Pharmacokinetics - Drug Elimination Flashcards
Routes of drug elimination
- Kidneys
- Liver - bile
- Intestines
- lungs
- Milk in pregnant women
What flows through capillaries into bowman’s capsule
Free drug (not any bound drug)
What does not influence the passage of drugs into the glomerular filtrate
- Lipid solubility
2. pH
What happens at the proximal tubule
- Secretion of weak acids and weak bases into the renal tubule
- Bases and acids carry bound drug into tubule via active transport (secretion)
What happens at the distal tubule
If drugs are not polar enough, they will be reabsorbed into circulation
Which part of the tubule is most sensitive to changes in pH and drug absorption
Distal tubule
How can you eliminate weak acids by manipulating the pH of the urine
Make the urine alkaline (which will keep drug in urine for elimination)
How can you eliminate weak bases by manipulating the pH of the urine
Make the urine acidic (which will keep drug in urine for elimination)
what is the purpose of changing the pH of the urine
You want to “trap” the ions in order to keep the drugs ionized (polar) in order for them to be excreted and not reabsorbed
The more ionized
The more easily excreted
The more lipid soluble the more
difficult to eliminate (will want to be reabsorbed)
The more polar
the easier to excrete
Half - life
The time it takes to reduce the plasma drug concentration by half
What causes 1/2 life to be increased
- Diminished renal plasma flow
- Diminished hepatic blood flow
- Renal disease
- Decreased metabolism (drug inhibition or hepatic insufficiency)
What causes 1/2 to be decreased
- Increased hepatic blood flow
- Decreased protein binding
- Increased metabolism
Duration of drug action
The total amount of time the drug is present in the plasma or tissues and produces clinical effects
Clearance
Estimates the amount of drug cleared from the body per unit of time
Time required for elimination of drug
Time it takes for body to eliminate the drug. Depends on the drugs half-life and other metabolic factors.
Steady state
A state in which the rate of administration equals that of elimination of the drug (drug concentration plateaus)
How are steady state and infusion rate related
Have a direct relationship. If the Infusion rate is doubled, the plasma concentration achieved at steady state is doubled
How are steady state and clearance related
Inverse relationship. If clearance is inhibited (decreases) steady state will increase.
What does Css stand for
Steady state concentration
What affect does a faster rate of infusion have on time needed to achieve steady state
None, a faster rate will only increase the concentration, not the time.
What if you need to reach steady state sooner
Use a loading dose
