module 6 Flashcards
what is clinical pharmicokinetics
relationship between effects of a drug and the concentration of a drug
what is the purpose of clinical pharmacokinetics?
- provide a quantitative relationship between drug
dose and effect - provide a framework to interpret measurements of drug concetrations in biological fluids to benefit drug therapy
what does clearance mean?
the bodys efficiency in drug elimination
irreversible drug elimination of the body
volume/time
can vary in route (hepatic, renal)
what is elimination half life?
a measure of the rate of removal of the drug from the body
what is bioavalibility?
the fraction of drug that reaches the systemic circulation unchanged
why dont we measure drug concentrations from the site of action?
becuase its too invasive! taking a drug concentration from the brain for schizo meds would do more harm than good!
how are drug concentrations measured?
-measured in the plasma
why is plasma a good site to measure drug concentrations
- non invasive
- there is a good correlation between plasma concentration and therapeutic/toxic effects
what are the characteristics of an oral administration drug concentration time curve?
- in the begining, the rate of absorption is greater than
elimination - so plasma concentrations increase - in the middle, the rate of absorption equal the rate of
elimination - in the end, elimination is greater than the rate of absorption, so plasma concentration declines
what is the Cmax
when the absorption and elimination are equal
What is the minimum effective concentration (MEC)
the minimum concentration required to have a therapeutic effect
what does duration mean in a time curve?
the amount of time that the drug concentration is above the MEC
what is the therapeutic range?
drug concentration are above the MEC but below toxic concentrations
what are the characteristics of a wide therapeutic range?
considered safe because the range between toxic and MEC is large - so its unlikely that the patient will reach toxic ranges if its taken as prescribed
what does the therapeutic range matter?
determines how safely a drug can be administered
what are the characteristics of a narrow therapeutic range?
- difficult to adminster safely
-small range where the drug will be effective but not
toxic
-often undergo therapeutic monitoring to ensure the concentrations are within toxic range
what is the onset of action for drugs?
how long it takes before the concentrations reach MEC
lag time varies from drug to drug
how soon the drugs effects will occur
what affects the onset of action
the rate and extent of absorption
what is required to maintain a steady state for continous IV?
absorption and eliminated are at the same rate
when has steady state been reached with PO or IV bolus meds?
when peaks and trough concentrations are the same between doses
you want the fluctuations to be within therapeutic range
what are strategies to avoid flucations in plasma concentrations?
- continous IV
- depot preparations - slow constant release
- change in dosing interval - total daily dose but given more times in a day
what is total clearance?
- sum of all clearance by all routes
- determines the dose required to maintain a certain
blood concentration of the drug
what is the dosing rate and what is the formula?/
helps you understand the dose to presribe
dosing rate = plasma concentration X clearance
what is the half life and what is its formula ?
the time it takes for a drug to reduce its plasma concentration by 50%
half life = 0.693 X Vd/Cl
how many half lives does it take for a drug to reach steady state
5
what is the purpose of a loading dose
to get patients into steady state concentrations quicker
what is the formula for loading dose
loading dose = target plasma concentration X Vd
