Excretion of Drugs Quiz
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Questions and Answers

Which factor does not influence glomerular filtration of drugs?

  • Charge of the drug
  • Patient's age and general health (correct)
  • Concentration of drug in the plasma
  • Molecular size of the drug

    • What happens to drugs during tubular reabsorption in acidic urine?

  • Reabsorption of drugs is completely stopped
  • Acidic drugs are more reabsorbed
  • Ionization of basic drugs decreases
  • Basic drugs are more reabsorbed (correct)

    • Which process is primarily responsible for transporting drugs into the distal convoluted tubule?

  • Active tubular secretion (correct)
  • Passive diffusion
  • Hepatobiliary excretion
  • Glomerular filtration

    • Which of the following drugs is likely to be excreted through the kidney?

    <p>A drug with a low molecular weight</p> Signup and view all the answers

    Which route of drug elimination helps maintain drug action when renal function is compromised?

    <p>Hepatobiliary excretion</p> Signup and view all the answers

    What is the consequence of enterohepatic cycling in drug excretion?

    <p>It prolongs the drug's action</p> Signup and view all the answers

    What type of drugs are primarily excreted through the bile?

    <p>Conjugated drugs with molecular weight more than 300 daltons</p> Signup and view all the answers

    During which excretion process does the concentration of unaltered drug typically decrease significantly?

    <p>Glomerular filtration</p> Signup and view all the answers

    Which of the following statements best describes enterohepatic recirculation?

    <p>It is the process where drugs concentrated in bile are reabsorbed into the bloodstream.</p> Signup and view all the answers

    What impact does aluminum hydroxide have on stool color?

    <p>It changes the stool color to white.</p> Signup and view all the answers

    Which of the following drugs is NOT known to be excreted through breast milk?

    <p>Ibuprofen</p> Signup and view all the answers

    Which factor does NOT influence the rate of drug excretion through the lungs?

    <p>Type of drug administered</p> Signup and view all the answers

    What is a characteristic of drugs that undergo gastrointestinal excretion?

    <p>Some part of the dose is excreted in the feces.</p> Signup and view all the answers

    Which of the following measures total clearance (Ct) of a drug?

    <p>Ct = Ch + Cr + Cothers</p> Signup and view all the answers

    What is defined as the half-life (t1/2) of a drug?

    <p>The period for half of the drug to be metabolized and eliminated.</p> Signup and view all the answers

    Which of the following is NOT a common method for drug excretion?

    <p>Cerebral excretion</p> Signup and view all the answers

    Renal excretion primarily involves glomerular filtration, active tubular secretion, and passive tubular absorption.

    <p>False</p> Signup and view all the answers

    Drugs with a molecular weight greater than 300 daltons are typically excreted through the kidney.

    <p>False</p> Signup and view all the answers

    Active tubular secretion allows drugs to be transported from the plasma into the tubular lumen.

    <p>True</p> Signup and view all the answers

    The reabsorption of drugs in the renal system decreases when urine is acidic for basic drugs.

    <p>True</p> Signup and view all the answers

    Hepatobiliary excretion is primarily responsible for the elimination of unaltered drugs from the body.

    <p>False</p> Signup and view all the answers

    Glomerular filtration is influenced by the concentration of drug in the plasma, molecular size, and glomerular filtration rate.

    <p>True</p> Signup and view all the answers

    The degree of ionization of acidic drugs increases in alkaline urine, which promotes their reabsorption.

    <p>False</p> Signup and view all the answers

    Entrohepatic cycling can prolong the action of drugs eliminated via hepatobiliary excretion.

    <p>True</p> Signup and view all the answers

    Chloramphenicol and oral estrogen are only excreted through the kidneys.

    <p>False</p> Signup and view all the answers

    Tetracyclines can be used for the treatment of biliary tract infections due to their biliary excretion.

    <p>True</p> Signup and view all the answers

    Pulmonary excretion rates are unaffected by the volume of air exchange and drug concentration gradient.

    <p>False</p> Signup and view all the answers

    Pregnant women should be cautious about the intake of weak basic drugs due to their accumulation in breast milk.

    <p>False</p> Signup and view all the answers

    Half-life of a drug is only determined by the time taken for its concentration to decline to zero.

    <p>False</p> Signup and view all the answers

    Sweat can be a medium through which certain drugs are excreted, such as rifampicin and arsenic.

    <p>True</p> Signup and view all the answers

    Ferrous sulfate alters stool color to a bright yellow.

    <p>False</p> Signup and view all the answers

    Total clearance (Ct) of a drug is generally calculated using changes in renal clearance alone.

    <p>False</p> Signup and view all the answers

    What is the primary function of glomerular filtration in the context of renal drug excretion?

    <p>To remove drugs from the plasma into the urine based on drug concentration and molecular characteristics.</p> Signup and view all the answers

    How does the pH of urine affect the reabsorption of drugs in the renal system?

    <p>In acidic urine, the reabsorption of basic drugs decreases due to increased ionization.</p> Signup and view all the answers

    What role do hepatocytes play in the process of drug excretion?

    <p>Hepatocytes excrete conjugated drugs into the bile, especially those with a molecular weight over 300 daltons.</p> Signup and view all the answers

    Explain the significance of enterohepatic cycling in drug pharmacokinetics.

    <p>It can prolong the action of drugs by reabsorbing them back into the portal vein from the intestine after biliary excretion.</p> Signup and view all the answers

    What types of drugs are mainly subjected to active tubular secretion in the kidneys?

    <p>Primarily polar drugs and those with low molecular weight, such as acetazolamide and histamine.</p> Signup and view all the answers

    Describe how the molecular weight of a drug affects its mode of hepatobiliary excretion.

    <p>Drugs with a molecular weight greater than 300 daltons are typically excreted through the bile.</p> Signup and view all the answers

    What impact does renal impairment have on the routes of drug excretion?

    <p>Renal impairment limits drug elimination through the kidneys, increasing reliance on hepatobiliary excretion.</p> Signup and view all the answers

    How does passive tubular reabsorption function in the context of drug excretion?

    <p>It allows for the reabsorption of drugs from the renal tubules back into the plasma, depending on urine pH.</p> Signup and view all the answers

    Describe the impact of enterohepatic recirculation on drug duration of action.

    <p>Enterohepatic recirculation prolongs the duration of action of drugs by allowing them to be reabsorbed from the intestines back into the bloodstream, thus reducing their elimination.</p> Signup and view all the answers

    What crucial consideration should lactating mothers keep in mind regarding drug intake?

    <p>Lactating mothers should be cautious about taking weak basic drugs, as these can accumulate in breast milk and potentially harm the nursing infant.</p> Signup and view all the answers

    What physiological factors influence the rate of pulmonary drug excretion?

    <p>The rate of pulmonary drug excretion is influenced by the volume of air exchange, depth of respiration, rate of pulmonary blood flow, and concentration gradient of the drug.</p> Signup and view all the answers

    What happens to a portion of the drug administered orally that is not absorbed?

    <p>A portion of the orally administered drug that is not absorbed is excreted in the feces.</p> Signup and view all the answers

    How does the presence of aluminum hydroxide affect stool appearance?

    <p>Aluminum hydroxide causes the stool to turn white.</p> Signup and view all the answers

    How does the half-life of a drug relate to its drug elimination phases?

    <p>The half-life of a drug consists of two phases: the half-life of distribution and the half-life of elimination, reflecting how the drug concentration decreases in the body.</p> Signup and view all the answers

    Why should tetracyclines be considered for treating biliary tract infections?

    <p>Tetracyclines are effective for biliary tract infections because they are excreted by the biliary tract, concentrating in bile.</p> Signup and view all the answers

    Define total clearance (Ct) of a drug and its components.

    <p>Total clearance (Ct) of a drug is the sum of hepatic clearance (Ch), renal clearance (Cr), and clearance from other organs, indicating the overall elimination capacity.</p> Signup and view all the answers

    Major processes of drug excretion include renal excretion, hepatobiliary excretion, and ______ excretion.

    <p>pulmonary</p> Signup and view all the answers

    The major part of renal excretion involves processes such as glomerular filtration, active tubular secretion, and passive tubular ______.

    <p>reabsorption</p> Signup and view all the answers

    Drugs that are excreted slowly tend to maintain their concentration in the body for a ______ period.

    <p>longer</p> Signup and view all the answers

    Only drugs that are not bound to plasma proteins can pass through the ______.

    <p>glomerulus</p> Signup and view all the answers

    The excretion of conjugated drugs occurs in the bile through the ______.

    <p>hepatocytes</p> Signup and view all the answers

    When the urine is ______, the degree of ionization of basic drugs increases, leading to decreased reabsorption.

    <p>acidic</p> Signup and view all the answers

    Drugs with a molecular weight greater than 300 daltons are primarily excreted through the ______.

    <p>bile</p> Signup and view all the answers

    Entrohepatic cycling refers to the reabsorption of drugs back into the portal vein after being excreted in the ______.

    <p>bile</p> Signup and view all the answers

    Chloramphenicol and oral estrogen are secreted into ______ and largely reabsorbed.

    <p>bile</p> Signup and view all the answers

    Tetracyclines are excreted by the biliary tract and can be used for the treatment of ______ tract infection.

    <p>biliary</p> Signup and view all the answers

    In gastrointestinal excretion, a part of the drug is not absorbed and is excreted in the ______.

    <p>faeces</p> Signup and view all the answers

    Aluminium hydroxide changes the stool into ______ color.

    <p>white</p> Signup and view all the answers

    Drugs that are readily vaporized are excreted through the ______.

    <p>lungs</p> Signup and view all the answers

    Many drugs, mostly weak basic drugs, are accumulated into ______.

    <p>milk</p> Signup and view all the answers

    Half-life (t1/2) of a drug refers to the time taken for the concentration of the drug in blood to decline to ______ of its original value.

    <p>half</p> Signup and view all the answers

    Total clearance (Ct) will be calculated by Ct = Ch + Cr + ______

    <p>Cothers</p> Signup and view all the answers

    Match the following types of drug excretion with their characteristics:

    <p>Renal excretion = Involves glomerular filtration and active tubular secretion Hepatobiliary excretion = Involves the excretion of conjugated drugs through bile Pulmonary excretion = Excretion of drugs via breath Minor routes of excretion = Include saliva, sweat, and tears</p> Signup and view all the answers

    Match the following processes with their descriptions in renal excretion:

    <p>Glomerular filtration = Depends on molecular size, shape, and charge of drugs Active tubular secretion = Involves transport from plasma to tubular lumen Passive tubular reabsorption = Aims to retain drugs in the body Tubular reabsorption = Influenced by the pH of urine</p> Signup and view all the answers

    Match the following drugs with their excretion processes:

    <p>Acetazolamide = Active tubular secretion Benzyl penicillin = Active tubular secretion Digoxin = Renal excretion via glomerular filtration Lithium = Renal excretion influenced by tubular reabsorption</p> Signup and view all the answers

    Match the following terms with their definitions related to renal excretion:

    <p>Passive reabsorption = Retention of drugs back into the bloodstream Active secretion = Transport of drugs against their concentration gradient Filtration = Process requiring the drug to be unbound to plasma proteins Reabsorption dynamics = Altered by acidity or alkalinity of urine</p> Signup and view all the answers

    Match the following concepts with their significance in drug pharmacokinetics:

    <p>Glomerular filtration rate = Determines the efficiency of drug removal from the body Enterohepatic cycling = Extends the duration of action for certain drugs Molecular weight over 300 daltons = Typically indicates biliary excretion Urine pH = Influences ionization and reabsorption of drugs</p> Signup and view all the answers

    Match the following mechanisms of drug excretion with their effects:

    <p>Resorption in acidic urine = Decreases reabsorption of basic drugs Biliary excretion = Provides a backup during renal impairment Active tubular secretion = Increases the elimination of polar drugs Enterohepatic cycling = Causes a secondary absorption of drugs</p> Signup and view all the answers

    Match the following examples of drug excretion with their respective drug types:

    <p>Tetracyclines = Excreted through hepatobiliary system in biliary tract infections Ethambutol = Excreted through renal system via glomerular filtration Histamine = Transported by active tubular secretion Aluminum hydroxide = Can affect consistency and color of stool</p> Signup and view all the answers

    Match the following roles with their corresponding excretion processes:

    <p>Hepatocytes = Excrete conjugated drugs into bile Proximal convoluted tubule = Site for active tubular secretion Glomerular capillaries = Site for filtration of drugs into urine Distal convoluted tubule = Involves reabsorption of selectively ionized drugs</p> Signup and view all the answers

    Match the following drugs with their respective excretion routes:

    <p>Chloramphenicol = Biliary excretion Rifampicin = Sweat Ampicillin = Mammary excretion Tetracyclines = Biliary tract excretion</p> Signup and view all the answers

    Match the following physiological processes with their descriptions:

    <p>Gastrointestinal excretion = Drug excretion in feces after oral administration Pulmonary excretion = Excretion of vaporized drugs through the lungs Enterohepatic recirculation = Reabsorption of drugs from intestines into bloodstream Mammary excretion = Accumulation of drugs in breast milk</p> Signup and view all the answers

    Match the following drug effects with their excretion-related changes in stool color:

    <p>Aluminium hydroxide = White stool Ferrous sulfate = Black stool Rifampicin = Orange-red stool Furosemide = No specific color change</p> Signup and view all the answers

    Match the following clearance types with their definitions:

    <p>Ct = Total clearance of a drug Ch = Hepatic clearance Cr = Renal clearance Cothers = Clearance by other organs</p> Signup and view all the answers

    Match the following terms with their explanations:

    <p>Half-life (t1/2) = Time taken for drug concentration to decline by half Active tubular secretion = Transport of drugs from plasma into tubular lumen Passive tubular reabsorption = Reabsorption of drugs back into the bloodstream Total clearance (Ct) = Sum of all clearance rates from various routes</p> Signup and view all the answers

    Match the following inhalation substances with their specific properties related to excretion:

    <p>Inhalation anesthetics = Excreted through lungs Alcohol = Readily vaporized and excreted via breath Narcotics = Often not excreted via the pulmonary route Chloroform = Known for its rapid excretion through respiratory system</p> Signup and view all the answers

    Match the following drug classes with their notable excretion characteristics:

    <p>Weak basic drugs = Accumulated in breast milk Heavy metals = Excreted through sweat Anaesthetics = Excreted through lung vaporization Tetracyclines = Used for treating biliary tract infections</p> Signup and view all the answers

    Match the following clinical considerations with their associated drugs:

    <p>Lactating mothers = Caution with ampicillin and diazepam Renal impairment = Alters drug excretion and reabsorption Pulmonary diseases = May affect excretion rate of inhalation drugs Chronic biliary infections = Consider using tetracyclines</p> Signup and view all the answers

    Study Notes

    Excretion of Drugs

    • Excretion involves the removal of drugs from the body, terminating their pharmacological activity.
    • Major excretion routes:
      • Renal excretion
      • Hepatobiliary excretion
      • Pulmonary excretion
    • Minor routes include saliva, sweat, tears, breast milk, vaginal fluid, nails, and hair.
    • Excretion rate affects drug duration and concentration in the body; slow excretion maintains drug effects longer.

    Renal Excretion

    • Key processes:
      • Glomerular filtration
      • Active tubular secretion
      • Passive tubular reabsorption
    • Glomerular filtration removes drugs based on:
      • Plasma drug concentration
      • Drug's molecular size, shape, and charge
      • Glomerular filtration rate (GFR)
    • Only unbound drugs (not bound to plasma proteins) pass through the glomerulus, e.g., digoxin and ethambutol.
    • Active tubular secretion transfers drugs from plasma to tubular lumen; examples include acetazolamide and benzyl penicillin.
    • Tubular reabsorption occurs in distal convoluted tubules; influenced by urine pH—acidic urine decreases basic drug reabsorption and vice versa.

    Hepatobiliary Excretion

    • Conjugated drugs are excreted by hepatocytes into bile; polar drugs over 300 daltons are also expelled through the bile.
    • The hepatobiliary route provides an alternative when renal function is compromised.
    • Bile excretion can lead to enterohepatic recirculation, prolonging drug action, seen in chloramphenicol and oral estrogens.
    • Biliary excretion can treat biliary tract infections with drugs like tetracyclines.

    Gastrointestinal Excretion

    • Oral drugs may remain unabsorbed and are excreted in feces.
    • Drugs without enterohepatic cycling are eliminated through stool, affecting stool color (e.g., aluminum hydroxide, ferrous sulfate).

    Pulmonary Excretion

    • Vaporized drugs, including inhalation anesthetics and alcohols, are excreted via the lungs.
    • Excretion rate through lungs is influenced by air exchange volume, respiration depth, pulmonary blood flow, and drug concentration gradient.

    Other Excretion Routes

    • Sweat: Drugs can be excreted through sweat via diffusion or active secretion (e.g., rifampicin, arsenic).
    • Mammary Excretion: Weak basic drugs can accumulate in breast milk, posing risks to lactating infants (e.g., ampicillin, aspirin, morphine).

    Clearance and Half-Life

    • Clearance is the volume of plasma devoid of the drug through metabolism (hepatic) and excretion (renal).
    • Total clearance formula:
      • Ct = Ch + Cr + C(other organs)
    • Half-life (t1/2) is the time required for blood/plasma drug concentration to reduce by half; consists of:
      • Half-life of distribution
      • Half-life of elimination.

    Excretion of Drugs

    • Excretion involves the removal of drugs from the body, terminating their pharmacological activity.
    • Major excretion routes:
      • Renal excretion
      • Hepatobiliary excretion
      • Pulmonary excretion
    • Minor routes include saliva, sweat, tears, breast milk, vaginal fluid, nails, and hair.
    • Excretion rate affects drug duration and concentration in the body; slow excretion maintains drug effects longer.

    Renal Excretion

    • Key processes:
      • Glomerular filtration
      • Active tubular secretion
      • Passive tubular reabsorption
    • Glomerular filtration removes drugs based on:
      • Plasma drug concentration
      • Drug's molecular size, shape, and charge
      • Glomerular filtration rate (GFR)
    • Only unbound drugs (not bound to plasma proteins) pass through the glomerulus, e.g., digoxin and ethambutol.
    • Active tubular secretion transfers drugs from plasma to tubular lumen; examples include acetazolamide and benzyl penicillin.
    • Tubular reabsorption occurs in distal convoluted tubules; influenced by urine pH—acidic urine decreases basic drug reabsorption and vice versa.

    Hepatobiliary Excretion

    • Conjugated drugs are excreted by hepatocytes into bile; polar drugs over 300 daltons are also expelled through the bile.
    • The hepatobiliary route provides an alternative when renal function is compromised.
    • Bile excretion can lead to enterohepatic recirculation, prolonging drug action, seen in chloramphenicol and oral estrogens.
    • Biliary excretion can treat biliary tract infections with drugs like tetracyclines.

    Gastrointestinal Excretion

    • Oral drugs may remain unabsorbed and are excreted in feces.
    • Drugs without enterohepatic cycling are eliminated through stool, affecting stool color (e.g., aluminum hydroxide, ferrous sulfate).

    Pulmonary Excretion

    • Vaporized drugs, including inhalation anesthetics and alcohols, are excreted via the lungs.
    • Excretion rate through lungs is influenced by air exchange volume, respiration depth, pulmonary blood flow, and drug concentration gradient.

    Other Excretion Routes

    • Sweat: Drugs can be excreted through sweat via diffusion or active secretion (e.g., rifampicin, arsenic).
    • Mammary Excretion: Weak basic drugs can accumulate in breast milk, posing risks to lactating infants (e.g., ampicillin, aspirin, morphine).

    Clearance and Half-Life

    • Clearance is the volume of plasma devoid of the drug through metabolism (hepatic) and excretion (renal).
    • Total clearance formula:
      • Ct = Ch + Cr + C(other organs)
    • Half-life (t1/2) is the time required for blood/plasma drug concentration to reduce by half; consists of:
      • Half-life of distribution
      • Half-life of elimination.

    Excretion of Drugs

    • Excretion involves the removal of drugs from the body, terminating their pharmacological activity.
    • Major excretion routes:
      • Renal excretion
      • Hepatobiliary excretion
      • Pulmonary excretion
    • Minor routes include saliva, sweat, tears, breast milk, vaginal fluid, nails, and hair.
    • Excretion rate affects drug duration and concentration in the body; slow excretion maintains drug effects longer.

    Renal Excretion

    • Key processes:
      • Glomerular filtration
      • Active tubular secretion
      • Passive tubular reabsorption
    • Glomerular filtration removes drugs based on:
      • Plasma drug concentration
      • Drug's molecular size, shape, and charge
      • Glomerular filtration rate (GFR)
    • Only unbound drugs (not bound to plasma proteins) pass through the glomerulus, e.g., digoxin and ethambutol.
    • Active tubular secretion transfers drugs from plasma to tubular lumen; examples include acetazolamide and benzyl penicillin.
    • Tubular reabsorption occurs in distal convoluted tubules; influenced by urine pH—acidic urine decreases basic drug reabsorption and vice versa.

    Hepatobiliary Excretion

    • Conjugated drugs are excreted by hepatocytes into bile; polar drugs over 300 daltons are also expelled through the bile.
    • The hepatobiliary route provides an alternative when renal function is compromised.
    • Bile excretion can lead to enterohepatic recirculation, prolonging drug action, seen in chloramphenicol and oral estrogens.
    • Biliary excretion can treat biliary tract infections with drugs like tetracyclines.

    Gastrointestinal Excretion

    • Oral drugs may remain unabsorbed and are excreted in feces.
    • Drugs without enterohepatic cycling are eliminated through stool, affecting stool color (e.g., aluminum hydroxide, ferrous sulfate).

    Pulmonary Excretion

    • Vaporized drugs, including inhalation anesthetics and alcohols, are excreted via the lungs.
    • Excretion rate through lungs is influenced by air exchange volume, respiration depth, pulmonary blood flow, and drug concentration gradient.

    Other Excretion Routes

    • Sweat: Drugs can be excreted through sweat via diffusion or active secretion (e.g., rifampicin, arsenic).
    • Mammary Excretion: Weak basic drugs can accumulate in breast milk, posing risks to lactating infants (e.g., ampicillin, aspirin, morphine).

    Clearance and Half-Life

    • Clearance is the volume of plasma devoid of the drug through metabolism (hepatic) and excretion (renal).
    • Total clearance formula:
      • Ct = Ch + Cr + C(other organs)
    • Half-life (t1/2) is the time required for blood/plasma drug concentration to reduce by half; consists of:
      • Half-life of distribution
      • Half-life of elimination.

    Excretion of Drugs

    • Excretion involves the removal of drugs from the body, terminating their pharmacological activity.
    • Major excretion routes:
      • Renal excretion
      • Hepatobiliary excretion
      • Pulmonary excretion
    • Minor routes include saliva, sweat, tears, breast milk, vaginal fluid, nails, and hair.
    • Excretion rate affects drug duration and concentration in the body; slow excretion maintains drug effects longer.

    Renal Excretion

    • Key processes:
      • Glomerular filtration
      • Active tubular secretion
      • Passive tubular reabsorption
    • Glomerular filtration removes drugs based on:
      • Plasma drug concentration
      • Drug's molecular size, shape, and charge
      • Glomerular filtration rate (GFR)
    • Only unbound drugs (not bound to plasma proteins) pass through the glomerulus, e.g., digoxin and ethambutol.
    • Active tubular secretion transfers drugs from plasma to tubular lumen; examples include acetazolamide and benzyl penicillin.
    • Tubular reabsorption occurs in distal convoluted tubules; influenced by urine pH—acidic urine decreases basic drug reabsorption and vice versa.

    Hepatobiliary Excretion

    • Conjugated drugs are excreted by hepatocytes into bile; polar drugs over 300 daltons are also expelled through the bile.
    • The hepatobiliary route provides an alternative when renal function is compromised.
    • Bile excretion can lead to enterohepatic recirculation, prolonging drug action, seen in chloramphenicol and oral estrogens.
    • Biliary excretion can treat biliary tract infections with drugs like tetracyclines.

    Gastrointestinal Excretion

    • Oral drugs may remain unabsorbed and are excreted in feces.
    • Drugs without enterohepatic cycling are eliminated through stool, affecting stool color (e.g., aluminum hydroxide, ferrous sulfate).

    Pulmonary Excretion

    • Vaporized drugs, including inhalation anesthetics and alcohols, are excreted via the lungs.
    • Excretion rate through lungs is influenced by air exchange volume, respiration depth, pulmonary blood flow, and drug concentration gradient.

    Other Excretion Routes

    • Sweat: Drugs can be excreted through sweat via diffusion or active secretion (e.g., rifampicin, arsenic).
    • Mammary Excretion: Weak basic drugs can accumulate in breast milk, posing risks to lactating infants (e.g., ampicillin, aspirin, morphine).

    Clearance and Half-Life

    • Clearance is the volume of plasma devoid of the drug through metabolism (hepatic) and excretion (renal).
    • Total clearance formula:
      • Ct = Ch + Cr + C(other organs)
    • Half-life (t1/2) is the time required for blood/plasma drug concentration to reduce by half; consists of:
      • Half-life of distribution
      • Half-life of elimination.

    Excretion of Drugs

    • Excretion involves the removal of drugs from the body, terminating their pharmacological activity.
    • Major excretion routes:
      • Renal excretion
      • Hepatobiliary excretion
      • Pulmonary excretion
    • Minor routes include saliva, sweat, tears, breast milk, vaginal fluid, nails, and hair.
    • Excretion rate affects drug duration and concentration in the body; slow excretion maintains drug effects longer.

    Renal Excretion

    • Key processes:
      • Glomerular filtration
      • Active tubular secretion
      • Passive tubular reabsorption
    • Glomerular filtration removes drugs based on:
      • Plasma drug concentration
      • Drug's molecular size, shape, and charge
      • Glomerular filtration rate (GFR)
    • Only unbound drugs (not bound to plasma proteins) pass through the glomerulus, e.g., digoxin and ethambutol.
    • Active tubular secretion transfers drugs from plasma to tubular lumen; examples include acetazolamide and benzyl penicillin.
    • Tubular reabsorption occurs in distal convoluted tubules; influenced by urine pH—acidic urine decreases basic drug reabsorption and vice versa.

    Hepatobiliary Excretion

    • Conjugated drugs are excreted by hepatocytes into bile; polar drugs over 300 daltons are also expelled through the bile.
    • The hepatobiliary route provides an alternative when renal function is compromised.
    • Bile excretion can lead to enterohepatic recirculation, prolonging drug action, seen in chloramphenicol and oral estrogens.
    • Biliary excretion can treat biliary tract infections with drugs like tetracyclines.

    Gastrointestinal Excretion

    • Oral drugs may remain unabsorbed and are excreted in feces.
    • Drugs without enterohepatic cycling are eliminated through stool, affecting stool color (e.g., aluminum hydroxide, ferrous sulfate).

    Pulmonary Excretion

    • Vaporized drugs, including inhalation anesthetics and alcohols, are excreted via the lungs.
    • Excretion rate through lungs is influenced by air exchange volume, respiration depth, pulmonary blood flow, and drug concentration gradient.

    Other Excretion Routes

    • Sweat: Drugs can be excreted through sweat via diffusion or active secretion (e.g., rifampicin, arsenic).
    • Mammary Excretion: Weak basic drugs can accumulate in breast milk, posing risks to lactating infants (e.g., ampicillin, aspirin, morphine).

    Clearance and Half-Life

    • Clearance is the volume of plasma devoid of the drug through metabolism (hepatic) and excretion (renal).
    • Total clearance formula:
      • Ct = Ch + Cr + C(other organs)
    • Half-life (t1/2) is the time required for blood/plasma drug concentration to reduce by half; consists of:
      • Half-life of distribution
      • Half-life of elimination.

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    Test your knowledge on the mechanisms and processes involved in the excretion of drugs from the body. This quiz covers major and minor routes of drug excretion, their impact on drug activity, and factors influencing excretion rates. Challenge yourself to understand how the body eliminates drugs effectively.

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