Week 2

Question 1

rate

equation

Answer 1

the rate of a chemical reaction is the velocity at which it occurs
drug A --> drug B
rate = - dXa/dt 
rate= dXb/dt
X = amount 
units: amount per time (ex: mg/hr)

Question 2

order of a reaction

Answer 2

concentration, C, or the amount, X, of
drug or reactants influences the rate
– zero order
– first order
– second order
– Michaelis-Menten

Question 3

zero order equation

Answer 3

constant
changes in the drug concentration (mg/L) doesn’t affect the rate (mg/hr)
doesnt depend on amount (or conc) of drug

Question 4

first order equation

Answer 4

changes in the drug concentration do affect the rate
similar to radiologic decay
k is 1/time (ex: min-1). whatever the x axis is, if its hours, then hours^-1

Question 5

– Michaelis-Menten equation

Answer 5

for saturable enzyme kinetics required to remove the drug from the body

Question 6

rate constant (k)

Answer 6

rate of the process
• independent variable is usually time, t
• dependent variable is usually amount, X,
or concentration, C
• the units for k depends on the order of the
reaction –> look at the equation

Question 7

order of a pk process

Answer 7

is the way the amount/concentration of the drug influences the rate of the process.

Question 8

linear processes

Answer 8

• zero-order
• first-order
• can be algebraically solved by Laplace Transformation

Question 9

non linear

Answer 9

• Michaelis-Menten

Question 10

the amount (X) can be converted to
concentration (C) by dividing both sides of
an equation by a ‘volume of distribution’ V

Answer 10

dX/dt = - k x X becomes dC/dt = -k x C

Question 11

• most (but not all) rate processes are

Answer 11

first or zero order

• numerical methods - Euler’s method
• analytical method - Laplace transform

Question 12

(k0) —> 1 (k1)—>2 (k2) –> 3

what do these mean?

Answer 12

k0- zero order
k1, k2 - first order rate constants 
1, 2, and 3 are compartments. you can assign diff meanings to these. example: 1 can be gi tract, 2 can be plasma, 3 can be urine. 
 write the mass balance equations around
each compartment

Question 13

direction of arrow

Answer 13

• Accumulation = IN – OUT

* Rate (dX/dt) = Rate IN – Rate OUT

Question 14

Rules for Writing Mass Balances
• the type of rate process
first order

zero order

Answer 14

• if first order: multiply first order rate constant by the amount/conc of drug in the component at the tail of the arrow
  – if zero order: just enter the rate constant

Question 15

(k0) —> 1 (k1)—>2 (k2) –> 3

example for compartment 1

Answer 15

dX1/dt = material in compartment 1 
dX1/dt = +k0 - k1 x X1

Question 16

(k0) —> 1 (k1)—>2 (k2) –> 3

example for compartment 2

Answer 16

dX2/dt = +k1 x X1 - k2 x X2

Question 17

(k0) —> 1 (k1)—>2 (k2) –> 3

example for compartment 3

Answer 17

dX3/dt = +k2 x X2

Question 18

laplace equation

Answer 18

• Laplace transform converts differential
equation f(t) into the Laplace f(s) domain
• Laplace equations can be rearranged
algebraically
• inverse transform to provide the solution

Question 19

transform of variable such as drug amount X

Answer 19

L bar (X) = X bar

Question 20

if a constant A is multiplied with X

Answer 20

L bar (A x X) = A x X bar

Question 21

• transform of a differential equation

Answer 21

L bar (dX/dt) = s × X bar - Xo
s = independent variable that replaces t in the laplace space
X bar = X as a function of s
Xo = initial amount of material in that compartment at time zero

Question 22

general steps of laplace equation

Answer 22

1. for each compartment, write the
differential equation(s) in time, t, domain
2. transform to the Laplace, s, domain
3. rearrange to solve algebraically 
4. using a chart, reverse transform to t
domain to obtain the integrated equation

Question 23

zero order kinetics
linear graph paper
semi log paper

Answer 23

straight line

gives a curve

Question 24

the value of ko may be taken from the slope of the line using

Answer 24

two points taken from the best fit line (not raw data points)

Question 25

zero order examples

Answer 25

administration
- IV infusion
- insulin pump
- controlled release dosage forms
 saturable processes
- zero-order absorption
- ethanol elimination
the most common PK elimination processes follow first-order kinetics

Question 26

if you plot a graph on linear graph paper and it is curved,

Answer 26

then it is 1st order. not zero order.

Question 27

first order kinetics
linear graph paper
semi log paper

Answer 27

curve

straight line

Question 28

pharmacokinetics for a drug that follows
first-order elimination is referred to
clinically as

Answer 28

having linear pharmacokinetics because AUC is proportional to dose