Pharmacokinetics Of Aspirin

Question 1

What is the One-compartment model?

Answer 1

A simplified pharmacokinetic model used to describe the absorption, distribution, and elimination of a drug in the body. In this model, the body is treated as a single, homogeneous compartment where the drug concentration is uniform throughout. Used for drugs that have uniform and rapid/instantaneous distributions.

Question 2

What does single compartment mean in the one-compartment model ?

Answer 2

Single compartment: the drug is assumed to distribute instantaneously and evenly within one compartment (e.g. plasma or the central compartment).

Question 3

What does input and output mean in the drug one-compartment model?

Answer 3

.Input refers to drug administration, such as intravenous (IV) bolus, IV infusion, or oral dosing.

.Output refers to drug elimination, which typically follows first-order kinetics ( a constant fraction of the drug is eliminated per unit of time)

Question 4

How would the concentration-Time curve look for IV bolus and oral administration ?

Answer 4

. For IV bolus, the concentration of the drug in the compartment decreases exponentially over time.

. For oral administration, the drug concentration rises as it is absorbed and then decreases as it is eliminated.

Question 5

What do each of the parameters mean :

1. Volume distribution (Vd):
2. Elimination Rate constant (k):
3. Clearance (Cl):

Answer 5

1. Volume distribution (Vd):
   Describes how extensively the drug is distributed in the body.
2. Elimination Rate constant (k):
   Represents the rate at which the drug is eliminated from the body
3. Clearance (Cl):
   The volume of the plasma cleared of the drug per unit time. It is a measure of the body’s ability to eliminate the drug through metabolism and excretion.
   Cl= k x Vd
   Cl= rate of elimination/ plasma concentration (C)
   E.g if a drug has a clearance of 100mL/min this means 100mL of plasma is cleared of the drug every minute.

Question 6

How is the human body different to the one-compartment model and how would this impact PK measurements?

Answer 6

In reality, the human body is described as a multi-compartment model. Examples of these compartments would be: tissues, muscle, gut, brain etc , each having a different time for the drug to be fully distributed (in a state of equilibrium)

Drugs bind to tissues, cells and organs equilibrate in different body systems which affect the PK measurements made

Question 7

What does equilibrate mean ?

Answer 7

To reach a state of equilibrium, where the concentrations of a drug, becomes equal or stable across different compartments. This term often refers to the process by which a drug distributes throughout the body until the concentrations in tissues or organs reach a steady relationship with the concentrations in the blood.

Question 8

What are examples of compartments where there is rapid drug distribution?
Name examples where there is slower drug distribution

Answer 8

Rapid- liver or kidneys

Slow- fat or bone

Question 9

Briefly outline the steps of the practical (4)

Answer 9

1. Create a calibration curve for salicylate (aspirin) by measuring absorbance of known concentrations of salicylate and plot a graph of the data-concentration (x) vs absorbance (y)
2. Collect a series of samples at timed intervals and measure the absorbance of each sample
3. Use your calibration curve to estimate the concentration of salicylate that corresponds to each absorbance
4. Then draw a semi-log graph of concentration is salicylate 0.5-25 minutes

Question 10

Define Pharmacokinetics (PK)

Answer 10

•It describes the mathematical relationships of drug dose/concentration-time relationships from which a number of PK parameters can be estimated.
The study of what the body does to the drug, focussing on how it is absorbed, distrusted, metabolized and eliminated.

Question 11

Define Pharmacodynamics (PD)

Answer 11

•Concentration-effect relationships; i.e. magnitude of effect at a particular concentration. The study of what the drug does to the body, describing the drugs biological effects and its mechanism of action at the site of activity. Concerned with drug effects such as pain relief, side effects etc

Question 12

What does the parameter Clearance mean (Cl)

Answer 12

Clearance (Cl):
The volume of the plasma cleared of the drug per unit time. It is a measure of the body’s ability to eliminate the drug through metabolism and excretion.
Cl= k x Vd
Cl= rate of elimination/ plasma concentration (C)
E.g if a drug has a clearance of 100mL/min this means 100mL of plasma is cleared of the drug every minute.