pod2ndyear's version from 2015-08-20 22:45

Pharmakokinetics lectre

Question Answer
Pharmacokinetics deftime if takes the body to deal with drug
first order kineticsconstant FRACTIONAL change per time. ex- with a .5/hr 50% of current amount will be eliminated every hour
0 order kineticsCONSTANT CHANGE per time. ex etOH has a 0 order of .2mg/hr so every hour an exact amount of 20mg is eliminated.
half-lifethe time it takes for half of the amount to be eliminated
clearanceThe volume of plasma cleared of the drug per unit time (each organ can have its own clearance rate but can be added together for a total system clearance) calcuated by elimination rate/concentration. also from AUC
what is the def of Vdratio of drug in the body to the plasma concentration
large Vdthe drug is being sequestred and not eliminated(extended half life)
small Vdlarge amount of drug is bound to protiens
(review)what are the rate limitng steps of fate of a drugDisentigration, dissolution, absorption
release from matrixliberation
process and rateabsorption
movment in bodydistribution
removal by biotransformation metabolism
physical removal from bodyexcretion
single compartment method
2 compartment modelcentral and peripherial compartments of the body where the drug goes in and out of, first order, elimination is from central compartment
Cmaxpeak plasma concentraion of drug
Tmaxtime it takes to get to Cmax
plateau principlea paltueau is reahed only when elimination equals administration (IV) otherwise the plasma concentration will keep increasing.
when is steady state reached4-6 half life times. complete elimination is also at 4-6 half life times
will an increased dosage make the steady stage come fasterNO. a higher dosage will just have a higher amont of drug. the steady state is still reached at 4-6 half life times
multiple dosesdrug will accumulate if time interval between doese is less than 4 half lives ???
oral multiple dosesbioavalbility will affect CSS (concentration steady state) plasma concentraion will fluctuate between a peak and a trough concentration)
dosage interval is depened on 2 acceptable dosage and pt convience
loading dosewhen reaching a steady state fast is important. dependant dose=Css x Vd. loading dose is usually folowed by a maintaince dose to keep the steady state
nonlinear eliminationsome drugs will exceed metablosm in that body cant eliminate in a linear rate. follows michaleis -menton
Fetal drug exposurefetus gets some degree of mothers drugs. single doese-takes about 20 min -4 hours to reach fetus. chronic-if mother reaches steady state then fetus will get drug too.
drug metabolism in elderyeven though the metabolism is slower, the liver is able to metabolize drugs the same (at a slower rate but to tis full extent)
cockroft-gault equation-estimates glomerul filtration but comparing to creatine (creatine decreases about 8 after age 30)
Question Answer
what are the options for dosage adjustment for renal dysfuntiondecrease dose but maintain interval (prefered) or maintain dose but increase interval