Drug Absorption Flashcards
What is pharmacokinetics?
What the body does to the drug (metabolism etc)
What does ADME stand for?
Absorption
Distribution
Metabolism
Excretion
What is absorption?
Process by which unchanged drugs enter the circulation
What is distribution?
Dispersion or a drug among fluids and tissues of the body
What is metabolism?
Transformation of a drug into daughter compounds
What is excretion?
Removal of drugs/ metabolites from the body
Why is ADME important (5)?
Safe and intelligent use of medicines by all doctors Designing dose regimens Monitoring treatment compliance Medicine licensing requirement Substance abuse monitoring
What does the choice of delivery rate depend on (4)?
Speed of onset
Convenience
Bioavailability
Side effects/ specificity of action
What is bioavailability?
Proportion of administered drug reaching the system circulation
What is the bioavailability for IV drugs?
100%
What are the routes of administration?
Oral
IV
What are the three options of delivery for IV drugs?
Subcutaneous
Intramuscular
Intravenous
Where is subcutaneous IV?
Under the epithelium
Where is intramuscular IV?
In the muscle
Where is Intravenous IV?
Into the blood vessel
What is the BAR availability of drugs?
Amount of drugs to reach the bloodstream
What is transcellular?
Through cells
What is paracellular?
Between cells
How can drug absorption occur?
Active transport through cells
Facilitated diffusion through cells
Passive diffusion
What is ficks law?
Rate of diffusion = surface area x concentration difference x permeability
What is drug permeability governed by?
Molecular size, lipid solubility and presence of charged or ionisable groups
What does the extent of drug ionisation depend on?
pH of environment and the acid/ base dissociation constant of the drug
What must drugs be to diffuse across cell membranes?
Uncharged
What drugs are absorbed most effectively?
Nonionisable, lipophilic drugs
What do the Henderson-hasselbalch equations do?
Predict the extent of ionisation
In the Henderson-hasselbalch equations, when does pH=pKa?
When drug is 50% ionised
What will happen to acidic drugs when the pH decreases?
More unionised
What will happen to alkali drugs when the pH increases?
More unionised
Is aspirin acidic or basic?
Weak acid
What form is aspirin in in the stomach?
Unionised
How can aspirin not move back from bloodstream to stomach?
Once it is absorbed into the bloodstream, it ionises so it can’t be reabsorbed
What is ion trapping?
Acidic drugs are absorbed efficiently into stomach whereas basic drugs aren’t and give versa
Where do oral basic drugs get absorbed into the bloodstream?
In the intestine, where the surface area compensates for low absorbance efficiency
What are the lipinski rules?
A set of rules that help to determine specific properties of a developing drug
Give the lipinski rules
Molecular weight <500Da
No more than 5 h-bond donors
No more than 10 h-bond acceptors
LogP<5 (partition coefficient)
