1
Q
pharmacokinetics
A
- Vd and clearance
- used to determine how often to dose, size of dose, length of effect, when to redose
2
Q
kinetic compartments
A
- the fluid space containing the drug
- useful for the mathematical calculations
- view the complete body as one or two compartments for simplicity
- CSF plasma interstitial fluid intracellular fluid
3
Q
movement of drug through the fluid compartments
A
-drug–>ka of absorption–> volume = Vd, concentration Ct—> Ke of elimination
4
Q
single dose therapy
A
- at top of curve absorption=elimination
- duration of drug is when reaches threshold to when it goes below
- intensity is from threshold to peak
- therapeutic range is from threshold to above peak
- onset is from admin to when it reaches threshold
- see picture
5
Q
absorption kinetics
A
-absorption rates are related to the transport processes involved, either zero order (carrier mediated with saturated carrier protein at Vmax- not sensitive to drug concentration) or at first order- sensitive to drug concentration
6
Q
zero order rate
A
- Ct= ka x t
- ct concentration of a drug in a volume of distribution of a single kinetic compartment after time t for zero order absorption
- amount per unit time
- IV infusion, transcutaneous patch
- when plotted quantity absorbed vs time- slope is ka and is a linear relationship
7
Q
first order rate
A
- Ct = (M/Vd) ^ (1-e^-kat)
- a proportion per unit time
- oral absorption of lipid soluble drug
- with time approaches a maximum amount absorbed that hopefully equals most of the dose
- the larger the dose, the faster the concentration rises in the compartment
- curves up
8
Q
elimination kinetics
A
- cl=clmet + cl renal
- a rate limiting step determines the rate of elimination
- independent of drug concentration occurs if rate limiting step is
1. insensitive to drug concentration
2. is saturated
9
Q
zero order elimination
A
- an amount per unit time
- enzyme systems are saturated at vmax
- ethanol-drops 0.02 per hour
- Ct = Co- ket
- slope is a negative linear relationship
- slope is negative ke
- phenytioin- small change in dose causes large increases in steady state concentrations, some patients are more sensitive
- hourglass
10
Q
first order elimination
A
- logCt= log Co- ket/2.303
- a proportion per unit time
- log paper line has negative linear relationship
- more capacity- isn’t saturated as colander
11
Q
experimental single dose administration
A
- half life can be determined
- half life only applies to first order processes
- take a concentration and cut it in half and find time it takes to get to new concentration
12
Q
rates of decrease
A
- when Ct «_space;km, it is k X ct (can drop Km
- when Ct»_space; Km, it is Vm- a constant in that system
- drugs can go from 1st order to zero order
- higher capacity to lower- half life becomes irrelevant
13
Q
half life
A
- different for different drugs
- can be the same type of drugs, just in different classes
- half life depends on what you are using drug for
- equal to 0.693/ke- physiologic parameter a person has
- therefore it is constant
14
Q
Vd, clearance, and half life
A
- c= dose/vd
- vd= dose/ co
- clearance = vd x ke
- half life = 0.693Vd/ Cl
- a decrease in clearance from renal or hepatic failure will increase half life
