Clearance

Question 1

What is clearance and what equation can we get from clearance?

Answer 1

The relationship between concentration and the rate of elimination of the drug from the body

Rate out= clearance x concentration

units are typically L/h

Question 2

How do we work out the maintenance dose rate?

Answer 2

At steady state the rate in equals the rate out, so

Rate out= clearance x conc.

Question 3

What organs cause drug clearance and what is an important parameter to consider?

Answer 3

The liver and the kidneys.
The blood flow to this organ (90 L/h max liver and 70 L/h for kidney)

Kidney- through glomerular filtration and tubular secretion

Question 4

What are some drugs with different clearance properties?

Answer 4

VERY FAST: glyceryl trinitrate for angina (150 L/h) just breaks down
FAST: morphine, liver, 60 L/h. opiod analgaesic
MEDIUM: Gentamicin by the kidney and digoxin by kidney and liver
SLOW: theophylline, liver
VERY SLOW: warfarin

Question 5

What are the three types of clearance?

Answer 5

Constant 99%
Conc dependent
flow dependent

Question 6

Constant clearance

Answer 6

is first order and linear. and example is glomerular filtration and most metabolism in liver

Question 7

Concentration dependent clearance

Answer 7

Mixed order or non linear
Examples are tubular secretion eg penicillin
and metabolism of phenytoin

Question 8

Flow dependent clearance

Answer 8

associated with the liver, so morphine for example

eg if reduced blood flow will have a longer lasting effect due to reduced clearance due to reduced flow