Unit 1 - Pharmokinetics

Question 1

explain kinetic compartments

Answer 1

compartments are the fluid space containing the drug, which is useful for mathematical calculations

Question 2

what determines the elemination constant (Ke) of a drug?

Answer 2

a rate limiting step

Question 3

what is significant about the “peak” of a single dose therapy?

Answer 3

the absorption = elimination

Question 4

explain absorption kinetics

Answer 4

absorption rates are related to transport processes involved, either zero or first order

Question 5

explain zero order rate of absorption

• what is the equation for concentration of a drug in Vd after a certain time?
• what does it look like on a graph?
• what are 2 examples?

Answer 5

carrier mediated with saturated carrier protein at Vmax; not sensitive to drugs

• Ct = Ka*t –> amount per time (straight line on normal graph)
• -Ka might be fast or slow, but it is always constant
• examples are IV infusions and transcutaneous patches (both have constant rates of delivery)

Question 6

explain first order rate of absorption

• what is the equation for concentration of a drug in Vd after a certain time?
• what does it look like on a graph?
• what is an example?

Answer 6

proportional to the amount of drug present; sensitive to drug concentration

• Ct = M / Vd * (1 - e^-Ka*t) –> proportion per time (hyperbole on normal graph)
• -with time, we approach a max amount absorbed that hopefully equals most of the dose
• -the larger the dose, the faster the concentration rises in the compartment
• example is oral

Question 7

what 4 things does pharmocokinetics determine?

Answer 7

1. how Often to Dose a Drug
2. What Size Dose to Give
3. How Long to Expect a Dose to Last
4. When to Re-dose a Drug to Sustain the Effect

Question 8

is elimination dependent or independent of drug concentration? what does the rate limiting step need?

Answer 8

independent of drug concentration, and rate limiting step must be:

1. insensitive to drug concentration
2. saturated

Question 9

explain zero order elimination, its equation, and what it looks like on a graph

Answer 9

an amount per unit time
Ct = Ci - Ke*t
-looks like a straight negative slope (slope - -Ke) on a normal graph

Question 10

explain first order elimination, its equation, and what it looks like on a graph

Answer 10

a proportion per unit time
log Ct = log Ci - (Ke * t)/2.303
-normal axis is negative hyperbole, log axis is negative straight line

Question 11

which order is it if:
Ct &laquo_space;Km
Ct&raquo_space; Km

Answer 11

when Ct &laquo_space;Km, v = k * Ct –> first order rate

when Ct&raquo_space; Km, v = Vm –> zero order rate (constant in that system

Question 12

what is the formula for half life of a drug in plasma when it’s first order elimination?

Answer 12

t 1/2 = 0.693 / Ke

-thus, t 1/2 is constant

Question 13

what is the relationship between Vd, Cl, and t 1/2?

Answer 13

Cl = Vd * Ke
since t 1/2 = 0.693 / Ke
t 1/2 = (0.693 * Vd) / Cl

Question 14

what will a decrease in clearance do?

Answer 14

increase t 1/2

-this can happen if there is renal or hepatic failure