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Questions and Answers
What is the primary characteristic of excretion, distinguishing it from other elimination processes?
What is the primary characteristic of excretion, distinguishing it from other elimination processes?
- It occurs exclusively through biliary routes.
- It is the removal of a drug molecule without chemical modification. (correct)
- It requires active transport mechanisms in the kidneys.
- It involves the metabolism of the drug molecule.
Which factor primarily determines whether a drug will be filtered in the glomerulus?
Which factor primarily determines whether a drug will be filtered in the glomerulus?
- The drug's size and protein binding characteristics. (correct)
- The drug's affinity for active secretion transporters.
- The extent to which the drug is metabolized by liver enzymes.
- The pH of the urine.
What is the approximate glomerular filtration rate (GFR) in a healthy adult?
What is the approximate glomerular filtration rate (GFR) in a healthy adult?
- 1 mL/min
- 650 mL/min
- 12.5 mL/min
- 125 mL/min (correct)
Which process in the kidney is responsible for the reabsorption of 99% of water?
Which process in the kidney is responsible for the reabsorption of 99% of water?
How does active secretion contribute to renal drug elimination?
How does active secretion contribute to renal drug elimination?
In the context of renal drug elimination, what does 'ion trapping' refer to?
In the context of renal drug elimination, what does 'ion trapping' refer to?
Probenecid can reduce the clearance of penicillin by what mechanism?
Probenecid can reduce the clearance of penicillin by what mechanism?
What is indicated by a drug having a renal clearance value greater than the glomerular filtration rate (GFR)?
What is indicated by a drug having a renal clearance value greater than the glomerular filtration rate (GFR)?
Why is creatinine clearance used to estimate GFR?
Why is creatinine clearance used to estimate GFR?
Which factors influence serum creatinine concentration?
Which factors influence serum creatinine concentration?
What is the primary limitation for biliary excretion of drugs?
What is the primary limitation for biliary excretion of drugs?
What structural modification to a drug typically enhances its biliary excretion?
What structural modification to a drug typically enhances its biliary excretion?
What is the role of bacteria in the colon regarding enterohepatic circulation?
What is the role of bacteria in the colon regarding enterohepatic circulation?
For which type of drug is pulmonary excretion most significant?
For which type of drug is pulmonary excretion most significant?
What distinguishes drug excretion into mammary milk from other excretion processes?
What distinguishes drug excretion into mammary milk from other excretion processes?
Why might a drug's presence in breast milk be clinically significant?
Why might a drug's presence in breast milk be clinically significant?
How does the concentration of neutral molecules in saliva relate to their concentration in plasma?
How does the concentration of neutral molecules in saliva relate to their concentration in plasma?
What is a primary challenge in using saliva to measure drug concentrations?
What is a primary challenge in using saliva to measure drug concentrations?
According to the Cockcroft & Gault equation, what patient characteristics are required to estimate creatinine clearance?
According to the Cockcroft & Gault equation, what patient characteristics are required to estimate creatinine clearance?
A patient with barbiturate overdose may be given sodium bicarbonate; how does this affect drug elimination?
A patient with barbiturate overdose may be given sodium bicarbonate; how does this affect drug elimination?
Flashcards
Excretion
Excretion
Removal of a drug from the body without chemical change, often via the kidneys.
Elimination by the kidney
Elimination by the kidney
Kidney filters blood, reabsorbing essentials and excreting waste as urine in two stages: glomerular filtration and tubular reabsorption/secretion.
Glomerular filtration
Glomerular filtration
Passive pressure-driven filtration where small molecules pass; large molecules and most proteins do not.
Active secretion
Active secretion
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Reabsorption
Reabsorption
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Ion trapping
Ion trapping
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High renal clearance
High renal clearance
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Low renal clearance
Low renal clearance
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Creatinine clearance
Creatinine clearance
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Pulmonary excretion
Pulmonary excretion
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Mammary excretion
Mammary excretion
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Study Notes
Excretion
- Removal of a drug molecule from the body without chemical modification.
- Occurs following IV administration
- Metabolism does not take place during excretion
- Elimination occurs 100% through renal excretion
Elimination by the Kidney
- Involves excretion
Glomerular Filtration
- Glomerular structure, size constraints, and protein binding influence this process
Tubular Reabsorption/Secretion
- Includes acidification/alkalinization
- Involves active transport
Kidney Function
- Glomerular Filtration Rate (GFR) is 125ml/min
- Plasma flow is 650ml/min
- Results in urine output of 1ml/min
- Filtration results in 99% reabsorption of H2O along with lipid-soluble drugs
- Active secretion involves acid and base
Glomerular Filtration
- Passive and pressure-driven
- 20% of plasma volume is filtered
- Small molecules are filtered
- Large molecules are not filtered
- Most proteins are not filtered
- Drugs extensively bound to proteins are also not filtered
Active Secretion
- Requires energy
- Can generate positive concentration gradients
- Involves two separate mechanisms for acids and bases
- Saturable process
- Potential for interactions
Acids and Bases
- Acids include frusemide, penicillins, and probenecid
- Bases include quinine, quaternary ammonium salts
Probenecid and Penicillins
- Share the same mechanisms
- Probenecid competes with penicillins
- Penicillin clearance is reduced because of competition
Renal Excretion
- Involves reabsorption, where 99% of water is reabsorbed
- Lipid-soluble drugs are reabsorbed along with water
- Only very water-soluble molecules can be efficiently excreted.
Ion Trapping
- Urine pH varies, ranging from 4.5-8.0
- In barbiturate overdose, sodium bicarbonate may be given to make the urine alkaline
- Barbiturate moves into the urine and is eliminated from the body
High Renal Clearance
- Renal clearance greater than GFR (active secretion)
Maximum Possible Renal Clearance
- Approximately 650 mL/min (all plasma cleared)
- Example: aminohippuric acid
Low Renal Clearance
- Renal clearance is less than the GFR (not filtered or extensively reabsorbed)
- Examples: antipyrine and thiopental
Creatinine Clearance
- Waste product formed continuously by muscle
- Filtered by the kidneys
- Almost no active secretion or reabsorption
Creatinine Clearance Approximation
- Approximates the filtration rate (GFR) and is used as an estimate of GFR
Clinical Significance of Creatinine Clearance and GFR
- Clearances of renally excreted drugs are closely linked to GFR, important in ADME
- Gentamicin clearance approximately equals GFR and approximates creatinine clearance
Dosage Regime
- Dssume gentamicin clearance is equal to creatinine clearance when calculating a dosage.
Factors Influencing Serum Creatinine Concentration
- Creatinine production rate depends on muscle mass, influenced by body weight, age (muscle declines), and gender (men have higher muscle percentage)
- Creatinine clearance rate
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