kinetics exam 2- IV Infusion

Question 1

Intravenous Infusion: Cp Changes Over Time

Answer 1

administer a dose

the concentration starts at zero and increases as the infusion rate > elimination rate

the line hits a plateau as the infusion rate = elimination rate

Question 2

Drugs Following A One- Compartment Model

Answer 2

Infusion is typically a zero-order process

• For most drugs, elimination is first-order
• The rate of change of the amount of drug in the
  body

where R = the infusion rate; DB = amount of the
drug in the body

• Since DB = CpVD, following integration, the
  equation becomes:

Question 3

Drugs Following A One-Compartment Model: The Steady State

Answer 3

• At infinite time, t= infinity and (1–e-kt) = 1

this represents the steady or plateau phase ie the plasma level at steady state
Css = R/Cl

Question 4

Drugs Following A One-Compartment Model: The Steady State II

Answer 4

The equation may also be arrived at using the fundamental fact that at steady state,
*
the Ratein = Rateout
i.e. Css is directly related to R and inversely related to the clearance (Cl) and the apparent volume of distribution (VD).

Question 5

Drugs Following A One-Compartment Model: The Steady State III

Answer 5

It takes an infinite amount of time to reach the true steady state i.e. the graph is asymptotic

• The number of half lives required to reach 90%, 95% and 99% of steady-state are 3.32, 4.32 and 6.65 respectively
• NB: An increase in the infusion rate will increase the Css, but will have no effect on the time needed to get there.

Question 6

Drugs Following A One-Compartment Model: Calculating Patient t1/2

Question 7

Drugs Following A One-Compartment Model: Simultaneous Loading Dose and IV Infusion

Answer 7

when the loading dose and the IV infusion are added together, the line reaches the concentration at steady state

Question 8

Drugs Following A One-Compartment Model: Clearance

Answer 8

The time needed to reach a steady state is inversely related to clearance, given a constant apparent volume of distribution

• This is important in patients with different renal functions and therefore different Cls

Question 9

Drugs Following A Two-Compartment Model:

Answer 9

This is the case for many drugs administered by i.v. infusion

• Requires distribution and equilibration before Css is attained
• At Css, drug levels in the tissue compartment remains the same