Pharmacology Drug Elimination Basics

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Drug elimination is the process of removing a drug from the body. What are the major routes of drug elimination?

Liver, Brain, Muscles

Stomach, Liver, Skin

Intestines, Heart, Lungs

Kidney, liver, lungs, and other routes (correct)

What is the term used to describe the theoretical volume of plasma from which a drug is completely removed in unit time?

Clearance (CL)

The ______ filtration rate (GFR) is a measure of the kidneys' ability to filter waste products from the blood.

glomerular

Tubular reabsorption is a process by which drugs are actively transported back into the bloodstream from the tubules in the kidneys.

False Signup and view all the answers

Tubular secretion is the process by which drugs are passed from the bloodstream into the tubules of the kidney.

True Signup and view all the answers

Which of these is an example of a drug that is often eliminated via the lungs?

General Anesthetics Signup and view all the answers

What is the difference between first-order and zero-order kinetics in drug elimination?

First-order kinetics: The rate of elimination is directly proportional to the drug concentration. This means a constant fraction of the drug is removed per unit time. Zero-order kinetics: The rate of elimination is constant, regardless of the drug concentration. This means a fixed amount of drug is removed per unit time. Signup and view all the answers

The time it takes for the plasma concentration of a drug to decrease by half is known as its ______.

half-life Signup and view all the answers

What is the term used to describe the stable concentration of a drug in the body after repeated doses?

Steady State Plasma Concentration Signup and view all the answers

A loading dose aims to rapidly achieve the therapeutic concentration of a drug.

True Signup and view all the answers

What is the purpose of a maintenance dose?

A maintenance dose maintains a steady-state plasma concentration of a drug after the loading dose, ensuring that the therapeutic levels are maintained over time. Signup and view all the answers

Which of the following is NOT an advantage of using a drug delivery system that prolongs drug action?

Increased risk of side effects Signup and view all the answers

Which of these is a method to prolong drug action in the body?

Retarding the rate of metabolism Signup and view all the answers

Study Notes

Drug Elimination

Drug elimination is the process of removing a drug from the body

Objectives

Understand drug clearance by various organs (kidney, liver, etc.)
Compare and contrast first-order and zero-order kinetics
Calculate loading dose, maintenance dose, and steady-state concentration
Identify methods for prolonging drug action

Excretion

Excretion is the passage of absorbed drugs and their metabolites out of the body
Drugs and metabolites are excreted through:
- Urine (primarily via the kidney)
- Feces
- Exhaled air
- Saliva
- Sweat
- Milk
Specific examples of drug excretion include:
- Erythromycin and ampicillin (via feces)
- General anesthetics and alcohol (via exhaled air)
- Lithium, potassium iodide (via saliva and sweat)
- Amphetamine and chloramphenicol (via milk)

Renal Excretion

Renal excretion involves three main processes:
- Glomerular filtration: Drugs pass through the glomerular capillaries into the filtrate.
- Tubular reabsorption: Drugs are reabsorbed from the filtrate back into the blood.
- Tubular secretion: Drugs move from the blood into the filtrate
Net renal excretion = (glomerular filtration + tubular secretion) - tubular reabsorption

Renal Excretion (Glomerular Filtration)

Glomerular capillaries have large pores
Drug filtration depends on plasma protein binding and renal blood flow
Glomerular filtration rate (GFR) is typically 120 mL/min and decreases with age and in renal failure

Renal Excretion (Tubular Reabsorption)

Primarily passive diffusion
Influenced by lipid solubility and ionization
Lipid-soluble, unionized drugs are readily reabsorbed
Clinical significance in poisoning
- Urine alkalization for barbiturates poisoning (acidic drugs)
- Urine acidification for morphine poisoning (basic drugs)

Renal Excretion (Tubular Secretion)

Active transport process
Primarily occurs in the proximal tubules.
Important for removing protein-bound drugs

Kinetics of Elimination

Clearance (CL): Theoretical volume of plasma from which a drug is completely removed per unit time
CL = Rate of elimination / plasma concentration

First-Order Kinetics

The rate of elimination is directly proportional to drug concentration.
Constant fraction of drug is eliminated per unit time.
Clearance remains constant
Follows an exponential decay curve

Zero-Order Kinetics

The rate of elimination is constant, irrespective of drug concentration.
A constant amount of drug is eliminated per unit time.
Clearance decreases with increasing concentration
Follows a linear decline

Plasma Half-Life

Time required for the plasma concentration of a drug to decrease by half
Multiple half-lives (4-5) result in near-complete drug elimination

Steady-State Plasma Concentration (Cpss)

Achieved after repeated dosing when elimination equals input.
Cpss = Dose rate / Clearance

Loading Dose

Used to quickly achieve target concentration.
Loading dose = (Vd) x (desired plasma concentration) / bioavailability

Maintenance Dose

Maintains steady-state plasma concentration
Dosing rate = (CL) x (desired plasma concentration) / bioavailability
CL = clearance

Prolongation of Drug Action

Methods for maintaining a drug's effect over time:
- Prolonging absorption rate at the site of administration
- Increasing plasma protein binding
- Retarding metabolism
- Retarding renal excretion

Studying That Suits You

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

Description

This quiz covers the essential concepts of drug elimination, focusing on how drugs are cleared by various organs like the kidneys and liver. You will explore first-order vs. zero-order kinetics, calculate loading and maintenance doses, and understand methods to prolong drug action. Test your knowledge on the mechanisms of drug excretion and renal processes involved.