drug routes (pharmacology 2 bds2) Flashcards
what are the routes of drug administration
enteral or parenteral ( ie via the gut or not via the gut) with subcategories
what is first pass metabolism
how is a drug transported in the blood
describe the stages of drug metabolism
what are the routes of excretion for drugs
what are the steps the drug takes from administration to excretion
administration
absorption
transport
clinical effect
metabolism
excretion
what are the routes of administration classified as enteral
this means via the gut and include
- oral
- rectl
- nasogastric
- nasointestinal
- PEG
what are the routes of administration under the parenteral classification
this means not via the gut and includes
- transdermal
- transmucosal
- intravenous
- intramuscular
- subcutaneous
- inhalation
what are the advantages of oral route drug administration
convenient
portable
painless
non invasive
cost effective
patient can self administer
what are the disadvantages of oral route drug administration
slow onset
may be inefficient
variable absorption
first pass metabolism
what is first pass metabolism
drugs entered via the gut can only enter circulation after passing through the liver, where it is metabolised. this means a portion of the drug can either be inactivated or activated, which is something that varies with liver disease and age.
what happens if the liver inactivates the drug via first pass metabolism
means that more will be needed by oral route to get the desired clinical effect
what happens if a drug is activated by the liver
less will be needed to be taken via the oral route if the liver can make an active form from an inactive drug
what are the advantages of intravenous// intramuscular drug administration
very rapid onset, predictable plasma levels and there is no first pass metabolism. this is because the drug is administered straight to the muscle or to circulation and will not have to pass through the liver first
what are the disadvantages of intravenous/ intramuscular drug administration
allergic reactions are more severe and the action duration is shorter
trained staff will have to administer it, it is more painful and the cost of the drug is higher
how does transdermal and subcutaneous drug administration work
this is when the drug is absorbed through the skin into the bloodstream and is usually just patches on the skin
what are the advantages of transdermal and subcutaneous drug administration
there is no first pass metabolism
allergic reactions can be very localised
action is prolonged, can stretch over days with patches
can be self administered
what are the disadvantages of transdermal and subcutaneous drug administration
the onset is very slow and the drugs cost is higher
the effect varies from person to person and from site to site
what is drug bioavailability
the proportion of an ingested drug that is available for clinical effect
how can bioavailability of drugs be modified
pharmaceutical factors: dosage, formulation, route of administration
physiological factors: destruction in the gut, poor absorption, first pass metabolism
what is drug distribution
this is the movement of a drug to and from the blood and various tissues
describe the route of drug distribution
- drug is dissolved in the blood and transported bound to carriers
- carries are usually plasma proteins like albumin
- bound drug is inactive but competitive binding could lead to drug interactions
which factors can impact the speed of diffusion into tissues from the blood
- blood flow to the area
- membrane characteristics
- pH
- active secretion of the drug into the tissue
what is planning drug use based on the idea of
body compartment model
describe the single compartment model for planning drug use
this is when the drug behaves as if it is evenly distributed throughout the body
body described as a single uniform compartment and there is rapid and homogenous distribution of the drug
describe the two compartment model for planning drug use
this is when the drug behaves as if it is in equilibrium with different tissues in the body
central and peripheral compartment - central is the highly perfused tissues with rapid drug distribution and the peripheral compartment has slower distribution because the tissues are not as well perfused
explain volume of distribution
different parts of the body receive different drug levels compared with plasma (relate to the compartment model)
drug selection may depend upon the preference of some drugs for some areas of the body, and some drugs are actively secreted into tissues or fluid rather than just simple diffusion
volume of distribution reflects the relationship between the amount of drugs in the body and plasma drug concentration. it is the apparent volume at which the current amount of drug in the body must be dispersed in order to give the current drug concentration and does not actually represent a physiological volume
advantage of drugs with lipid binding in tissues
slow release from accumulation gives the drug a more prolonged effect
describe how drugs are prepared for elimination from the body
phase 1 reactions are modification, including oxidation reduction and hydrolysis
phase 2 reaction are conjugation, ie when a compound is formed from combining two or more substances, including glycuronidation, sulphating, methylation and acetylation
what is the name for the super family of enzymes found mainly in the liver involved in the metabolism of drugs through a series of oxidation and reduction reactions
cytochrome p450 mono-oxygenate system
why is the basis for drug testing in the police usually some form of body fluid
this is how drugs are excreted from the body
what does the most extensive secretion if drugs occur through
renal excretion of water soluble metabolites via urine
liver metabolism and excretion via bile
lungs via inhaled gases and volatile fractions of other drugs
what are the drugs related to plasma concentration excreted through
sweat
saliva
tears
what are the three stages to drug elimination through the kidneys
glomerular filtration
reabsorption
secretion
how can renal disease interfere with drug excretion
chronic renal failure meaning filtration of blood is not efficient
in these cases the drug doses must be reduced
how can liver disease interfere with drug excretion
liver failure resulting in improper metabolism of drugs, again the drug doses must be reduced
when reducing drug use in an individual case of renal or liver disease, which factors can impact how much the drugs are reduced
depending on the organ function and which drug is being used
what is the plasma half life of a drug
this is the time taken to eliminate half of the drug
describe first order kinetics in relation to drugs
drug elimination increases as the drug concentration increases, excretion is through passive diffusion
describe zero order kinetics in relation to drugs
drug elimination is at a fixed rate, and is an active process irrespective of drug concentration. there can be drug accumulation if the saturation is exceeded
first order kinetics
first order kinetics
zero order kinetics
zero order kinetics
describe elimination of blood alcohol
zero order process where alcohol is removed from the body at a constant rate independent of its concentration, but this relationship does not exist at a lower blood alcohol concentration and will switch to a first order process
what happens if drug dosing is too frequent
plasma levels that may be toxic, depending on the drugs therapeutic index
what happens if drug dosing is too infrequent
will result in sub therapeutic plasma levels and no clinical effect
summarise paracetamol overdose
- manufacturer recommended safe dose of 4g over 24 hour period
- toxicology of these drugs arises from metabolic processes
- metabolism occurs mainly in the liver
- formation of toxic metabolites can cause liver damage, acute hepatotoxicity and liver failure
which route of drug absorption is the least reliable
oral route
