract pass through the liver (first-pass metabolism) and then the general circulation.
- First-pass metabolism in the liver often reduces the efficacy of oral drugs.
- Food can affect the absorption of some drugs, like insulin and penicillin.
Sublingual Route: Drugs placed under the tongue diffuse directly into capillaries and enter systemic circulation, bypassing the liver.
Rectal Route: Fifty percent of blood draining from the rectum bypasses the liver, minimizing biotransformation. This route is used for anti-emetic agents.
Parenteral Route: Used for drugs poorly absorbed by the gut or for those that are unstable in the GI tract, such as insulin.
- Intravascular (IV): Provides the most control over drug delivery to the body. Avoids first-pass metabolism and has a rapid onset of action. However, it can be contaminated, and is painful.
- Intramuscular (IM): Injection into muscle. Absorption from aqueous solutions is faster than from depot preparations.
- Subcutaneous (SC): Minimizes intravascular injection risks. Epinephrine, a vasoconstrictor, can be used to slow drug absorption.
Intradermal (ID): Injection into the dermis, commonly used for vaccines.
Intraarticular: Injection into joints for local effects.
Intrathecal/Intraventricular: Administration into cerebrospinal fluid (CSF), used in specific cases like leukemia.
Inhalation: Used for drugs that are gases (e.g., anesthetics, bronchodilators). Absorption is rapid due to the large surface area of the lungs.
Intranasal: Used for drugs such as desmopressin.
Topical: Applied directly to the skin or mucous membranes, causing local effects (e.g., creams, eye drops).
Transdermal: Applies drugs directly to the skin, often using a patch, achieving systemic effects.

Absorption of Drugs

Absorption is the transfer of a drug from its site of administration into the bloodstream.
Transport of drugs from the GI tract: Passive diffusion and active transport are the two mechanisms.
Passive diffusion: Drugs move from high to low concentration due to the concentration gradient, not requiring a carrier protein.
Active transport: Drugs move against the concentration gradient using carrier proteins and energy (ATP).
pH effect on absorption: Weak acids and weak bases exist in both ionized and unionized states; their absorption is highly pH dependent; un-ionized forms are typically absorbed readily.
Physical factors influencing absorption: Blood flow to the absorption site is a crucial factor. Greater absorption occurs in areas with higher blood flow and larger surface areas (e.g., small intestine).

Bioavailability

Bioavailability is the fraction of a drug that reaches systemic circulation in a chemically unchanged form.
Bioavailability is determined by comparing plasma concentrations achieved after oral administration with those after intravenous administration.
Factors affecting bioavailability include first-pass hepatic metabolism, drug solubility, chemical instability, and drug formulation.
- First-pass metabolism: Rapid liver metabolism after absorption decreases the amount of drug reaching the systemic circulation.

Drug Distribution

Distribution is the process of transferring a drug from the bloodstream into the extracellular fluid and tissues.
Factors influencing distribution include blood flow, capillary permeability, and drug binding to plasma proteins.
Blood flow: The rate of blood flow to tissues influences drug distribution, with tissues receiving more blood flow receiving higher drug concentrations.
Capillary permeability: Capillary structure, especially the presence of slit junctions, influences drug penetration into tissues. Lipid-soluble drugs pass through cell membranes easily, while water-soluble drugs are often impeded.
Drug binding to plasma proteins: Reversible binding to plasma proteins like albumin reduces free drug levels and affects tissue distribution.

Volume of Distribution

Volume of distribution (Vd) is a hypothetical volume of fluid in which the drug is distributed.
Vd is calculated by dividing the administered dose by the plasma concentration at time zero.
Drugs with high Vd are often found in tissues, while drugs with lower Vd remain primarily in plasma.
Water compartments in the body (plasma, extracellular and intracellular) determine the distribution of a drug.

Drug Metabolism (Biotransformation)

Metabolism involves the biotransformation of drugs into more polar molecules.
The liver is the primary site of drug metabolism; however, other tissues can metabolize certain drugs.
Drugs can be metabolized into inactive or active metabolites.
Phase 1 metabolism often involves oxidation, reduction, or hydrolysis, increasing polarity.
Phase 2 metabolism involves conjugation with endogenous substrates to form a more water-soluble form that can be excreted.
Zero-order kinetics mean a constant amount of drug is metabolized per unit of time.
Drugs with high concentrations saturate the enzyme, leading to zero-order kinetics.

Drug Elimination

Elimination describes the removal of a drug from the body.
The kidney is the primary organ for drug elimination.
Elimination processes include glomerular filtration, proximal tubular secretion, and passive tubular reabsorption.
Some drugs are excreted through the bile, lungs, or milk.
Renal elimination, a key aspect of the overall body clearance, is affected by various factors such as plasma flow, extraction ratio and ionization.
Total body clearance is the sum of clearance from the kidneys, liver, lungs and other organs.

Clinical Situations Affecting Drug Half-Life

Certain situations can prolong drug half-life, requiring dosage adjustments.
- Decreased renal function (reduced blood flow to the kidneys).
- Binding competition of multiple drugs.
- Decreased metabolic capacity.

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Description

Test your knowledge on key concepts of drug absorption and metabolism from Pharmacology Chapter 5. This quiz covers topics including bioavailability, hepatic metabolism, and the physical factors affecting drug absorption. Understand how these processes influence therapeutic outcomes in clinical practice.