9 renal excretion of drugs Flashcards
What is drug elimination? in simple terms
Excretion and metabolism
What do physicochemical properties influence?
The amount and rate of drug absorption
How does a drug being retained in plasma affect half life?
if in plasma because it’s water soluble - half life decreases
if in plasma and highly bound to proteins/tissue - half life increases
How does a drug being bound to plasma proteins affect half life?
if in plasma because it’s water soluble - half life decreases
if in plasma and highly bound to proteins/tissue - half life increases
How does a drug being distributed throughout tissues affect half life?
It takes longer to reach the organs of elimination because it has been sequestered from the circulation so its half life can be extended
How does a drug being retained in tissues affect response
Less of it can reach its target so clinical response is reduced
How is elimination rate measure?
Using half-life
What is drug metabolism?
The transformation of a drug into a form that is readily excreted by modification of its molecular properties (to a more water soluble species)
What does drug metabolism involve?
Enzyme-mediated biotransformation that alter pharmacological activity of both endogenous and exogenous compounds
What does metabolism aim to do?
Lower lipophilicity of the drug
What do biotransformation do?
Increase hydrophilic character to render metabolites water soluble which aids urinary excretion
What is drug excretion?
The removal of modified species from the body, primarily the kidney for water soluble species
How is drug detected in urine?
- At the macro level via colour and smell
- At the micro level via analytical spectroscopy/ spectrometry
How is hydrophilicity of drugs increased?
By introducing polar functional groups or removing lipophilic groups
How does metabolism lower logP?
Either by adding hydrophilic groups or lowering hydrophobic groups
Why is the PCT convoluted?
To increase SA
What occurs at the loop of Henle?
Water and solute reabsorption
Describe the blood vessel in the nephron
It is in the glomerulus
Describe the difference in afferent and efferent arteriole of the nephron
The afferent is wider than efferent so there is a huge increase in BP inside the capsule
There are holes in the blood vessels to squeeze fluid out the blood to produce filtrate that forms urine
Give an example of substances filtered out at the Bowman’s capsule
Water
What are the determinants of drug filtration?
Size restriction and protein binding
Why can drugs bound to plasma proteins not enter the urine?
Their MW is equal to that of the plasma protein
What is the RBF?
1200ml/min (the amount of plasma that flows through both kidneys)
What is the GFR?
125ml/min (the amount of filtrate removed from the blood by both kidneys)
