Drug Elimination and Dosing Flashcards
what the body does to the drug
pharmacokinetics
what the drug does to the body
pharmacodynamics
the central dogma states that the plasma concentration of a drug (Cp) determines ________
the drug’s clinical effects
this way of administering drug has no lag time (goes directly into bloodstream)
IV administration
what determines the loading dose (LD)
volume of distribution (Vd)
what determines the maintenance dose-rate (MD)
clearance (CL)
the time during which plasma concentration becomes half of the initial concentration
half-life (t1/2)
what determines the time to steady state and the dosing interval
half-life (t1/2)
what happens when a drug is eliminated from the body at a fast rate
have to administer that drug more often
volume of plasma cleared of drug in unit time
Clearance (CL)
2 main ways a drug is eliminated:
excretion (renal)
metabolism (hepatic)
measures the proportion of red blood cells in the blood
hematocrit
only applies to drugs w/ first-order kinetics (most drugs)
Clearance (CL)
CL=
elimination rate/Cp
this order of kinetics is directly proportional to the plasma concentration of drug; deals with exponential decay
First-Order Kinetics
Cp=
D/Vd
D-dose
Vd-volume of distribution
elimination rate constant (k)=
CL/Vd
t1/2=
(0.7 x Vd)/CL
this type of elimination does not care how much concentration you have, the same amount is being eliminated per unit of time
zero order elimination
the 3 drugs that use zero-order elimination
Phenytoin, Ethanol, Aspirin (PEA)
k0=
- (change in Cp)/t
logarithmic Y axis means what kind of elimination
first order
linear Y axis means what kind of elimination
zero order
t1/2 (for zero order)=
1/2 Cp0 (initial drug conc.)/k0
solution for waiting for 4-6 half-lives to achieve effective concentration in plasma
give loading dose
solution for effective concentration that cannot be maintained
give maintenance dose
for intravenous drugs, what is always 1 or 100%
F (bioavailability of drug)
a larger one-time dose to get patient up to the desired plasma concentration w/out having to wait for 4-6 half-lives
loading dose
LD=
(Cp x Vd)/F
MD=
(Cp x CL)/F
the dose at which the elimination of drug= rate of administration
MD
F=
area of PO curve/area of IV curve
fraction (F) of an orally administered dose that reaches the systemic circulation
bioavailability
creatinine drug clearance formula:
CL=(urine flow x drug conc. in urine)/Cp
this is used if 24 hour urine can’t be collected
Cockcroft-Gault
Cockcroft-Gault formula:
CL= [body weight x (140-age)]/[72 x Cr serum conc.]
