Minimum effect concentration
To achieve a desired effect it must reach this concentration in the plasam
Maximum tolerated concentration
Drug concetration must be below this to not cause significant unwanted effect
Between MTC and MEC
Equation for the therapeutic window?
TR= MTC/ MEC
For a safe drug?
The therapeutic window must be large.
If there was a low therapeutic window?
The drug would be less safe
What causes any drug to be toxic?
The dose rate
Definition of pharmacokinetics?
Mathematical anaylsis of all drug disposition factors
The equation for the initial concentration when the drug is first added into the body?
Co= D/ Vd
Rate of elimination is directly proportional to the drug concentration
First order-kinetics equations?
On average, how many half lives does it take for the all the drug to be eliminated?
5 half lives.
What is not effected by changes in plasma concentration?
Elimination rate and half-life
What happens when you double the dose of drug?
Increase the biological action by 1 half life.
The volume of plasma cleared of drug in unit time.
Applies only to first-order kinetic drugs
It is a constant
Equation for the rate of elimination?
Rate of elimination (Litres/hr) = Cl x Cp
Maintenance dose ratio
Determined by clearance
Dose per unit time required to maintain a given plasam concentration
At steady state?
Rate of drug administration = rate of drug elimination
Equation for the rate of elimination at steady state?
Rate of elimination= clearance x Cpss
Graph of dosing to steady state
Equation for the plasma concentration at steady state?
Maintenance dose rate / clearance
Equation for the plasma at any one time at steady state?
Clearance is the sum?
Of all clearance processes
What must you increase in order to increase the plasma concentration at steady state?
Increase maintenance dose
Rate of drug being given.
Linearlly related to Css
What determines the time to reach Css
Determined by half life not the infusion rate
After how many half life is the concentration at steady state?
Averagely 5 half lives
Dosing orally graph?
Css equation for dosing orally?
First order kinetics is for?
Instead of orally administered as it is continously infusioned
The fraction of the drug administered that enters the systemic circulation
Difference in graphs between IV and oral administration?
Volume of distribution?
Volume in which a drug appears to be distributed with a concentration equal to that of plasma
Equation for the amount of drug in the body?
Graph representating the volume of distribution
Equation for the plasma concentration initially?
Co= Dose/ Vd
Ab stands for?
Amount of drug in the body
An initial higher dose of a drug given at the beginning of a course of treatement before going to a lower maintenance dose
Why is loading dose used?
Employed to decrease time to steady state for drugs with longer half lives
Loading dose for IV and oral treatment?
Why does Vd correspond to a real anatomical compartment?
As it can change between people
Change in disease such as liver failure
Is elimination value the a constant?
It can vary between different people and other factors such as other drugs present, disease etc
The time for the concentration of drug in plasma to reach half
What 3 things can half life give an index of?
- The time course of drug accumulation (aver. 5)
- The time course of drug elimination (aver. 5).
- The dose interval needed
Equation to work out the half life?
t1/2 = (ln2 x Vd)/ CL
Zero order kinetics?
Few clinically significant drugs are eliminated at a constant rate.
Elimination is initially zero order and converts to first order at low concentrations.
For zero order kinetics what is the relationship between plasma concentrate (At steady state) and dose rate
Not linearly anymore AS20