Pharmacokinetics Flashcards
Name the four stages a drug goes through in the body.
A - Absorption
D -Distribution
M - Metabolism
E - Excretion
What are the six route of drugs administration?
GI tract: Oral, Sublingual, Rectal
Parenteral: Intravenous, Subcutaneous, Intramuscular
What four ways can drugs be absorbed into cells?
Passive diffusion
Facilitated diffusion
Primary/secondary active transport
Pinocytosis
What drugs can pass through passive diffusion?
Weak acids/bases
Lipophilic drugs - can pass epithelium e.g. Blood brain barrier
What is bioavailability?
The fraction of a defined dose that makes its way to a specific body compartment.
What happens to the concentration of a drug as it passes through the plasma, interstitial fluid and into the cells?
Conc goes down
What symbol is used to signal volume of distribution?
Vd
High = good penetration
Low = bad penetration
Where are drugs metabolised?
In the liver
What enzyme is involved in Phase 1 elimination?
Cytochrome P450
What do ‘pro drugs’ do? Example?
Are partially activated by cytochrome p450 in phase 1.
E.g. 0-15% codeine is metabolised by CYPD6 into morphine, whilst the other 85% is eliminated.
What happens in Phase II drug elimination?
Involves hepatic enzymes
More rapid kinetics
Increase ionic charge for elimination - sent to kidney
What is CYP450 induction?
Administration of certain drugs can INDUCE specific enzymes
So next time rate of elimination will increase
What is CYP450 inhibition?
Administration of certain drugs can INHIBIT enzymes
E.g. Grapefruit juice can inhibit CYP3A4 which eliminates blood pressure drug Verapimil - so patients taking both can get low BP and dizziness.
Apart from renal elimination, what are some others routes of drug elimination?
Lungs, milk, sweat, saliva
What is glomerular filtration?
When an unbound drug is filtered to the bowman’s capsule - 20% of filtration
What is active tubular secretion?
Where ionised molecules are passed to the proximal tubules through OATs and OCTs.
What is passive tubular reabsorption?
If drug is lipophilic, will be passed BACK down the concentration gradient and reabsorbed.
What is clearance?
Volume of plasma that is completely cleared of a drug per unit time.
What is the symbol for drug clearance?
Cd
What is drug half life?
The time in which a drug will decrease to one half of that concentration when it was first measured.
What is the equation for drug half life?
T 1/2 = 0.693 x Vd / Cl
What does it mean when the drug conc against drug half life graph is linear?
The rate of excretion of proportional to the conc of the drug
What is zero order kinetics?
The drug cannot be eliminated any faster - saturated
Shown by drugs at high doses - can be fatal
Like bmax/vmax in graph - FULL SATURATION
What is a therapeutic window?
The conc. of drug which has a noticeable effect on the body but isn’t toxic.
