Exam 1 Constant Rate Regimen

Question 1

What is a constant rate regimen?

Answer 1

1. the drug is administered systemically at a constant/zero order rate
2. constant plasma concentration can be best accomplished by infusing a drug at a constant rate

Question 2

What are different examples of infusing a drug at a constant rate?

Answer 2

1. IV infusion via infusion pump
2. orally administered drugs: slow release tablets
3. transdermal patches

Question 3

Why is a constant rate regimen used over an IV bolus dose?

Answer 3

IV bolus dose has a rapid elimination which means that it falls under the therapeutic range quickly → want to keep the drug at a constant concentration to keep it in the therapeutic range via IV infusion

Question 4

What is steady state of an IV infusion?

Answer 4

where the concentration does not change much → essentially where it plateaus

Question 5

What happens when steady state is reached and the IV infusion is stopped?

Answer 5

the drug begins to be eliminated → elimination rate is like the elimination rate of an IV bolus dose

Question 6

At steady state, what is dA/dt?

Answer 6

dA/dt = 0

Question 7

What is the equation for the concentration at steady state?

Answer 7

Css = R0/CL (in which R0 is the infusion rate)

Question 8

What is the time to reach steady state?

Answer 8

considered to be 90% of steady state

Question 9

What is the relationship between % eliminated (IV bolus) and % steady state (IV infusion)?

Answer 9

they are equal! (for example, at 3 half lives, 90% of the IV bolus dose has been eliminated while 90% of steady state has been reached with the IV infusion)

Question 10

What is the equation for time to reach steady state (Tss)?

Answer 10

Tss = 3.3 t1/2

Question 11

What is the equation for the concentration reached before steady state?

Answer 11

C = Css(1-e^-k*t)

Question 12

What is the equation of the concentration after stopping infusion?

Answer 12

C = Css*e^-kt (like the IV bolus dose equation)

Question 13

Example question: What would be the plasma t-PA concentration at 10 min after stopping infusion? (Css is about 2, t1/2=5)

Answer 13

C = Csse^-kt = 2e^(-0.693/5*10) = 0.5 mg/L

Question 14

What is the equation to find Cp at a certain time point after the end of the infusion?

Answer 14

Cp = Cp0*e^-kt (where Cp0 is the concentration when infusion stopped and t is the time since the end of the infusion)

Question 15

If the dose (infusion rate) is doubled, what happens to the plasma concentration at steady state?

Answer 15

the plasma concentration at steady state would double as well (since Css = R0/CL)

Question 16

What happens if steady state is already reached and you increased the dose to double?

Answer 16

the new steady state concentration would be doubled the original steady state concentration

Question 17

How do you determine the concentration at steady state after infusing for a certain amount of time but it hasn’t reached the steady state concentration yet?

Answer 17

use the Css = R0/CL equation with the new infusion rate to get the steady state concentration

Question 18

How do you calculate the IV bolus dose if you are infusing a drug but want to increase the Cp to a certain concentration immediately?

Answer 18

dose = Vd*Cp in which Vd should be given and Cp is the concentration you want subtracted by the concentration you already have at that time period from the infusion

Question 19

After infusing a drug and given an IV bolus dose and then discontinued IV infusion, what is the expected Cp profile?

Answer 19

drops because the only thing happening is the drug elimination from the body

Question 20

If you infused a drug for a certain amount of time, then give an IV bolus dose at the same time as continuing the infusion, how do you calculate Css?

Answer 20

Css = R0/CL and that is what the Cp profile would decline to and taper off (reaching steady state but not)

Question 21

How do you find infusion rate to achieve a specific Css concentration?

Answer 21

Css = R0/CL so you would rearrange to get R0 = Css*CL to get the infusion rate (since kel and Vd is known and given)

Question 22

What is the benefit of combining an IV infusion with an IV bolus dose?

Answer 22

combining the IV infusion with an IV bolus loading dose can maintain Cp near Css from the beginning of drug administration → so that it won’t be far off the therapeutic range and cause toxicity since IV bolus dose can be toxic at high concentrations when first starting out

Question 23

What is the equation to find the concentration at a specific time point for the combined IV infusion and IV bolus dose?

Answer 23

Ccombined = Cinfusion + Cbolus = Css(1-e^-kt) + Css*e^-kt = Css

Question 24

What equation would you use to find the IV bolus loading dose to maintain a certain concentration from the beginning?

Answer 24

dose = Vd*Cp (in which Cp is that certain concentration from the question)

Question 25

How would you find the expected Css if the recommended regimen is changed?

Answer 25

calculate Css using Css = R0/CL → the Css should not change if the infusion rate remained the same

Question 26

True/false: Time to reach steady state depends on the dose.

Answer 26

false → it depends on the half life (and kel)

Question 27

True/false: Doubling the dose will double the steady state concentration.

Answer 27

true → Css = R0/CL so if R0 is doubled, Css would double as a result

Question 28

True/false: Doubling the dose will shorten the time to reach steady state.

Answer 28

false → time to reach steady state only depends on the half life/kel which is not dependent on the dose

Question 29

True/false: Doubling dosing interval will lead to greater fluctuation in plasma concentration.

Answer 29

true?