Lecture 4 Flashcards
Explain half life and how it’s calculated
a measure of how long it takes the body for
see beginning of lecture 4
**it is independent of the dose of the drug
After how many half lives have you eliminated 98.4% of the drug?
6 (critical number of half lives to essentially eliminate drug from the body)
Why does half life need to be considered when switching medication?
because you need to know how long to wait before the previous drug is out of their system and take this into account if you don’t want them to overlap
What needs to be considered in addition to the half life of the parent drug?
What is an example of this?
the half life of metabolites of that compound that may be therapeutically active
Prozac (it’s metabolites can remain for as much as 14 days)
What is ‘steady state concentration’
how is it calculated
see book/lecture
it is about 6 times he drug’s half life
What are the basic premises of therapeutic drug monitoring?
Need to assume things because using blood levels of a drug as a proxy
- Blood concentrations of psychotropic drugs correlate well with concentrations at sites of action (assumption - because we are checking the blood levels so we need to assume this, but usually accurate assumption)
- the bio-availability of a drug must be at the threshold or above in order to induce and maintain a pharmacological response (need to know based on published data what the estimate for the correct level of drug at the site should be? i think? check lecture)
What are the goals of therapeutic drug monitoring?
- figure out if the patient is taking the med as prescribed and that blood levels are sufficiently high to have a therapeutic effect
- maximize the therapeutic effectiveness by elevating the blood levels slowly over time (if give too much initially might be toxic or have side effects, so this allows to give a dose and monitor and keep increasing it until you’ve reached the level you want)
- avoid toxicity (especially serious or potentially fatal side effects)
- > Cary also notes that in addition to blood levels we also measure other indicators of overall health that could be impacted by the drug (e.g., clorpromaize? antipsychotic which can have a bad side effect on white blood cells so need to monitor for this)
Tolerance?
body likes to remain at homeostasis, so there are compensatroy mechanisms it uses when it’s exposed to a drug
what is metabolic tolerance
See lecture
what does physiological tolerance lead to?
physical dependence (which results in withdrawl symptoms
What is physiological tolerance
physiological, cellular-adaptive or pharmacodynamic tolerance that occur due to cellular compensatory mechansims that occur in response to the drug’s specific efect (e.g., receptor up or down regulation)
so if there is a lot of a neurotransmitter it can actually reduce the number of receptors to try and get back to homeostasis
what type of half life is better for withdrawal?
if a drug has a long half life and is more slowly eliminated from the body it helps by giving the body more time to adapt (weaning off it)
What is behavioural tolerance?
learning to decrease or compensate for the effects of a drug
example he gave was contexual cues around someone with a drug problem resulting in them requiring more of a drug to reach the same high, but if those contextual cues were changed they would require less
also mentioned someone driving while under the influence
what is behavioural (or psychological) dependence?
repeated re-administration of the drug, not because of withdrawl symptoms, but because it promotes a sense of wellbeing
- example is somking (nicotine withdrawal only takes a week but it’s the psychological aspects of the addiction that remain and are more challenging to quit)
What is pharmacodynamics
the study of the mechanisms of the drug action at the molecular level
e.g., What does the drug do to the body at the (often) receptor level?
How do most psychotropic drugs work?
by altering synaptic functioning
What are the possible mechanisms of action for a psychotropic drug?
what should be noted
- changes in production of neurotransmitters
- interference with neurotransmitter storage or release
- direct interaction with pre and/or post synaptic receptors
- interfernence with neurotransmitter reuptake or destruction
*because of tolerance and changes in the cellular makeup as a result of the drug, there could be longer term effects of the drug that could actually lead to the therapeutic effect of the drug
so these are the direct mechanisms of action but there are longer term adaptations
What are the classification of drugs (based on action)
- Agonist
- Antagonist
- Competitive binding (direct)
- Non-competitive binding (indirect)
- Partial agonists/partial antagonists
What does it mean for a drug to be a partial agonist and partial antagonist?
drugs that act like an agonist or an antagonist depending on the level of neurtransmister that’s present. They bind to the receptor but aren’t as effective as the natural ligand meaning if there is a lot of neurotransmitter in the area competing for receptors, it would act as an antagonist
if there is very little neurotransmitter present it would at least stimulate the receptor a bit so it would act as an agonist
What is competitive binding?
A way of drugs interacting with a receptor
- the simplest way is direct competition for the site on the recptor
What is competitive binding?
A way of drugs interacting with a receptor
- the simplest way is direct competition for the site on the recptor
- to be effective the dose of the drug needs to be present for it to be able to out compete the neuro transmitter
(can occur for agonists and antagonists)
what is non-competitive binding?
when the drug binding site is different from the binding site of the neurotransmitter (not competing for the same binding site)
can exist for agonist and antagonist
What does it mean for a drug to be a partial agonist and partial antagonist?
drugs that act like an agonist or an antagonist depending on the level of neurtransmister that’s present. They bind to the receptor but aren’t as effective as the natural ligand meaning if there is a lot of neurotransmitter in the area competing for receptors, it would act as an antagonist
if there is very little neurotransmitter present it would at least stimulate the receptor a bit so it would act as an agonist
What is drug affinity?
the readiness with which two molecules join together (how sticky a drug is to a certain receptor)
what is drug specificity?
the selectvity of the drug for a specific receptor
- the same drug can bind to multiple types of receptors whereas other medications are more specific to a certain kind of receptors
Whar are autoreceptors versus heterorecptors
receptors on the pre synaptic neuron that are for the same NT the neuron is releasing (the one releasing the NT) are known at autoreceptors
heteroreceptors are receptors on pre synaptic neuron that is different from the NT that the neuron is releasing
Low number of affinity means?
low number means high affinity (so 1 is very high affinity) anything above 50 is pretty low affinity
What are dose reponse curves used for?
to quanitfy drug receptor interactions -> how the drug affects the body
looking at the theraputic effect
see textbook
What is a graded dose response curve
plotted as a function of the intensity of some effect
what is a quantal dose repose curve
plotted as a function of cumulative percentage of people responding to a certain measureable threshold
so really looking at how a group of people respond to a medication
Why do we need to look at dose response curves
because it tells us about the dose needed for a therapeutic effect but also a toxic effect so important to know how far apart these are
also other reasons (being able to find the lowest dose with the maximal response)
What info does a graded dr curve give us
- see slides
What is the therapeutic index?
the distance between a therapeutic/effective dose to a toxic dose
What is the therapeutic index?
the distance between a therapeutic/effective dose to a toxic dose
so it’s LD50/ED50 (see textbook)
ratio of the leathal dose for 50% of animals tested OVER the effective dose for 50% of the animals tested
Big ratio is good (want it to be a big number)
ratio of 1 means helping half and killing half = BAD
What are 3 indices of drug safety?
- Therapeutic index
- Certain safety factor
- Srandard safety margin
What is the certain safety factor
leathal dose of 1% OVER the dose effective for 99%
what is the standard safety margin
see slides
what are biological theories of depression (note this is the second one he discussed and first he talked about the simpler one need to add to FCs)
a slightly more contemporary theory that focuses on the receptors (rather than NT) and that genetic, epigenetics, and experience has affected circuits regulated by monoamine brain circuits
posists that depleted NT at some point has led to an upregulation of receptors which is the cause of depression
Note that there is not a lot of evidence to support this either
what do the most recent biological theories of dperession suggest
that molecular events downstram of the monoamine receptors are dysregulated in depression
- one of the genes that is thought to be affected is BDNF which keeps neurons viable and under conditions of stress is suppressed
hippocampal and amygdalar neurons important for suppressing the HPA axis
basic idea is rather than looking at the NT or receptor level we need to look at epigenetics
