Define
Excretion
The removal of drug molecules from the body without chemical modifcation
Exretion and metabolism
IV administration
- No metabolism takes place
- Elimination is 100% renal
Where is the
primary source of excretion
Kidney
Which FOUR factors
Effefect drug excretion
(4)
- Glomerular Filtration
- Secretion
- Protein Binding
- Reabsorption
- Modify Excretion
Modified excretion aka ion trapping
Explain
Filtration
The process of hydrostetic pressure pushing drug molecules out of the plasma into the bowmans capsule
What can result from a
reduction in GFR
A reduction in GFR means less plasma is crossing into the bowmans capsule, therefore less drug is transported across. This can cause an increased plasma concentration of the drug, which can lead to toxicity
Explain the process of
Secretion
The process by which cations and ions are used to actively or passivley transport drug molecules that failed filtration into the kidney, ready for excretion.
What can DECREASE Glomerular filtration rate
- Acute Kidney Injurt
- Chronic kidney disease
Less drug filtered across glomerulus into the bowmans capsule
What can result from an
Increased protien binding
(excretion)
Increased protien bound drugs means the drug is too big too be filtered, reuslting in decreased filtration of the drug and increased drug plasma concentration, leading to toxicity.
Drug: non-polar, lipid-soluble, small (low conc. tub, high conc. blood)
Explain the process by which this drug is secreted
- Passive diffusion
- No ATP required as crossing down a concentration gradient
Drug: polar, water-soluble, large (high conc. tub, low conc. blood)
Explain the process by which this drug is secreted
This drug cannot passively diffuse into the tubules. It is an active process by which organic anion/cation transports are used to transport the drug into the tubules, requiring ATP.
What can happen if a drug interacts with the OAT/OCT, and give an example of a drug that does this.
- Trimethoprim
- The OAT/OCT or inhibited and so the drug cannont be secreted
- Could result in toxic concentrations of drug in plasma.
Explain the process of
Reabsorption
Excretion
- At this stage in excretion the drug concentration in the blood is low and the concentration in the tubule is high.
- Non-polar, Lipid-soluble, small drugs will passivley difuse back into the blood
- They will be transported to the liver where they may undergo phase 1/2 metabolism and become too polar to be reabsorbed again.
Explain the process of
Modifying excretion
Ion trapping
- overdose
- preventing reabsorption
- Weak acids will be alkalanized (Sodium Bicarb) to create a charge and make it polar
- Weak bases will be acidified to create a charge and and make it polar
- This essentialy traps the drug into the urine
