Pharmacokinetics Flashcards
What is pharmacokinteticse
The effect the body has on the drug
What is pharmacodynamics
The effect the drug has on the body
The amount of drug which reaches the site of action depends on what?
- Rate of absorption of drug
- Rate of distribution around the body
- Rate of metabolism by the body
- Rate of excretion by the body
What is the rate of passive diffusion dependent on?
- Solubility of lipid
- area of the membrane
- magnitude of concentration gradient across the membrane
Are non-ionised lipid soluble?
Yes
Are ionised lipid soluble?
No - relatively lipid insoluble
What does a drugs relative proportions (amount of non-ionised drug) depend on?
Drug’s intrinsic tendency to ionise & pH of solution
Why do most drugs not ass through the cell membrane via diffusion through aqueous pore?
Most drug molecules are too large
What is the paracellular route for drugs to enter a cell?
Diffusion through intercellular pores for larger drugs and large proteins e.g. insulin
What molecules enter a membrane via carrier-mediated transport?
Relatively insoluble lipids e.g. amino acids, sugars & neurotransmitters.
What factors influence the rate of dissolution?
- particle size
- pH conditions
- dosage form
- influences of additives
Why in inhaltion of anaesthetic likely to cause systemic effects?
They are lipophilic molecules that are readily absorbed by passive diffusion through the lungs
What is the absorption of anaesthetic gases dependent on?
- rate of entry to tissues
- solubility
- rates of pulmonary blood flow
- rates of respiration
Where is inhaled anaesthetic excreted?
Lungs??
When/ where is percutaneous administration quickest?
- Where skin is thinnest
- warming skin
- hydrated skin
Why must drugs be lipid soluble to diffuse quickly into the brain?
- CNS is protected by blood-brain barrier:
- CNS surrounded by specialised barrier which is an obstacle to the penetration of hydrophilic substances
- Endothelial cells in the brain do not have intercellular pores but have tight junctions
- Glial cells associated with capillaries in the brain are another barrier to the diffusion of non-lipid soluble molecules.
What is the main factor that influences the rate of drug distribution?
How well the molecule crosses the membrane
What is a drug interaction?
when one drug displaces another drug from a protein it was bound to
What protein do most drugs bound to?
Albumin (produed by liver)
What is meant by drug metabolism?
When the body attempts to transform drugs into hydrophilic (water soluble) substance which are usually less pharmacologically active and can be excreted via urine and bile.
Name all the organs involved in drug metabolism
- LIVER
- skin
- lings
- kidneys
- intestine
Can drug interactions can occur during drug metabolism?
Yes - the metabolism of one drug may affect the metabolism of another drug.
Is the metabolite always less pharamolcogically active than the parent compound?
No-once metabolised, metabolite is usually less pharmacologically active but can be more active than parent compund can lead to toxicity.
What are the 2 phases of drug metabolism?
Phase I - chemically reactive groups are added or uncovered (and used up)
Phase II - addition of pharamologically inactive groups (for conjugation reaction)
