Untitled Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What characterizes the initial phase of drug administration via IV when absorption is not a factor?

It is when adverse reactions occur.

It represents the elimination phase.

It is characterized by absorption in the GI tract.

It represents the distribution phase. (correct)

Which organs primarily receive the drug during the initial distribution phase?

Lungs, heart, and stomach

Pancreas, spleen, and intestines

Muscle, skin, and fat

Liver, kidney, and brain (correct)

How is drug distribution to the brain primarily determined?

By the rate of metabolism in the liver

By the drug's solubility in water

By the permeability of the blood-brain barrier (correct)

By the length of the drug's action

What phenomenon occurs when a drug moves from an area of high blood flow to low blood flow?

Redistribution Signup and view all the answers

What effect does the lipid solubility of a drug have on its redistribution?

Greater lipid solubility leads to faster redistribution. Signup and view all the answers

What is the primary consequence of redistribution for drugs with rapid onset of action?

Termination of drug action Signup and view all the answers

What process allows the passage of drugs from an area of high concentration to an area of low concentration without energy use?

Facilitated diffusion Signup and view all the answers

What happens when a drug is administered repeatedly or continuously over long periods?

High-capacity sites gradually fill up. Signup and view all the answers

Active transport is characterized by which of the following?

It requires energy to move substances against a concentration gradient. Signup and view all the answers

Which of the following best describes the nature of adverse drug reactions during the initial phase?

They may result from distribution to non-target organs. Signup and view all the answers

Which factor does not influence absorption of drugs?

Presence of specific carrier proteins Signup and view all the answers

What is the primary role of P-glycoprotein in drug absorption?

It inhibits the uptake of certain drugs. Signup and view all the answers

Which process describes the engulfment of a drug molecule by the cell membrane?

Endocytosis Signup and view all the answers

How does food in the stomach affect drug absorption?

It dilutes the drug and slows gastric emptying. Signup and view all the answers

Which statement about the intestine and stomach regarding drug absorption is accurate?

Absorption is favored from the intestine over the stomach due to higher blood flow. Signup and view all the answers

Which condition is likely to delay drug absorption in the gastrointestinal (GI) tract?

Presence of food in the stomach Signup and view all the answers

What is the primary definition of pharmacokinetics?

What the body does to a drug. Signup and view all the answers

Which pharmacokinetic property is primarily responsible for getting a drug into the bloodstream?

Absorption Signup and view all the answers

What happens during the distribution phase of pharmacokinetics?

The drug leaves the bloodstream and enters body tissues. Signup and view all the answers

Which of the following routes of administration provides 100% bioavailability?

Intravenous delivery Signup and view all the answers

What is NOT a mechanism of drug absorption from the gastrointestinal tract?

Chemical decomposition Signup and view all the answers

What characteristic primarily affects the rate and efficiency of drug absorption?

The route of administration Signup and view all the answers

Which pharmacokinetic parameter helps determine the frequency of drug dosing?

Route of administration Signup and view all the answers

Which mechanism allows drugs to enter cells through specialized proteins?

Facilitated diffusion Signup and view all the answers

What is primarily responsible for the secretion of drugs in the proximal tubule?

Active transport systems Signup and view all the answers

In what scenario would premature infants and neonates be likely to retain certain drugs?

Incomplete tubular secretory mechanism Signup and view all the answers

Which of the following can be a method to improve the clearance of an undesirable drug?

Manipulating urine pH Signup and view all the answers

Which type of drug elimination is enhanced by the acidification of urine?

Weak bases Signup and view all the answers

What process allows compounds with a molecular weight greater than 300 to be excreted?

Active secretion in bile Signup and view all the answers

How does glucuronidation facilitate drug excretion?

By facilitating excretion via bile Signup and view all the answers

What is the term for the recycling process that occurs when conjugated drugs are hydrolyzed back into free drugs in the intestine?

Enterohepatic recycling Signup and view all the answers

What is the effect of alkalinizing urine on drugs like phenobarbital?

It keeps them ionized and decreases reabsorption Signup and view all the answers

How does the pH of the environment affect the ionization of acidic drugs?

At a pH below the pKa, more acidic drugs are in their non-ionized form. Signup and view all the answers

What effect does age have on the volume of distribution (Vd) of drugs?

Vd decreases for many drugs due to reduced muscle mass and water content. Signup and view all the answers

Which factor is likely to alter the drug distribution based on protein levels?

Lower protein levels can result in larger than expected volumes of distribution. Signup and view all the answers

What is a consequence of using lipid-soluble drugs regarding their volume of distribution?

Lipid-soluble drugs can have high volumes of distribution. Signup and view all the answers

What cannot be expected if the pH of the environment is significantly different from the drug's pKa?

The drug will remain completely ionized regardless of pH. Signup and view all the answers

In what situation might the volume of distribution (Vd) of a drug not increase?

In cases of increased tissue protein binding. Signup and view all the answers

What impact does pregnancy have on drug distribution?

Pregnancy increases the volume of distribution for many drugs. Signup and view all the answers

What happens to the amount of drug in the central compartment when a drug binds to tissue proteins?

It decreases the amount of drug in the central compartment. Signup and view all the answers

Which of the following agents can interrupt the enterohepatic cycle?

Cholestyramine Signup and view all the answers

What is the primary role of the lungs in drug clearance?

Excretion of anesthetic gases Signup and view all the answers

How does a clinician utilize the information regarding elimination order?

To maintain therapeutic concentration Signup and view all the answers

Which of the following is true regarding first-order elimination kinetics?

Higher concentration leads to greater elimination per unit time. Signup and view all the answers

What is the significance of drug excretion into breast milk?

It poses a risk of undesirable side effects for the infant. Signup and view all the answers

What characterizes zero-order kinetics in drug elimination?

Elimination occurs at a constant rate regardless of concentration. Signup and view all the answers

Which method is least involved in the excretion of most drugs?

Sweat Signup and view all the answers

What happens to drug metabolites during elimination?

They generally become polar for efficient elimination. Signup and view all the answers

Study Notes

Pharmacokinetics

Pharmacokinetics describes what the body does to a drug.
Four pharmacokinetic properties determine drug action: speed of onset, intensity, and duration.
Drug administration through various routes leads to absorption, distribution, metabolism, and elimination.

Absorption

Absorption is the transfer of a drug from its administration site to the bloodstream.
Absorption rate and efficiency depend on the drug's properties and the route of administration.
IV drug delivery results in 100% bioavailability.
Other routes may result in only partial absorption .

Mechanisms of Absorption

Passive diffusion: Drug movement from high to low concentration across a membrane. Water-soluble drugs go through channels, lipid-soluble drugs cross lipid bilayers.
Facilitated diffusion: Special transmembrane carrier proteins facilitate drug or molecule passage across cell membranes. It doesn't require energy.
Active transport: Energy-dependent transport against a concentration gradient using specific carrier proteins that span the membrane.
Endocytosis / exocytosis: Transport of exceptionally large molecules across the cell membrane.

Factors Influencing Absorption

Blood flow to absorption site (intestine has a higher blood flow than stomach).
Total surface area available for absorption (intestine has a much larger surface area).
Contact time at absorption surface. Fast transit times impair absorption.
Expression of P-glycoprotein (reduces drug absorption).

Bioavailability

Bioavailability is the fraction of administered drug reaching systemic circulation.
Important for calculating drug dosages in non-intravenous routes.
Affected by administration route and drug properties.

Determination of Bioavailability

Measured by comparing plasma drug levels after different routes with intravenous injection.
Area under the curve (AUC) is calculated after plotting plasma concentrations versus time.

Factors Influencing Bioavailability

First-pass hepatic metabolism.
Solubility of the drug.
Chemical instability.
Nature of the drug formulation (e.g., particle size, salt form, coatings).

Drug Distribution

Drug distribution is the movement of a drug between intravascular and extravascular compartments (blood/plasma, interstitial fluid, and cells).
Drugs exist in bound or free form within each compartment.
Drugs are metabolized and excreted by the liver and kidneys.
IV administration bypasses drug absorption and immediately enters the distribution phase.

Understanding Drug Distribution

The amount of drug available at the target organ is crucial.
Drug distribution to other organs can cause adverse reactions.
Loading doses account for drug distribution into non-target organs.

Phases of Drug Distribution

Initial Phase: Drugs first distribute into highly vascular organs (e.g. brain, liver).
Second Phase: Drugs distribute to less vascular organs (e.g.muscle, skin, fat).

Redistribution

Movement of a drug from an area of high to low blood flow.
Lipid solubility of the drug affects redistribution rate (faster for more lipid-soluble).

Factors Affecting Drug Distribution

Cardiac output and blood flow.
Capillary permeability.
Plasma protein binding.

Plasma Protein Binding

Some drugs bind to plasma proteins (e.g., albumin, alpha-1-acid glycoprotein).
Only unbound drug can leave the vascular system.
The concentration of bound and unbound drug influences distribution.

Tissue Binding

Drugs can bind to tissue proteins and phospholipids acting as reservoirs.
Prolongs drug half-life and can lead to tissue toxicity.

Volume of Distribution (Vd)

Represents the ratio of total amount of drug to plasma concentration.
aVd (apparent volume of distribution) indicates how a drug distributes within the body compared with plasma concentration.

Factors Affecting Volume of Distribution

Drug factors: molecular size, charge, pKa, affinity to tissue proteins, lipid solubility, aqueous solubility.
Patient factors: age, gender, pH, protein levels, displacement, pregnancy, edema.

Effect of Vd on Drug Half-life

Larger Vd implies more distribution to tissues, resulting in a longer half-life.
The rate of drug elimination in some cases depends on which organs it is delivered to.

Estimating the Loading Dose

Apparent volume of distribution helps determine the loading dose.
Drugs with larger volumes of distribution often require higher loading doses.

Drug Distribution to Fetus/Newborn

Drug distribution to the fetus/newborn depends on lipid solubility, plasma protein binding, and pKa of the drug.
Fetal pH is lower than maternal, and weak bases can accumulate in the fetus.

Drug Distribution to Breast Milk

pH and lipid concentration of breast milk can influence drug distribution.
The drug's pKa, plasma protein binding, and molecular weight are factors influencing distribution.

Metabolism

Metabolism is the chemical alteration of a drug by various bodily systems.
Creates compounds that are more easily excreted (metabolites).
Occurs in liver, kidneys, lungs, etc.

Phases of Metabolism

Phase I: Converts lipophilic drugs to hydrophilic drugs by adding polar functional groups (e.g., hydroxylation, oxidation).
Phase II: Conjugates hydrophilic drugs with larger polar molecules (e.g., glucuronidation, sulfation) to increase water solubility.

Types of Metabolites

Active: Have therapeutic effects.
Inactive: Have no therapeutic or toxic effect.
Toxic: Can have harmful effects.

Factors Influencing Drug Metabolism

Age: P450 activity and enzyme production reduce with age.
Gender: Males generally metabolize faster.
Liver size and function: Liver disease or smaller liver reduce metabolism.
Body temperature: Fever reduces the activity of metabolizing enzymes.
Diet: Food can induce or inhibit P450 enzyme activity.
Genetics: Polymorphisms in drug metabolism genes can affect drug metabolism.
Environmental factors: Exposure to certain substances like pesticides and smoke alters metabolism.

Drug Clearance

Elimination of drugs can be through metabolism and excretion.
Kidney clearance is a main method for drug removal.

Renal Elimination

Drugs enter through renal arteries and form capillaries.
Small molecular weight, unbound drugs are filtered.
Active secretion and passive reabsorption in the proximal and distal tubules.

Hepatobiliary Elimination

Drug metabolites and larger compounds are eliminated via the liver's biliary system.
Drug glucuronide is an example.
Enterohepatic recirculation may exist.

Clearance by Other Routes

Feces, lungs, and milk (nursing mother) can be routes of elimination.
Excretion of drugs into sweat, saliva, tears, hair, and skin is minimal.

Clinical Situations Affecting Clearance

Changes like decreased liver or kidney function impact drug clearance resulting in dosage adjustments.

Kinetics of Elimination

Drugs are removed in first-order or zero-order kinetics.
Half-life is the time it takes for drug concentration to decrease by half.
Some drugs can exhibit variable kinetics.

Important Formulas

CL = 0.693 * Vd / t1/2
This formula is important for calculating drug clearance, given the half-life and volume of distribution(vd) in the body. Vd is typically constant for many drugs and the equation can be used to estimate how quickly a drug is removed from the body.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.