Clearance

Question 1

What is renal clearance?

Answer 1

The volume of body fluid cleared of a substance per unit time. (L.hr / ml.min)

Question 2

Why is renal clearance predicted?

Answer 2

To predict the method of elimination or metabolism of a drug and to predict its changes in plasma concentration over time.

Question 3

What substance is used to measure GFR and which to measure RBF?

Answer 3

GFR uses creatinine

RBF uses PAH

Question 4

What is clearance of any substance equal to?

Answer 4

Excretion rate / plasma concentration

Question 5

What can be determined if renal clearance of a substance is 0?

Answer 5

Not filtered or excreted by the kidneys e.g. large proteins

Question 6

What can be determined if renal clearance < GFR?

Answer 6

Filtered and partially reabsorbed

rate of being cleared < rate of filtration

Question 7

What can be determined if renal clearance = GFR?

Answer 7

Filtered but not reabsorbed

rate of being cleared = rate of filtration

Question 8

What can be determined if renal clearance GFR?

Answer 8

Filtered and partially secreted

rate of being cleared is < blood flow but >filration

Question 9

What can be determined if renal clearance = RBF?

Answer 9

Filtered and secreted

Question 10

What can be determined if renal clearance > RBF?

Answer 10

Produced in the kidney

Question 11

What is whole body clearance?

Answer 11

The sum of organ clearance measured using the concentration changes of a substance over time.

Question 12

What is the equation for whole body clearance using the curve and what does it show?

Answer 12

Cl = dose / Area in curve

If a substance is cleared QUICKLY the area under the curve is SMALL showing a LARGE clearance value.

Question 13

What is the rate of removal proportional to and what equation is this shown by?

Answer 13

Rate of removal is proportional to concentration as long as Tm is not reached.
dC / dt = -kC

Question 14

How is the concentration calculated using Cmax?

Answer 14

C = CmaxE ^ -kt

Concentration will fall exponentially with time.

Question 15

How is half life calculated?

Answer 15

T1/2 = ln2 / k = 0.6931 / k
or
C = Cmax(1/2) ^no. of T1/2

Question 16

What is Vd and clearance used to predict?

Answer 16

Cl = KVd (volume of plasma from which a substrate is completely cleared by kidney per unit time)
Predicts how the concentration of a substance will change in circulation overtime.

Question 17

What is K?

Answer 17

The elimination rate constant

Question 18

What piece of information is required to calculate a Pt’s Vd?

Answer 18

Weight as Vd is measured in L.Kg

Question 19

What is meant by bioavailability?

Answer 19

The portion of a substance reaching systemic ciruclation UNCHANGED

Question 20

Absorbed dose =

Answer 20

Dose x bioavailability

Question 21

Vd in ECF (L) =

Answer 21

Vd of drug (L.kg) x mass (kg)

Question 22

Cl of L.hr =

Answer 22

Cl of L.min x 60

Question 23

Cpeak = (Peak concentration

Answer 23

Absorbed dose / Vd

Question 24

K =

Answer 24

Clearance / Vd

Question 25

Why are regular drug dose intervals used?

Answer 25

To allow the plasma concentration of the drug to fall before the next, to prevent accumulation.

Question 26

How does a dose affect rate of Cl?

Answer 26

Clearance is independent to dose. | A higher dose will still be cleared within the same amount of time. Dose only affects the starting concentration.

Question 27

After an overdose, when can the normal drug dose be resumed?

Answer 27

After the normal drugs interval time without causing accumulation, as the overdose concentration will have fallen to the resting concentration within this time. Body can eliminate any dose within the same period of time.

Question 28

When is an overdose an issue for resuming normal drug intervals?

Answer 28

When pt has renal failure due to the reduced GFR meaning that the concentration of the drug fails to reach the resting concentration between each dose. As excretion is slower, accumulation will occur.

Question 29

For how long will accumulation of a drug occur in a pt with renal failure?

Answer 29

Until the drug reaches an equilibrium with the body fluids.

Question 30

What needs to be altered about a drug for a pt with renal failure?

Answer 30

Need to increase the interval time between each dose.