Pharmacology exam Flashcards
What is pharmacokinetics?
The effect that the processes of the body have on a drug - how the drug moves through the body
What is pharmacodynamics?
The effect that a drug has on the processes of the body - The response the body has to the drug
The 4 processes involved in pharmacokinetics
Absorption, distribution, metabolism, excretion
Define Absorption
Absorption - how the drug crosses a biological membrane and enters the circulation (none if given IV)
Define Distribution
Distribution - how the drug is transported by the circulation around the body
Define metabolism
Metabolism - how the drug is inactivated or transfomed by enzyme action.
Usually metabolites are produced which are more water soluble so can be excreted
Define Excretion
How the drug is removed from the body
Steps a prescriber can use to minimise ADR’s
Avoid giving medication unless you have to
Check previous reactions/allergies
Assess other medications including OTC and herbal
Be aware of age, renal function and hepatic disease
Prescribe as few drugs as possible
Give clear indications for administration
Consider if exipients could cause reaction
Factors that affect a patients ability to metabolise drugs
Liver funtion and disease
Genetics - ie codeine metabilism
Age - delayed production and elimination of metabolites may prolong drug action
Reduced hepatic blood flow
Tolerance - if drugs have been given repeatedly.
Name sites of drug excretion
KIDNEYS - most drugs and metabolites are excreted here
Bile - excreted from liver to bile and eventually faeces
Lungs - Alcohol and anaesthetics
Breast milk
Sweat
Saliva
Tears
What factors do you need to consider when prescribing for an elderly patient?
Do they take other medicines?
Can they take the medicine - remember/ open container/ swallow / read instructions etc
Decreased renal function - may affect elimination
Size/weight
Decreased gastric emptying - so reduced absorbption of oral drugs
Decreased plasma proteins
Define steady state…
The point at which the rate of ELIMINATION (not excretion) of an orally administered drug is equal to its rate of absorption
Define volume of distribution
The (theoretical) amount of drug in the body (dose) to the concentration that is measured (in blood, plasma etc)
What is an agonist
b) a drug which binds to a receptor and elicits an effect
What is an antagonist?
A drug that blocks or dampens a biological response by binding to and BLOCKING a receptor
What is therapeutic drug monitoring?
When regular plasma blood levels are taken - ie to ensure drugs with a narrow theraputic index are used effectively
Define therapeutic index
Its the range between the toxic dose and the amount of drug required to have a theraputic effect.
Define the purpose of metabolism on a drug…
Modifying the chemical composition of the drug, usually to remove the pharmacological activity of the drug. Metabolites are usually more water soluble then the drug which promotes excretion from the body. Most metabolism occurs in the liver by hepatic enzymes. Metabolic processes include oxidation, reduction, hydrolysis and conjugation. Metabolism can also make a drug active - ie codiene to morphine
What factors can affect oral absorption of a drug?
Gut motility - less absorbed if increased gastric emptying - speeds up absorption gut ph blood flow presence of food and fluid antacids drug composition - liquid preparations nore readily absorbed then solids Lipid solubility
What is meant by bioavailability?
the fraction of an administered dose which reaches the general systemic circulation in an unbound / unaltered form and is able to exert its mode of action.
How could bioavailability of a drug be increased or decreased?
Increased metabolism at first pass Decreased absorption from site of action Protein binding in plasma Distribution into other body tissues Intravenous route
Define loading dose…
A dose which is larger than normal to allow the plasma steady state to be reached quickly
What does half-life mean?
It’s the time taken for the concentration of the drug ion the blood to fall by half its original value - used to allow a dose to be calculated to produce a stable plasma concentration
What is an adverse drug reaction?
An unwanted or unintended effect of a medicine which occurs during proper use at a normal dose
What is first pass metabolism?
When a drug gets absorbed from the GI tract, and travels to the liver via the portal vein and gets metabolised there resulting in loss of active drug to continue to the general circulation and reduced bioavailability.
Which ONE of the following is a true statement ?
a) A drug which binds readily to plasma proteins must be given by the I.V route
b) A drug which binds readily to plasma proteins is known as an agonist
c) A drug which binds readily to plasma proteins may be displaced by another drug competing for binding sites
d) A drug which binds readily to plasma proteins cannot be absorbed from the GI tract
c) A drug which binds readily to plasma proteins may be displaced by another drug competing for binding sites
So… the drug has entered the blood stream but become bound to the protein (like riding in a taxi) so in general are not active (when bound they are too big to pass through cell membranes). Warfarin in 98% plasma bound - so only 2% active however if asprin comes along it may displace some (like fighting for a taxi) and therefore there will be more UNBOUND warfarin in the circulation - more active drug.
Give an example of a pharmacokinetic drug interaction
So an interaction involving how the processes of the body effect the drug - ie absorption, distrobution, metabolism, excretion.
Warfarin binds to plasma proteins. Asprin may knock it off these hence increasing the active amount in the blood stream.
Give an example of a pharmacodynamic drug interaction
So an interaction that involves how the drug affects the processes of the body
ie drugs which could cancel each other out or reduce effects
ACE inhibitors and NSAIDS
Which symbol is used in the BNF to identify a drug where there has been limited use and the MHRA require that all suspected adverse reactions are reported
A Black triangle
Briefly explain the purpose of metabolism of a drug
To change an administered drug into its active form
To change an active drug into an inactive or less active compound
To change a drug into a more water soluble form to allow it to be excreted by the kidney.
What do you understand by the term “steady state” and how might this inform your prescribing?
This is the term used to describe the point when, after repeated doses of a drug , the rate of absorption is equal to the rate of elimination
The plasma level at this point remains constant within a particular range
This can be used to determine the optimal dose for therapeutic effect and minimal side effects
For drugs with a long half life a loading dose may be needed to achieve this therapeutic range within a suitable time frame.
Whats the difference between elimination and excretion?
Excretion is the irreversable removal of the drug from the body ie via kidneys, sweat, etc. Elimination is the metabolism of the drug to an inactive state which may then be excreted
List factors which may be important to consider when prescribing for a child
Can they take the preparation? Is it liscenced for use with children Weight Age Is the dosing schedule appropriate
