9 renal excretion of drugs Flashcards
(35 cards)
What is drug elimination? in simple terms
Excretion and metabolism
What do physicochemical properties influence?
The amount and rate of drug absorption, how extensively a drug is distributed and how rapidly a drug is eliminated
How does a drug being retained in plasma affect half life?
If it is retained in plasma, it is water soluble and can reach the organs of elimination quicker so shortens the duration of action and needs administered more often
How does a drug being bound to plasma proteins affect half life?
It cannot be filtered and removed by the kidney as effectively so duration of action extended
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 half life?
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 via the kidney for water soluble species
Where are drugs and metabolites excreted?
In urine
How is drug detected in urine?
At the macro level via colour and smell and 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 reabsorption
Describe the blood vessel in the nephron
It is in the glomerulus, in the Bowman’s capsule and comes out of the glomerulus to wrap itself around the PCT and DCT
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 within the blood vessels to squeeze fluid out the blood to produce filtrate which will form urine
Give an example of substances filtered out at the Bowman’s capsule
Water, amino acids, sugars, fatty acids and small drug molecules
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)
