psychopharmacology - week 6 part 1 Flashcards
psychoactive drugs are drugs which:
alter neurotransmission
affect mood/behaviour
effective in managing psychological problems
- not naturally present in body
- may be found in plants
- compounds synthesised in a chemical lab
psychopharmacology
study of the interaction between psychoactive drugs and the body
why learn about psychopharmacology
tells us something about how the brain works
- role of specific transmitters + receptors in psychological processes
- causes of psychiatric illness
helps us understand and deal with problematic drug use
- concerns w/ health conc. of drugs
- controversy over drug usage in psychiatry
- education allows responsible assessment of costs/benefits of drug use in society
what is pharmacokinetics concerned with
route of administration
absorption/distribution
metabolism
elimination/excretion
routes of administration
oral
rectal
sublingual
buccal
nasal
transdermal
inhalation
injection
routes of administration - oral
ingestion
most common - dissolves in stomach - intestines - blood stream via intentional membrane
adv
- self administered
- pain free
- easy
dis
- not suitable for emergencies (slow action)
- gastric irritation
- some drugs destroyed by acid in stomach
examples: paracetamol, calpol
routes of administration - rectal
common if unconscious
adv
- avoids nausea
- potentially only option if cannot take orally
- drug cannot be destroyed by enzymes
dis
- invasive
- uncomfortable (irritation of rectum)
- reduced SA may limit absorption
examples: laxatives, acetaminophen
routes of administration - sublingual
tabs under tongue
adv
- rapid and easy absorption
- alternatives to tablet
- drug directly into blood
dis
- accidentally swallowed
- unpleasant taste
- may irritate mucous membrane
examples; oxytocin, nitroglycerin
routes of administration - transdermal
patches on skin
adv
- less frequent drug use
- painfree self administration
- drug released at steady rate
dis
- potential for allergicc reactions
examples; nicotine patches, contraception, anti-nausea
routes of administration - inhalation
adv
- quick effect - straight into lungs
- fewer doses required
- can be used for unconscious patients
dis
- can lead to further breathing issues
- special apparatus needed
examples; asthma medication, anaesthetics
routes of administration - intravenous injection
in veins
adv
- quick and precise
- preferred method fro unconscious patients
- can control exactly how much drug
dis
- requires skill
- greater risk of infection
- can be painful
- can lead to inflammation of blood vessel (phlebitis)
examples; chemotherapy drugs, some antibiotics (meropenem)
routes of administration - intramuscular injection
in muscles
adv
- absorption rapid
- can control exact vol.
- slow-releasing drugs are also given this way
dis
- requires skill
- nerve damage
routes of administration - subcutaneous injection
under the skin
adv
- absorption slow + constant
- hygienic
dis
- might lead to abscess formation
- absorption limited blood flow
examples; insulin, adrenaline, norplant
absorption
unless give IV drug must cross cell membranes before can get to blood plasma
diffusion of drugs across lipid membranes effected by
- qualities of drugs
–> lipid soluble and small diffuse best
–> unionized drug molecules are more lipid-soluble
distribution
target for psychoactive drugs usually in brain
in blood plasma so reach all parts of body
side effects due to bindng at receptor outside of brain
some drugs are temporarily inactivated by storage in fat or attached to blood plasma proteins
- may prevent them reaching target sites
the blood brain barrier acts as a selective barrier to drug distribution
- glial cells –> large or non lipid soluble cannot enter (brain capillaries different from normal ones as they are protected)
metabolism
converts the drug chemically into another compound
- can be inert
- can be active (more active)
mainly takes place in the liver
- contains enzymes that help metabolism
sometimes essential for drug to be eliminated
elimination
different routes
urine
- via kidneys (main route)
- water soluble compounds
- fat-soluble drugs may be metabolised to make them water soluble
breath
- alcohol
sweat + hair
- often unmetabolised
- hair analysis (drug testing)
what is the duration of a drug affected by?
the rate at which it is metabolised and eliminated from the body
what does the route of administration effect
how much of the drug is absorbed and the onset of the effects
how to psycoactive drugs achieve their effects
by interacting with receptor sites in the brain
how do psychoactive drugs reach receptor sites
may enter the blood stream to be distributed around the body
what does the effect of a drug depend on?
the amount avaliable at receptor sites
principle of drug action: drug effects related to drug dose
for most psychoactive drugs amount of drug at receptor = amount in blood plasma
what does the onset of the drug depend on
factors relating to absoption
- the time taken to reach peak plasma levels affects the response of drugs
after peak levels reached the amount of drug reaching receptors is affected by distribution around the body, rate of metabolism and elimination
- most drugs distribute rapid
- main factor = time to detoxicfy drug for elimination
- metabolism to activate drug prolomgs drug action
what is half life
a measure of the duration of action of the drug and is defined as the time taken for the levels in the plasma to fall by half
short half life = needs to be administered more frequently
