MEC?

Minimum effect concentration

To achieve a desired effect it must reach this concentration in the plasam

MTC?

Maximum tolerated concentration

Drug concetration must be below this to not cause significant unwanted effect

Therapeutic window

Between MTC and MEC

Equation for the therapeutic window?

TR= MTC/ MEC

For a safe drug?

The therapeutic window must be large.

eg. penicillin

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?

C_{o}= D/ V_{d}

First-order kinetics?

Rate of elimination is directly proportional to the drug concentration

First order-kinetics equations?

See AS13

On average, how many half lives does it take for the all the drug to be eliminated?

5 half lives.

More theretical

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.

Clearance

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 C_{p}

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?

AS15

Rate of elimination= clearance x C_{pss}

Graph of dosing to steady state

AS15

Equation for the plasma concentration at steady state?

Maintenance dose rate / clearance

Equation for the plasma at any one time at steady state?

C_{t}= C_{S}_{S}(1-0.5^{n})

as15

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

Infusion rate

Rate of drug being given.

Linearlly related to C_{ss}

What determines the time to reach C_{ss}

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?

AS16

C_{ss} equation for dosing orally?

AS16

First order kinetics is for?

IV

Instead of orally administered as it is continously infusioned

Oral bioavailability?

The fraction of the drug administered that enters the systemic circulation

Difference in graphs between IV and oral administration?

See AS17

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?

See AS18

Graph representating the volume of distribution

AS18

Equation for the plasma concentration initially?

C_{o}= Dose/ V_{d}

AS18

Ab stands for?

Amount of drug in the body

Loading dose?

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?

AS19

Why does V_{d} 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?

No

It can vary between different people and other factors such as other drugs present, disease etc

Half-life

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?

t_{1/2} = (ln2 x V_{d})/ CL

Zero order kinetics?

Saturable.

Few clinically significant drugs are eliminated at a constant rate.

Elimination is initially zero order and converts to first order at low concentrations.

AS20

For zero order kinetics what is the relationship between plasma concentrate (At steady state) and dose rate

Not linearly anymore AS20