PHAR 7633 Chapter 4

One Compartment IV Bolus

return to the Course index
previous | next

IV Bolus - Example 2

We can also calculate the pharmacokinetic parameters kel and V if we know the dose given and the plasma concentrations at two (or more) times after an IV bolus administration. This time we will use Equation 4.12.1

Equation 4.12.1 Kel calculated from Two Concentration Values

Question: If Cp^{2 hours} is 4.5 mg/liter and Cp^{6 hours} is 3.7 mg/liter after a 400 mg IV bolus dose what are the values of kel and V.

Now using either the 2 hour or the 6 hour data point calculate the concentration at time zero.

And now

Equation 4.12.2 V from Dose and Cp⁰

and

Equation 4.12.3 Clearance from kel and V

Try your own calculation

Calculator 4.12.1 Calculate Parameter Values from Two Data Points Collected after an IV Bolus

IV Bolus Dose:

First concentration:

Time of first Cp value:

Second concentration:

Time of second Cp value:

kel is:

t_1/2 is:

Cp⁰ is:

V is:

and Clearance is:

If you get the Error Message Value is not a numeric literal or NaN this probably means that one of the required parameter fields is empty or a value is inappropriate.

Another example. A 45 yr, 74 kg male patient with severe nafcillin-resistent Staph. aureus infection is started on a new drug. He is given 1000 mg as a loading dose over 60 minutes (however, we will assume this is an IV bolus). This patient has poor renal function so we sample his blood at 2 and 12 hours to determine the pharmacokinetics of this drug in this patient. The concentrations were 18.6 and 13.1 mg/L, respectively. If the minimum effective concentration is 10 mg/L calculate the when the next dose should given AND the dose required to increase the concentration back close to the maximum therapeutic concentration or 25 mg/L. HINT: Calculate kel, Cp⁰, t(10mg/L), V, and next dose.

Answers

References

Winter, M.E. 1988 Basic Clinical Pharmacokinetics, 2nd. ed., Applied Therapeutics, Vancouver, WA ISBN 0915486083

return to the Course index
previous | next

This page (http://www.boomer.org/c/p4/c04/c0412.html) was last modified: Friday 30 Jan 2009 at 02:17 PM

Material on this website should be used for Educational or Self-Study Purposes Only

IV Bolus Dose:
First concentration:
Time of first Cp value:
Second concentration:
Time of second Cp value:

kel is:
t_1/2 is:
Cp⁰ is:
V is:
and Clearance is: