Pharmacokinetics Flashcards
What is distribution?
The transfer of the drug from the blood stream to other areas of the body.
This can be reversible, as drug can be transferred back into the blood stream. If it doesn’t return to th blood it has been eliminated.
The rate and extent of distribution is determined by perfusion rate,protein binding, permeability of tissue to the drug, p-glycoproteins and pKA.
Once in the systemic circulation, distribution is often uneven.
What is absorption?
The movement of a drug front the site of administration to the blood stream.
Influenced by water and lipid solubility, and concentration gradients. Passive, facilitated or active transport.
What are p-glycoproteins?
Cells in the apical cell membrane(facing the gut contents)
They are a defence against foreign substances, as when substances are absorbed, they are actively pimped back into to the gut.
This process is ATP dependant.
Why should we consider g-glycoproteins?
Some drugs such as rifampicin increase the amount of p-gp in the intestinal epithelium, which means there is less absorption of other substances.
Other drugs such as verapamil will saturate the p-gp, which means there will be better absorption of other substances as less will be pumped back out.
Which patient factors can affect distribution?
Level of hydration ( oedema, dehydrated ) Weight - obese, underweight Gender Ethnicity Pregnancy Age Other conditions
What is the volume of distribution?
A convenient way to describe how well a drug is removed from the plasma and distributed to the tissues. It doesn’t provide any edifice information about where the drug is or hat the concentration is like in different tissues.
What is bioavailability?
The extent and rate of the drug which enters the systemic circulation and is therefore accessible to the site of action.
What factors might cause a failure of absorption?
Binding in the gut
Too polar to undergo the passive diffusion
Pumped back into the gut by glycoproteins
What is the fractional availability?
The fraction of a dose that reaches the systemic circulation in a chemically unaltered form. Often used in oral dosing as Foral.
Where can a drug be eliminated from?
The main route of elimination is through excreation through the renal system. There is also significant excreation through the biliary system and the pulmonary system.
The is also loss through the mammary glands, which is important as there may be delivery of the drug through milk, and through the salivary glands, which can provide a route for drug testing.
What is clearance in pharmokinetics?
The measure of efficiency of drug removal from the body.
Where does the first pass effect occur?
The first pass effect can be in the livery, or in the gut wall, where drugs are metabolised by cytochrome p450. Important to remember that not all the first pass breakdown occurs in the liver.
