Pharmacokinetics 1 Flashcards
what does ADME stand for ?
absorption - is the administration of the drug into the systemic circulation
distribution- is the movement of the drug from the systemic circulation to the target tissue
metabolism - breaking down the drug down
excretion - removal of the drug from the body
define pharmacokinetics :
it is how the body affects a drug
what is pharmacokinetics important for ?
important for constructing dosage and administration regimes
- many drugs fail due to poor kinetics in man
what does an effective drug require a balance between ?
between its ADMET properties
- adsorption
- distribution
- metabolism
- excretion
- toxicity
what is the Cmax?
it is the maximum concentration that a drug achieves in tested area after administration and before second dose
what is Cmin ?
it is the minimum concentration achieved in a tested area after administration
what is Tmax ?
it is the time at which C max is achieved
what does disposition equal ?
absorption, distribution, metabolism and excretion
what is T0.5?
it is the time at which half the Cmax is achieved
what are Cmax, Tmax and T0.5 dependent upon after oral administration ?
dependent on drug absorption rates and disposition profile of the drug
what does AUC stand for ?
area under the curve
the are under the curve of a plot of concentration of drug in plasma against time
what does the AUC show us ?
shows the total exposure that the body gets from a single dose
also shows the maximum drug concentration that the body receives and shows the speed of drug metabolism
what is the therapeutic index?
= toxicity in 50% of population/ minimum effective dose 50%
also known as therapeutic window
= TD50/ED50
if a drug x can regress cancer cells by binding to R1 receptor and its KD is 2nM and it also binds to R2 causing cell death of healthy cells with a KD of 800nM, what is drug x’s therapeutic index?
= 800/2 = 400
this ratio allows us to see at what point a highly beneficial therapeutic becomes a lethal toxin
what does a narrower therapeutic index mean ?
the narrower range means it is more likely to cause toxicity/overdose
what is absorption ?
it is the movement of drug from the site of administration to systemic circulation - NOT THE SITE OF ACTION
what is bioavailability a measure of ?
it is a measurement of the rate and extent to which a drug reaches the systemic circulation(expressed as F) and applies to all routes of administration
- it is defined by the rate it appears in the blood and the relative amount of drug from the administration dosage which enters the systemic circulation
what is the ROA ?
route of administration- it is very important and the most appropriate route must be considered
describe the different speeds of absorption for different methods of administration :
from fasted to slowest
- intravenous
- pulmonary
- intramuscular
- subcutaneous
- oral
how is bioavailability determined and what is the bioavailability of intravenous drugs ?
= AUC(oral)/AUC(i.v)
bioavailability of i.v is 100% beccause 100% is placed in the circulation
what information does the Cmax and Tmax provide?
gives the rate of absorption
what does i.v admin avoid ?
it avoids first pass metabolism
what are the advantages/disadvantages of i.v. admin ?
advantages
- very rapidly acting- 5-10seconds, very useful for pain relief
disadvantages
- not useful for drug compliance
- increased chance of infection, overdose, arterial damage
how does oral admin work ?
it is the most common and onset is about 10-20mins but it needs to be absorbed
- absorbed by small intestine, which has a large surface area and a rich blood supply
