Pharmacokinetics Flashcards
Pharmacodynamics
What a drug does to the body
Mechanism of action and effects on cellular functions
Pharmacokinetics
What the body does to a drug
ADME
What is ADME?
Absorption
Distribution
Metabolism
Excretion
What are well perfused organs and how does this impact drug action?
Lungs and kidneys
Takes up and releases drug quickly
What are poorly perfused tissues and how does this impact drug action?
Fat
Takes up and releases drug slowly
How does the size of a drug effect the diffusion coefficient?
The smaller the drug, the higher the diffusion coefficient
Why is vacular endothelium more complicated in terms of diffusion?
Its anatomical disposition and permeability varies from one tissue to another
Gaps between endothelial cells are packed with a loose matrix of proteins that act as filters so large molecules are retained
Lipid solubility
One of the most important factors in pharmacokinetic characteristics of a drug
Non polar molecules dissolve freely and can penetrate membranes freely
How does pH effect pharmacokinetic properties of a drug?
Affects steady state distribution of drugs between aqueous compartments
Basic environments
Favour dissociation of acids
Weak acids
Become trapped in basic compartments
Urinary acidification
Retards the excretion of weak acids
What effects does increasing plasma pH have on drugs?
Causes weakly acidic drugs to be extracted from the CNS into the plasma where they get trapped
Causes neurotoxicity
Bioavailability
Fraction of ingested dose that gains access to circulation
Low if drugs is metabolised in gut or liver or if there is vomiting
Intravenous administration
Most direct and reliable route and is fast acting
Used in emergencies
Subcutaneous or intramuscular injection
Next fastest route
Variable absorption depending on the site of injection and local blood flow
What is an intrathecal injection as a method of drug administration?
Lumbar puncture used to produce regional anaesthesia
Oral administration
Most common and easiest
Most drug absorption occurs in the gut by large SA and passive diffusion
What factors effect the rate of absorption when using oral administration?
Gut motility, presence of food, particle size and encasing of tablet and physiochemical factors
What carriers are involved in carrier mediated transport?
Solute carrier transporters
ATP binding cassette transporters
What substances take part in carrier mediated transport?
Sugars, amino acids, metal ions, neurotransmitters
Where are solute carrier transporters present in the body?
Blood brain barrier, GI tract, renal tubule, biliary tract and placenta
What are free form drugs?
Weak acids or bases that will exist at equilibrium between charged and uncharged form depending on the pH of the compartment
What drugs do not readily enter interstitial and intracellular compartments?
High molecular weight drugs like insulin or heparin
