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?
