Pharmacokinetics

Question 1

What is pharmacokinetics?

Answer 1

The study of a concentration-time profile of a drug in the body

Question 2

In a time course of plasma drug conc what do the different areas represent?

Answer 2

Area under time-conc curve = the wexposure mg.h/L

The absorption iss at the first steep increase, the distribution is at the top and the elimination is the exponential decrease

Question 3

Why is IV administration the gold standard for drug absorption?

Answer 3

Because it has 100% absorption

Question 4

What is bioavailability?

Answer 4

The fraction of dose reaching the systemic circulation.

F = (AUCpo/AUCiv) x (doseiv/dosepo)

Question 5

What is the first pass effect?

Answer 5

The loss of drug occurring before the drug reaches the systemic circulation ( as it passes through the gut wall and the rest of the body)

Question 6

Waht are the pharmacokinetic parameters?

Answer 6

Volume of distribution (V)
Plasma clearance (CL)
Plasma half life (T1/2)

Question 7

What is the Volume of Distribution?

Answer 7

V = amount of drug in the body/plasma drug concentration

If plasma conc is small compared to body drug then it shows there is a large volume of distribution

Question 8

What are the determinants of the Volume of Distribution

Answer 8

body mass
Tissue binding (increases V as there is less in blood)
Drug binding to plasma elements (decreases V as there is more in blood)

Question 9

What is the Loading Dose?

Answer 9

The first dose of drug treatment and is required to achieve a target concentration rapidly

LD(mg) = V (L) x target concentration (mg/L)

Question 10

What is drug elimination?

Answer 10

Includes both metabolism and excretion

Refers to the irreversible remonval of the drug from the body

Defined by clearance

Question 11

What is clearance?

Answer 11

The Volume of plasma cleared of drug per unit time (L/h)

Elimination rate (mg/h) = CL (L/h) x conc (mg/L)

CL = dose/AUC

Question 12

What is the maintenance does rate?

Answer 12

The dose rate to achieve and maintain a target concentration.

At a steady state dose in = rate of elimination

MD (mg/h) = CL (L/h) x target conc (mg/L)

Round up to nearest 50mg

Question 13

What is the Half life?

Answer 13

The tiem required for drug concentration to fall by half.

Depends on volume and clearance
Usually constant irrespective of drug conc
the amount of drug in the body at any time is related to the number of half lives from administration

Question 14

How do you calculate half life?

Answer 14

T1/2 = 0.7 V/CL

Question 15

When do you consider that a drug has been eliminated from the body?

Answer 15

After around 4 half lives as that is >90% eliminated

Question 16

What is accumulation?

Answer 16

With repeated dosing or an infusion a drug will accumulate in the body until

input = elimination

This steady state occurs when drug concs have plateaued. The time required to reach steady state is related to half life

accumulation is >90% after 4x half lives