Principles of pharmacology Flashcards
What is the difference between pharmacology and therapeutics?
- pharmacology is more focused on the ‘drugs’
- therapeutics is concerned with drug prescribing and the treatment of disease…more focused on the ‘patient’
What is the difference between pharmacodynamics and pharmacokinetics?
pharmacodynamics deals with ‘what the drug does to the body’, whereas pharmacokinetics deals with ‘what the body does to the drug’
What are the four classes of drug target proteins?
- receptors
- enzymes
- ion channels
- transport proteins
What is the drug target of aspirin?
- enzyme cyclooxygenase
- blocks production of prostaglandins
What is the drug target of local anaesthetics?
they block sodium ion channels, thus preventing nerve conduction
What is the drug target of anti-depressant Prozac?
block serotonin carrier proteins, preventing serotonin from being removed from the synapse
What is the drug target of nicotine?
it binds to and activates the nicotinic acetylcholine receptor
How does dose affect the selectivity/specificity of a drug?
at a low dose, the effect is more specific, due to the fact that the drug will only interact w/ 1 target…but as the dose increases, the effect becomes less specific, as the drug starts to interact w/ other drug targets–> producing unwanted side effects
What types of chemical interactions can be involved in drug-receptor interactions?
- electrostatic interactions: most common; includes H-bonds and vdw forces
- hydrophobic interactions: most important for lipid soluble drugs
- covalent bonds: least common, as irreversible
- stereospecific interactions: many drugs exist as stereoisomers
What is the difference between agonists and antagonists?
- both can bind to receptors, but only agonists bind and ACTIVATE receptors
- antagonists bind and BLOCK receptors
What is meant by the affinity of a drug?
the strength of binding of the drug to the receptor–> strength of each drug-receptor complex–> increased likelihood of receptor occupancy
What is meant by efficacy?
the ability of an individual drug molecule to produce an effect once bound to a receptor
e.g. no response, partial response or complete response… antagonists, partial agonists and full agonists
What is meant by potency?
- the concentration/dose of a drug required to produce a defined effect (THE LESS DRUG YOU REQUIRE FOR EFFECT, THE MORE POTENT IT IS)
- OR standard measure of potency= conc./dose required to produce 50% tissue response (EC50/ED50)
What is the difference between EC50 and ED50?
EC50:
- for in vitro experiments
- specific concentrations of drug added to test effectiveness
- EC50= the conc. that produced a 50% response
ED50:
- for clinical trials
- specific dose of drug given to individuals
- ED50= dose that produced desired effect in 50% of individuals tested
What is the clinical relevance of the difference between potency and efficacy?
efficacy is more important, as you want to know if drug can induce maximal response…potency simply determines dose needed to produce response
*if you have 2 drugs w/ equal efficacy, it doesn’t matter which is more potent, as you can still produce maximal response w/ the less potent drug (you just need to give a slightly higher conc.)
What is meant by absorption in pharmacokinetics?
the passage of a drug from the site of administration into the plasma
What is meant by bioavailability in pharmacokinetics?
the fraction of the initial dose that gains access to the systemic circulation
What are some common forms of drug administration?
- intravenous (bulk flow transfer in bloodstream)
- oral
- dermal (percutaneous)
- inhalation
- intranasal
What is pinocytosis?
when a small part of the cell membrane envelops a chemical molecules and forms a vesicle containing the drug, which then releases the chemical on the other side of the membrane
Why is diffusion across aqueous pores not a major route for movement of drugs?
because most pores <0.5nm in diameter and there are very few drugs this small
How do most drugs move across membranes?
by diffusing across lipid membranes (need to be lipid soluble) or by carrier mediated transport, involving a transmembrane protein that binds drug molecules on 1 side of membrane and transfers them across to other side
Why are most drugs water soluble, not lipid soluble?
if given orally, need to be water soluble to dissolve in the aqueous environment of the GI tract and so be available for absorption
N.B. most drugs are either weak acids or bases, so exist ionised and unionised
What two things determine whether a drug is ionised or not?
- the dissociation constant (pKa)
2. the pH in that part of the body
If pKa of a drug= pH of the tissue are equal, then what % of the drug is ionised?
the drug will be equally dissociated–> 50% ionised and 50% unionised
N.B. a weak acid will be more unionised in areas of low pH like the stomach and a weak base will be more unionised in areas of high pH like blood and urine
