M&R - pharmacokinetics Flashcards
What is oral bioavailability?
Proportion of drug given orally for any other route except IV that reaches circulation unchanged
What are some examples of sites of administrations?
Inhalation, oral, IV, transdermal patch, topical, rectal,
How is bioavailability measured?
AUC oral
———— x 100
AUC injected
How is the therapeutic ratio worked out?
ED50 ( effective dose in 50% of people)
What is the therapeutic window?
The zone where the desired effect occurs but without the unwanted adverse effect
In what instances is the first pass metabolism avoided?
In IV injection, rectal and sublingual administration
What is the volume of distribution?
Theoretical volume into which drug is distributed of this occurred instantaneously.
What does free drug determine?
Action at receptors
What is protein binding drug interactions?
This is when there is partial displacement of drugs from binding sites due a seconds drug reacting
What is the first drug administered and what is the name of the second drug that displaces it?
Object drug
And precipitate drug
What is first order kinetics?
When the rate of drug elimination is proportional to drug level
What is zero order kinetics?
When the rate of elimination is constant
During repeated drug administration when is steady state achieved?
After 5 half lives
In reality how is steady state reached?
Loading dose given up to the therapeutic dose and then give maintenance doses to keep this up
How do ,most drugs behave?
By first order kinetics
Where does drug metabolism occur?
Liver
Where does drug elimination occur?
Kidneys
Why is drug metabolism susceptible to drug interaction?
The isoenzymes of Cytochrome P450 are inducible and inhibitable
Where are the drugs in the kidney filtered?
In the glomerula
What is passive reabsorption of drug in the kidneys down to?
pH
Which for, of drug passes across the membrane of the glomerulus?
Non-ionised
What happens to absorption in acidic urine?
Increases
What happens to absorption in alkali urine?
Decreased absorption
