Pharmacology Flashcards
what is distribution
the process by which a drug leaves the circulation and enters tissues perfused by blood
what is metabolism
the process by which tissue enzymes catalyse the chemial conversion of a drug to a more polar form that is more readily excreted from the body
what is excretion
the process by which the drug is removed from the body
what is pharmacodynamics
what a drug does to the body
what is pharmacokinetics
what the body does to a drug
what is an agonist
a drug that binds to a receptor to produce a cellular response
what is affinity
strength of assoiation between a ligand and a receptor, as affinity increases dissociation rate decreases
what is efficacy
ability of an agonist to evoke a cellular response, as efficacy increases the response rate also increases
what is an antagonist
drug that blocks the action of an agonist, possess affinity but not effcacy
competitive antagonism
binding of an agonist and antagonist occur at the same site and is therefore competitive- reduced potency of agonist, does nothing to efficacy of agonist. causes parallel right shift of angoist concentration with no depression in maximal response
non-competitive antagonism
agonist and antagonist do not bind at the same site, does not effect the potency of the agonist but decreases the efficacy of the agonist and the depresses the slope and maximum response curve.
factors controlling drug absorption
- solubility
- chemical stability
- lipid to water partition coefficient- the relatice solubility of a drug in lipid compared to water and rate of diffusion of drug increases with lpid solubility
- degree of ionisation- most drugs exist in equilibrium, on unionised forms readily diffuse across the lipid bilayer
5 factors for drug absorption in the gut
- GI motility
- pH at the absorptive site
- blood flow
- the way in which the drug is manufactured ie is it slow released
- physiochemical interactions
enteral route of administration
oral (convienent, non-sterile, good absorption generally, not good for some drugs due stomach acid and enzymes, first pass metabolism and GI irritation)
sublingual (by passes portal system so avoids first pass metabolism, avoids gastric acid)
rectal (by passes portal system, so avoids first pass metabolism, avoids gastric acid and variable absorption)
parenteral route of administration
IV (100% systemic availability, rapid onset, continuous infusion, can be used for drugs that cuases local tissue damage, sterile, risk of sepsis, high drug level at heart)
IM (rapid onset of lipid soluble drugs, slow prolonged release, painful, tissure damage and absorption variable)
inhalation (lungs have higher surface area, good for volitle agents, good for local effect)
topical (ideal for local effect)
First order kinetics
rate of elimination is directly proportional to drug concentration. Half life is inversely proportional to elimination rate constant
First order kinetics
rate of elimination is directly proportional to drug concentration. Half life is inversely proportional to elimination rate constant
rate of elimination=
clearance x plasma conc
what is volume of distribution
volume into which a drug appears to be distributed with a conc equal to that of the plasma
factors which affect drug disposition
ADME- absorption, distribution, metabolism and excretion
Phase 1 of drug metabolism:
oxidation, reduction and hydrolysis (making a drug more polar, adds a chemically reactive gorup permitting conjugation)
Phase 2 of drug metabolism:
conjugation, adds endogenous compound increasin polarity
renal excretion of drugs:
- glomerular filtration (occurs freely for most drugs)
- active tubular secretion (organic anion transporter- handles acidic drugs and organic cation transporter- handles basic drugs)
- passive reabsorption
what is depolarisation
the membrane potential has become less negative or even positive
what is Hyperpolarisation
the membrane potential becomes even more negative
sodium channels
Na+ flows inwards
concentration of 140mm outside cell and 10-15mm inside cell
negative driving force- inward movement of sodium