Pharm 4 - Pharmacokinetics and Drug Metabolism Flashcards
State the 5 stages of the journey of a drug through the body.
Administration Absorption Distribution Metabolism Excretion
What is the difference between enteral and parenteral administration?
enteral = using GI tract parenteral = everything but the GI tract
What are the advantages of IV administration?
Rapid + high bioavailability
State two ways in which drug molecules move around in the body.
Bulk Flow Transfer
Diffusion transfer
State 4 ways drugs can cross lipid membrane barriers.
Diffusion through lipid membrane if lipid enough
Diffusion across aqueous pores
carrier moleculues
pinocytosis
Most drugs are either …
weak acids or weak bases
Which factors affect the ratio of ionized to non-ionised drug?
pKa of the drug
pH of the environment
Describe and explain the difference in absorption of aspirin in the stomach and in the small intestine.
Aspirin has a pKa of 3.4
in the acidic conditions of stomach, aspirin takes an unionised form.
because it is unionised it is rapidly absorbed.
in the small intestine, the pH is much more basic, higher pKa than the pKa of aspirin. So aspirin exists in an ionised form. This is not absorbed quickly.
What is ion trapping?
Some ionised aspirin will enter systemic circulation
there it will exist in an ionised form
because it is ionised it cannot move into tissues
therefore ‘trapped’
State 4 factors affecting drug distribution
Regional blood flow
extracellular binding
capillary permeability
localisation in tissues
In which state can albumin bind to drugs, ionised or non-ionised?
Both
State three types of capillary architecture.
Continuous
Fenestrated
Discontinuous
Give a broad example of localisation of a drug in tissue.
Lipophilic drugs tend to localise in fatty tissue e.g. brain and testes
What are the two main routes of drug excretion?
Kidneys - main
Liver
What type of molecules tend to get excreted via the biliary route?
Large molecular weight molecules
Via what form of molecular movement do most drugs tend to get excreted into the urine?
Active secretion
What happens to drug-protein complexes at the glomerulus?
Not filtered into the filtrate
Where does active secretion of acids and bases occur in the nephron?
Proximal Convoluted Tubules
What can happen to lipid soluble drugs in the proxiaml and distal convoluted tubules?
Could be reabsorbed
Why might treatment with iV sodium bicarbonate increase aspirin excretion?
IV sodium bicarbonate will increase pH of blood
so aspirin is more ionised and more water soluble so more likely to be excreted by kidneys
What is the main purpose of the active transport systems that secrete drugs into the bile?
There to excrete bile acids but drugs can hitch a ride
What is a potential problem with biliary excretion of xenobiotics?
enterohepatic cycling - reabsorbed
Define bioavailabily.
The proportion of the administered drug that is available within the body to exert its pharmacological effect
Define apparent volume of distribution
the volume in which a drug appears to be distributed
Define biological half life
time taken for the concentration of a drug to fall to half its original value
Define clearance
Volume of plasma cleared of drug per unit time
Define first order kinetics
when the rate of excretion of a drug is proportional to the concentration remaining within the body
e.g. more drug in body = more excretion
Define zero order kinetics
Constant amount of the drug is removed from the body per unit time
What does zero order kinetics suggest about the enzymes involved?
Saturated
