Drug Emlimination

Question 1

What is the MEC?

Answer 1

The minimum effective concentration - the critical concentration in the plasma for a drug to achieve an effecr

Question 2

What is the MTC?

Answer 2

The maximum tolerate concentration - the maximum concentration in the plasma before significant unwanted effects happen

Question 3

In terms of therapeutic window and ratio what would a safe drug have?

Answer 3

A safe drug would have a large therapeutic window and a high therapeutic ratio - examples are penicillins and benzodiazepines

Question 4

In terms of therapeutic window and ratio what would an unsafe drug have?

Answer 4

An unsafe drug would have a small therapeutic window and a small therapeutic ration - examples are barbiturates and cardiac glycosides

Question 5

What is pharmacokinetics?

Answer 5

the mathematical analysis of all drug disposition factors (absorption, distribution, metabolism and excretion)

Question 6

What is first order kinetics?

Answer 6

where the rate of elimination is directly proportional to drug concentration

most drugs exhibit first order kinetics

Question 7

What is half life of a drug?

Answer 7

The time taken for Ct to fall buy 50%

It is inversely related to Kel

T(1/) = 0.69/Kel

Question 8

If a drug exhibits first order kinetics, what does the dose administer change and not change/affect?

Answer 8

The dose administered change Cp in direct proportion
The dose administered does not affect Kel or T(1/2)

E.g double the dose, the Cp changes but the half life is the same.

Question 9

What is clearance?

Answer 9

‘The volume of plasma cleared of drug in unit time’

‘A constant relating the rate of elimination to plasma concentration’

Applies only to the drugs that exhibit first order kinetics

Question 10

What does Cl determine?

Answer 10

The maintenance dose rate (the dose per unit time required to maintain a given plasma concentration)

Question 11

At a steady state what does rate of drug administration =?

Answer 11

rate of drug administration = rate of drug elimination

Question 12

For drugs that exhibit first order kinetics, the stead state plasma concentration (Css) is _________ related to the infusion rate?

Answer 12

For drugs that exhibit first order kinetics, the stead state plasma concentration (Css) is linearly related to the infusion rate?

Question 13

When is the Css reached?

Answer 13

After 5 half lives approx

Question 14

The time to reach Css is determined by __, but not the ____ rate?

Answer 14

The time to reach Css is determined by t½, but not the infusion rate

Question 15

How is drug dosing to a steady state in oral different to IV?

Answer 15

The plasma concentration fluctuates about an average steady state value

Question 16

What is the volume of distribution?

Answer 16

‘The volume into which a drug appears to be distributed with a concentration equal to that of plasma’

Question 17

What is the loading dose?

Answer 17

an initial higher dose of a drug given at the beginning of a course of treatment before stepping down to a lower maintenance dose

Question 18

Why is the loading dose employed?

Answer 18

TO decrease the time to steady state for drugs with a long half life such as digixoin

Question 19

What does half life give an index of?

Answer 19

the time course of drug accumulation
the time course of drug elimination
choice of dose interval

Question 20

What is the equation that links, half life, clearance and Vd?

Answer 20

T(1/2) = (0.693 x Vd) / Cl

Question 21

What is zero order elimination?

Answer 21

A few drugs of clinical significance (e.g. ethanol, phenytoin) are initially eliminated at a constant rate, rather than at a rate that is proportional to their concentration (this can occur, for example, when the plasma concentration of a drug is greater than the Km of an enzyme that metabolises it)