0402 - Pharmacology - pharmacokinetics Flashcards
What is pharmokinetics
Effectively, this is what the body does to the drug (as opposed to pharmodynamics which is what the drug does to the body). It can be classified as the branch of pharmacology which deals with the fate of substances delivered to the body.
What are the main routes of drug administration and elimination
Administration: - Oral- Rectal- Intravenous- Intramuscular (injection into the muscle)- Intrathecal (this is an injection into the potential space inside of a sheath)Excretion:- Urine- Faeces- Milk- Sweat- Expired air
Describe some features of plasma protein binding
This is the process by which a drug will bind to a protein the blood plasma. It is an important process as it is only the drug which is free in the blood plasma which is active. A drug that is not bound to the plasma protein but is in the blood plasma is able to move to the site of pharmacologic activity. Conversely if too much of the drug is bound to the blood plasma, then there is fairly little that can move to the site of pharmacologic activity. Albumin is the most important protein in the plasma related to this.
Explain what is meant by clearance and describe how it is quantified
This is the irreversible elimination of a drug either through excretion or metabolism into another drug. We quantify clearance as being the volume of blood that is cleared of a drug per unit time. i.e. L/h. This can be by a particular organ or by the whole body. This is an important quantity to know as it helps us to determine the maintenance dose (This is the does required to keep the drug concentration at a steady state.)
Explain what is meant by volume distribution and why is it important to know
This is a quantity which relates the plasma drug concentration to the total amount of drug in the body. It is expressed as a volume however it is not a real volume. In other words, it tells you the amount of plasma required for the total quantity of drug administered to still be in your blood plasma and for the concentration of drug in the plasma to be at that level. A high volume of distribution indicates that the drug has been sequestered out of the blood.A low volume of distribution would indicate that the drug has predominantly remained in the blood plasma. This is important to know as it helps us to calculate the loading dose for a drug.This is the quantity of drug that should be administered in the initial dose to immediately put the blood plasma concentration into the desired range.
What is the significance of the half-life of a drug
The half-life of a drug, is the time take for the quantity of the drug within the body to reduce by half. Assuming the drug follows first order kinetics, the half-life of the drug will not change with increased dose. Knowing the half-life is important because it allows us to calculate:- The drugs duration of action after a single dose- The time to reach steady states with constant dosing- The dosing frequency
Explain the difference between dosing frequency and maintenance dose
Dosing frequency: how often a dose is administeredMaintenance dose: this is the maintenance rate (mg/h) that is equal to the rate of elimination at a steady stateDifferent dosing frequencies can equate to the same maintenance dose.
What is the first pass effect
This refers to the excretion and metabolism of orally ingested drugs before they reach the systemic circulation. This is achieved by the liver.
What is bioavailability
This is simply the amount of drug that reaches the systemic circulation
