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WorksheetsIntroduction to Drug Excretion
Total questions: 68
Worksheet time: 34mins
Which statement best defines drug excretion in the context of this lesson?
The chemical conversion of a drug into active metabolites
The passage of absorbed drugs and their metabolites out of the body
The transport of drugs from the site of administration into the bloodstream
The binding of drugs to plasma proteins to prevent filtration
A patient has high plasma protein binding for a particular drug. Based on glomerular filtration principles, which outcome is most likely?
Increased filtration because protein-bound drug passes freely
Decreased filtration because only free drug is filtered
No change in filtration because binding does not affect glomerular pores
Complete elimination as unchanged drug regardless of binding
Which statement best describes tubular reabsorption of drugs in the kidney?
It is an active transport process independent of drug properties.
It occurs mainly by passive diffusion influenced by lipid solubility, drug ionization (pKa), and urine pH.
It relies solely on glomerular filtration rate and protein binding.
It depends only on hepatic enzyme activity.
Clinically, why is sodium bicarbonate administered in salicylate or barbiturate poisoning?
To acidify urine and increase reabsorption of weak acids
To alkalinize urine and enhance excretion of weakly acidic drugs
To inhibit tubular secretion of all drugs
To increase lipid solubility of morphine
Urine is generally acidic. Which consequence follows from this regarding weak acids and bases?
Weakly acidic drugs have more chance of reabsorption; acidifying urine with ascorbic acid increases morphine excretion.
Weakly basic drugs have more chance of reabsorption; alkalinizing urine with sodium bicarbonate reduces salicylate elimination.
Weakly acidic drugs have more chance of reabsorption; alkalinizing urine can increase elimination of salicylates, while acidifying urine can increase excretion of morphine.
Urine pH does not affect reabsorption or excretion of drugs.
Which statement best describes tubular secretion in renal drug excretion?
A passive diffusion process in distal tubules
An energy-requiring, carrier-mediated active transport in proximal tubules
A filtration process driven by blood pressure at the glomerulus
A process limited to protein-bound drugs only
Which transporter primarily handles organic acids during tubular secretion?
OATP
OCT
OAT
P-glycoprotein
Which drug is MOST appropriately classified as a substrate for organic base transport (OCT) during tubular secretion?
Penicillin
Probenecid
Salicylates
Morphine
A patient taking methotrexate begins high-dose aspirin therapy. Based on competition for tubular secretion, what is the most likely effect on methotrexate?
Increased tubular secretion and decreased toxicity
Decreased tubular secretion and potential accumulation
No change in renal handling
Enhanced glomerular filtration only
Probenecid is an organic acid with high affinity for which tubular transport system, leading to reduced active transport of penicillin and uric acid?
OAT (organic anion/acid transporter)
OCT (organic cation/base transporter)
P-glycoprotein efflux pump
Na+/K+ ATPase
Quinidine’s inhibition of p-glycoprotein will most directly cause which effect on digoxin?
Increased renal and biliary clearance of digoxin
Decreased renal and biliary clearance of digoxin
No effect on digoxin disposition
Conversion of digoxin to inactive metabolites in the kidney
Which list correctly groups drugs predominantly transported by the OAT system?
Morphine, quinidine, procaine, thiazides
Penicillin, probenecid, uric acid, salicylates, indomethacin
Furosemide, morphine, procaine
Digoxin, quinidine, aspirin
Which renal process primarily decreases the amount of a drug in the tubular fluid by moving it back into blood?
Glomerular filtration
Tubular reabsorption
Tubular secretion
Biliary excretion
Penicillin, an exogenous substance, is mainly cleared by which renal mechanism under normal conditions?
Glomerular filtration only
Tubular reabsorption
Active tubular secretion
Passive diffusion into urine
What is the effect of probenecid on penicillin handling by the kidney?
Enhances tubular secretion of penicillin, increasing excretion
Prevents tubular secretion of penicillin, causing retention
Increases glomerular filtration of penicillin
Promotes tubular reabsorption of penicillin, increasing excretion
Uric acid is primarily subject to which renal process, according to the diagram?
Active tubular secretion leading to excretion
Tubular reabsorption leading to retention
Glomerular filtration with no further handling
Biliary secretion
Probenecid alters uric acid handling in what way?
Stimulates reabsorption so uric acid is retained
Blocks reabsorption so uric acid is excreted
Blocks secretion so uric acid is retained
Stimulates secretion so uric acid is retained
Which transporter family is most directly associated with active secretion of organic acids such as penicillin?
OCT (Organic Cation Transport)
OAT (Organic Anion Transport)
P-glycoprotein in bile
GLUT glucose transporters
Renal elimination of weak acids can be enhanced by altering urine pH in which direction?
Acidifying urine to increase nonionized form
Alkalinizing urine to increase ionized form and reduce reabsorption
Maintaining neutral pH to maximize passive diffusion
pH adjustments do not affect weak acids
Which intervention from the slide directly increases urine flow and thus can enhance renal elimination?
Probenecid
Diuretics
Beta blockers
Proton pump inhibitors
Which drug is classically used to competitively inhibit tubular secretion of penicillin, thereby prolonging its plasma levels?
Probenecid
Aspirin
Quinidine
Acetaminophen
A patient taking low-dose aspirin and probenecid develops higher plasma salicylate levels than expected. The most likely mechanism is:
Enhanced glomerular filtration of aspirin
Inhibition of hepatic CYP enzymes by probenecid
Competition for organic anion transporters in proximal tubular secretion
Increased biliary excretion of aspirin conjugates
Quinidine increases plasma concentrations of digoxin primarily by which renal mechanism?
Induction of P-glycoprotein in the gut
Competition for tubular secretion transporters reducing digoxin clearance
Increased reabsorption in the collecting duct due to pH trapping
Enhanced biliary secretion via OATP
Which statement best describes the effect of probenecid on uric acid handling in the kidney when used chronically for gout?
It increases uric acid reabsorption via URAT1
It decreases uric acid reabsorption, enhancing urinary excretion
It blocks glomerular filtration of uric acid
It alkalinizes urine to increase uric acid solubility
A patient receiving intravenous penicillin for a severe infection is also given a second drug to maintain higher penicillin levels between doses. Which co-therapy is most appropriate and why?
Aspirin; it blocks hepatic metabolism of penicillin
Probenecid; it competes for renal organic anion transporters, slowing tubular secretion
Quinidine; it inhibits glomerular filtration of penicillin
Acetazolamide; it acidifies urine and reduces penicillin excretion
Which intervention directly enhances renal elimination of weakly acidic drugs by increasing their ionization in the renal tubules?
Administration of a loop diuretic
Alkalinization of urine
Acidification of urine
Inhibition of tubular secretion
A patient has taken a toxic dose of a weak base. Which strategy is most appropriate to enhance renal clearance?
Acidify the urine and consider using a diuretic to increase flow
Alkalinize the urine to trap the base in its ionized form
Administer a potassium-sparing diuretic only
Reduce urine flow to increase reabsorption time
Which statement best describes biliary excretion in drug elimination?
Active transport of drugs and metabolites from hepatocytes into bile for fecal elimination
Passive diffusion of drugs from the kidney into urine
Enzymatic breakdown of drugs in the stomach prior to absorption
Filtration of drugs through glomeruli followed by tubular secretion
Enterohepatic circulation most directly increases which pharmacokinetic feature of a drug?
Clearance
Half-life
Protein binding at the site of action
Volume of distribution
A polar drug conjugated as a glucuronide in the liver is secreted into bile. In the intestine, bacterial enzymes hydrolyze the conjugate and the parent drug is reabsorbed. Which transporters are primarily involved in the original hepatic uptake from blood?
OATP and OCT families
P-glycoprotein only
SGLT and GLUT transporters
CFTR chloride channel
Which property most favors a drug’s biliary excretion and participation in enterohepatic cycling?
Low molecular weight and high lipophilicity
High molecular weight and polarity (e.g., glucuronides)
Extensive renal filtration with low protein binding
Rapid pulmonary diffusion due to volatility
A drug shows secondary peaks in its plasma concentration–time profile several hours after dosing. Which is the most plausible explanation?
Saturable renal secretion
Enterohepatic reabsorption after biliary excretion
Autoinduction of hepatic CYP enzymes
Formation of insoluble precipitates in plasma
Which scenario would most likely reduce enterohepatic circulation of a drug that undergoes biliary excretion as a glucuronide?
Co-administration of a broad-spectrum antibiotic that suppresses gut flora
Inhibition of renal organic anion transporters (OAT)
Increased gastric emptying rate
Administration with a high-fat meal
Organic cation transporter (OCT) and organic anion transporting polypeptide (OATP) in the liver primarily contribute to which step relevant to biliary excretion?
Uptake of drugs from portal blood into hepatocytes
Efflux of drugs from hepatocytes into bile canaliculi
Hydrolysis of drug-glucuronide conjugates
Reabsorption of drugs from the intestine
Which route primarily eliminates volatile anaesthetics from the body?
Renal excretion in urine
Alveolar exhalation via lungs
Biliary secretion into bile
Faecal bacterial metabolism
Faecal excretion most commonly accounts for elimination of which drug fraction?
Highly protein-bound drugs absorbed systemically
Unabsorbed drugs remaining in the gut lumen
Drugs actively secreted into sweat glands
Volatile substances dissolved in plasma
Alcohol presence in breath has medico-legal importance primarily because it reflects:
Hepatic conjugation rate
Renal clearance ratio
Alveolar excretion proportional to blood levels
Enterohepatic recirculation extent
A patient receives a volatile general anaesthetic. Which elimination pattern best predicts its recovery profile?
Predominantly renal clearance with active secretion
Hepatic biotransformation followed by faecal loss
Rapid alveolar washout depending on ventilation and blood–gas solubility
Slow sweat gland excretion independent of pulmonary function
Which scenario best exemplifies faecal excretion by direct secretion rather than non-absorption?
Drug passes through gut unabsorbed and is expelled in stool
Drug is taken up by hepatocytes and secreted into the intestinal tract via bile
Drug is exhaled unchanged through lungs
Drug accumulates in adipose tissue and slowly redistributes
Why can breath analysis be used to estimate recent alcohol intake?
Alcohol is actively pumped into saliva
Alcohol undergoes enterohepatic cycling
Alcohol is volatile and undergoes alveolar excretion correlated with blood alcohol concentration
Alcohol binds strongly to faecal matter
Which substance is classically detectable in hair due to follicular deposition through minor excretion routes?
Arsenic
Insulin
Heparin
Nitrous oxide
A patient on rifampicin notices orange-red discoloration of sweat and saliva. Which excretion routes explain these findings?
Renal only
Biliary only
Skin and salivary excretion
Pulmonary excretion
Select the minor excretion route most relevant for long-term forensic detection of arsenic exposure.
Sweat
Hair follicles
Saliva
Expired air
A clinician wants a noninvasive body fluid to monitor drug presence when urine testing is impractical. Which specimen best reflects rifampicin excretion via a minor route?
Cerebrospinal fluid
Saliva
Peritoneal fluid
Synovial fluid
Which property increases a drug’s passage into breast milk and thus the infant’s exposure?
High lipid solubility
High protein binding
Strong ionization at milk pH
Large molecular size
Breast milk is slightly more acidic than plasma. For a weakly basic drug, what is the likely effect on its concentration in milk?
It concentrates in milk due to ion trapping
It is excluded from milk
It precipitates and is not absorbed by the infant
Its concentration equals that in plasma
Which factor most directly lowers the free (transferable) fraction of a drug into milk?
High maternal protein binding
High lipid solubility
Alkaline milk pH
Enterohepatic recycling
Which drug class is generally considered compatible with breastfeeding when used in standard therapeutic doses?
Penicillins and cephalosporins
Antineoplastics (e.g., cyclophosphamide)
Ergot alkaloids (e.g., ergotamine)
Radioactive iodine
A lactating patient requires migraine therapy. Which medication is contraindicated due to risk of ergotism and suppression of lactation?
Sumatriptan
Ergotamine
Acetaminophen
Ibuprofen
Which maternal medication is contraindicated in lactation because it can cause fetal/neonatal goitre?
Levothyroxine
Iodides (e.g., radioactive iodine)
Propranolol
Amoxicillin
Which strategy best minimizes infant exposure when a necessary but potentially risky drug must be taken during lactation?
Dose immediately before the longest infant sleep interval and use the lowest effective dose
Increase dosing frequency to spread exposure evenly
Breastfeed immediately after each dose to dilute drug in milk
Avoid timing; exposure is unaffected by dosing schedule
Which combination best describes drugs most likely to accumulate in breast milk and affect the infant?
Lipid-soluble, weak bases with low protein binding
Hydrophilic, weak acids with high protein binding
Highly ionized, large molecules
Drugs extensively metabolized before reaching milk
Which statement best describes how excretion pattern influences therapeutic effect for weak acids and bases when urine is alkalinized or acidified?
Alkalinizing urine increases reabsorption of weak acids, prolonging their effect
Alkalinizing urine enhances excretion of weak acids, reducing their effect
Acidifying urine enhances excretion of weak acids, reducing their effect
Acidifying urine has no impact on the excretion of weak bases
A patient with renal failure is prescribed a drug that is primarily renally excreted and known to accumulate in kidney dysfunction. What is the most appropriate dosing strategy?
Maintain the same dose and frequency
Increase the dose to overcome reduced excretion
Reduce dose or extend dosing interval to prevent accumulation
Switch to IV route to avoid accumulation
Which scenario most likely increases the risk of nephrotoxicity in renal failure?
Using a hepatically cleared drug at standard dose
Administering a renally excreted drug without dosage adjustment
Alkalinizing urine during therapy with a weak base
Acidifying urine during therapy with a weak acid
Alkalinizing the urine is clinically used to accelerate elimination of which type of drugs?
Weak acids
Weak bases
Highly lipophilic neutral drugs
Protein-bound drugs only
In renal failure, why might extending the dosing interval be preferred over reducing the single dose for certain drugs?
It avoids changes in peak concentration while allowing more time for excretion
It eliminates the need to monitor renal function
It increases therapeutic effect by causing drug accumulation
It converts the drug to hepatic elimination
Which practice aligns with preventing toxicity when a drug is known to accumulate in renal impairment?
Dose according to usual creatinine clearance
Base dosing on estimated GFR or creatinine clearance and adjust accordingly
Ignore urine pH and focus only on route of administration
Prefer acidifying urine for all renally excreted drugs
Which statement best defines first-order kinetics of drug elimination as presented?
A constant amount of drug is eliminated per unit time regardless of concentration.
A constant fraction of drug is eliminated per unit time, so the rate increases with concentration.
Elimination occurs only after enzymes are saturated.
The clearance decreases as plasma concentration rises.
In first-order kinetics, if plasma concentration doubles, what happens to the rate of elimination?
It stays the same because a fixed amount is removed.
It halves because clearance is constant.
It doubles because a constant fraction is removed.
It becomes zero due to saturation.
According to the provided relationship CL = Rate of Elimination / Concentration for first-order kinetics, what remains constant as concentration changes?
Clearance (CL)
Rate of elimination
Half-life
Volume of distribution
A diagram shows organs of drug elimination removing 500 μg per minute from plasma with 10 μg/mL concentration, yielding CL = 500 μg/min ÷ 10 μg/mL. What is the calculated clearance?
5 mL/min
10 mL/min
50 mL/min
500 mL/min
Which scenario most closely represents zero-order kinetics rather than first-order kinetics?
Elimination rate increases as plasma concentration increases.
A constant fraction of the drug is removed per unit time.
The same amount of drug is removed per unit time regardless of concentration.
Clearance remains constant over a wide concentration range.
If a drug follows first-order kinetics at a plasma concentration of 10 μg/mL with a clearance of 50 mL/min, what is the expected rate of elimination?
5 μg/min
50 μg/min
250 μg/min
500 μg/min
Which statement best defines drug clearance in pharmacokinetics?
The percentage of drug bound to plasma proteins
The theoretical volume of plasma cleared of drug per unit time
The total amount of drug eliminated from the body
The time required for the plasma concentration to fall by half
According to the standard clearance relationship, which formula correctly expresses clearance (Cl)?
Cl = Concentration × Volume of distribution
Cl = Rate of elimination ÷ Plasma concentration
Cl = Half-life × Plasma concentration
Cl = Bioavailability ÷ Dose
A drug is eliminated at a constant rate of 25 mg/min when its steady plasma concentration is 5 mg/L. What is the clearance? Choose the best answer and units.
5 L/min
125 L/min
0.2 L/min
25 L/min
Which units are most appropriate for expressing drug clearance?
mg/L
L/min
mg/min
L
