Clearance

Question 1

What is clearance

Answer 1

• important first order concept in pharmacokinetics
• version of the rate constant scaled by the volume of distribution, and allows for the use of concentration in the model of the first order elimination process, rather than the absolute quantity of a drug (i.e. it is a unit of conversion device)
• we use clearance to understand the behaviour of drugs in the blood

Question 2

Why is concentration the best quantity to use in pharmacokinetics

Answer 2

• manner in which drug acts on receptors is dependent on its concentration in the blood
• something we can actually measure and use to infer the amount of drug

Question 3

Clearance definition

Answer 3

• how many volume units you clear per unit time/ how many volume units are completely cleared of the relevant substance in a given time

Question 4

Creatinine clearance

Answer 4

CuVu/ Cup T
- Cu: [creatinine] in urine
- Cup: [creatinine in plasma] stays constant during experiment
-> dividing by [creatinine in plasma] gives a quantity representing the no. Of volume units completely cleared of creatinine in that period
- Vu: collected urine volume over period of time (24h)
- CuVu: total mass/ quantity of creatinine cleared over the time period (24h)
-T: dividing by time gives clearance in ml/min
CuVu/ Cp = V