Pharmacokinetics

Question 1

Four processes of pharmocokinetics?

Answer 1

1. absorption
2. distribution
3. metabolism
4. elimination

Question 2

Factors used to calculate dosing regimens?

Answer 2

1. bioavailability (F)
2. volume of distribution
3. half life
4. clearance

Question 3

How to calculate bioavailability from plasma concentration and time?

Answer 3

AUC oral/AUC IV * 100%

Question 4

Calculate actual amount of drug absorbed?

Answer 4

Dose * F

Question 5

Calculate a new dose using old and new bioavailability?

Answer 5

Old dose * (F old/F new)

Question 6

Calculate volume of distribution?

Answer 6

Vd = (Dose * F)/Co

Co = initial concentration

Question 7

Calculate loading dose?

Answer 7

LD = (Vd * Cp)/F

Cp = target concentration

Question 8

One compartment model?

Answer 8

• body is one compartment
• drug concentration in different tissues not equal, but at equilibrium and proportional to blood concentration
• applies to water soluble drugs
• Vd is smaller

Question 9

Two compartment model?

Answer 9

• central (heart, organs) and peripheral compartments
• drugs always has to go through central compartment to get to peripheral
• applies to lipid soluble drugs
• Vd is larger

Question 10

First order metabolism equation?

Answer 10

v = (Vmax * [C])/Km

• Km is much larger than [C]
• v is proportional to [C]
• linear kinetics, constant fraction metabolized
• fixed half life
• can reach steady state

Question 11

Zero order metabolism equation?

Answer 11

v = Vmax

• Km is much smaller than [C]
• non linear, constant amount metabolized
• does not depend on amount of drug present
• no half life
• does not reach steady state

Question 12

What drugs follow zero order kinetics?

Answer 12

• alcohol
• high doses of aspirin
• phenytoin

Question 13

calculate clearance?

Answer 13

CL = Vd * (.7/T half life)

Question 14

calculate rate of elimination?

Answer 14

CL * Cp

-rate out

Question 15

Corrected dose of patient with renal dysfunction?

Answer 15

Normal Dose * Ratio between patient and normal renal function

-use creatinine clearance as indicator

Question 16

Continuous infusion method to reach steady state?

Answer 16

• rate of infusion does not change the time to reach steady state, only steady state concentration changes
• always takes 4 or 5 half lives
• concentration will be different

Question 17

calculate maintenance dose?

Answer 17

(Cpss * CL * T)/F

Question 18

calculate plateau (steady state) concentration? (Cpss)

Answer 18

rate in/CL

(Dose * F/T)/CL

Question 19

What does steady state concentration depend on?

Answer 19

• dose
• dose interval
• F value
• clearance

Question 20

Accumulation principle of first order drugs?

Answer 20

Half lives:

1- 50% to steady state
2- 75%
3- 87.5
4- 93.75
5- 96.88

-therapeutic at 90%

Question 21

Elimination principle of first order drugs?

Answer 21

Half lives:

1- 50% remaining
2- 25%
3- 12.5%
4- 6.25%
5- 3.125%

-no effects at 6.25%